diff --git a/2016-10-16-lecture09.md b/2016-10-16-lecture09.md index 8ca1d54..43adbbe 100644 --- a/2016-10-16-lecture09.md +++ b/2016-10-16-lecture09.md @@ -95,7 +95,9 @@ pain, temperature, itch | free nerve endings | C (**unmyelinated**) | 0.2–1.5 - + Note: @@ -334,7 +336,7 @@ pacinian corpuscle ## Activity patterns in different mechanosensory afferents as Braille is read -
Neuroscience 5e Fig. 9.6
+
Neuroscience 5e Fig. 9.6
Note: @@ -995,8 +997,8 @@ Innervation of same neuron in the dorsal horn of the spinal cord. ## Pain perception is subjective -* Rubbing the site of injury can make pain less severe -* Pain is somewhat subjective. Depends on context. Soldiers wounded in battle feel less pain than if one gets the same injury at home +* Rubbing the site of injury can make pain less severe. Soldiers wounded in battle feel less pain than if one gets the same injury at home +* Pain can be subjective. Depends on context. * There is a descending pain pathway that can impinge on the dorsal horn to quiet neurons Note: @@ -1017,9 +1019,6 @@ Note: ## Modulation of ascending pain signal transmission -1. Axons from neurons with mechanoreceptors can synapse onto inhibitory interneurons in spine to dampen pain response -2. Descending pathways from the brainstem can dampen pain response -
Neuroscience 5e Fig. 10.8
@@ -1027,7 +1026,7 @@ Note: enkephalins, endorphins, dynorphins— present in the periacq. gray matter, ventral medulla, and in spinal cord regions in dorsal horn. -Also CB1 and endocannabinoids work similiarly here in the dorsal horn. +Also CB1 and endocannabinoids work similiarly here in the dorsal horn. CB1 on presynaptic terminals of dorsal horn nociceptive terminals can be activated by endocannabinoid release in a retrograde fashion and decrease the release of neurotransmitters such as GABA and glutamate. *Interestingly, the analgesic effecs of PAG stimulation is blocked if CB1 antagonists are administered* highlighting the importance of endocannabinoids in descending control of pain transmission. -- diff --git a/2016-10-31-lecture11.md b/2016-10-31-lecture11.md index 4deeaa3..59c4c2e 100644 --- a/2016-10-31-lecture11.md +++ b/2016-10-31-lecture11.md @@ -1,19 +1,26 @@ ## Vision -* A glance at an object lets us know where it is, its size, shape, color, texture, direction and speed of movement. -* We can do this at many different intensities of light from faint light to bright sunlight. -* Two main components of the CNS are responsible for this: the retina in the eye and the visual centers of the brain. +* A glance at an object lets us know where it is, its size, shape, color, texture, direction and speed of movement +* We can do this at many different intensities of light from faint light to bright sunlight +* Two main components of the CNS are responsible for this: the retina in the eye and the visual centers of the brain + +
[H. Kolb Webvision, med.utah.edu](http://webvision.med.utah.edu/book/part-i-foundations/gross-anatomy-of-the-ey/)
Note: ---- - ## Today’s learning goals -* Be able to identify the different parts of the eye and their functions. -* Understand the main proteins involved in the signal transduction pathway that leads to changes in neurotransmitter release by photoreceptors in response to light. -* Learn the neural pathway that takes information from photoreceptors to the brain. -* Understand the concept of the receptive field. +* Be able to identify the different parts of the eye and their functions +* Understand the main proteins involved in the signal transduction pathway that leads to changes in neurotransmitter release by photoreceptors in response to light +* Learn the neural pathway that takes information from photoreceptors to the brain +* Understand the concept of the receptive field + +--- + +## Anatomy of the human eye + +
Neuroscience 5e Fig. 11.1
+ Note: @@ -21,84 +28,59 @@ Note: --- -## The human eye +## Anatomy of the human eye video -
+
Neuroscience 5e Animation 11.1
Note: - ---- - -## Anatomy of the Human Eye - -
- -Note: - - - ---- - -## Title Text - -[http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation11-01AnatomyoftheHumanEye.mov](http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation11-01AnatomyoftheHumanEye.mov) - -
- -Note: - - - --- ## Parts of the eye +
+
+ * Outside: -* Sclera– outer layer composed of white fibrous tissue. -* Cornea– front part of eye, transparent, provides 80% focusing power of the eye + * **Sclera**– outer layer composed of white fibrous tissue + * **Cornea**– front part of eye, transparent, provides 80% refractive power of the eye * Middle: -* Iris– colored portion of the eye, contains muscles that adjust the pupil size under neural control. Open during dim light, closed during bright light. -* Ciliary body– ring of tissue that encircles the lens and includes both a muscle component and a vascular component. -* Choroid– composed of a rich capillary bed that serves as the main blood supply for the photoreceptors and contains melanin containing cells. + * **Iris**– colored portion of the eye, contains muscles that adjust the pupil size under neural control. Open during dim light, closed during bright light + * **Ciliary body**– ring of tissue that encircles the lens and includes both a muscle component and a vascular component + * **Choroid**– composed of a rich capillary bed that serves as the main blood supply for the photoreceptors and contains melanin containing cells * Inside: -* Retina– neural part of the eye, detects light, processes information, and sends it to the brain. -* Lens– transparent structure that and change shape to allow fine focus. -* Aqueous humor– in anterior chamber, supplies nutrients to anterior eye. -* Vitreous humor– gelatinous substance in posterior chamber, provides shape, contains macrophages that removes debris. + * **Retina**– neural part of the eye, detects light, processes information, and sends it to the brain + * **Lens**– transparent structure that and change shape to allow fine focus + * **Aqueous humor**– in anterior chamber, supplies nutrients to anterior eye + * **Vitreous humor**– gelatinous substance in posterior chamber, provides shape, contains macrophages that removes debris + +
Note: - +*Lasik procedure involves reshaping the cornea-- flattening it for nearsighted people, or making it more steeply curved for farsighted people* --- ## Anterior of the human eye in the unaccommodated and accommodated state -Accommodation to focusing on near objects involves the contraction +Accommodation to focusing on near objects involves the contraction of the ciliary muscle, which reduces tension of the Zonule fibers and the lens is allowed to increase its curvature -of the ciliary muscle, which reduces tension of the Zonule fibers +
Neuroscience 5e Fig. 11.2
-and the lens is allowed to increase its curvature +
Distance and near object focus
CC BY-SA 2.5 [commons.wikimedia](https://commons.wikimedia.org/wiki/File:Focus_in_an_eye.svg)
-
- -
Note: - - Increased curvature in an optical lens increases the refraction of light, allowing closer focal distance. +Lens held in place by zonule fibers (connective tissue bands). Two opposing forces-- tension of lens tends to keep it rounded up (into a sphere if removed) and tension of zonule fibers which tend to flatten it. +Contraction of ciliary muscle as a ring around the lens causes zonule fibers to reduce tension on lens allowing lens to increase curvature. -Contraction of ciliary muscle - - - - +Pupil has circular muscles that contract when pupil closes, and radial bands of muscles that contract when pupil dilates. --- @@ -107,24 +89,13 @@ Contraction of ciliary muscle * Myopia: eyeball too long or cornea too curved while lens is as flat as can be. Image focuses in front. Near sightedness * Hyperopia: eyeball too short or refracting system too weak. Image focuses behind eye. Far sightedness -Getting old sucks…need reading glasses +
Reduced accommodation with age
Neuroscience 5e Box 11A
-
Note: - - Getting old lens loses elasticity with age. - - - - - - - - diopter (us), is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres (that is, 1/metres) --- @@ -132,25 +103,17 @@ diopter (us), is a unit of measurement of the optical power of a lens or curved ## Diseases of the anterior eye * Cataracts– clouding of the lens -* Floaters– happens when the vitreous slowly shrinks, it becomes stringy and the strands cast a shadow on the retina. -* Refractive errors, near and far sightedness. +* Floaters– happens when the vitreous slowly shrinks, it becomes stringy and the strands cast a shadow on the retina +* Refractive errors, near and far sightedness -
- -
+
[cataracts, Mayo Clinic](http://www.mayoclinic.org/diseases-conditions/cataracts/home/ovc-20215123)
Note: - - - - Lens proteins denature and degrade over time, and this process is accelerated by diseases. genetic disorder, diabetes, surgery, long term steroid use, UV light - - [from: https://en.wikipedia.org/wiki/Lens_(anatomy)](https://en.wikipedia.org/wiki/Lens_(anatomy)) >Crystallins are water-soluble proteins that compose over 90% of the protein within the lens @@ -175,43 +138,36 @@ genetic disorder, diabetes, surgery, long term steroid use, UV light ## The retina -* The retina, despite its peripheral location, is part of the CNS. -* Contains neural circuitry that converts light energy into action potentials that travel out of the eye within the optic nerve into the brain. -* Is a layered structure, relatively simple for a CNS structure. -* Surrounded on one side by pigmented epithelium which contains melanin that helps reduce backscattering of light. Also plays a role in maintenance of photoreceptors. -* 5 types of neurons in the retina: photoreceptors, bipolar cells, retinal ganglion cells, horizontal cells, and amacrine cells. -* A direct 3 neuron chain is the basic unit of transmission. Photoreceptor to bipolar cell to ganglion cell. +* The retina, despite its peripheral location, is part of the CNS +* Contains neural circuitry that converts light energy into action potentials that travel out of the eye within the optic nerve into the brain +* Is a layered structure, relatively simple for a CNS structure +* Surrounded on one side by pigmented epithelium which contains melanin that helps reduce backscattering of light. Also plays a role in maintenance of photoreceptors +* 5 types of neurons in the retina: photoreceptors, bipolar cells, retinal ganglion cells, horizontal cells, and amacrine cells +* A direct 3 neuron chain is the basic unit of transmission. Photoreceptor to bipolar cell to ganglion cell Note: - - - - neural crest—> PNS neural tube—> CNS (and retina) +
Public domain [commons.wikimedia](https://en.wikipedia.org/wiki/Neural_crest#/media/File:Neural_crest.svg)
+spiral ganglion neurons in cochlea are also from neural tube/CNS --- ## Anatomy of the retina -* Light travels through the retina to hit the photoreceptors in the photoreceptor layer +Light travels through the retina to hit the photoreceptors in the photoreceptor layer -Neuroscience 5e Fig. 11.5 +
Neuroscience 5e Fig. 11.5
+
Neuroscience 5e Fig. 11.5
-
- -
Note: - - - [from: http://www.huffingtonpost.com/2015/03/18/human-retina-backwards_n_6885858.html](http://www.huffingtonpost.com/2015/03/18/human-retina-backwards_n_6885858.html) >researchers at Technion–Israel Institute of Technology in Haifa built a computer model of a human retina and then compared how light behaves in the model with the way it behaves in the retinas of guinea pigs. @@ -224,8 +180,6 @@ However >"We should also remember that several animal classes do not have a 'bac >study was presented at a meeting of the American Physical Society on March 5, 2015 in San Antonio, Texas. - - [from: http://hubel.med.harvard.edu/book/b8.htm](http://hubel.med.harvard.edu/book/b8.htm) >Because the rods and cones are at the back of the retina, the incoming light has to go through the other two layers in order to stimulate them. We do not fully understand why the retina develops in this curious backward fashion. @@ -236,22 +190,11 @@ number of rods and cones vary across the retina. In the center where vision is b 125 million rods and cones in each eye. But only 1 million ganglion cells. How is visual information then preserved. Think of two paths: the direct path and an indirect path involving lateral interactions mediated by horizontal cells between receptors and bipolars and amacrine cells between bipolars and ganglion cells. - >The total area occupied by the receptors in the back layer that feed one ganglion cell in the front layer, directly and indirectly, is only about one millimeter +>The total area occupied by the receptors in the back layer that feed one ganglion cell in the front layer, directly and indirectly, is only about one millimeter high degree of convergence, together with more direct path in and near fovea (one cone—>one bipolar—>one ganglion cell) can explain the 125:1 ratio of receptors to optic nerve fibers without having really bad vision. - - - - - - - - - - - --- ## Layers of the retina @@ -259,9 +202,10 @@ high degree of convergence, together with more direct path in and near fovea (on * Three main cell body layers (photoreceptor cell bodies, inner nuclear layer, and ganglion cell layer) * Two main synaptic transmission layers (outer plexiform and inner plexiform) -
+
[H. Kolb Webvision, med.utah.edu](http://webvision.med.utah.edu/book/part-i-foundations/gross-anatomy-of-the-ey/)
+ +
Neuroscience 5e Ch. 11
-
Note: @@ -271,9 +215,9 @@ Note: ## Phototransduction -* Unlike most sensory system neurons, photoreceptors do not exhibit action potentials– light causes a graded change in membrane potential that changes the rate at which neurotransmitter is released. -* Within the retina projections are rather short– do not need action potentials. -* Light absorption leads to hyperpolarization of the photoreceptor. This leads to less release of neurotransmitter to the post-synaptic cell. +* Unlike most sensory system neurons, photoreceptors do not exhibit action potentials– light causes a graded change in membrane potential that changes the rate at which neurotransmitter is released +* Within the retina projections are rather short– do not need action potentials +* Light absorption leads to hyperpolarization of the photoreceptor. This leads to less release of neurotransmitter to the post-synaptic cell Note: @@ -283,7 +227,7 @@ Note: ## Cones and rods hyperpolarize in response to light -
+
Neuroscience 5e Fig. 11.7
Note: @@ -293,42 +237,40 @@ Note: ## What does light do? -* In the dark, the resting potential of the photoreceptor is -40 mV. -* Light shining onto outer segment leads to the hyperpolarization of the photoreceptor and reduction of neurotransmitter released. -* In the dark the number of Na⁺ channels open at the synaptic terminal is relatively high, and therefore the rate of neurotransmitter release is high. In the light the number of open Na⁺ channels is reduced and rate of neurotransmitter release is reduced. -* Of course, this seems kind of backwards compared to what you’ve have learned thus far. +* In the dark, the resting potential of the photoreceptor is -40 mV +* Light shining onto outer segment leads to the hyperpolarization of the photoreceptor and reduction of neurotransmitter released +* In the dark the number of voltage-gated Ca²⁺ channels open at the synaptic terminal is relatively high, and therefore the rate of neurotransmitter release is high. In the light the number of open voltage-gated Ca²⁺ channels is reduced and rate of neurotransmitter release is reduced +* This of course seems kind of counterintuitive to what you’ve have learned thus far Note: - +*reason for this backwards arrangement of hyperpolarization to depolarization is not currently known* --- ## cGMP gated Na⁺ channels are key -in dark channel open due +In the dark channels open due to cGMP binding. Na⁺ rushes in and cell is depolarized -to cGMP binding. +
Neuroscience 5e Fig. 11.8
- -Na⁺ rushes in - -cell depolarized - -
- Note: +cyclic nucleotide gated cation channel + +the nucleotide cyclic guanosine monophosphate + +*these cGMP gated channels are permeable to both Na+ and Ca2+ actually* --- ## In the dark -* cGMP gated Na⁺ channels in outer segment are open allowing ions to flow inside the cell. This leads to a resting potential of -40 or so. -* The probability of these channels being open is regulated by the levels of cGMP. -* In the dark, high levels of cGMP keep the channels open. +* cGMP gated Na⁺ channels in outer segment are open allowing ions to flow inside the cell. This leads to a resting potential of -40 mV or so +* The probability of these channels being open is regulated by the levels of cGMP +* In the dark, high levels of cGMP keep the channels open Note: @@ -338,46 +280,41 @@ Note: ## In the light -* A photon of light is absorbed by photopigment (retinal or retinaldehyde, an aldehyde of Vitamin A) that is coupled to a protein in the outer segment called opsin. Absorption causes a change in conformation of retinal that in turn changes the conformation of opsin. -* This leads to the disassociation of trimeric G-proteins (special α subunit called transducin) from the receptor. -* Transducin activates a cGMP phosphodiesterase which degrades cGMP to GMP. Channel opening probability decreases, cell gets hyperpolarized. +* A photon of light is absorbed by photopigment (retinal or retinaldehyde, an aldehyde of Vitamin A) that is coupled to a protein in the outer segment called opsin. Absorption causes a change in conformation of retinal that in turn changes the conformation of opsin +* This leads to the disassociation of trimeric G-proteins (special α subunit called transducin) from the receptor +* Transducin activates a cGMP phosphodiesterase which degrades cGMP to GMP. Channel opening probability decreases, cell gets hyperpolarized Note: - - --- -## Phototransduction +## Phototransduction in rod photoreceptors -
+
rhodopsin
Neuroscience 5e Fig. 11.9
+
retinaldehyde
Neuroscience 5e Fig. 11.9
-
Note: - - - - - - Vertebrates typically have four cone opsins (LWS, SWS1, SWS2, and Rh2) - - [from: https://en.wikipedia.org/wiki/Opsin](https://en.wikipedia.org/wiki/Opsin) -long-wave sensitiveLWScone500–570 nmgreen, yellow, redOPN1LW "red" / OPN1MW “green" +long-wave sensitive | LWS | cone | 500–570 nm | green, yellow, red | OPN1LW "red" / OPN1MW “green" +short-wave sensitive 1 | SWS1 | cone | 355–445 nm | ultraviolet, violet OPN1SW "blue" +short-wave sensitive 2 | SWS2 | cone | 400–470 nm | violet, blue (extinct in therian mammals) +rhodopsin-like 2 | Rh2 | cone | 480–530 nm | green (extinct in mammals) +rhodopsin-like 1 (vertebrate rhodopsin) | Rh1 | rod | ~500 nm | blue-green OPN2 = Rho = human rhodopsin -short-wave sensitive 1SWS1cone355–445 nmultraviolet, violetOPN1SW "blue" +Melanopsin OPN4 +: circadian rhythms, pupillary reflex, and color correction in high-brightness situations -short-wave sensitive 2SWS2cone400–470 nmviolet, blue(extinct in therian mammals) - -rhodopsin-like 2Rh2cone480–530 nmgreen(extinct in mammals) - -rhodopsin-like 1 (vertebrate rhodopsin) Rh1rod~500 nmblue-greenOPN2 = Rho = human rhodopsin +therian mammals +: giving birth to live young +: eutherians (placental mammals) and metatherians (marsupials) +: not egg laying monotremes +Interesting table, [Opsins in the human eye, brain, and skin](https://en.wikipedia.org/wiki/Opsin) >Like type II opsins, type I opsins have a seven transmembrane domain structure similar to that found in eukaryotic G-protein coupled receptors. @@ -394,65 +331,55 @@ rhodopsin-like 1 (vertebrate rhodopsin) Rh1rod~500 nmblue-greenOPN2 = Rho = huma ## Phototransduction in rod photoreceptors -
+
+ Note: - - - +PDE phosphodiesterase catalyses breakdown of cGMP to GMP cGMP, cyclic nucleotide gated channel - - - - [more info: http://webvision.med.utah.edu/book/part-ii-anatomy-and-physiology-of-the-retina/photoreceptors/](http://webvision.med.utah.edu/book/part-ii-anatomy-and-physiology-of-the-retina/photoreceptors/) - - - - --- -## Title Text +## Phototransduction summary video -[http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation11-02Phototransduction.mov](http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation11-02Phototransduction.mov) - -
+
Neuroscience 5e Animation 11.2
Note: - --- ## Signal amplification -* One photon of light can activate 800 transducin molecules. This leads to about 800 phosphodiesterases activated. Each phosphodiesterase cleaves 300 or so cGMPs/second. This can result in the closing of about 200 ion channels (2% of total). 106–107 Na⁺ ions per second are prevented from entering the cell for a period of ~1 second. -* Changes membrane potential about 1 mV. +* One photon of light can activate 800 transducin molecules. This leads to about 800 phosphodiesterases activated. Each phosphodiesterase cleaves 300 or so cGMPs/second. This can result in the closing of about 200 ion channels (2% of total). 106 – 107 Na⁺ ions per second are prevented from entering the cell for a period of ~1 second +* Changes membrane potential about 1 mV Note: +Tremendous amplification. Single photon hitting rhodopsin is estimated to activate 800 transducin molecules, about 8% of transducin molecules on disk surface. Each transducin molecule activates a single phosphodiesterase molecule and ea PDE can catalyze the breakdown of 6 cGMP molecules. Results in closure of 200 ion channels or ~2% of n channels in ea rod open in dark, resulting in net change in membrane potential of 1 mV. - - - -~30 mV working (dynamic) range for photoreceptors. But adaptation scales this to work for different background light levels. +*~30 mV working (dynamic) range for photoreceptors. But adaptation scales this to work for different background light levels.* --- ## Need to inactivate opsin signaling after a light flash -* Rhodopsin kinase/arrestin– activated rhodopsin can be phosphorylated by a specific kinase and intracellular Ser/Thr residues. This creates binding sites for arrestin which binds and prevents the activation of transducin. -* All-trans retinol gets shed, transported to pigment epithelium cells, changed to cis-retinol and reincorporated into opsin. +* Rhodopsin kinase/arrestin– activated rhodopsin is phosphorylated by rhodopsin kinase, permitting the protein arrestin to bind to rhodopsin. **Prevents further activation of transducin**, thus ending the phototransduction cascade +* All-trans retinol gets shed, transported to pigment epithelium cells, changed to cis-retinol and reincorporated into opsin Note: +Rhodopsin is a seven-transmembrane g protein coupled receptor. +*Rhodopsin kinase/arrestin– activated rhodopsin is phosphorylated by rhodopsin kinase and intracellular Ser/Thr residues.* ---- +Retinoid cycle one important part of light adapation (other being horizontal cell-photoreceptor interactions). Rate of retinal regeneration sufficient even under bright illumination. + + --- ## Cell types of the retina: photoreceptors -* Rods and cones– have an outer segment comprised of membranous disks that contain photopigment and an inner segment that contains the cell nucleus and synaptic terminals. -* The absorption of light by photopigment in outer segment initiates a signal transduction cascade that changes the membrane potential of the cell, and therefore the amount of neurotransmitter released plus or minus light energy. -* Photoreceptors synapse with bipolar cells and horizontal cells in the outer plexiform layer. +* Rods and cones– have an outer segment comprised of membranous disks that contain photopigment and an inner segment that contains the cell nucleus and synaptic terminals +* The absorption of light by photopigment in outer segment initiates a signal transduction cascade that changes the membrane potential of the cell, and therefore the amount of neurotransmitter released plus or minus light energy +* Photoreceptors synapse with bipolar cells and horizontal cells in the outer plexiform layer Note: - - ---- - -## Rods and cones - -
- -Note: - - - --- ## Structural Differences Between Rods and Cones -
+
+ +
Neuroscience 5e Fig. 11.5
+ Note: - - - - - - Why the cone shape? Shape of cone preferentially accepts light directed straight into the eye through the pupil instead of off axis. Known as the Stiles–Crawford effect. - - - - - - ---- - -## EM section through a kangaroo rat rod cell - -stalk - - - -Outer segment - -Inner segment - -
- -Note: - - + --- @@ -546,25 +435,24 @@ Note: * distribution across the retina * pattern of synaptic connections * specialized for different aspects of vision -* * Rod system– low spatial resolution but extremely sensitive to light -* Cone system– high spatial resolution but is relatively insensitive to light. +* Cone system– high spatial resolution but is less sensitive to light Note: - --- ## Range of luminance values over which the visual system operates * Rods– used mostly for dim light to almost indoor lighting -* When only rods are used called scotopic vision. Not very good. -* Cones dominant in visible light. Called photopic. -* Twilight uses both called mesopic vision. +* When only rods are used called scotopic vision. Not very good +* Cones dominant in visible light. Called photopic +* Twilight uses both called mesopic vision + +
Neuroscience 5e Fig. 11.11
-
Note: @@ -574,37 +462,38 @@ Note: ## More factoids -* Rods produce a reliable response to a single photon of light, it takes over a 100 photons to produce a comparable response in a cone. -* Cones adapt better than do rods– about 200 ms for a cone, 800 ms for a rod. -* - -* Rods synapse onto specific bipolar cells (rod bipolars) that synapse onto amacrine cells which contact both cone bipolars and ganglion cells. Cones go bipolar to RGC directly. -* Rods exhibit convergence– many rods synapse onto a single bipolar cell, many bipolars onto a single amacrine cell. +* Rods produce a reliable response to a single photon of light, it takes over a 100 photons to produce a comparable response in a cone +* Cones adapt better than do rods– about 200 ms for a cone, 800 ms for a rod +* Rods synapse onto specific bipolar cells (rod bipolars) that synapse onto amacrine cells which contact both cone bipolars and ganglion cells. Cones go bipolar to RGC directly +* Rods exhibit convergence– many rods synapse onto a single bipolar cell, many bipolars onto a single amacrine cell * Cones can be 1 cone - 1 bipolar - 1 ganglion cell Note: +Rods --> rod bipolar <--> (gap junc/chemical synapse) amacrine cell --> RGC +Cones --> cone bipolar --> RGC --- -## Differential responses of human rods and cones +## Differential properties of primate rods and cones -
+
outward currents after light flashes
Neuroscience 5e Fig. 11.12, Baylor J Physiol 1984, 1987
+ +
convergence in rod pathway
Neuroscience 5e Fig. 11.12
-
Note: +Figure show electrical recordings (suction electrodes) of the current flowing across the photoreceptor membranes of primate (*Macaca fasciculari* / cynomolgus monkeys/crab-eating macaque) rods and cones for ligh flashes of successive higher intensity. +Cone response over in about 200 ms (with an overshoot of inward current), whereas the rod response can continue for more than 600 ms. Both rods and cones adapt to operate over a range of luminance values, but the adaptation mechanisms of cones are more effective. -cone response over in about 200 ms, whereas the rod response can continue for more than 600 ms. +[Ca2+] in outer segment plays key role in light adaptation (light induced modulation of photoreceptor sensitivity). More light leads to less [Ca2+] leading to more guanylate cyclase activity and more cGMP production and higher [cGMP]. Less [Ca2+] also leads to incr activity of rhodopsin kinase and more arrestin binding to rhodopsin so that rhodopsin is inactivated quicker. This is the basis of the enhanced cone light adaptation and the briefer cone response and the outward current overshoot compared with rods. +*15-30 rod to bipolar cell convergence, reduces spatial resolution of rod system but increases light detection* - - - -[from https://en.wikipedia.org/wiki/Adaptation_(eye):](https://en.wikipedia.org/wiki/Adaptation_(eye):) +[from https://en.wikipedia.org/wiki/Adaptation_(eye)](https://en.wikipedia.org/wiki/Adaptation_(eye)) >The human eye can function from very dark to very bright levels of light; its sensing capabilities reach across nine orders of magnitude. This means that the brightest and the darkest light signal that the eye can sense are a factor of roughly 1,000,000,000 apart. @@ -619,122 +508,109 @@ cone response over in about 200 ms, whereas the rod response can continue for mo >Dark adaptation is far quicker and deeper in young people than the elderly - --- ## Rods and cones are not distributed equally in the retina -* Human retina– 91 million rods, 4.5 million cones. -* In most places the density of rods exceeds that of cones. -* Changes dramatically in the fovea, central retina (1.2 mm in diameter). -* Cones increase in density 200 fold, become highly packed. Center of the fovea, called foveola is totally rod free. -* Gives high visual acuity, which decreases rapidly away from the fovea. -* Reason why we are constantly moving our heads to center our eyes toward what we want to look at. -* Reason why it it best to see a dim object by looking away from it. +
+
+ +* Human retina– 91 million rods, 4.5 million cones +* In most places the density of rods exceeds that of cones +* Changes dramatically in the fovea, central retina (1.2 mm in diameter) +* Cones increase in density 200 fold, become highly packed. Center of the fovea, called foveola is totally rod free +* Gives high visual acuity, which decreases rapidly away from the fovea +* Reason why we are constantly moving our heads to center our eyes toward what we want to look at +* Reason why it it best to see a dim object by looking away from it + +
+ Note: - --- ## Distribution of rods and cones in the human retina -
+
Neuroscience 5e Fig. 11.13
+ Note: + --- ## Cones and color vision -* 3 types of cones, each having different absorption spectra- called blue (S-cones), green (M-cones), and red (L-cones) opsin. -* Most people can match any color by changing the intensities of these three colors (RGB). -* 5-6% of males are color blind- due to mutations in the red or green opsins. They are X-linked and near each other. +* 3 types of cones, each having different absorption spectra- called blue (S-cones), green (M-cones), and red (L-cones) opsin +* Most people can match any color by changing the intensities of these three colors (RGB) +* 5-6% of males are color blind- due to mutations in the red or green opsins. They are X-linked and near each other Note: - - --- ## Cone absorption spectra and distribution in the retina -
+
Neuroscience 5e Fig. 11.14, Hofer 2005
+ Note: - --- ## Many deficiencies of color vision are the result of genetic alterations in the red or green cone pigments -
+
Neuroscience 5e Fig. 11.15
+ Note: - - ---- - + - ---- +-- ## Color blindness -[http://www.prokerala.com/health/eye-care/eye-test/color-blindness-test.php](http://www.prokerala.com/health/eye-care/eye-test/color-blindness-test.php) - -
+
[http://www.prokerala.com/health/eye-care/eye-test/color-blindness-test.php](http://www.prokerala.com/health/eye-care/eye-test/color-blindness-test.php)
Note: - --- -## Rods and cones +## Rods and cones summary -Rods +
+
+ +**Rods** * 90 – 120 million * Peripheral vision @@ -745,9 +621,12 @@ Rods * Highly convergent * Black and White +
+
+
-Cones +**Cones** * 4-6 million * Central vision @@ -758,6 +637,8 @@ Cones * Nonconvergent * Color vision +
+ Note: @@ -766,11 +647,16 @@ Note: ## Other cell types of the retina -* Bipolar cells– cell bodies in the inner nuclear layer. Gets info from photoreceptors in outer plexiform layer and transmits it to ganglion cells and amacrine cells in inner plexiform layer. Rods and cones use specific types of bipolars. -* Ganglion cells– cell bodies in ganglion cell layer. Output neurons of the retina. Receives info from bipolar and amacrine cells and sends it out through the optic nerve. -* Horizontal cells– cell bodies in inner nuclear layer. Makes multiple contacts with photoreceptors and bipolar cells. Largely responsible for luminance contrast. +
+
+ +* Bipolar cells– cell bodies in the inner nuclear layer. Gets info from photoreceptors in outer plexiform layer and transmits it to ganglion cells and amacrine cells in inner plexiform layer. Rods and cones use specific types of bipolars +* Ganglion cells– cell bodies in ganglion cell layer. Output neurons of the retina. Receives info from bipolar and amacrine cells and sends it out through the optic nerve +* Horizontal cells– cell bodies in inner nuclear layer. Makes multiple contacts with photoreceptors and bipolar cells. Largely responsible for luminance contrast * Amacrine cells– cell bodies in inner nuclear layer. Makes contact in the inner plexiform layer with bipolar cells and ganglion cells. Several distinct subclasses. Coordinate ganglion cell activity. e.g. motion +
+ Note: luminance contrast = luminance difference/average luminance @@ -778,41 +664,47 @@ luminance contrast = luminance difference/average luminance : same as antagonistic center-surround RFs - - - --- ## Retinal ganglion cells (RGC) -* RGCs are the cell that sends action potentials to the brain. -* Much of the information in vision has to do with changes in light intensity. Example black and white movies. -* In order to understand how the brain makes sense of the differences in light intensity that the eye sees, it is important to know what makes RGCs fire. +
+
+ +* RGCs are the cell that sends action potentials to the brain +* Much of the information in vision has to do with changes in light intensity. Example black and white movies +* In order to understand how the brain makes sense of the differences in light intensity that the eye sees, it is important to know what makes RGCs fire * Record from an RGC and shine light onto different photoreceptors. Find: -* Even in the dark RGCs are spontaneously active. -* Receptive fields of RGCs are circular. Smaller in the center of the retina and bigger in the periphery. -* Find two classes of RGCs. Those that have receptive field profiles that are ON center and those that are OFF center. -* The receptive fields of RGCs overlap so that multiple RGCs see each point of space. + * Even in the dark RGCs are spontaneously active + * Receptive fields of RGCs are circular. Smaller in the center of the retina and bigger in the periphery + * Find two classes of RGCs. Those that have receptive field profiles that are ON center and those that are OFF center + * The receptive fields of RGCs overlap so that multiple RGCs see each point of space + +
Note: +Now because RGCs are the output neurons of the eye, there has been a long interest in understanding the response properties of these cells, i.e. what their receptive fields look like. --- ## Stephen Kuffler 1950s -* Measured the action potentials from specific RGCs after shining light on the retina. -* Determined that RGCs have receptive fields. Found that a receptive field can be divided into center and a surround. -* Ganglion cells come in two types- ON-center/OFF surround and OFF-center/ON surround, in roughly equal proportions. -* ON center RGCs fire more when light that hits the center is brighter than that of the surround and fire less when it is darker in the center than in the surround. OFF center fire less when it is brighter in center and more when it is darker in the center. -* Acts like having separate luminance channels. Changes in intensity whether increases or decreases, are always conveyed by action potentials. RGCs are not photodetectors but are detecting the contrast between areas. +
+
+ +* Measured the action potentials from specific RGCs after shining light on the retina +* Determined that RGCs have receptive fields. Found that a receptive field can be divided into center and a surround +* Ganglion cells come in two types- ON-center/OFF surround and OFF-center/ON surround, in roughly equal proportions +* ON center RGCs fire more when light that hits the center is brighter than that of the surround and fire less when it is darker in the center than in the surround. OFF center fire less when it is brighter in center and more when it is darker in the center +* Acts like having separate luminance channels. **Changes in intensity** (increases or decreases), are conveyed by action potentials. **RGCs are not photodetectors but are detecting the contrast** between areas + +
Note: - - ---- + --- ## On- and off-center retinal ganglion cell responses to stimulation of different regions of their receptive fields -
+
Neuroscience 5e Fig. 11.17
Note: - ---- - + --- ## Responses of On-center ganglion cells whose receptive fields are distributed across a small spot -
+
Neuroscience 5e Fig. 11.19
+ Note: @@ -864,7 +749,8 @@ Note: ## Responses of On-center ganglion cells whose receptive fields are distributed across a light-dark edge -
+
Neuroscience 5e Fig. 11.19
+ Note: @@ -872,175 +758,169 @@ Note: --- -## Run that by me again +## ON center RGC receptive field summary -* For an ON- center/OFF-surround RGC, a point of light that fills the entire center but not in the surround will give maximal stimulation (increased action potentials). i.e. brighter in center than in surround. -* A point of light in surround but not in the center will hyperpolarize the RGC (reduce baseline spike rate). -* Light that crosses into both will be in the middle depending on the relative amounts. -* Both center and surround illuminated is basically the same as being in the dark (background levels). -* RGCs fire depending on contrast, not by absolute light intensity. -* +
+
+ +* For an ON- center/OFF-surround RGC, a point of light that fills the entire center but not in the surround will give maximal stimulation (increased action potentials). i.e. brighter in center than in surround +* A point of light in surround but not in the center will hyperpolarize the RGC (reduce baseline spike rate) +* Light that crosses into both will be in the middle depending on the relative amounts +* Both center and surround illuminated is basically the same as being in the dark (background levels) +* RGCs fire depending on contrast, not by absolute light intensity + +
Note: - - ---- - + --- -## Title Text +## Information flow in the retina video summary -[http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation11-03InformationProcessingintheRetina.mov](http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation11-03InformationProcessingintheRetina.mov) - -
+
Neuroscience 5e Animation 11.3
Note: - --- ## ON and OFF RGCs -* Have dendrites that arborize in separate strata of the inner plexiform layer, forming selective synapses with different types of bipolar cells. ON in sublamina A and OFF in sublamina B. -* Synapse with bipolar cells. Bipolar cells do not use action potentials, but use graded potentials to release transmitter. -* There are two types of bipolar cells– ON center and OFF center. OFF center uses AMPA receptors (ionotropic) that cause the cell to depolarize in response to glutamate released by photoreceptors. ON center use metabotropic glutamate receptors that lead to the closing of Na⁺ channels and hyperpolarize the cell. +
+
+ +* Have dendrites that arborize in separate strata of the inner plexiform layer, forming selective synapses with different types of bipolar cells. ON in sublamina A and OFF in sublamina B +* Synapse with bipolar cells. Bipolar cells do not use action potentials, but use graded potentials to release transmitter +* There are two types of bipolar cells– ON center and OFF center. OFF center uses AMPA receptors (ionotropic) that cause the cell to depolarize in response to glutamate released by photoreceptors. ON center use metabotropic glutamate receptors that lead to the closing of Na⁺ channels and hyperpolarize the cell + +
Note: +off center bipolars: AMPA receptors (sign conserving) +on center bipolars: mGluR6 (sign inverting) - ---- - + --- ## Circuitry responsible for generating receptive field center responses -* Light hits cone causes hyperpolarization of cone, leads to less release of glutamate. -* Two bipolar cells synapse with cone, an on-center and off center bipolar cell. -* On center bipolars are normally inhibited by glutamate, less glutamate, less inhibition, more release of neurotransmitter onto RGCs which increases of on-center RGC firing. -* Off center bipolars are normally activated by glutamate, become hyperpolarized, decrease transmitter release, which leads to a decrease in firing rate of Off-center RGCs +
+
+ +* Light hits cone causes hyperpolarization of cone, leads to less release of glutamate +* Two bipolar cells synapse with cone, an on-center and off center bipolar cell +* **On center bipolars are normally inhibited by glutamate**, less glutamate, less inhibition, more release of neurotransmitter onto RGCs which increases of on-center RGC firing +* **Off center bipolars are normally activated by glutamate**, become hyperpolarized, decrease transmitter release, which leads to a decrease in firing rate of Off-center RGCs + +
Note: - --- ## Light in center causes ON ganglion cells to increase firing rate and OFF ganglion cells to decrease their firing rate -
+
Neuroscience 5e Fig. 11.18
+ +
Neuroscience 5e Fig. 11.18
+ Note: -Explain the graphs better. Make the distinction of graded potential vs. action potentials +Explain distinction of graded potential vs. action potentials + +middle panels are membrane potential/graded potential. Bottom is spikes/APs. --- ## Horizontal cells create circuitry that is responsible for generating the antagonistic surrounds of RGCs -* Light hitting surround cones hyperpolarizes causing less glutamate to be released onto horizontal cell dendrites. -* Horizontal cells hyperpolarize because of less glutamate (have AMPA receptors) and decrease their rate of transmitter release (GABA) onto the synaptic terminals of the nearby photoreceptors. -* Horizontal cells normally inhibit cones (use GABA), thus now cones are less inhibited (depolarized), and release more glutamate than without surround. -* This leads to a depolarization of off-center RGCs, causing them to increase their firing rate. -* And hyperpolarizes on-center RGCs, causing them to decrease their firing rate. +
+
+ +* Light hitting surround cones hyperpolarizes causing less glutamate to be released onto horizontal cell dendrites +* Horizontal cells hyperpolarize because of less glutamate (have AMPA receptors) and decrease their rate of transmitter release (GABA) onto the synaptic terminals of the nearby photoreceptors +* Horizontal cells normally inhibit cones (use GABA), thus now cones are less inhibited (depolarized), and release more glutamate than without surround +* This leads to a depolarization of off-center RGCs, causing them to increase their firing rate +* And hyperpolarizes on-center RGCs, causing them to decrease their firing rate + +
Note: - - --- ## Circuitry that generates the antagonistic surrounds of retinal ganglion cell receptive fields -
- -Note: - - - -A bunch of photoreceptors, but all the 1-1-1 circuits are overlapping giving series of slight shifted center-surround receptive fields. - ---- - -## Circuitry that generates the antagonistic surrounds of retinal ganglion cell receptive fields +
+
* Light hits cone in surround * Less glutamate released on horizontal cell -* Horizontal cell is hyperpolarized, releases less GABA onto cone in center. This depolarizes center cone relative to before light. -* More glutamate released by center cone to ON and OFF bipolars. -* Off-center depolarized, on-center hyperpolarized. +* Horizontal cell is hyperpolarized, releases less GABA onto cone in center. This depolarizes center cone relative to before light +* More glutamate released by center cone to ON and OFF bipolars +* Off-center depolarized, on-center hyperpolarized * Off-center ganglion cell fires more -* On-center fires less. +* On-center fires less + +
+ +
Neuroscience 5e Fig. 11.21
+ +
Neuroscience 5e Fig. 11.21
-
Note: +plus sign: sign conserving synapse +minus sign: sign inverting synapse - ---- + -
- -Note: - - - ---- - + --- ## Summary -* Light falls on photopigment, that is transformed to action potentials that ganglion cells convey to the brain. -* Phototransduction occurs in rods and cones that have different properties that meet the conflicting demands of sensitivity and acuity. -* RGCs have a center-surround arrangement of receptive fields that makes them good at contrast detection and relatively insensitive to background illumination. +* Light falls on photopigment, that is transformed to action potentials that ganglion cells convey to the brain +* Phototransduction occurs in rods and cones that have different properties that meet the conflicting demands of sensitivity and acuity +* RGCs have a center-surround arrangement of receptive fields that makes them good at contrast detection and relatively insensitive to background illumination Note: - --- - ---- - diff --git a/2016-10-31-lecture12.md b/2016-10-31-lecture12.md index 36903d3..f3d60ac 100644 --- a/2016-10-31-lecture12.md +++ b/2016-10-31-lecture12.md @@ -1,76 +1,10 @@ -## Brain damage and visual perception - -
- -
- -Note: - -Let’s begin by going discussing one of the fantastic true stories told by the famous NYC neurologist, Oliver Sacks, who passed away just a few months ago and who weaved engaging clinical accounts and wrote a number of best selling books regarding cases of patients having extraordinary behaviors that resulted from strange or unknown neurological disorders including this one called The Man Who Mistook his Wife for a Hat. —>Indeed one of these accounts was about a man who actually mistook his wife’s face for a hat. This man, who was an accomplished musician and teacher at a school of music had developed trouble seeing faces and recognizing many types of objects in general as a result of degeneration in the visual system, likely from a stroke or something. - - - -…these types of stories summarize a large bit of what neuroscience is about— understanding fundamental circuits that comprise brain function and animal behavior as well as the dually fascinating and devastating consequences that occur when the formation of those fundamental circuits goes awry. - - - - - ---- - -## Brain damage and visual perception - -* The patient (‘Dr. P’): -* good visual acuity & color vision -* good recognition of abstract geometric objects (cubes, spheres, etc) -* Trouble recognizing friends, family, pupils -* Trouble recognizing complex objects -* - -* Describing a rose: “About six inches in length. A convoluted red form with a linear green attachment” -* Describing a glove: “A continuous surface, infolded on itself. It appears to have five outpouchings” - -👵🏻 - -🎩 - -2016-02-16 12:29:41 - -Note: - -Let’s begin by going discussing one of the fantastic true stories told by the famous NYC neurologist, Oliver Sacks, who passed away just last summer and who weaved engaging clinical accounts and wrote a number of best selling books regarding cases of patients having extraordinary behaviors that resulted from strange or unknown neurological disorders including this one called The Man Who Mistook his Wife for a Hat. —>Indeed one of these accounts was about a man who actually mistook his wife’s face for a hat. This man, who was a well regarded and accomplished musician and teacher at a NY school of music had developed trouble seeing faces and recognizing many types of objects in general as a result of degeneration in the visual system, likely from a stroke. - - - -This patient (let’s call him Dr. P)… was cognitively sharp, had good vis… - -Hard time - - - -visual agnosia, prospognosia, lesion somewhere in temporal lobe of the cerebral cortex for reasons we will hopefully discover partially by the end of today’s class. - - - -For him the visual world was a series of lifeless abstractions, seeing and describing the world almost the way a machine would see it without grasping the big picture. - - - -…these types of stories summarize a large bit of what neuroscience is about— understanding fundamental circuits that comprise brain function and animal behavior as well as the dually fascinating and devastating consequences that occur when the formation of those fundamental circuits goes awry. - - - - - ---- - ## Central visual pathways: retinal targets -* The retina projects to multiple areas in the brain. Each area is specialized for different functions. -* Dorsal lateral geniculate nucleus (dLGN)- located in the thalamus- receives visual info from retina and sends it to the visual cortex. Most important visual projection with respect to visual perception. -* Pretectum-located at midbrain-thalamus boundary. Responsible for pupillary light reflex. -* Superior colliculus-in midbrain, coordinates head and eye movements. -* Suprachiasmatic nucleus- in hypothalamus-involved in day night cycles. +* The **retina** projects to multiple areas in the brain. Each area is specialized for different functions +* Dorsal **lateral geniculate nucleus** (dLGN)– located in the thalamus- receives visual info from retina and sends it to the visual cortex. Most important visual projection with respect to visual perception +* **Pretectum**– located at midbrain-thalamus boundary. Responsible for pupillary light reflex +* **Superior colliculus**– in midbrain, coordinates head and eye movements +* **Suprachiasmatic nucleus**– hypothalamus, involved in day/night cycles Note: @@ -78,52 +12,27 @@ Last time --- -## Title Text +## The human visual system -* - -The human visual system +
Hubel, 1988
-* Hubel, 1988 - -
- Note: The output neurons of the eye-- the retinal ganglion cells-- form synaptic connections in two visual centers the lateral geniculate nucleus and the superior colliculus. - - And the geniculate neurons have in turn formed synaptic connections with the visual cortex, thus forming the basic visual pathway from the eye to the cerebral cortex. - - - --- -## Title Text +## Important visual system terms -[http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation12-01VisualPathways.mov](http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation12-01VisualPathways.mov) - -
- -Note: - - - ---- - -## Some important visual system terms: - -* - -* Optic disc, optic nerve- All the retinal ganglion cell (RGC) axons exit the eye at the optic disk (results in a blind spot) and form a big myelinated nerve called optic nerve (cranial nerve II). -* Optic chiasm- where the optic nerve enters the brain, at the base of the hypothalamus. -* Optic radiation- portion of the internal capsule (connection between thalamus and cortex) containing the axons from dLGN that project to the visual cortex -* Primary visual cortex (V1), area 17, striate cortex +* **Optic disc, optic nerve**- All the retinal ganglion cell (RGC) axons exit the eye at the optic disk (results in a blind spot) and form a big myelinated nerve called optic nerve (cranial nerve II). +* **Optic chiasm**- where the optic nerve enters the brain, at the base of the hypothalamus. +* **Optic radiation**- portion of the internal capsule (connection between thalamus and cortex) containing the axons from dLGN that project to the visual cortex +* **Primary visual cortex**– V1/area 17/striate cortex Note: @@ -131,23 +40,10 @@ finger test --- -## Title Text +## Human visual system -The human visual system +
Neuroscience 5e Fig. 12.1
-
- -Note: - - - ---- - -## Title Text - -The human visual system - -
Note: @@ -157,147 +53,77 @@ Note: ## The pupillary light reflex -* Light hits retina, sends out axons to both sides of brain that go to the pretectum. -* Pretectal neurons project to contra- and ipsi-lateral Edinger-Westphal nuclei (in midbrain). -* Edinger-Westphal nucleus projects to the ciliary ganglion (PNS). -* Ciliary ganglion projects to the constrictor muscle in the iris. Shining light in one eye leads to constriction of both eye’s muscles. +* Light hits retina, sends out axons to both sides of brain that go to the pretectum +* Pretectal neurons project to contra- and ipsi-lateral Edinger-Westphal nuclei (in midbrain) +* Edinger-Westphal nucleus projects to the ciliary ganglion (PNS) +* Ciliary ganglion projects to the constrictor muscle in the iris. Shining light in one eye leads to constriction of both eye’s muscles -[- atropa belladona](https://en.wikipedia.org/wiki/Atropa_belladonna) - -- ‘deadly nightshade’ - -* : atropine -* : mydriasis -* : dilation of the pupil - - - -
+
+
+[atropa belladona](https://en.wikipedia.org/wiki/Atropa_belladonna) + :'deadly nightshade' + : atropine + : mydriasis + : dilation of the pupil +
+
Note: - +* atropine blocks contraction of the **circular **pupillary constrictor muscles muscle (classified as an anticholinergic drug) by being a competitive inverse agonist for muscarinic ACh receptors +* allows the radial pupillary dilator muscle to contract and dilate the pupil +* mydriasis (dilation of the pupil) --- ## Circuitry responsible for the pupillary light reflex -Typical test question: Where is the site of injury if shining a light into the left eye +* Question: Where is the site of injury if shining a light into the left eye causes both eyes to constrict but shining light into the right eye does not cause either eye to constrict? + * **right optic nerve** -causes both eyes to constrict but shining light into the right eye does not -cause either eye to constrict? +
Neuroscience 5e Fig. 12.2
-[http://library.med.utah.edu/kw/animations/hyperbrain/parasymp_reflex/reflex.html](http://library.med.utah.edu/kw/animations/hyperbrain/parasymp_reflex/reflex.html) - -Neuroscience 5e Fig. 12.2 - -
Note: - - - - answer: right optic nerve ---- - -## Title Text - -Intrinsically photosensitive RGCs (containing melanopsin) are required for day/night activity cycles - -
- -
- -Note: - +[http://library.med.utah.edu/kw/animations/hyperbrain/parasymp_reflex/reflex.html](http://library.med.utah.edu/kw/animations/hyperbrain/parasymp_reflex/reflex.html) --- -## The spatial relationships among the RGCs are maintained in their targets. +## The spatial relationships among the RGCs are maintained in their targets -* Referred to as visual maps or topographic maps. -* Images are inverted and left-right reversed as they are projected onto the retina through the lens. -* The left half of the visual world is represented in the right half of the brain and vice versa (compare to somatosensory system). -* Because humans are binocular, some inputs from each eye project ipsilaterally and some contra-laterally. +* Referred to as visual maps or topographic maps (e.g. retinal topography or 'retinotopy') +* Images are inverted and left-right reversed as they are projected onto the retina through the lens +* The left half of the visual world is represented in the right half of the brain and vice versa (compare to somatosensory system) +* Because humans are binocular, some inputs from each eye project ipsilaterally and some contra-laterally Note: - ---- - -## Title Text -* Hubel, 1988 - -The visual pathway– retinotopy - - - - - -retina - - - - - - - -superior - -colliculus, - -dLGN, - -visual cortex - - - -
- -
- -Note: - Neighboring retinal ganglion cells in the eye detect changes in contrast from similar portions of the visual field, thus forming a 2D map of visual space in the retina. This spatial representation of objects in the retina is then projected onto -->multiple down stream visual areas, so that maps of retinal topography, or retinotopy, are maintained at multiple levels in the visual system. - - Other visual functional organization that is present at birth includes maps of ocular dominance, where the responses of neuronal groups is dominated by that of one eye or the other and orientation selectivity where the responses of neighboring neurons is dominated by high contrast edges of particular orientation. - - - ---- - -## Title Text - -The visual scene is inverted on the retina - -
- -
- -Note: - -or vicious little cujo - --- ## Binocular vision -* There is an overlap in visual fields, such that most objects are seen by both eyes. -* Objects in the left visual field are seen by the nasal retina of the left eye and the temporal retina of the right eye. -* Objects on extreme periphery are seen only by the nasal retina on that side. -* Nasal retinal derived axons cross the midline at the optic chiasm (contra lateral) and temporal retinal axons do not cross at the chiasm (ipsilateral). -* Images in the left visual field project onto the nasal retina of the left eye and the temporal retina of the right eye. These go to the same side of the brain. Therefore the left visual field is mapped onto the right side of the brain. -* The visual map is maintained all the way to V1. The two halves of the visual fields only merge after getting connections from the other half through the corpus callosum. +
+
+ +* There is an overlap in visual fields, such that most objects are seen by both eyes +* Objects in the left visual field are seen by the nasal retina of the left eye and the temporal retina of the right eye +* Objects on extreme periphery are seen only by the nasal retina on that side +* Nasal retinal derived axons cross the midline at the optic chiasm (contra lateral) and temporal retinal axons do not cross at the chiasm (ipsilateral) +* Images in the left visual field project onto the nasal retina of the left eye and the temporal retina of the right eye. These go to the same side of the brain. Therefore the left visual field is mapped onto the right side of the brain +* The visual map is maintained all the way to V1. The two halves of the visual fields only merge after getting connections from the other half through the corpus callosum + +
Note: @@ -309,31 +135,27 @@ this is crucial for stereopsis, or depth perception (finger disparity) ## Projection of the visual field onto the retina -Neuroscience 5e Fig. 12.3 +
visual field
Neuroscience 5e Fig. 12.3
-
- -
+
+
retinal visual hemi-fields
+ + + + +
Neuroscience 5e Fig. 12.3
+
Note: -So now lets go over the projection of the visual field on to the retina in a little more detail that our cujo example a minute ago. - - - +So now lets go over the projection of the visual field on to the retina in a more detail --- -## Title Text +## Binocular visual field -Binocular visual field - - - -Neuroscience 5e Fig. 12.4 - -
+
binocular vision (overlapped color in middle)
Neuroscience 5e Fig. 12.4
Note: @@ -341,51 +163,13 @@ Projection of the Binocular Field of View Relates to Crossing of Fibers in Optic --- -## Title Text +## Visual pathways summary video -Binocular visual field - -[http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation12-01VisualPathways.mov](http://courses.pbsci.ucsc.edu/mcdb/bio125/Animation12-01VisualPathways.mov) - -
- -Note: - - - ---- - -## Title Text - -* At the optic chiasm, visual information from the two sides of the head cross. -* In animals with eyes on the sides of the head, the entire visual field for each side is sent to the opposite side of the brain (to the tectum). -* In forward-looking animals, the visual image is split -* An object on the right side of the visual field is seen by both left hemi-retinae (but not by the right hemi-retinae). The optic nerves leave the retinae, and at the optic chiasm, the two left hemi-retinae projections go left, while the two right hemi-retinae go right. - -Fig 16-2 Neurobiology, - -by Gary G. Matthews, Blackwell Science - -Binocular visual field: species differences - -
- -Note: - -dev book - ---- - -## The human visual system - - - -LGN - -
+
Neuroscience 5e Animation 12.1
Note: +start at binocular vision point --- @@ -393,26 +177,31 @@ Note: ## Lateral geniculate nucleus (LGN) * 90% of the retinal axons go to the dLGN in the thalamus -* dLGN projects to visual cortex (striate cortex). -* Contains 6 layers, that are specific with respect to eye (ipsi vs contra) and with respect to type of ganglion cell— magnocellular (detects gross shape and movement) and parvocellular (form and color). -* Layers align in order to align visual fields. -* Each dLGN receives input from 1 or 2 RGCs therefore like RGCs there also have center-surround responses that are either on or off. +* dLGN projects to visual cortex (striate cortex) +* Contains 6 layers, that are specific with respect to eye (ipsi vs contra) and with respect to type of ganglion cell— magnocellular (detects gross shape and movement) and parvocellular (form and color) +* Layers align in order to align visual fields +* Each dLGN receives input from 1 or 2 RGCs therefore like RGCs there also have center-surround responses that are either on or off Note: +*show human visual system slide from earlier, thalamus slide?* --- ## Laminar organization of the LGN -* Neurons along the projection line see the same point in space -* But neurons in different layers are receiving info from different types of RGCs. +
Human LGN
[Brain Biodiversity Bank MSU, NSF](https://msu.edu/~brains/brains/human/coronal/montage.html)
+
+
+Neurons along the dotted line see the same point in visual space. +Neurons in different layers receive info from different types of RGCs. +
+
LGN, adapted from Neuroscience 5e Fig. 12.15
+
-
- Note: @@ -422,130 +211,84 @@ Note: ## Laminar organization of the LGN: segregation of optic tract inputs * Each LGN layer is eye-specific -* The projections from the retinal ganglion cells maintain the field of view as it was seen - this is called a retinotopic map. The LGN contains 6 layers of cell bodies; each layer receives input from only one eye. The two most ventral layers receive M (magno) ganglion cell inputs, while the other 4 receive P (parvo) inputs. +* The projections from the retinal ganglion cells maintain the field of view as it was seen - this is called a retinotopic map. The LGN contains 6 layers of cell bodies; each layer receives input from only one eye. The two most ventral layers receive M (magno) ganglion cell inputs, while the other 4 receive P (parvo) inputs -
+ Note: - - - - - - what is parvo and magnocellular? Different subtypes of RGCs that we’ll cover more in just a minute… --- ## Visual cortex -* The first point in the central visual pathway where the receptive fields of cells are significantly different from those of the retina. -* located in occipital lobe near the parieto-occipital sulcus. -* There is topographic organization of each visual hemifield. -* Upper visual field is represented below the calcarine sulcus, the lower field above the calcarine sulcus. +* The first point in the central visual pathway where the receptive fields of cells are significantly different from those of the retina +* Located in occipital lobe near the parieto-occipital sulcus +* There is topographic organization of each visual hemifield +* Upper visual field is represented below the calcarine sulcus, the lower field above the calcarine sulcus * Superior and inferior visual fields take different routes to the visual cortex. Meyer’s loop, where superior axons diverge and go into temporal lobe before going to occipital lobe Note: - ---- - -## Title Text - -
- -Note: - - - --- ## Projection to cortex -* The visual field is projected in a retinotopic fashion. -* The right visual field is projected onto the left cortex, while the left visual field is represented on the right.. -* The region of the fovea, because of its high sensitivity and density of cones, is represented by a huge amount of the cortex. +* The visual field is projected in a retinotopic fashion +* The right visual field is projected onto the left cortex, while the left visual field is represented on the right +* The region of the fovea (highest density of cones and central to our visual attention) is represented by a huge amount of the cortex -
+ Note: -Incr representation sound familiar? think of hand and lip representation in human somatosensory cortex we discussed a couple classes ago… - - - - +Incr representation sound familiar? think of hand and lip representation in human somatosensory cortex we discussed a couple classes ago… --- ## Visuotopic organization in the right occipital lobe -* PN12060.JPG +
Neuroscience 5e Fig. 12.5
-Neuroscience 5e Fig. 12.5 - -
Note: - --- -## Optic radiation paths to the visual cortex +## Thalamocortical projections to the visual cortex ('optic radiation') -Lower visual field (dorsal retina) +
lower visual field (dorsal retina): purple, upper visual field (ventral retina): green
Neuroscience 5e Fig. 12.7
-Upper visual field- ventral retina - -(c) 2001 Sinauer Associates, Inc. - -
Note: - --- ## Visual field defects -* The spatial relationships in the retina are maintained in the brain… -* Careful analysis of the visual field defects of a patient can often indicate where brain damage is located. +* The spatial relationships in the retina are maintained in the brain +* Careful analysis of the visual field defects of a patient can often indicate where brain damage is located * Anopsias— relatively large deficits -* Scotomas— smaller deficits. +* Scotomas— smaller deficits Note: - --- ## Visual field deficits resulting from damage along the primary visual pathway -Black means blind +
Neuroscience 5e Fig. 12.6
-Blue means see - -Neuroscience 5e Fig. 12.6 - -Blindness in R eye - -Bitemporal hemianopsia - -L homonymous hemianopsia - -Upper quadrant hemianopsia - -Homonymous hemianopsia with macular sparing - -
Note: +*Reasons for macular sparing not known. Has been proposed that there is overlap in the pattern of crossed and uncrossed ganglion cells that provide central vision* --- @@ -564,143 +307,138 @@ Now let’s go over the structural and functional organization of visual neocort ## Anatomical organization of visual cortex -Neuroscience 5e Fig. 12.10 - -
+
Neuroscience 5e Fig. 12.10
Note: +*4Ca: magnocellular* +*4Cb: parvocellular* + +--- + +## Neurons in the primary visual cortex respond selectively to oriented edges + +* David Hubel and Torsten Wiesel— measured responses of neurons in visual cortex. Found not center-surround like RGCs and LGN neurons but found that they respond to bars or lines but only of a particular orientation +* Two types of cells: + * Simple, respond to stimulus only if matches orientation. Spots of light don’t do much, bars or lines make them fire. They also have surround inhibition. Receptive fields can be generated by having 3-4 LGN neurons innervate one simple cell + * Complex cells- bigger receptive fields, not strongly orientation selective, no clear on or off zones, detect movement + +Note: + --- ## Neurons in the primary visual cortex respond selectively to oriented edges -* David Hubel and Torsten Wiesel— measured responses of neurons in visual cortex. Found not center-surround like RGCs and LGN neurons but found that they respond to bars or lines but only of a particular orientation. -* Two types of cells: Simple, respond to stimulus only if matches orientation. Spots of light don’t do much, bars or lines make them fire. They also have surround inhibition. Receptive fields can be generated by having 3-4 LGN neurons innervate one simple cell. -* Complex cells- bigger receptive fields, not strongly orientation selective, no clear on or off zones, detect movement. +
Neuroscience 5e Fig. 12.8
+ Note: - --- ## Neurons in the primary visual cortex respond selectively to oriented edges -Neuroscience 5e Fig. 12.8 +
+
+Spiking response from a V1 neuron +to oriented visual stimuli +
+
Neuroscience 5e Fig. 12.8
+
+
Oriention tuning curve for a single V1 neuron
Neuroscience 5e Fig. 12.8
-
Note: - +* neurons in primary visual cortex typically respond strongly to a bar presented at a particular orientation and less strongly at other orientations. +* orientation tuning curve for a single example neuron in visual cortex, highest spike rate at its preferred orientation --- ## Neurons in the primary visual cortex respond selectively to oriented edges -Neuroscience 5e Fig. 12.8 - -
- -
- -Note: - - - ---- - -## Neurons in the primary visual cortex respond selectively to oriented edges - -Neuroscience 5e Fig. 12.9 - -
+
+
+Simulated edge components from a natural visual +scene detected across a population of V1 neurons +
+
Neuroscience 5e Fig. 12.9
+
Note: Natural scenes consist of a spectrum of high contrast, oriented edges. +Selective filtering using Fourier transform (from training in linear algebra and signal processing) + --- -## Information from multiple LGN inputs are used to make cortical neuron receptive fields +## Hubel and Wiesel model circuit underlying a V1 neuron receptive field (RF) -* Filtering of info from multiple LGN cells is used to make simple and complex cells in visual cortex +
Inputs from several RGC center-surround RFs may be integrated to create a oriented edge RF for V1 neurons
D. Hubel. *Eye, Brain, and Vision* p. 74
-red dots inhibitory synapses -[LGN on cell: http://www.youtube.com/watch?v=jIevCFZixIg](http://www.youtube.com/watch?v=jIevCFZixIg) +Note: -[V1 simple cell: http://www.youtube.com/watch?v=Cw5PKV9Rj3o](http://www.youtube.com/watch?v=Cw5PKV9Rj3o) +- monkey 70-80% of cells have orientation specificity +- cat all cells appear to be orientation selective -[Hubel: https://www.youtube.com/watch?v=y_l4kQ5wjiw](https://www.youtube.com/watch?v=y_l4kQ5wjiw) +complex cells are also all orientation selective and retinotopic, but need moving lines. Do not react to stationary stimuli. Most common functional cell type in striate cortex, maybe 75% of population. Glass slide in field of view was first stimulus. -
+ + +0.25 degs RF size (fovea) to 1 degree RF (peripheral retina) + +-- + +## On- and off-center retinal ganglion cell responses to stimulation of different regions of their receptive fields + +
Neuroscience 5e Fig. 11.17
+ +Note: + + + +--- + +## Visual cortex neuron receptive fields + + + +Filtering of info from multiple LGN cells is used to make receptive fields for neurons in visual cortex + +
LGN ON neuron receptive fields
+ + + +
V1 neuron receptive fields, D. Hubel, M. Pavel
+ + Note: other hubel vid I saw and marked times… - * david hubel 1:24-2:18: -* 125 million rods and cones in each eye. -* misha pavel, sobel filter -* try to build a robot to see and interpret images and it's hard. +* 125 million rods and cones in each eye +* misha pavel + * try to build a robot to see and interpret images and it's hard 3:15-3:30 + * sobel filter cat 4:00-4:20 + * perception of motion for visual detection cat 4:44 : 4:45 nice example of movement and perception of cat face - - - --- -## Types of simple cell receptive fields +## The basis of functional maps in primary visual cortex -
+
Neuroscience 5e Fig. 12.11
-Note: - - - ---- - -## Some cells are selective for the direction of movement - -We use multiple types of visual information for perception: - -[https://www.youtube.com/watch?v=y_l4kQ5wjiw](https://www.youtube.com/watch?v=y_l4kQ5wjiw) - -
- -Note: - -others selective for movement, disparity - - - -* david hubel 1:24-2:18: -* 125 million rods and cones in each eye. -* misha pavel, sobel filter -* try to build a robot to see and interpret images and it's hard. - -: 4:45 nice example of movement and perception of cat face - - - - - ---- - -## Figure 12.11 The basis of functional maps in primary visual cortex - -The basis of functional maps in visual cortex - -Neuroscience 5e Fig. 12.11 - -
Note: @@ -710,11 +448,11 @@ Note: ## Mapping receptive fields in the living brain -* Illuminator adds red light to help measure oxy-deoxy hemoglobin levels (a sign of increased neural activity). -* Show monkey monitor that contains a given orientation of a line. Tell computer to color-code areas that respond to a certain orientation. -* Repeat for all such orientations, get a pinwheel affect. +* Illuminator adds red light to help measure oxy-deoxy hemoglobin levels (a sign of increased neural activity) +* Show monkey monitor that contains a given orientation of a line. Program computer to color-code areas that respond to a certain orientation +* Repeat for all such orientations, get a pinwheel affect -
+
Note: @@ -724,7 +462,7 @@ data display, surface of brain ## Repeating units of orientation columns in visual cortex -
+
Neuroscience 5e Fig. 12.12, D. Fitzpatrick (left), Ohki et al. *Nature* 2006 (right)
Note: @@ -734,303 +472,204 @@ Note: ## Mixing of pathways from the two eyes first occurs in the visual cortex -Fig. Neuroscience (c) 2001 Sinauer Associates, Inc. - -
+
contralateral: blue, ipsilateral: green
Neuroscience 5e Fig. 12.13
Note: - --- ## Ocular dominance bands in layer 4 of primary visual cortex (V1, area 17) -Hubel, Wiesel, and Levay 1976 +
Histological stain of thalamocortical afferents, section through L4 of V1
Hubel, Wiesel, and Levay 1976
-
Note: - - If we were to peer at layer 4 only and perform a histological procedure that labels thalamocortical inputs from only one eye we would see a pattern like this in primate cortex, resembling ocular dominance bands or stripes. - --- -## Columnar organization of ocular dominance +## The Nobel Prize in Physiology or Medicine (1981) -
+>"for their discoveries concerning information processing in the visual system" -
- -Note: - - - ---- - -## The Nobel Prize in Physiology or Medicine (1981) - -“for their discoveries concerning information processing in the visual system” - -David H. Hubel +
+David H. Hubel +
+
Torsten N. Wiesel +
- -
- -
- -
- Note: - ---- - -## Maps in the visual system- ocular dominance columns and orientation selectivity in visual cortex - - - - - - - -Ocular - -dominance - -Orientation - -selectivity - -
- -
- -Note: - -The organization of connections from each eye is shown here where if we were to look at a chunk of primary visual cortex from ferrets, cats, or monkeys we would find ocular dominance columns where the response properties of neighboring cells is dominated by that of one eye or the other and which can be demonstrated by electrophysiological recordings or by histological staining for cytochrome oxidase. - - - -Overlaid on this map of alternating ocular dominance columns is a map of orientation pinwheels in visual cortex shown by the isocontour lines on the surface *here* and by the colored orientation map *here* -->where the colored map represents the preferred response of neighboring neurons to high contrast edges presented at different orientations in the visual field. - --- ## Parallel processing in the visual system -* Separate pathways for color and movement. -* In human retina there are three main types of retinal ganglion cells, called M, P , and K types. M and P types best characterized. -* M cells are bigger, have larger receptive fields, faster conduction velocities, and respond transiently to visual stimulation. P cells smaller, respond in a sustained fashion. -* P cells respond to color. This is because their center and surround are from different cones. -* M cells do not respond well to color because center and surround are from the same type of cones. -* M, P, and K RGCs go to different layers in the LGN which in turn project to different layers in V1. +
+
+ +* Separate pathways for color and movement +* In human retina there are three main types of retinal ganglion cells, called M, P , and K types. M and P types best characterized +* M cells– are bigger, have larger receptive fields, faster conduction velocities, and respond transiently to visual stimulation. P cells smaller, respond in a sustained fashion +* P cells– respond to color. This is because their center and surround are from different cones +* K cells– less understood, but known to transmit some aspects of color vision such information from short wavelength cones +* M cells do not respond well to color because center and surround are from the same type of cones +* M, P, and K RGCs go to different layers in the LGN which in turn project to different layers in V1 + +
Note: - ---- - -## P type RGCs are sensitive to color contrast - -
- -Note: - - - --- ## Magno-, parvo-, and konio-cellular streams of information in the visual system -
+
RGC subtypes
Neuroscience 5e Fig. 12.15
+ +
RGC subtype projections in LGN
Neuroscience 5e Fig. 12.15
+ +
+LGN projections associated +with RGC subtypes in V1 +
+
Neuroscience 5e Fig. 12.15
+
+ Note: - --- ## Extrastriate visual areas -* There are many other areas of the brain that process visual information, each gets info derived from primary visual cortex (V1). -* Specialized for different functions. -* MT middle temporal area, responds to direction of a moving edge without regard to its color. -* V4, responds to color of a stimulus without regard to form. -* 10 different visual areas, each with a topographic map. -* Damage in these areas can really give weird experiences. +* There are many other areas of the brain that process visual information, each gets info derived from primary visual cortex (V1) +* Specialized for different functions +* MT middle temporal area, responds to direction of a moving edge without regard to its color +* V4, responds to color of a stimulus without regard to form +* 10 different visual areas, each with a topographic map +* Damage in these areas can really give weird experiences Note: - --- ## Subdivisions of the extrastriate cortex in the macaque monkey -Neuroscience 5e Fig. 12.16 +
Neuroscience 5e Fig. 12.16, Maunsell & Newsome 1987
-
+
Neuroscience 5e Fig. 12.16, Felleman & Van Essen 1991
-
Note: +* extrastriate areas V2, V3, V4, MT +* +V2 +: orientation, spatial frequency, and color like V1 +: secondary visual cortex +: feedforward connections from V1 (direct and via the pulvinar) +: feedback to V1 +: sends connections to V3, V4, and V5 +: binocular disparity +: illusion contours +: some attentional modulation ---- - -## Localization of multiple visual areas in the human brain using fMRI - -Neuroscience 5e Fig. 12.17 - -
- -Note: +V3 +: global motion +MT +: middle temporal area +: neurons responding selectively to direction of moving edge, but don't care about color +V4 +: neurons that selectively respond to color, but don't care about direction of its movement --- ## Organization of the dorsal and ventral visual pathways -Dorsal stream: object location (Where?) +
+
-* Knowing location of objects in space. Linking visual data with movement/action +* **Dorsal stream**: object location (**Where**?) + * Knowing location of objects in space. Linking visual data with movement/action +* **Ventral stream**: object recognition (**What**?) + * Color: V4 (temporal-parietal junction) + * Face recognition: fusiform gyrus -Ventral stream: object recognition. (What?) +
-* Color: V4 (temporal-parietal junction). -* Face recognition: fusiform gyrus +
Neuroscience 5e Fig. 12.18
-Neuroscience 5e Fig. 12.18 - -
Note: - --- ## Hierarchical visual processing -
+
MT– motion, V4– color, LIP, FEF– eye movements
adapted from Felleman, Van Essen 1991
+ Note: -“the brain is a complex of widely and reciprocally interconnected systems and that the dynamic interplay of neural activity within and between systems is the very essence of brain function”. And indeed if you look at this—> anatomical wiring diagram for different visual areas represented by different colors you will notice that we use an organized constellation of brain regions to process and route different types of visual information +“the brain is a complex of widely and reciprocally interconnected systems and that the dynamic interplay of neural activity within and between systems is the very essence of brain function” (V. Mountcastle). And indeed if you look at this—> anatomical wiring diagram for different visual areas represented by different colors you will notice that we use an organized constellation of brain regions to process and route different types of visual information ---- +LIP +: lateral intraparietal area +: involved in eye movements +: electrical stimulation elicits saccades +: role in working memory as well -## Subdivisions of the extrastriate cortex in the macaque monkey - -Van Essen 1992 - -
- -
- -Note: - -but he also emphasized that “the brain is a complex of widely and reciprocally interconnected systems and that the dynamic interplay of neural activity within and between systems is the very essence of brain function”. And indeed if you look at this—> anatomical wiring diagram for different visual areas represented by different colors you will notice that we use an organized constellation of brain regions to process and route different types of visual information and each one of these brain regions consists of many thousands of these basic cortical column building blocks described on the previous slide. +FEF +: frontal eye field +: connections to superior colliculus +: important for saccades --- ## Face recognition cells in the fusiform gyrus -
+
Bruce, Desimone, & Gross, 1981
Note: -responses of a monkey’s neuron in their homologous area to fusiform gyrus to various facelike or non facelike stimuli. +responses of a monkey’s neuron in their homologous area to the fusiform gyrus (area IT) to various facelike or non facelike stimuli. +fusiform gyrus +: long strip of cortex in ventral temporal lobe, tracking along hippocampal gyrus in rostral-caudal extent, but separate from entorhinal or parahippocampal cortex +macaque monkey, http://jn.physiology.org/content/46/2/369 color synesthesia: association of colors with certain numbers, letters, or objects -prosopagnosia: face blindness. Our patient Dr. P from earlier? - ---- - -## Grandmother neurons in the human brain? - -[http://www.youtube.com/watch?v=Y7BZlDfVR6k](http://www.youtube.com/watch?v=Y7BZlDfVR6k) - -Quiroga et al., Nature 2005 - -
- -Note: - -Invariant visual representation by single neurons in the human brain. Quiroga et al., Nature 2005 - - - -Recordings were made in medial temporal lobe of the cerebral cortex including entorhinal cortex and hippocampus course of clinical procedures to treat epilepsy. - - - -Interestingly this cell did not respond to pictures of Jennifer Aniston with Brad Pitt, maybe this cell had ‘moved on’ just like Miss Aniston. But other cells in this work did respond to selectively to Aniston with her friend’s costar Lisa Kudrow. - - - -One object per neuron? - - - -however these results may be best understood in a non-visual context. Some of the example cells responded not only to pictures but also to the printed name of a particular person or object. So this type of invariance must be based off learned associations. - - - ---- - -## Grandmother neurons: a sparse neural code - -C. Connor, Nature 2005 - -
- -Note: - -invariant visual representation by single neurons in the human brain. Quiroga et al., Nature 2005 - - - -Connor Nature 2005, N&V on Quiroga et al: - ->a more technical term for the grandmother issue is ‘sparseness’. - ->At earlier stages in the object recognition pathway the neural code for an object is a broad activity pattern distributed across a population of neurons, each responsive to a discrete visual feature. At later, higher order processing stages, neurons become increasingly responsive for combinations of features and the code becomes increasingly sparse. - - - -sparse and non-variant +prosopagnosia: face blindness. Our patient Dr. P from earlier? --- ## Weird visual defects * Cerebral achromatopsia -* Do not see in color-only black and white. Legions in extrastriate cortex regions like V4 or in ventral stream. -* Lesions in MT regions cause people to have defects in detecting motion (Hard to pour drinks accurately, see moving cars, etc). + * Do not see in color- only black and white. Lesions in extrastriate cortex areas such as V4/ventral stream +* Lesions in MT regions cause people to have defects in detecting motion (Hard to pour drinks accurately, see moving cars, etc) * Blind sight -* Disruptions in V1 cause blindness. -* However some people can “guess” what an object is. Implies that there are other projections from eye to brain (superior colliculus) that can somehow compensate for loss of V1. + * Disruptions in V1 cause blindness + * However some patients can still "guess" what an object is. Implies that there are other projections from eye to brain (superior colliculus) that can somehow compensate for loss of V1 Note: +-- ---- - ---- - +Midterm 2 will cover lectures 07 – 13, including material from Chapters 5 (p. 96 – 106), 6, 9, 10, 11, 12 diff --git a/2016-11-03-extra.md b/2016-11-03-extra.md new file mode 100644 index 0000000..ae81ed2 --- /dev/null +++ b/2016-11-03-extra.md @@ -0,0 +1,280 @@ + +## Brain damage and visual perception + +
+
+ +Note: + +Let’s begin by going discussing one of the fantastic true stories told by the famous NYC neurologist, Oliver Sacks, who passed away just a few months ago and who weaved engaging clinical accounts and wrote a number of best selling books regarding cases of patients having extraordinary behaviors that resulted from strange or unknown neurological disorders including this one called The Man Who Mistook his Wife for a Hat. —>Indeed one of these accounts was about a man who actually mistook his wife’s face for a hat. This man, who was an accomplished musician and teacher at a school of music had developed trouble seeing faces and recognizing many types of objects in general as a result of degeneration in the visual system, likely from a stroke or something. + +…these types of stories summarize a large bit of what neuroscience is about— understanding fundamental circuits that comprise brain function and animal behavior as well as the dually fascinating and devastating consequences that occur when the formation of those fundamental circuits goes awry. + +--- + +## Brain damage and visual perception + +
+
+ +* The patient (‘Dr. P’): + * good visual acuity & color vision + * good recognition of abstract geometric objects (cubes, spheres, etc) + * Trouble recognizing friends, family, pupils + * Trouble recognizing complex objects + +* Describing a rose: “About six inches in length. A convoluted red form with a linear green attachment” +* Describing a glove: “A continuous surface, infolded on itself. It appears to have five outpouchings” + +
+ +👵🏻 +🎩 + + +Note: + +Let’s begin by going discussing one of the fantastic true stories told by the famous NYC neurologist, Oliver Sacks, who passed away just last summer and who weaved engaging clinical accounts and wrote a number of best selling books regarding cases of patients having extraordinary behaviors that resulted from strange or unknown neurological disorders including this one called The Man Who Mistook his Wife for a Hat. —>Indeed one of these accounts was about a man who actually mistook his wife’s face for a hat. This man, who was a well regarded and accomplished musician and teacher at a NY school of music had developed trouble seeing faces and recognizing many types of objects in general as a result of degeneration in the visual system, likely from a stroke. + +This patient (let’s call him Dr. P)… was cognitively sharp, had good vis… + +Hard time... + +visual agnosia, prospognosia, lesion somewhere in temporal lobe of the cerebral cortex for reasons we will hopefully discover partially by the end of today’s class. + +For him the visual world was a series of lifeless abstractions, seeing and describing the world almost the way a machine would see it without grasping the big picture. + +…these types of stories summarize a large bit of what neuroscience is about— understanding fundamental circuits that comprise brain function and animal behavior as well as the dually fascinating and devastating consequences that occur when the formation of those fundamental circuits goes awry. + +--- + +## The visual pathway– retinotopy + +Hubel, 1988 +retina +superior colliculus, +dLGN, +visual cortex + + +
+ +
+ +Note: + +Neighboring retinal ganglion cells in the eye detect changes in contrast from similar portions of the visual field, thus forming a 2D map of visual space in the retina. This spatial representation of objects in the retina is then projected onto -->multiple down stream visual areas, so that maps of retinal topography, or retinotopy, are maintained at multiple levels in the visual system. + +Other visual functional organization that is present at birth includes maps of ocular dominance, where the responses of neuronal groups is dominated by that of one eye or the other and orientation selectivity where the responses of neighboring neurons is dominated by high contrast edges of particular orientation. + +--- + + +## Intrinsically photosensitive RGCs (containing melanopsin) are required for day/night activity cycles + +
+
+ + +--- + +## The visual scene is inverted on the retina + +
+
+ +--- + +## Binocular visual field: species differences + +* At the optic chiasm, visual information from the two sides of the head cross +* In animals with eyes on the sides of the head, the entire visual field for each side is sent to the opposite side of the brain (to the tectum) +* In forward-looking animals, the visual image is split +* An object on the right side of the visual field is seen by both left hemi-retinae (but not by the right hemi-retinae). The optic nerves leave the retinae, and at the optic chiasm, the two left hemi-retinae projections go left, while the two right hemi-retinae go right + +
Fig 16-2 Neurobiology, G.G. Matthews, Blackwell Science
+ +--- + +## P type RGCs are sensitive to color contrast + +
+ +Note: + +--- + +## Projection to cortex + +* The visual field is projected in a retinotopic fashion +* The right visual field is projected onto the left cortex, while the left visual field is represented on the right +* The region of the fovea, because of its high sensitivity and density of cones, is represented by a huge amount of the cortex + +
+ +Note: + +Incr representation sound familiar? think of hand and lip representation in human somatosensory cortex we discussed a couple classes ago… + +--- + + +## Information from multiple LGN inputs are used to make cortical neuron receptive fields + +* Filtering of info from multiple LGN cells is used to make simple and complex cells in visual cortex + +red dots inhibitory synapses + +[LGN on cell: http://www.youtube.com/watch?v=jIevCFZixIg](http://www.youtube.com/watch?v=jIevCFZixIg) + +[V1 simple cell: http://www.youtube.com/watch?v=Cw5PKV9Rj3o](http://www.youtube.com/watch?v=Cw5PKV9Rj3o) + +[Hubel: https://www.youtube.com/watch?v=y_l4kQ5wjiw](https://www.youtube.com/watch?v=y_l4kQ5wjiw) + +
+ +Note: + +other hubel vid I saw and marked times… + + +* david hubel 1:24-2:18: +* 125 million rods and cones in each eye. +* misha pavel, sobel filter +* try to build a robot to see and interpret images and it's hard. + +: 4:45 nice example of movement and perception of cat face + + + +--- + +## Types of simple cell receptive fields + +
+ +Note: + + + +--- + +## Some cells are selective for the direction of movement + +We use multiple types of visual information for perception: + +[https://www.youtube.com/watch?v=y_l4kQ5wjiw](https://www.youtube.com/watch?v=y_l4kQ5wjiw) + +
+ +Note: + +others selective for movement, disparity + +* david hubel 1:24-2:18: +* 125 million rods and cones in each eye. +* misha pavel, sobel filter +* try to build a robot to see and interpret images and it's hard. + +: 4:45 nice example of movement and perception of cat face + + +--- + +## Maps in the visual system- ocular dominance columns and orientation selectivity in visual cortex + +Ocular + +dominance + +Orientation + +selectivity + +
+ +
+ +Note: + +The organization of connections from each eye is shown here where if we were to look at a chunk of primary visual cortex from ferrets, cats, or monkeys we would find ocular dominance columns where the response properties of neighboring cells is dominated by that of one eye or the other and which can be demonstrated by electrophysiological recordings or by histological staining for cytochrome oxidase. + +Overlaid on this map of alternating ocular dominance columns is a map of orientation pinwheels in visual cortex shown by the isocontour lines on the surface *here* and by the colored orientation map *here* -->where the colored map represents the preferred response of neighboring neurons to high contrast edges presented at different orientations in the visual field. + +--- + +## Columnar organization of ocular dominance + +
Neuroscience 2e Sinauer 2001
+
Neuroscience 2e Sinauer 2001
+ +Note: + +--- + +## Localization of multiple visual areas in the human brain using fMRI + +
Neuroscience 5e Fig. 12.17
+
Neuroscience 5e Fig. 12.17
+ +Note: + +--- + +## Subdivisions of the extrastriate cortex in the macaque monkey + +Van Essen 1992 + +
+ +
+ +Note: + +but he also emphasized that “the brain is a complex of widely and reciprocally interconnected systems and that the dynamic interplay of neural activity within and between systems is the very essence of brain function”. And indeed if you look at this—> anatomical wiring diagram for different visual areas represented by different colors you will notice that we use an organized constellation of brain regions to process and route different types of visual information and each one of these brain regions consists of many thousands of these basic cortical column building blocks described on the previous slide. + + +--- + +## Grandmother neurons in the human brain? + +[http://www.youtube.com/watch?v=Y7BZlDfVR6k](http://www.youtube.com/watch?v=Y7BZlDfVR6k) + +Quiroga et al., Nature 2005 + +
+ +Note: + +Invariant visual representation by single neurons in the human brain. Quiroga et al., Nature 2005 + +Recordings were made in medial temporal lobe of the cerebral cortex including entorhinal cortex and hippocampus course of clinical procedures to treat epilepsy. + +Interestingly this cell did not respond to pictures of Jennifer Aniston with Brad Pitt, maybe this cell had ‘moved on’ just like Miss Aniston. But other cells in this work did respond to selectively to Aniston with her friend’s costar Lisa Kudrow. + +One object per neuron? + +however these results may be best understood in a non-visual context. Some of the example cells responded not only to pictures but also to the printed name of a particular person or object. So this type of invariance must be based off learned associations. + + +--- + +## Grandmother neurons: a sparse neural code + +C. Connor, Nature 2005 + +
+ +Note: + +invariant visual representation by single neurons in the human brain. Quiroga et al., Nature 2005 + +Connor Nature 2005, N&V on Quiroga et al: + +>a more technical term for the grandmother issue is ‘sparseness’. + +>At earlier stages in the object recognition pathway the neural code for an object is a broad activity pattern distributed across a population of neurons, each responsive to a discrete visual feature. At later, higher order processing stages, neurons become increasingly responsive for combinations of features and the code becomes increasingly sparse. + +sparse and non-variant + +--- \ No newline at end of file diff --git a/2016-11-10-lecture13.md b/2016-11-10-lecture13.md new file mode 100644 index 0000000..46851a3 --- /dev/null +++ b/2016-11-10-lecture13.md @@ -0,0 +1,856 @@ +## The chemical senses + +* Chemical Senses +* Olfaction +* Taste +* Trigeminal chemosensory +* Irritant system + +Note: + +phylogenetically oldest sense. + +not considered very important in humans compared to other senses, but think about the fantastically strong emotional memories tied to smells— the olfactory system when robustly stimulated can have much influence over the formation of olfactory tied memories through its direct connectivity to the limbic and memory systems of the brain. We’ll learn a bit about this connectivity later. + +Mucus membranes of eyes face mouth + +--- + +## Olfaction + +* The olfactory system detects airborne molecules called odorants. +* Provides information about food, self, others, animals, plants, etc. +* Influence feeding behaviors, social interactions, and even reproduction. +* Processes information about the identity, concentration, and quality of a wide range of chemical stimuli. + +Note: + + + +--- + +## The route of olfaction + +
+
+ +* Starts in the nose, odorants bind to specific receptors found in the olfactory epithelium +* Olfactory epithelium projects to neurons in the ipsilateral olfactory bulb, which in turn sends projections contra and ipsi to the piriform cortex in the temporal lobe and other forebrain structures +* Piriform cortex is only 3-layered (sometimes called the archicortex), and is considered phylogenetically older than the neocortex +* Unique among senses in that it does not include a thalamic relay between primary receptors and the cerebral cortex +* Piriform cortex relays information via the thalamus to the associational cortex to initiate motor, visceral, and emotional reactions to olfactory stimuli + +
+ +Note: + + + +--- + +## Human olfactory bulb + +
Neuroscience 5e Fig. 15.2
+ +Note: + + + +--- + +## The flow of olfactory information + +
[nobelprize.org, 2004](http://www.nobelprize.org/nobel_prizes/medicine/laureates/2004/press.html)
+ + +Note: + + +--- + +## Organization of the human olfactory system + +
Neuroscience 5e Fig. 15.1
+ + +Note: + + +--- + +## Olfactory perception + +* Is not as acute in humans as in a number of other animals +* Less acute in humans because of a smaller variety of functional olfactory receptor proteins, less receptor neuron density, and also a lesser amount of relative cortex used to process information +* Mice have ~1000 olfactory receptor genes, humans several hundred + +Note: + +--- + +## Fun olfaction factoids + +* Odors can be detected at very low concentrations (bell peppers 0.01 nM) +* Small changes in molecular structure can change perception +* Anosmics are people who cannot smell specific odors. 1/100 people cannot smell skunk, 1/10 hydrogen cyanide + +Note: + + +--- + +## Human odor detection thresholds + +
+
+ +Compound | Odor threshold in air (parts per billion) +--- | --- +methanol | 141,000 +acetone | 15,000 +formaldehyde | 870 +menthol | 40 +T-butyl mercaptan | 0.3 + +
Devol et al., 1990
+
+ + + +Note: + +rats 8-50 times more sensitive to odors than humans + +dogs 300-10000 times more sensitive + +humans have 10 million ORNs, dogs have 1 billion + +butyl mercaptan: similar to major constituent of defensive spray in skunk + +tert-butyl mercaptan: natural gas additive + + +--- + +## Combinatorial coding + +* Distributed code for face representation +* Color coding by S, M, L cones +* Language is combinatorial +* 26 letters gives many different words + +Note: + +alphabet +: a set of letters or symbols in a fixed order, used to represent the basic sounds of a language +: the basic elements in a system that combine to form complex entities + +--- + +## The vomeronasal organ + +* Many species have a specialized structure that recognizes species-specific odorants called pheromones that play important roles in innate social, reproductive, and parenting behaviors +* The vomeronasal organ (VNO) projects to the accessory olfactory bulb, which in turn projects to the hypothalamus +* The VNO is absent or not very prominent in primates (including humans) and there is debate as to whether humans detect pheromones +* In animals a lesion in the main olfactory projection leaves reproductive behaviors intact, however lesions of the VNO projection severely compromises sexual selection and dominance hierarchies + +Note: + +rudimentary VNO found in 8% of adults. And VNO projects to special region of ob called accessory olfactory bulb which is also largely absent in primates. + +mating, aggression behaviors etc + +loss of sex discrimination and male male aggression in mice without TRP2 + +TRP2/TRPC2: Transient receptor potential cation channel, subfamily C, member 2. Not expressed in humans + +Stowers, L.; Holy, T. E.; Meister, M.; Dulac, C.; Koentges, G. (2002). "Loss of sex discrimination and male-male aggression in mice deficient for TRP2". Science 295 (5559): 1493–1500. Bibcode:2002Sci...295.1493S. doi:10.1126/science.1069259. + +[http://science.sciencemag.org/content/295/5559/1493.full-text.pdf+html](http://science.sciencemag.org/content/295/5559/1493.full-text.pdf+html) + + +--- + +## Pheromones and the VNO + +
Neuroscience 5e Box 15B
+ + +Note: + + +--- + +## Mouse pheromones + +Record from a neuron in the AOB, pink area is when mouse is sniffing at face. Yellow are is when sniffing genitals. + +
[Lou and Katz Science 2003](http://www.sciencemag.org/cgi/content/full/299/5610/1196/DC1)
+ +Note: + +--- + +## Human pheromones? + +* Female rodents (mice) grouped together synchronize their estrous cycle upon exposure to pheromones in male mouse urine (‘Whitten effect’). This depends on pheromone receptors and VNO—>AOB connectivity. +* VNO is vestigial in humans: VRs and TRPC2 are pseudogenes +* Myth: women who live in close proximity synchronize their menstrual cycle (the ‘McClintock effect’, after McClintock, Nature 1971). The current scientific evidence for this effect in human is not strong. +* However there’s some evidence for odorants working as pheromone-like molecules to influence behaviors (attraction, fear) mediated by the main olfactory system + +Note: + +Human pheromones?? + +vestigial. VNO anatomy is non-functional in human. + +myth of mcclintock effect. statistical issues with these studies, no one has reported human estrous cycle synchrony over more than 6-9 months as indeed the original study was on college women at wellsey over the period of one academic calendar year. Windshield wiper, coupled oscillator analogy. Just out of phase. + +But other animals… + +And olfactory cues that aren’t necessarily odorless certainly can affect our behavior and pheromone like molecules may act through our olfactory system + +[from: http://www.sciencedirect.com/science/article/pii/S2090123211000397](http://www.sciencedirect.com/science/article/pii/S2090123211000397) + +mother-child interactions at birth + +[from http://www.ncbi.nlm.nih.gov/books/NBK55967/](http://www.ncbi.nlm.nih.gov/books/NBK55967/) + +> Different works have shown that odor-cued memories are more emotional than memories triggered by visual or verbal cues + + +from one website: + +Pheromones are naturally occurring odorless substances the fertile body excretes externally, conveying an airborne signal that provides information to, and triggers responses from, the opposite sex of the same species. + + +oxford dictionary doesn’t include the word ‘odorless’. + +wikipedia: A pheromone (from Ancient Greek φέρω phero "to bear" and hormone, from Ancient Greek ὁρμή "impetus") is a secreted or excreted chemical factor that triggers a social response in members of the same species. + +>the adult human VNO, in different studies, has been reviewed as non-functional as it contains few neurons and has no sensory function where no cells were shown to express olfactory marker protein, have synaptic contacts or have evidence for a nerve connecting to/from the VNO + +VNO is vestigial in humans: VRs and TrpC2 are pseudogenes + +myth: women who live in close proximity synchronize their menstrual cycle (the McClintock effect, McClintock, Nature 1971) + +However there’s some evidence for pheromone like molecules and behaviors (attraction, fear) mediated by the main olfactory system + +whitten effect: exposure of grouped female mice to phermones in male mouse urine synchronizes their estrous cycle. The pheromones in male urine are dependent on male sex hormones like testosterone. + +[from http://www.informatics.jax.org/silver/chapters/4-3.shtml](http://www.informatics.jax.org/silver/chapters/4-3.shtml) + +>The normal estrus cycle of a laboratory mouse is 4-6 days in length + +vandenburgh effect: early estrous cycle induction in prepubertal female mice exposed to urine from dominant male + +lee-boot effect: suppression or prolongation of estrous cycle in female mice (and other rodents) when mice housed in groups and isolated from other males + +bruce effect: female mouse pregnancy termination from exposure to scent of unfamiliar male + +[http://www.ncbi.nlm.nih.gov/pubmed/22087345](http://www.ncbi.nlm.nih.gov/pubmed/22087345) + +>Latent toxoplasmosis, a lifelong infection with the protozoan Toxoplasma gondii, has cumulative effects on the behaviour of hosts, including humans. The most impressive effect of toxoplasmosis is the "fatal attraction phenomenon," the conversion of innate fear of cat odour into attraction to cat odour in infected rodents. + +phylogenetic distance human, mouse, rat: + +[from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC524408/ 2003](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC524408/) + +>human and rodents diverged ∼75 million years ago, whereas mouse and rat diverged ∼12-24 million years ago[Waterston et al. 2002; Rat Sequencing Project Consortium 2004] + +-human has equal genetic distance from both rodents + +-human has been evolving from human/rodent common ancestor at slower rearrangement rate and thus has a more ancestral genome + +>Rat Closer to Human? + +>rearrangement differences between the two rodents suggest that, except for the small inversions, overall, the rat genome might have a structure on a large scale closer to the human genome than the mouse genome. + +>lacking the extra interchromosomal changes of mouse (Table 3), many rat fragments are closer to human. + +>In terms of chromosome morphology (and possibly the genome size as well), rat is also between mouse and human. + +[from https://www.genome.gov/11511308 2012](https://www.genome.gov/11511308) + +Humans have 23 pairs of chromosomes, while rats have 21 and mice have 20. + +>all three organisms to be related to each other by about 280 large regions of sequence similarity - called "syntenic blocks" - distributed in varying patterns across the organisms' chromosomes. + +> 50 chromosomal rearrangements occurred in each of the rodent lines after divergence from their common ancestor + +>number of chromosomal rearrangements, as well as other types of genome changes, was found to be much lower in the primate lineage, indicating that evolutionary change has occurred at a faster rate in rodents than in primates. + +--- + +## Olfactory receptors + +* Discovered by Linda Buck and Richard Axel. Shared nobel prize in 2004 +* They found that olfactory receptors comprise a large GPCR gene family (~1000 olfactory receptors) +* Each olfactory neuron expresses a single olfactory receptor (even inactivates one copy of each allele) +* Each receptor can bind to multiple odorants +* Each neuron that expresses a given receptor targets to the same glomeruli in the olfactory bulb + +Note: + +Linda Buck and Richard Axel "for their discoveries of odorant receptors and the organization of the olfactory system" + +--- + +## Olfactory receptors + +
Neuroscience 5e Fig. 15.9
+ + +Note: + +--- + +## Olfactory receptors + +
Neuroscience 5e Fig. 15.9
+ +Note: + +red arrows indicate intron locations of splice sites in other animals. Mammalian genes for ORs lack introns. + +largest single known gene family in all mammals. Representing 3-5% of genome. Perhaps 60% of these 950 OR genes are not transcribed in humans and chimps rendering them pseudogenes, vs 15-20% in mice and dogs. + +pseudogene + +: sequence of DNA containing a promoter and transcription initiation site, but due to sequence changes the DNA cannot be transcribed into a stable mRNA or the transcript cannot be translated into a protein. + +--- + +## Anatomy of the olfactory epithelium + +
Neuroscience 5e Fig. 15.7
+ + +Note: + +--- + +## ORN receptor potentials generated in cilia + +
Neuroscience 5e Fig. 15.8
+ + +Note: + + + +--- + +## ORNs are continuously generated from basal cells + +* Turnover of 6-8 weeks in rodents +* Susceptible to pollutants, allergens... +* Source of neural stem cells + +
Neuroscience 5e Fig. 15.7
+ + +Note: + +basal cells and progeny in labeled in red + +blue is all cell nuclei + +green for OMP at right + +--- + +## Olfactory receptor signal transduction + +* Binding of odorant to receptor activates a Gα (Called G-olf) that in turn activates adenylyl cyclase +* cAMP gates a Na+/Ca2+ cation channel. Calcium rushes in and activates a Cl- channel. Chloride normally high in-low out in olfactory neurons and thus Cl- leaving also depolarizes cell + +Note: + + + +--- + +## Olfactory receptor signal transduction + +
Neuroscience 5e Fig. 15.11
+ + +Note: + +How would you desensitize odorant pathway? PDE, Ca-Cam blocks cAMP channel + +Adaptation comes from calmodulin binding up the Ca2+ and closing + +Cl- channels and also from being pumped out. + +--- + +## Molecules critical to odorant signal transduction + +
Neuroscience 5e Fig. 15.11
+ + +Note: + +Minty odor + +EOG electroolfactorogram + +--- + +## A single olfactory receptor can be activated by single or groups of stimuli + +
Neuroscience 5e Fig. 15.12
+ + +Note: + +Eucholipyol, banana oil + +But there is also broad OSN tuning-- + +* Primary olfactory sensory neurons are broadly tuned to odorants +* Sicard and Holley (1984) Brain Research 292:283 + +Eucalyptol is cineole + +Camphor is the smell of turpintine. Aromatic + +--- + +## Dogs smell better than humans + +
Neuroscience 5e Fig. 15.2
+ +
Neuroscience 5e Fig. 15.3
+ +Note: + +--- + +## Olfactory system summary video + +
Neuroscience 5e Animation 15.1
+ + +Note: + + +--- + +## The olfactory bulb + +* A small structure above the nasal passages +* Site where sensory information is collected and gets sorted +* Sensory neurons project to glomeruli +* Olfactory receptor neurons synapse onto the dendrites of mitral cells which then project to the cerebral cortex + +Note: + +ORNs that carry same olfactory receptors converge upon same glomeruli (Mombaerts et al Cell 1996) + +--- + +## Olfactory receptors are localized into discreet areas + +
+ +
olfactory cilia, all ORNs, I7 ORNs, M71 ORNs
Neuroscience Fig. 15.10
+ + +Note: + +omp (green all ORNs). Adenylyl cyclase II (red) limited to olfactory cilia + +all ORNs + +I7 ORNs + +M71 ORNs + + +--- + +## Localization preserved in the olfactory bulb + +
+ +Note: + + +* fig from luo principals of neurobiology? + + +--- + +## Subtle changes in a molecules structure can be detected by different receptors + +* Johnson, Woo, Hingco, Pham and Leon (1999) J. Comp. Neurol. 409:529 + * n-amyl acetate, (control) + * Acetic acid, (2)COOH + * Propanoic acid, (3)COOH + * Butanoic acid, (4)COOH + * Pentanoic acid, (5)COOH + * Hexanoic acid, (6)COOH + + + +Note: + + +* acid series of similar structures +* 2-deoxyglucose activation patterns in the rat olfactory bulb in response to an aliphatic acid series +* Johnson, Woo, Hingco, Pham and Leon (1999) J. Comp. Neurol. 409:529 + +--- + +## Neurons of olfactory bulb + +* Mitral cell, dendrites to a single glomerulus and axon to brain +* Tufted cell contacts multiple glomeruli +* Interneurons (PG) also participate in processing (inhibition) +* Bulb also gets info from the cortex + +
Mitral Cell, MC. Tufted Cell, TC. Granule cell, GC. Periglomerular Cell, PG.
+ + +Note: + +* fig origin unknown. No find through image search + +--- + +## Neurons of olfactory bulb + +
Periglomerular cells
J. Ackman 2003
+ +Note: + + +--- + +## Olfactory pathways + +* OB axons go to piriform (olfactory) cortex, amygdala (fear), entorhinal cortex (hippocampus, memory) +* VNO axons go directly to amygdala (fear) + +
+ + +Note: + +* fig origin unknown. No find through image search + +--- + +## Organization of the human olfactory system + +* piriform ctx and OFC: conscious odor perception, multimodal association +* olfactory tubercle: reward, motivation +* amygdala, hypothalamus: fear, aggression, feeding, reproduction +* entorhinal ctx, hippocampal formation: memory + +
Neuroscience 5e Fig. 15.1
+
Neuroscience 5e Fig. 15.1
+ + +Note: + +piriform ctx and OFC: conscious odor perception, multimodal association + +olfactory tubercle: reward, motivation + +amygdala, hypothalamus: fear, aggression, feeding, reproduction + +entorhinal ctx, hippocampal formation: memory + +--- + +## Taste (gustation) + +* Used to determine whether food should be ingested (together with smell, touch, and pain). +* Provides information about the identity, concentration, and pleasant or unpleasant quality of a substance. +* Works together with the GI system to get it ready to receive food (saliva and swallowing) or reject food (regurgitation). +* Information of texture and temperature of things in mouth processed by somatic sensory system receptors. +* Contains both peripheral receptors and central processing. + +Note: + + +--- + +## The gustatory system + +
+ +Note: + + +These afferent fibers all end in the nucleus of the solitary tract (NST) in the medulla. From there the information flows mainly to the thalamus and then to the gustatory cortex. + +pathways + +* afferents from tongue and epiglottis to gustatory nucleus (in medulla next to 4th ventricle, part of solitary nuclear complex) and then to VPM +* from taste bud to solitary nuclear complex and then to VPM +* Solitary nuclear complext to nucleus ambiguous to salivary glands +* Other somatosensory to parabrachial nuclei + +--- + +## Cortical projections of gustatory pathway + +
+ + +Note: + +* fig origin unknown. + +From the VPM projections reach the gustatory cortex: anterior insular cortex and frontal operculum. + +Information derived from different areas of the tongue is spatially segregated in the n. of the solitary tract, the thalamus, and the cortex. (Still true?) + +--- + +## Gustatory cortex + +* Primary somatosensorycortex (Postcentral gyrus) +* Gustatory Cortex (frontal operculum andanterior insular cortex) +* Fronto-parietal operculum +* Lateral sulcus +* Insular cortex + + +
+
+ + +Note: + +* fig origin unknown. + +Note that the gustatory cortex is very close to the tongue area on the somatosensory cortex! + +--- + +## Organization of the gustatory system + +
Neuroscience 5e Fig. 15.17
+ +Note: + +--- + +## Taste perception + +* Most tastes are hydrophilic molecules solubilized in saliva +* Tastants include salts, amino acids, sugars, acids, plant alkaloids +* quantity of substance also perceived, the higher the concentration the more intensity the taste +* Tastants act in the millimolar range, except for bitter things (strychnine 0.1 µM) +* The tongue is not strictly regionalized by taste although some areas are more sensitive than others + +Note: + +--- + +## 5 basic tastes + +* Sweet (sucrose, aspartame, glycine, etc.) +* Sour (H+) +* Salty (Na+, some other salts) +* Umami (savory, glutamates) +* Bitter (alkaloids) + +
+ +Note: + +* fig origin unknown. No find through image search + + +--- + +## The organization of the taste system + +* Taste receptors are organized in taste buds +* Taste buds contain between 30-100 taste cells +* 75% of all taste buds are found in papillae +* 3-types: fungiform (25%, localized in anterior tongue), circumvallate (50%, rear of tongue) and foliate (25%, posterolateral edge) +* There is great variability in the human population with respect to the number of taste buds + +Note: + +--- + +## Tongue anatomy + +
Neuroscience 5e Fig. 15.18
+ +Note: + +Types of papillae: + +Circumvallatepapillae + +Foliatepapillae + +Fungiformpapillae + +--- + +## Structure of a taste bud + +
Neuroscience 5e Fig. 15.18
+ +Note: + + +--- + +## Tastes + +
Neuroscience 5e Fig. 15.19
+ + +Note: + + +Composite fMRI image showing different locations of activation in insular cortex to each of these tastes. + +--- + +## Taste receptors + +* 5 distinct classes of taste receptors +* Salty and sour generally transduced by ions (Na+ or H+) that open channels +* This depolarizes neuron, that then leads to opening of voltage gated Na+ channels +* This depolarizes neuron more and leads to opening of voltage gated Ca2+ channels +* Leads to the release of serotonin + +Note: + + +--- + +## Transduction mechanisms in a generic taste cell + +
Neuroscience 5e Fig. 15.20
+ + +Note: + + +--- + +## Taste receptors + +* Sweet and Unami receptors are GPCRs that share a subunit called T1R3 +* T1R3 is paired with T1R2 for sweet and T1R1 for amino acids +* T1R1 and T1R2 are expressed in non-overlapping neurons +* T1R2/3 activation leads to activation of PLC, increases IP3 and opens Ca2+channels (TRPM5). Ca2+ channel opening depolarizes cell +* Bitter taste receptors (T2R) have 30 subtypes. Multiple members are expressed in same neurons but not in same neurons as the others. These use a specific Gα called gustucin + +Note: + + +--- + +## Taste receptors + +
Neuroscience 5e Fig. 15.21
+ + +Note: + + +--- + +## Taste coding specificity and segregated representation + +
Neuroscience 5e Fig. 15.22
+ + +Note: + +sweet a.a. and bitter receptors are expressed in diff subsets of taste cells. + +gene from the TRPM5 channel is inactivated in ko mice and behavioral responses measured with taste preference test. Mouse gets two drinking spouts (one with water and one with tastant and relative frequency of licking is measured). + +pleasant tastes (sugar and umami), incr concentration gives incr response. For bitter there is decr response. + +KO the PLCB2 (phospholipase) and responses are eliminated to sweet, umami, and bitter but rescuing expression only in T2R expressing cells recovers just the bitter taste response to wildtype levels. + +* Sour receptor is expressed in every taste bud but isn’t in the same neurons as other receptors +* An experiment to show that T1R2 is a sweet receptor and PKD2L1 is a sour receptor +* Taste pathways remain segregated in the cortex (Zuker lab imaging?) + +--- + +## Putting the bitter receptor into sweet receptor neurons will cause mice to be attracted to bitter! + +
Based on Fig. 5 from Zhang et al., Cell 2003
+ +Note: + +Based on/adapted from Fig. 5 from Zhang et al., Cell 2003 + +[http://www.sciencedirect.com/science/article/pii/S0092867403000710](http://www.sciencedirect.com/science/article/pii/S0092867403000710) + +And the Zuker lab has recently silenced specific brain areas for bitter and sweet in mouse to alter perceptive sense of these tastes: + +[http://newsroom.cumc.columbia.edu/blog/2015/11/18/scientists-turn-tastes-on-and-off-by-activating-and-silencing-clusters-of-brain-cells/](http://newsroom.cumc.columbia.edu/blog/2015/11/18/scientists-turn-tastes-on-and-off-by-activating-and-silencing-clusters-of-brain-cells/) + +Peng et al, Nature 2015 + +[http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature15763.pdf](http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature15763.pdf) + +--- + +## Stimulation of the ‘bitter’ taste cortex is sufficient to make a mouse pucker + +
[Video 1 from Peng et al., Nature 2015](http://www.nature.com/nature/journal/vaop/ncurrent/fig_tab/nature15763_SV1.html)
+ +Note: + +Based on/adapted from Fig. 5 from Zhang et al., Cell 2003 + +[http://www.sciencedirect.com/science/article/pii/S0092867403000710](http://www.sciencedirect.com/science/article/pii/S0092867403000710) + +And the Zuker lab has recently silenced specific brain areas for bitter and sweet in mouse to alter perceptive sense of these tastes: + +[http://newsroom.cumc.columbia.edu/blog/2015/11/18/scientists-turn-tastes-on-and-off-by-activating-and-silencing-clusters-of-brain-cells/](http://newsroom.cumc.columbia.edu/blog/2015/11/18/scientists-turn-tastes-on-and-off-by-activating-and-silencing-clusters-of-brain-cells/) + +Peng et al, Nature 2015 + +[http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature15763.pdf](http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature15763.pdf) + +Bradbury J (2004) Taste Perception: Cracking the Code. PLoS Biol 2(3): e64. [doi:10.1371/journal.pbio.0020064](http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0020064) + +--- + +## The physiology of flavor perception + +* Responses from taste and smell are first combined in the orbital frontal cortex (OFC) +* OFC also receives input from the primary somatosensory cortex and the inferotemporal cortex in the visual what pathway +* Bimodal neurons in this area respond to taste and smell as well as taste and vision +* Firing of these neurons is also affected by the level of hunger of the animal for a specific food + +
+ +Note: + + + +--- + +## Multimodal integration in orbitofrontal cortex + +
+ +Note: + +The orbital frontal cortex (OFC) receives inputs from vision, olfaction, and touch, as shown. It is the first area where signals from the taste and smell systems meet. (info based on E. T. Rolls (2000). The orbitofrontal cortex and reward. Cerebral Cortex, 10, 284-294, Fig. 2.) + +--- + diff --git a/2016-11-14-lecture14.md b/2016-11-14-lecture14.md new file mode 100644 index 0000000..786ea26 --- /dev/null +++ b/2016-11-14-lecture14.md @@ -0,0 +1,658 @@ +## Movement + +* Movement is the planning, coordination & execution of a motor program that relies on information provided by the sensory system +* Movement is controlled by the motor systems of the brain and spinal cord +* Motor systems translate neural signals into contractile force in muscles +* Allows us to maintain balance and posture, move our body, limbs, eyes, tongue & communicate through speech + + +Note: + + +--- + +## Types of movement + +* Reflex responses– knee jerk, withdrawal from pain, swallowing. Muscle contractions and relaxations that are rapid, stereotyped, involuntary and coordinated +* Rhythmic motor patterns– walking, running, chewing. Typically initiation and termination are voluntary and triggered by peripheral stimuli +* Voluntary movements– initiated movements to accomplish a specific goal (e.g. piano playing, writing). These are goal directed and largely learned movements that improve with practice, as one learns to anticipate and correct for environmental obstacles + +Note: + + +--- + +## Overall organization of neural structures that control movement + +
Neuroscience 5e Fig. 16.1
+ + +Note: + + + +--- + +## Control of movement + +* Motor systems responsible for the control of movement can be divided into four distinct but highly interactive subsystems +* Lower motor system– Gray matter of spinal cord and brainstem-contain lower motor neurons and lower circuit neurons. The final common path of all motor output +* Upper motor systems– Send information to spinal cord and brain stem, initiate voluntary movements. Contains motor cortex and some brainstem centers +* Cerebellum– No direct access to lower motor systems. Connects to upper motor systems. Responsible for motor learning +* Basal ganglia– Suppresses unwanted movements and primes neurons for the initiation of movements. Parkinson’s and Huntington’s diseases affect the basal ganglia + +Note: + + + +--- + +## Muscles + +* Relaxation and contraction +* Muscles can pull but not push. Thus separate sets of muscles at the opposite sides of joints must mediate flexion or extension +* Movements at a joint engage two opposing sets of muscles + +Note: + +Muscles only pull they do not push, therefore we have opposing/antagonistic muscles + +EMG– electromyograph, measures electrical activity in muscles. Bicep/tricep figure with EMG histogram around elbow joint. + + + +--- + +## Coupling of excitation and contraction + +* Action potential in motor axon +* End plate potential at neuromuscular junction +* Action potential in muscle fiber +* The AP in the muscle fiber is followed by a twitch in the muscle fiber +* Twitch– transient all-or-none contraction + +Note: + +* Each muscle fiber is innervated by only one motor neuron. Group of muscle fibers in a muscle innervated by a single motor neuron is a motor unit +* twitch happens after small small latency, 5-10 ms +TODO: motor neuron AP --> muscle fiber EPP --> muscle fiber AP. AP and Vm in muscle fiber, latency, and muscle tension rise and decay + +--- + +## Organization of lower motor neurons in the ventral horn of the spinal cord + +
gastrocnemius, soleus muscle
Gray's Anatomy
+
retrograde motor neuron labeling
Neuroscience 5e Fig. 16.2, Burke et al., 1977
+ + +Note: + +* Motor neurons id. by injecting a retrograde tracer into medial gastrocnemius or soleus muscle of cat. Labels neuronal cell bodies and their spatial distribution +* Lower motor neurons form distinct clusters (motor pools) + +--- + +## Motor pools + +
+
+ +* Retrograde labeling of muscles show that the cell bodies of motor neurons are found in ventral horn of the spinal cord +* Each motor neuron innervates muscle fibers within a single muscle +* All the motor neurons innervating a single muscle are grouped together in clusters called motor pools +* Motor pools are located with a slight spread along the A-P axis +* There is topography along medial-lateral axis of the spinal cord. Neurons that innervate axial musculature (trunk) are located medially, neurons that innervate distal muscles are located laterally + +
+ +
Neuroscience 5e Fig 16.2
+ + +Note: + + + +--- + +## Somatotopic organization of lower motor neurons in the ventral horn + +
Neuroscience 5e Fig. 16.3
+ +Note: + +somatotopic mapping of body parts + +--- + +## Location of local circuit neurons that supply the medial region of the ventral horn + +
+
+ +* Medially localized local circuit motor neurons deal with posture, project over a few segments both contra and ipsilaterally +* Lateral circuit motor neurons deal with fine movements, project ipsilaterally + +
+ +
Neuroscience 5e Fig. 16.4
+ + +Note: + + + +--- + +## Types of motor neurons + +* α motor neurons– innervate the extrafusal muscle fibers, the striated muscle fibers that generate the forces needed for movement +* γ motor neurons– innervate specialized muscle fibers in the muscle spindles that are embedded within connective tissue in the muscle, known as intrafusal muscle fibers. These fibers are also innervated by sensory axons that send info to the brain and spinal cord about the length and tension of muscle + +Note: + + + +--- + +## Amyotrophic lateral sclerosis (ALS) + +* 'Lou Gehrig’s disease' +* A disease of α- motor neurons and upper motor neurons +* 30,000 Americans have it at any given time +* Both genetic and spontaneous mechanisms to contract ALS +* Superoxide dismutase (SOD1) is a gene that when mutated leads to ALS (autosomal dominant) + +Note: + +axon transport disease in neurons with long axons + +Superoxide dismutase +: enzyme +: helps break down potentially harmful oxygen molecules in cells + +--- + +## The motor unit + +* A motor unit is the sum total of extrafusal skeletal muscle fibers within a muscle that are innervated by a single α motor neuron +* An action potential normally brings to threshold all muscle fibers it contacts + +
Neuroscience 5e Fig. 16.5
+ +Note: + +motor unit + +* motor unit in soleus (important for posture) has ~180 muscle fibers/per motor neuron +* gastrocnemius has large and small motor units with 1000-2000 muscle fibers per motor neuron. Generates forces for sudden changes in body position. +* extraocular motor units very small (~3 fibers/unit). High proportion of fibers that can contract at max velocity +* but lots of use dependent motor unit plasticity (atheletes, hypogravity conditions) + + + +--- + +## Types of motor units + +* Slow (S) motor unit– Small motor neurons innervate relatively few muscle fibers and generate small forces. They innervate small “red” muscle fibers that contract slowly but are relatively resistant to fatigue. These are rich in mitochondria and myoglobin, and are important for activities that require sustained muscular contraction such as posture +* Fast fatigable (FF) motor unit– Large motor neurons innervate larger, more powerful units. Larger α motor neurons innervate larger pale muscle fibers that generate more force, have sparse mitochondria and are easily fatigued +* Fast fatigue-resistant (FR) motor unit– are of intermediate size, not as fast as FF units but less fatigable + +Note: + +* oxidative metabolism in slow type I to generate ATP, more mitochondria, greater capillary density +* type II are less oxidative more glyolytic by storing glycogen, white due to low myoglobin. + * muscles have short term energy store in creatine phosphate that is used to regenerate ATP from ADP with creatine kinase + * Glucose used for glycolysis anaerobically forming 2ATP and 2 lactic acid molecules. Fat globules during anaerobic excercise. For aerobic conditions lactate not formed, pyruvate and citric acid instead + +myoglobin +: related to hemoglobin +: iron and O2 binding pigment protein in muscle tissue +: cetaceans have particular high abundance of myoglobin +: not found as much in smooth muscle + + +neuroglobin +: present in neurons, maybe astrocytes +: seals +: CSF +: structure determined for human in 2003 and mouse soon after +: NO dynamics, neuron survival under reduced O2 conditions? + +-- + +## Skeletal muscle fiber types + +* Histochemical staining for myosin ATPase at different shows the different fiber types + * Type I slow (innervated by S pools) are darkest at low pH + * Type IIa fast fatigable are lightest + * Type IIx (IIb in other mammals) fast fatigue-resistant are light to intermediate in staining + +
human diaphragm myofiber myosin ATPase histology, pH 4.60
Levine et al., *J Applied Physiol* 2002 Fig. 1a. 50 µm scalebar
+ + +Note: + +Variation in histochemical staining for myosin ATPase activity at different pHs for the fiber types due to different Myosin heavy chain (MHC) type in the type I, IIa, IIx (formerly IIb) fibers. + +IIb not actually expressed humans, but in other mammals. Human MHC IIb is actually IIx [Smerdu-1994] + +Type II includes IIa, IIax, IIx, IIc (other species) + + +Muscles made up of fascicles, which are multiple bands of cells called muscle fibers. During development muscle fibers form from fusion of several myoblasts into long multinucleated cells. Cell size can then be regulated thereafter (e.g. with excercise). But no new muscle cells are added. + +Myosatellite cells are between basemente membrane and sarcolemma of muscle fibers. Normally quiescient, but can become activated by exercise or pathology and provide extra myonuclei for muscle growth and repair[#Zammit-2006]. + + +* Sexually dimorphic muscles include the perineal, masticatory, laryngeal muscles [#Berchtold-2000] +* hypogravity conditions affects mostly postural muscles. Body core [#Berchtold-2000] +* hypogravity conditions induced by walking on crutches or hindlimb suspension results in reduced muscle mass and strength [#Berchtold-2000] + * reduction more pronounced in extensors than in flexors [#Berchtold-2000] + +[Smerdu-1994]: Smerdu, V; Karsch-Mizrachi, I; Campione, M; Leinwand, L; Schiaffino, S (Dec 1994). "Type IIx myosin heavy chain transcripts are expressed in type IIb fibers of human skeletal muscle.". The American journal of physiology. 267 (6 Pt 1): C1723–8. PMID 7545970. + +[#Zammit-2006]: Zammit, PS; Partridge, TA; Yablonka-Reuveni, Z (November 2006). "The skeletal muscle satellite cell: the stem cell that came in from the cold.". Journal of Histochemistry and Cytochemistry. 54 (11): 1177–91. doi:10.1369/jhc.6r6995.2006. PMID 16899758. + +[#Berchtold-2000]: Berchtold, M. W., Brinkmeier, H., and Müntener, M. (2000). Calcium ion in skeletal muscle: its crucial role for muscle function, plasticity, and disease, Physiol Rev, 80(3), 1215-65. PMID 10893434 + + +--- + +## Force and fatiguability of the three different types of motor units + +Stimulation of single α motor neurons from different classes + +
Single stimulation
Neuroscience 5e Fig. 16.6, after Burke et al, 1974
+
Repetitive stimulations
+
Time to fatigue (minutes)
+ + + +Note: + +-muscle tension in resp to single AP +-change in tension in resp to repetitive stimulation. Notice summation +- notice time axes in right + +--- + +## Contributions to muscle tension + +* Size principle– more stimulation leads to more contraction (force produced) by the muscle +* At low stimulation, only slow groups are recruited. Additional stimulation recruits FR, while FF are recruited by the highest stimulation +* Provides a range of forces to perform different motor tasks +* Frequency of action potentials also plays a role in muscle tension. If muscle fibers are activated by a new action potential before they have had time to fully relax from the previous time, they produce more force + +Note: + + + +--- + +## Recruitment of motor neurons to medial gastrocnemius (leg muscle) + +
Neuroscience 5e Fig. 16.7, after Walmsley et al., 1978
+ +Note: + +slow for standing + +FR for walking or running + +FF for sprinting, jumping + +--- + +## Motor unit activity as voluntary force is increased + +
small motor units ----> large motor units
Neuroscience 5e Fig. 16.9, after Monster and Chan 1977
+ + +Note: + +* This is in the human hand +* low threshold motor units gen least amount of force and are first + +--- + +## Summation of force as a function of stimulation rate + +
Neuroscience 5e Fig. 16.8
+ + +Note: + +-id. twitches +- higher freq, tet stim gives sum of twitches to produce greater force + +--- + +## Spinal reflexes + +* Simple reflexes are stereotyped movements elicited by the activation of skin or muscle receptors, and are the basic unit of movements (Charles Sherrington, 1906) +* Complex sequences of movements can be produced by combining simple reflexes + +
Neuroscience 5e Fig. 1.7
+ + +Note: + +myotactic reflex, first lecture. + + +--- + +## The muscle spindle: a sensory organ for determining muscle length and stretch + +
Neuroscience 5e Fig. 16.10
+ + +Note: + +* spindle is organ for stretch +* spindles comprise 8-10 intrafusal fibers + * nuclear bag fibers + * dynamic subclass + * static subclass + * most spindles have 2-3 bag fibers + * nuclear chain fibers + * most spindles have 4-6+ chain fibers + + +Ia afferent activity +: mostly from dynamic type of nuclear bag fiber +: phasic response +: emphasize velocity of stretch + +II afferents +: innervate static nuclear bag fibers and nuclear chain fibers +: signal sustatined fiber stretch by firing tonically, little dynamic sensitivity +: muscle tone + +There are also dynamic and static classes of gamma momtor neurons + +helps form negative feedback loop + +-- + +## Types of somatosensory afferents + +
+
+ +sensory function | receptor type | afferent axon type | axon diameter (µm) | conduction velocity (m/s) +--- | --- | --- | --- | --- +proprioception | muscle spindle | Ia, II (**myelinated**) | 13–20 | 80–120 +touch | Merkel, Meissner, Pacinian, and Ruffini cells | A𝛽 (**myelinated**) | 6–12 | 35–75 +pain, temperature | free nerve endings | Aδ (**myelinated**) | 1–5 | 5–30 +pain, temperature, itch | free nerve endings | C (**unmyelinated**) | 0.2–1.5 | 0.5–2 + +
+ + +--- + +## The stretch reflex + +
Neuroscience 5e Fig. 16.10
+ + +Note: + + + +--- + +## The stretch reflex + +* Large diameter sensory fibers (Ia afferents, fast) are coiled around muscle spindles +* Stretch imposed on a muscle stretches intrafusal muscle fibers, which in turn initiates action potentials by activating mechanically gated ion channels in Ia axons +* Ia sensory neurons synapse with motor neurons in the ventral horn of the spinal cord that innervate the same muscle (homonymous muscle) or synergistic muscles +* Ia sensory neurons activate local inhibitory connections for the antagonistic muscles + +Note: + + + +--- + +## The stretch reflex + +
Neuroscience 5e Fig. 16.10
+ + +Note: + +* So next time your boss says why are you standing around doing nothing, just say that you're busy utilzing your lower motor neurons and type Ia sensory afferents ;) + + +--- + +## γ motor neurons + +
+
+ +* γ motor neurons control the functional characteristics of the muscle spindles +* When muscles contract, spindle afferents do not fall silent. Instead γ neurons that terminate at spindle poles cause intrafusal fiber contraction at the poles, and lead to tension across the fiber in the presence of muscle contraction. This allows spindles to function at all muscle lengths and tensions +* Gain or γ bias refers to the fact that spindles can adjust how much output will happen when they are stretched. Large gain means a small amount of stretch applied to the intrafusal fibers will produce a large increase in the number of motor neurons recruited and an increase in firing rates. Gain is continually adjusted to meet circumstances + +
+ +
Neuroscience 5e Fig. 16.10
+ + + +Note: + +But the infrafusal muscle fibers are muscle-- why not just have the muscle spindle feedback and be done with it... + +Need to adjust the muscle spindles so that they can provide useful feedbac across a range of muscle lengths. +Provide gain to keep muscle spindles active at all lengths. + +Think about your big guns you use to hold that glass of oktoberfest... changing length of biceps + +--- + +## γ motor neuron activity affects responses of muscle spindles + +
Neuroscience 5e Fig. 16.11
+ + +Note: + + + +--- + +## Stretch reflex video summary + +
Neuroscience 5e Animation 16.1
+ +Note: + + + +--- + +## Golgi tendon organs + +
+
+ +* Encapsulated afferent nerve endings located at the junction of the muscle and tendon +* Each tendon is innervated by a single sensory group Ib sensory axon +* Unlike spindle fibers, golgi tendon organs fire when muscle contracts +* Ib axons from Golgi tendon organs contact inhibitory local circuit neurons in the spinal cord (Ib inhibitory neurons) that synapse with the α motor neurons that innervate the same muscle +* Helps prevent fatigue + +
+ +
Neuroscience 5e Fig. 16.12
+ + +Note: + +* spindle system is feedback system to monitor and maintain muscle stretch +* Golgi tendon organ is feedback system to maintain muscle force + +--- + +## Negative feedback regulation of muscle tension by Golgi tendon organs + +
+
+ +* Negative feedback provided by by Golgi tendon organs +* When muscle contracts there is a feedback mechanism to prevent more contractions. Prevents damage and fatigue + +
+ +
Neuroscience 5e Fig. 16.13
+ + +Note: + + + +--- + +## Comparison of the function of muscle spindles and Golgi tendon organs + +
Neuroscience 5e Fig. 16.12
+ + +Note: + + + +--- + +## Comparison of the function of muscle spindles and Golgi tendon organs + +
Neuroscience 5e Fig. 16.12
+ + +Note: + +## Muscle reflexes: response to load and overload + + + +--- + +## Flexion reflex pathways + +* Reflexes that compensate posture when we withdraw from pain +* Involves several synaptic links +* Excitation of nociceptor leads to ipsilateral and contralateral responses +* Flexion reflex– stimulation of cutaneous receptors in the foot leads to activation of spinal cord local circuits that both withdrawal stimulated side and extend other side to provide compensatory support + +Note: + + +CPG interneurons Type Axon projection in embryonic cord +V0 Commissural Rostrally +V1 Inhibitory (Renshaw cells and Ia interneurons) Rostrally and ipsilaterally +V2 Glutamatergic V2a and Inhibitory V2b Ipsilaterally and caudally +V3 Excitatory Commissural Caudally + + +Goulding M (July 2009). "Circuits controlling vertebrate locomotion: moving in a new direction". Nature Reviews. Neuroscience. 10 (7): 507–18. doi:10.1038/nrn2608. PMC 2847453free to read. PMID 19543221. + +--- + +## Spinal cord circuitry responsible for the flexion reflex + +
Neuroscience 5e Fig. 16.14
+ + +Note: + + + +--- + +## Flexion reflex video summary + +
Neuroscience 5e Animation 16.2
+ +Note: + + + +--- + +## Locomotion– an essential feature of animal life + +
+
+ +* Locomotion is a stereotyped action involving repetitions of the same movement +* Locomotion– a single limb can be thought of having two phases, a stance phase (limb is extended and in contact with the ground) and a swing phase (limb is flexed to leave the ground and then brought forward to begin next stance phase) +* Increases of speed reduce the amount of time it takes to complete the cycle. Stance phase gets quicker, swing phase stays relatively constant +* For quadrupeds, changes in speed are also accompanied by changes in the order of steps taken. At low speeds, back to front occurs first on one side then on the other. At a trot, right forelimb and left hindlimb are synchronized. At high speeds, two front limbs are synchronized as are the two hind limbs +* Pattern generators– once initiated by upper motor pathways or sensory input, pattern generators can keep locomotion going quite well until there is a signal to get out + +
+ +Note: + + +* Flexion describes a bending movement that decreases the angle between a segment and its proximal segment +* Extension describing a straightening movement that increases the angle between body parts +* Abduction refers to a motion that pulls a structure or part away from the midline of the body +* Adduction refers to a motion that pulls a structure or part toward the midline of the body + + + +--- + +## Central pattern generators organize the cycle of locomotion for terrestrial mammals + +
Neuroscience 5e Fig. 16.15
+ + +Note: + +* Defects in spinal cord connectivity interrupt pattern generation + * [cell article](http://www.cell.com/action/doSearch?searchType=quick&searchText=locomotion+eph&occurrences=all&journalCode=&searchScope=fullSite&contentType=video&startPage=) + +* activating the mesencephalic locomotor region can trigger locomtion and change speed of movement by amount of input to spinal cord. Transection at thoracic level will still allow for coordinated locomotor movements. But not just a stretch reflex, due to CPGs present for each limb. These are all connected together in spanning circuits. Transection not allow for good walking in humans though-- maybe bipedalism requires more upper motor neuron control because of greater postural control requirements... + +--- + +## Central pattern generators organize the cycle of locomotion for terrestrial mammals + +
Locomotion in decerebrate cat
+ +--- + +## Central pattern generator model circuit + +
+
Interlimb coupling (C) with mutually inhibitory connections. +E, extensor. F, flexor. Arrows, excitatory. Closed circles, inhibitory +
+ +
Ting et al., *J Neurophysiol* 1998, Fig. 8
+ + + +Note: + +simple network of neurons that could result in alternating flexor and extensor muscle movements for locomotion and be basis of a central pattern generator circuit. + +spinal locomotor and brainstem respiratory CPGs (Yuste et al, Nat Rev Neurosci 2005) +: have an 'excitatory core' of mutually excitatory interneurons +: ea. hemisegment of the spinal cord has this a core +: reciprocal inhibition between contralateral hemisegments results in alternating left–right motor output + + + +--- diff --git a/2016-11-14-lecture15.md b/2016-11-14-lecture15.md new file mode 100644 index 0000000..c24e2da --- /dev/null +++ b/2016-11-14-lecture15.md @@ -0,0 +1,1138 @@ +## Overall organization of neural structures that control movement + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +Lower motor + +system + +State of muscle + +contraction/relaxation + +Execute + +movement + +Output + +system + +Upper motor + +system + +Gating + +Motor + +learning + +2016-03-01 09:46:39 + +
+ +Note: + + + +--- + +## Upper motor control + +* Axons from the upper motor neurons descend to influence the local circuits in the brainstem and spinal cord that organize movements. + +* Upper motor pathways include several brainstem centers and a number of cortical areas in the frontal lobe. + +* Brainstem centers are especially important for postural control. + +* Motor and premotor cortex are responsible for the planning and precise control of complex sequences of voluntary movements. + +Note: + + + +--- + +## Arrangement of motor neurons and local circuit interneurons within the spinal cord + +* Medial ventral horn: motor neuron pools that innervate axial muscles and proximal limb muscles + +* Lateral ventral horn: motor neurons that innervate distal limb muscles. + +* Local circuit interneurons lie in the intermediate zone of the spinal cord grey matter. + +Neuroscience 5e Fig. 16.3 + + + +
+ +Note: + + + +--- + +## Overview of descending motor control + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +
+ +Note: + +somatotopic organization of the ventral horn in the cervical enlargement. Locations of descending projections from the motor cortex in the lateral white matter and from the brainstem in the anterior-medial white matter are shown. + + + +--- + +## Arrangement of motor neurons and local circuit interneurons within the spinal cord + +* Medial intermediate zone local circuit neurons project to medial ventral horn motor neurons. + +* Medial local circuit neurons have axons that may project to targets along the entire length of the cord, and also cross the midline to innervate contralateral side. + +* Lateral regions of the intermediate zone contain local neurons that synapse with motor neurons in the lateral ventral horn. + +* Lateral circuit neurons project over a smaller area and do not cross the midline. + +* Allows distal regions to act independently of each other. + +
+ +Note: + + + +--- + +## Overview of descending motor control + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +Neuroscience 5e Fig. 17.1 + + + +
+ +Note: + +med ventral horn has lower motor neurosn for posteure balance and orienting movements of head and neck during shits of visual gaze. receipve descending input from the pathways orginating mainly in the brainstem, course through the anterior medial white matter of the spional cord and terminate bilaterally. + + + +lateral ventral horn contains lower motor neurons that mediate skilled voluntary movements of the distal extremities. Receive descending projection from the contralateral motor cortex via lateral division of the corticospinal tract. + + + + + +--- + +## Medial brainstem pathways modulate theaction of motor neurons in the ventromedial area + +* Vestibular nuclei: + +* Receive information from inner ear + +* Project to medial regions of spinal gray matter. + +* Controls axial muscles and proximal limbs. + +* Called the vestibulospinal tract. + +
+ +Note: + +info from semicircular canals in inner ear. balance. feedback postural control + +--- + +## Medial brainstem pathways modulate theaction of motor neurons in the ventromedial area + +* Reticular formation: + +* Receives input from higher motor cortex. + +* Complex network of circuits located in the core of the brainstem-from midbrain to medulla. + +* Important for posture. + +* Called the reticulospinal tract. + +
+ +Note: + +feedforward postural control. stabilization during ongoing movements. + +--- + +## Location of the reticular formation in relation to some other major landmarks + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +
+ +Note: + + + +--- + +## Medial brainstem pathways modulate theaction of motor neurons in the ventromedial area + +* Superior colliculus + +* Projects to medial cell groups in the cervical cord + +* Influences neck muscles (colliculospinal tract) + +* But major output of superior colliculus to spinal cord mediated by reticular formation. Axial musculature control of neck and performing orienting movements of head and eye movements. + +
+ +Note: + +tectospinal tract. + +--- + +## The medial descending motor pathways + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + + + +
+ +Note: + + + +--- + +## Feedforward processing + +* Able to predict changes in posture, and generate an appropriate stabilizing response. + +* Some muscles fire in anticipation of a need for postural adjustment. + +* Reticulospinal tract important for this process. If it is severed in a cat, no change in compensatory muscles occur during the process. + +* Stimulate motor cortex in the right place can induce paw lifting, and several limb muscles to fire. Inhibition of the reticulospinal tract will allow the paw to move but will prevent the movement of other limbs. + +Note: + + + +--- + +## Anticipatory maintenance of body posture + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +Severed reticulospinal tract will allow biceps to fire but + +will not allow the gastrocnemius to fire for posture. + +EMG= electromyography. Measure muscle APs + +Neuroscience 5e Fig. 17.13 + + + +
+ +Note: + + + +--- + +## Feedforward and feedback mechanisms of postural control + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +
+ +Note: + + + +--- + +## Primary motor cortex and premotor cortex are in the frontal lobe + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +
+ +Note: + + + +--- + +## Primary motor cortex + +* Located in the precentral gyrus + +* Receives inputs from S1, posterior parietal structures (incorporates multiple sensory modalities, used for planning). + +* Controls contralateral side of the body + +* Topographic organization- body represented across the medial-lateral axis. More space given to areas of fine motor control. Multiple neurons can get the same muscle to fire- not located in exact same place in cortex. + +
+ +Note: + + + +--- + +## Somatotopic representation across S1 and M1 + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +[http://www.pbs.org/wgbh/aso/tryit/brain/probe.html](http://www.pbs.org/wgbh/aso/tryit/brain/probe.html) + +
+ +
+ +Note: + + + +--- + +## Motor cortex + +* Located in the frontal lobe + +* Several adjacent and interconnected areas + +* Primary motor cortex located in the precentral gyrus + +* Gets input from sensory cortex, basal ganglion and cerebellum + +* Has 6 layers, layer V is the output layer (pyramidal cells, including the large Betz cells consisting of about 5% of projection to spinal cord and concerned with fine distal movements) + +* Primary pathway- the corticospinal tract. Axons cross in the caudal medulla, and innervate in lateral ventral horns + +
+ +Note: + + + +--- + +## Pathways from the motor cortex to the spinal cord + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +Indirect pathway: postural + +adjustments, especially for + +axial and proximal muscles. + + + +Corticospinal tract + +(direct pathway) + + + +Corticobulbar tract (indirect pathway. “bulbar” == brainstem nuclei) + +Neuroscience 5e Fig. 17.5 + + + +
+ +Note: + + + + + +90% of corticaospinal axons at caudal end of medulla cross (decussate, lateral corticospinal tract). 10% remain ipsilaterally (ventral corticospinal tract). + + + +most corticobulbar inputs (except lower face and tongue) terminate bilaterally. + + + +maps: muscle, movement sequences, intention? + +--- + +## The corticospinal and corticobulbar tracts + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +Neuroscience 5e Fig. 17.4 + + + +
+ +Note: + +Corticobulbar is blue, corticospinal in red. Note that corticospinal cross the midline in the caudal medulla. Corticobulbar is for facial muscles. + +--- + +## Facial pathway + +* The primary pathway to facial muscles is the corticobulbar pathway. + +* Projection from motor cortex to motor nuclei in brainstem that control facial muscles. + +* Some of these projections are bilateral and some only contralateral. + +* Important for diagnosis where motor damage occurs after a stroke. + +Note: + + + +--- + +## Patterns of facial weakness and their importance for localizing neurological injury + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +Neuroscience 5e Box 17A + + + +
+ +Note: + + + +--- + +## Motor fields + +* A stimulation of a neuron in the primary motor cortex will get multiple muscles to fire, and will inhibit other muscles. + +* Stimulating any of multiple upper neurons can get the same muscle to fire. + +* The “receptive field” of a upper motor neuron has to do with organized movements rather than specific muscle groups. + +* Upper motor neurons therefore act upon more than one motor pool. + +Note: + + + +--- + +## What do motor maps represent? + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +
+ +Note: + +Topographic distribution of microstimulation sites that evoke behavorially relevant movements in a macaque monkey. + + + +Shaded region in map of stimulation sites indicates cortex folded into the anterior bank of the central sulcus. + + + +--- + +## Activity of single upper motor neurons is correlated with muscle movements + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +Neuroscience 5e Fig. 17.6 + + + +
+ +
+ +Note: + +left illustrates spike triggered averaging method for correlating muscle activity with the discharges of single upper motor neurons. + + + +right shows the response of a thumb muscle by a fixed latency to the single spike discharge of a pyramidal tract neuron. This can be used to determine all muscles influenced by a given motor neuron. + + + + + + + + + +--- + +## Purposeful movements resulting from prolonged microstimulation of the primary motor cortex + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +
+ +Note: + +Coordinated movements of hand and mouth after stimulation near the middle of the precentral gyrus towards head (like for eating). + +Coordinated movements of hand towards belly as if inspecting an object. Notice clustering of centralized trajectories after many trials instead of just random movements. + +--- + +## Directional tuning of an upper motor neuron in the primary motor cortex + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +Monkey trained to move joystick in response to light + +
+ +Note: + + + +--- + +## Directional tuning of an upper motor neuron in the primary motor cortex + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +Activity of a single neuron recorded in motor cortex + +is dependent on the direction of the future movement. + +Neuroscience 5e Fig. 17.8 + + + +
+ +Note: + +Notice that the neuron is broadly tuned, even with this colored shading. + +--- + +## Directional tuning of an upper motor neuron in the primary motor cortex + +* Individual neurons are tuned too broadly to accurately predict direction of movement + +* By comparing populations of neurons, one can calculate a direction. + +* Can use the activity of motor cortex to control robots. + +[https://www.youtube.com/watch?v=7kctOHnrvuM](https://www.youtube.com/watch?v=7kctOHnrvuM) + +Neuroscience 5e Fig. 17.8 + + + +
+ +
+ +Note: + +Summing response from a bunch of neurons shows that the direction is better encoded from an ensemble or population of neurons— so that different movement directions/sequences are represented by overlapping and distributed populations of neurons giving rise a series of neuronal population vectors rep all the different directions. + +--- + +## Section of pyramidal tracts in monkeys produces loss of independent digit control + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +Intact (normal) + +After section of + +corticospinal fibers + +
+ +Note: + +corticalspinal, lateral dorsal input for control of distal/fine movements of the fingers. + +--- + +## Primary motor cortex and the premotor area in human + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +Note: + + + +--- + +## Primary motor cortex and the premotor area in macaque monkey + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +
+ +Note: + +Divisions of the motor cortex in the macaque monkey brain. + + + +lateral premotor and supplementary motor areas are involved in selecting and organizing purposeful movements of the limbs and face. + + + +the frontal eye fields organize voluntary gaze shifts. The cingulate motor areas are involved in expression of emotional somatic behavior. + + + + + +--- + +## The premotor cortex + +* Lies adjacent (rostral) to the primary motor cortex + +* Makes extensive reciprocal connections with the primary motor cortex + +* Projects directly to spinal cord (30% of axons in the corticospinal tract). + +* Lateral premotor cortex- has neurons that are tuned to a particular direction of movement (like primary motor cortex) but differs in that they fire earlier than neurons in the primary motor cortex. This is especially important in conditional motor tasks, that pair a movement with a visual cue. + +* During the pairing of a visual cue with a motor task, the neurons will fire before any initiation of the task. This is used for intentions. + +* Lesions in monkey prevent vision conditioned tasks, although vision is fine and the task can be done in other ways. + +Note: + +thes neurons encode intention to perform a movement rather than just the movement itself. + +--- + +## Mirror motor neuron activity in a ventral-anterior sector of the lateral premotor cortex + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +[https://www.youtube.com/watch?v=RuK2Y8JojN8](https://www.youtube.com/watch?v=RuK2Y8JojN8) + +
+ +Note: + +Indeed a nice way to understand this is by examining portions of the lateral premotor cortex that contain so called mirror neurons that have been focus of a bit of attention over recent years. + + + +peristimulus response histograms + + + +passive observation of human hand interacting with (placing food on) tray and also during motor monkey’s own movement to retrieve food + + + +based on Giacomo Rizzolatti et al, 1996 + + + +--- + +## Mirror motor neuron activity in a ventral-anterior sector of the lateral premotor cortex + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +
+ +Note: + +does not respond when pliers are used to interact with food. + + + + + +--- + +## Mirror motor neuron activity in a ventral-anterior sector of the lateral premotor cortex + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +
+ +Note: + +Also fires when the behavior is executed behind a visual barrier. + + + +Suggests that parts of the premotor cortex play a role in encoding the actions of others. + + + +Studies of this mirror neuron system is an active area of neurosci research and some hypotheses anticipate that this connections in the mirror neuron system could be disrupted in neurodevelopmental disorders such as autism or schizophrenia— but it is still important to note that these are active investigations and hypotheses still be tested. + + + + + +http://nautil.us/blog/mirror-neurons-are-essential-but-not-in-the-way-you-think + + + +--- + +## Premotor cortex – two-hand coordination + +* The monkey has learned the task: push the object through the hole and catch it with the other hand + +* With damage to premotor cortex, cannot coordinate two hands to do the task + +
+ +Note: + + + +--- + +## Medial premotor cortex + +* Mediates the selection of movements. + +* Specified by internal rather than external cues. + +* Important for selecting movements based on memory, not in response to cues. + +* Cells will fire when just thinking about an event. + +Note: + + + +--- + +## Planning movement sequence without moving activates supplemental motor area (medial premotor area) + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +Mental rehearsal of finger sequence + +Motor cortex + +Sensory cortex + +Repeated simple finger flexion + +Repeating sequence finger-thumb apposition + +Supplementary + +motor area + +
+ +Note: + +First neuroimaging data + +--- + +## Activation of motor areas depend different on behavioral context + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + + + + + +Primary motor cortex + +Lateral premotor area + +Medial motor area + +1st key touch + +1st key touch + +1st key touch + +Visual + +Cue + +Learned + + Sequence + +
+ +Note: + + + +--- + +## Effects of damage to the cerebral cortex + +* By investigating patients with various types of brain damage we can see how the various components of motor performance may be affected. Examples: + +* Lesions to primary motor cortex (e.g. from a stroke) result in loss of voluntary movements on the contralateral (opposite) side of the body. + +* Apraxia is the specific loss of the ability to plan and correctly perform co-ordinated motor skills, mainly as a result of damage to the supplementary motor area. Speech disorders result from damage to motor cortex. + +* Patients can move muscles, and walk on command but can no longer link gestures to a coherent act, or to recognize the appropriate use of an object even though they can recognize what an object is. + +Note: + + + +--- + +## Damage to cortex: alien limb syndrome + +* A disorder in which person feels unable to control movements of a body part, believes that the limb is alien, or believes that the body part has its own personality + +* It is typically associated with lesions in the supplementary motor area or those affecting blood flow to the anterior regions of the corpus callosum and the anterior cingulate + +* Man who simultaneously tried to strangle and save his wife from himself. + +[https://www.youtube.com/watch?v=dIBBDuQrd-I](https://www.youtube.com/watch?v=dIBBDuQrd-I) + +Note: + + + +--- + +## The Babinski sign + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +[https://www.youtube.com/watch?v=ZFu7bdbnZx8](https://www.youtube.com/watch?v=ZFu7bdbnZx8) + +[https://www.youtube.com/watch?v=oI_ONptx2Ns](https://www.youtube.com/watch?v=oI_ONptx2Ns) + +Neuroscience 5e Fig. 17.16 + + + +
+ +Note: + +normal response on left. Following damage to descending corticospinal pathways stroking sole give abnormal fanning of toes. + + + +Also common in infants during maturation of the descending corticospinal pathways + + + + + +spinal shock and decr activity deprived of input from motor cortex and brainstem + + + +after several days recovery begins (not fully understood) and includes + +-babinski sign + +-spasticity (decerebrate rigidity). Cause by removal of suprresive infl by cortex on postural centre of vesitbulaer nuclei and reticular formation.. Rep abnormal incr in the gain of th spinal corste strech reflesxes. + +-loss of ability of fine movements. + + + + + + + +--- + +## Signs of motor neuron lesions + +* Body Level One + +* Body Level Two + +* Body Level Three + +* Body Level Four + +* Body Level Five + +
+ +Note: + + + +--- + +## Principles + +* Motor + +* Output to muscles via ventral root + +* Two main pathways: + +* 1. Ventromedial system for balance, posture and controlling head & eye movements. Important for muscles of legs & trunk needed for walking. + +* 2. Dorsolateral system for controlling movements of upper limbs & extremities such as fingers and toes as well as movement of facial muscles. + +* + +* Sensory + +* Input to primary somatosensory area via dorsal root + +* Two main pathways: + +* 1. Dorsal spinothalamic tract for proprioception (body awareness and position in space) and haptic feedback (sensation of fine touch and pressure)– crosses in medulla + +* 2. Ventral spinothalamic tract for nocioceptive information– crosses over in spinal cord + +Note: + + + +--- + +--- +