* Circuits that do the same kinds of things are grouped into 'systems', e.g. sensory systems and motor systems
* Many neurons function between these systems, called associational systems. Associational systems are the most complex and least well characterized systems.
Last time we learned some of the basic cellular anatomy of the nervous system. Today we will put the system in nervous system–– because nervous systems really are greater than the sum of its parts… in other words our brain is not just a blob of cells but it is the interconnections between cells, groups of cells, and brain regions that allow our fantastic feats of emergent biological computation. So lets discuss the overall the structure of the nervous system.
First of all it is a system of systems. In other words…
<div><figcaption class="big">central nervous system (CNS)</figcaption><video height=200px controls loop src="figs/cns_overview.m4v"></video><figcaption>[C. Krebs CC BY-NC-SA, Univ. British Columbia](http://www.neuroanatomy.ca/3D_files/3D_index.html?id=1)</figcaption></div>
<div><img src="figs/Neuroscience5e-Fig-01.10-1R_cfe2e3e.png" height="400px"><figcaption>Neuroscience 5e Fig. 1.10</figcaption></div>
<div><img src="figs/Neuroscience5e-Fig-01.10-2R_b4b3e07.png" height="400px"><figcaption>Neuroscience 5e Fig. 1.10</figcaption></div> <!-- .element: class="fragment fade-in"-->
This illustrates the two top level systems of the nervous system, the CNS containing the brain and spinal cord and the PNS containing nerves and ganglia exiting the spinal cord.
This diagram outlines the functional hierarchy of different components or systems within the whole nervous system including relations between internal and external environment and sensory receptors in the PNS as well as skeletal muscle and smooth, cardiac muscles that the nervous system controls.
right vagus nerve primarily innervates the SA node, whereas the left vagus innervates the AV node
pns supplies smooth muscles, cardiac muscles, and glands. functions to maintain homeostasis, and is concerned with involunary functions.
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## Anatomy terms
* Nerves– bundles of axons, enveloped by glial cells that myelinate them
The term we use for cell bodies grouped together in the PNS is ganglia. In the CNS cell bodies are accumulated together as nuclei or if they are arranged in highly ordered sheets or lamina it is called cortex.
<figure><figcaption class="big">Cerebral cortex and thalamic nuclei</figcaption><img src="figs/2060_cell_abf6617.jpg" height="300px"><figcaption>[Brain Biodiversity Bank MSU, NSF](https://msu.edu/~brains/brains/human/coronal/2060_cell_labelled.html)</figcaption></figure>
Note:
Here is one of those cell body violet stained sections-- you can see the cortical sheet and different subcortical nuclei in the thalamus, etc. We will go over this in more detail later.
: nerves that innervate the pelvic organs and lower limbs. Includes motor innervation of the hips, knees, ankles, feet, internal anal sphincter and external anal sphincter.
* Extends from the base of the skull to the first lumbar vertebra
* Receives sensory info from skin, joints, and muscles of trunk and limbs and contains motor neurons responsible for both voluntary and reflexive movements
* Nerve fibers bundled in 31 pairs of spinal nerves. There is a sensory division (dorsal root ganglia) and a motor division (ventral root)
From the brain stem there emerges 12 left-right pairs of cranial nerves that carry afferent or efferent information mostly concerned with sensory and motor functions of the head. The exception is the the vagus nerve arising from the medulla which carries critical autonomic signals for your visceral organs and heart without which you cannot live.
III | Oculomotor Nerve | Eye movement; pupil constriction
IV | Trochlear Nerve | Eye movement
V | Trigeminal Nerve | Somatosensory information (touch, pain) from the face and head; muscles for chewing
VI | Abducens Nerve | Eye movement
VII | Facial Nerve | Taste (anterior 2/3 of tongue); somatosensory information from ear; controls muscles used in facial expression
VIII | Vestibulocochlear Nerve | Hearing; balance
IX | Glossopharyngeal Nerve | Taste (posterior 1/3 of tongue); Somatosensory information from tongue, tonsil, pharynx; controls some muscles used in swallowing
X | Vagus Nerve | Sensory, motor and autonomic functions of viscera (glands, digestion, heart rate)
XI | Spinal Accessory | Nerve Controls muscles used in head movement
XII | Hypoglossal Nerve | Controls muscles of tongue
This lists these 12 cranial nerves and their relevant sensory and/or motor function they carry. Notice that many of the nerves carry mixtures of sensory and motor information, which you could see with the color coding on the previous slide. Also notice that 4 of the 12 nerves concern sensory and motor information from the eyes. In fact the cranial nerve containing the most fibers is the optic nerve which contains 1.2 million axons that carries all the information necessary to perceive the visual world around you (compare with 130 million photoreceptors and 0.7 to 1.5 million RGCs)
<figure><img src="figs/mri_midbrain_170-labels_3f3d983.png" height="400px"><figcaption>[C. Krebs CC BY-NC-SA, Univ. British Columbia](http://www.neuroanatomy.ca/MRIs/mri_sagittal.html?id=1)</figcaption></figure>
The tectum of the midbrain, which is latin for ‘roof’ contains the superior and inferior colliculi and is important for processing visual and auditory information as well as shaping motor commands for orienting the head and body.
Ventral to the cerebral aqueduct through which cerebral spinal fluid circulates, you will find the tegmentum of the midbrain which contains the —>
substantia nigra pars compacta, a nucleus containing neurons making the neurotransmitter dopamine that are important for regulating motor movements via their connections with the basal ganglia and which are devastated in parkinson’s disease.
Now you’ve all heard the phrase ‘running around like a chicken with its head cut off’ —>
Cerebellum is latin for ‘little brain’, and it does have a striking organization with lobes and fissures similar to the folding of the cerebral cortex to increase surface area and packing density of neuronal interconnections. You can see here its main cell body layer, obvious in this purple nissl stain for cell bodies here. It’s in this layer where you will find the beautiful purkinje neurons that we saw images of in lecture 01.
: the principal and most anterior part of the brain in vertebrates, located in the front area of the skull and consisting of two hemispheres, left and right, separated by a fissure
* Thalamus– 'relay station to the cerebral cortex'– an essential link in the transfer of most sensory information from periphery to cerebral cortex. Also plays a role in filtering information from the periphery
* Hypothalamus– lies ventral to thalamus. Controls a variety of functions, growth, eating, drinking, maternal behavior by regulating hormonal secretions of the pituitary gland Connects to virtually every part of brain. Important in initiating and maintaining behaviors that the organism finds rewarding
The thalamus can be generally thought of as the relay station to the cortex.
The hypothalamus lies ventral to the thalamus and controls an array of important physiological functions such as feeding, fluid balance, and hormonal secretions of the endocrine system.
Thalamus is essentially the relay nuclei that routes sensory information into the cortex. This routing of information is highly organized with different subdivisions sending information in parallel pathways to different visual, auditory, and somatosensory regions of the cerebral cortex. But the connections are highly reciprocal with cortical areas, such that the thalamus is integral to many sensory, motor, and cognitive functions as well as the generation of different electrical rhythms that underly different sleep states.
…and is the gateway for routing information into the cerebral cortex. It contains a number of different nuclei and subdivision that take information from other brain regions including the brain stem and sends to appropriate primary sensory or higher order regions of the cerebral cortex.
<div><figcaption class="big">hypothalamus, coronal section</figcaption><img src="figs/coronal5b-hypothalamus_32b4364.png" height="300px"><figcaption>B. Crawford and K. McBurney, Univ. of Victoria</figcaption></div>
Controls a variety of functions, growth, eating, drinking, maternal behavior by regulating hormonal secretions of the pituitary gland. Connects to virtually every part of brain. Important in initiating and maintaining behaviors that the organism finds rewarding
Limbic system includes the amygdala, as well as the part of the basal ganglia, part of the thalamus, prefrontal cortex, and the hippocampus. It is the integrative center for emotions, emotional behavior, and motivation
- *Meynert 1884, frontal lobe and cortex of calcarine fissure. First to describe cortical layering (bats, but also human and other animals). Sections fixed in potassium dichromate, stained with carmine, and cleared in oil of cloves.*
it’s a bit of a trick question because both of these answers are partially right depending on how you define a part of the brain or what kind of function you’re talking about, but it is not the case that
* particular regions of the cerebral cortex controlled specific functions, i.e. the brain does not act as a single organ.
* each function grew with use such as a muscle with exercise
* this growing causes the skull to budge creating a pattern of bumps “phrenology”
## Franz Joseph Gall– phrenology
Standing at his lectern, the priest stared steadily upon one man in the congregation: Franz Joseph Gall. With his angry voice echoing off the church's hallowed walls, he pronounced,"There are those amongst us, who have lost their way from our Lord's divine path. With pomposity, they state the mind is situated in an organ as mushy and insubstantial as the brain. What ludicrousness is this, when all intelligent men know that God has imbued our thinking into our very soul, whereupon no one can put his finger precisely on the spot!"
Note areas 4 (primary motor cortex), 1,2,3 (primary somatosensory cortex), area 17 (primary visual cortex), area 18 (secondary visual cortex), area 41,42 (primary auditory cortex, also part of 22)
*Comparative localization teachings of the cerebral cortex in their principles, illustrated on the basis of Zellenbaues. Leipzig, Johann Ambrosius Barth Verlag, 1909 . 2nd edition, 1925. English translation by Laurence J. Garey: Localisation in the Cerebral Cortex by Korbinian Brodmann. Smith-Gordon, 1994; new impression: Imperial College Press., 1999*
* Believed that functions could be localized in the brain
* Studied patients with aphasia– language disorders found in patients who have had a stroke
* Had a patient that could understand language but could not speak, problems with the organizational aspects of language. Found lesion in posterior frontal lobe (Brodmann areas 44/45)
* This kind of aphasia is called a motor or expressive aphasia
* Eight patients with similar problems all had similar lesions, always on the left side
* "Nous parlons avec l’hemisphere gauche!" "We speak with the left hemisphere!"
We also define regions of the brain based on studies of brain lesions in patients. Recall the guy with the railroad spike from last lecture. Well the French physician Paul Broca in the 19th c.
* Had a patient that could speak but not understand language. Called receptive aphasia
* Damage was to a different area– left side, posterior part of the left temporal lobe (Brodmann areas 22/39/40)
* Argued that simple perceptual and motor activities were localized to a specific area and that most functions result from interconnections between areas. Idea of "distributive processing"
*Broca's aphasia patients have limited writing. Loss of the ability to produce language (spoken or written)*
Apraxia
: verbal apraxia is difficulty starting and making voluntary movements (motor plans) needed for speech (with no paralysis or weakness of speech muscles)
dysarthria
: inability to move the muscles of the tongue and mouth to produce speech
:in linguistics it is set of structural rules governing the composition of clauses, phrases, and words in any given natural language. The term refers also to the study of such rules, and this field includes morphology, syntax, and phonology, often complemented by phonetics, semantics, and pragmatics
* Fritsch and Hitzig (1870)– discrete limb movements in dogs can be produced by electrical stimulation of the contra-lateral motor cortex. Thus the right hand is controlled by the left hemisphere. 'Dominant' hemisphere
* Wilder Penfield (1950)– neurosurgeon, localized motor functions by stimulating specific areas of the brain
* Roger Sperry (1960s)– split brain patient studies
And there is lots of other evidence for localization of brain function, especially for sensory and motor information for limbs and body. In fact Fritsch…
And the Canadian physician Wilder Penfield performed classical mapping of motor function in the cerebral cortex by localized electrical stimulation.
And then there is the fascinating split brain studies of Sperry and Gazzaniga in the 1960s
* The corpus callosum and anterior commissure are the two axon tracts that connect the two sides of the brain. They are sometimes cut to prevent the spread of severe epilepsies
The classic split brain studies which Roger Sperry got the Nobel for in 1981 showed the lateralized localization of language that Broca and Wernicke anticipated as well as several other higher functions. They took advance of the fact that in patients with severe epilepsies, sometimes the commissures connecting the two hemispheres are cut to prevent the spread of seizures.
* Humans are 90% right handed as a population and the degree of lateralization among individuals is strong, regardless of left or right-handedness
* 96% of right handers having left hemisphere speech, compared with 70% of left handers
* Twin studies have demonstrated some genetic influence on handedness, but 75% of the variance is nongenetic and individually specific, with only 25% explained by genes [#Bishop:2013]. Even the segregation of of handedness and language laterality suggests a complex polygenic set of factors, with 96% of right handers having left hemisphere speech, compared with 70% of left handers [#Bishop:2013].
Here is an illustration of the experiment performed by by Sperry and his colleagues for these split brain studies.
After the corpus callosum connecting the two hemisphere was cut to alleviate epileptic seizures, the patients were asked to fixate on a point and name objects presented in each visual field.
Now you haven’t learned about the visual system yet, but just as sensory information from your left hand goes to your right hemisphere, visual information from the lateral part of your left visual field goes to your right visual cortex.
Split brain patients could not correctly name objects presented in their left visual field, presumably because that info could not reach the left hemispheres because the callosal connections were severed. But split brain patients could correctly name an object when presented in their right visual field, because that information was received by the left visual cortex and could be passed onto the language centers.
In all Sperry and his colleagues showed that language, mathematical, and logical reasoning is dominant in the left hemisphere and that shape recognition, spatial attention, emotional processing, and creativity in more dominant in the right hemisphere.
*right hemisphere: 'coloring' language with emotive tonal variation, 'prosody'. Adds additional meaning to verbal communication. Mandarin chinese. Monotone professor lecture*. Evidence suggest similar areas of the right hemisphere associate with this emotive coloring of language.
Similar areas used in sign language thus this constellation of brain regions specializes in symbolic representation and communication, rather than just spoken language.
PET:
: positron emission tomography
: detects pairs of gamma rays emitted indirectly by a radioactive tracer injected into bloodstream (positron-emitting radionuclide)
CT:
: computerized tomography
: a series of X-ray images from different angles
: computer processing to create cross-sectional images
Babbling sounds from a baby shows that there is a pattern of sounds produced sequentially that are related to the phones necessary for producing spoken language. Language imitation follows other imitations (mirror neurons?) during developmental learning and behavioral acquistion. Brain is continuously simulating the future based on past experienced training patterns.
