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somatosensory.md
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## Somatic sensory system
* Touch, vibration, pressure, position of limbs (sense of self), pain, temperature
* Monitors the external and internal forces acting on the body at any moment
* Leads to the ability to identify shapes and textures of objects
* Detects potentially harmful circumstances
#### Roles
* Monitoring the external and internal forces acting on the body at any moment
* Discrimination of shapes and textures of objects
* Detection of potentially harmful circumstances
#### Includes
1. tactile input (touch– vibration, pressure, stretch)
2. proprioceptive input (positioning of self– muscle fiber feedback )
3. nociceptive input (pain– injury, extreme temperatures, pH)
Note:
@@ -21,9 +29,9 @@ soma
: the parts of an organism other than the reproductive cells
: the body as distinct from the soul, mind, psyche
--
## Sensory systems
Sensory systems:
* The nervous system consists of discrete systems for each of the sensory modalities (touch, vision, hearing, taste, smell)
* Each functional system involves several CNS regions that carry out different types of information processing
@@ -31,14 +39,8 @@ soma
* Each part of the brain projects in an orderly fashion onto the next, creating sensory (e.g. topographic) maps. Neural maps not only reflect the position of receptors on a sensory surface, but also their density
* Functional systems on one side of the body generally respond/control the other side of the body
Note:
Parallel processing of sensory information
<!-- <div><img src="tmp/image_739a8b8.png" height="100px"><figcaption></figcaption></div> -->
Totally fascinating to think out how all this works. Talk about which ones we will go over, common principles, all can get linked together.
---
@@ -67,17 +69,17 @@ In this inset you see both mechanosensory and pain sensitive fibers connected to
---
## There are many types of somatic sensory receptors
## Various types of somatic sensory receptors
* Different functions– pain, temperature, touch, and proprioception
* Different morphologies– free nerve endings or encapsulated
* Different conduction velocities– fast vs. slow
* Differ locations– skin, muscle, tendon, hair
* Different rates of adaptation– slow vs. fast
* Functions– pain, temperature, touch, and proprioception
* Morphologies– free nerve endings or encapsulated
* Conduction velocities– fast vs. slow
* Locations– skin, muscle, tendon, hair
* Rates of adaptation– slow vs. fast
Note:
Variety of somatosensory receptors.
Variety of somatosensory receptors
---
@@ -86,12 +88,12 @@ Variety of somatosensory receptors.
<div style="font-size:0.8em;">
<div></div>
sensory function | receptor type | afferent axon type | axon diameter (µm) | conduction velocity (m/s)
sensory function | receptor type | afferent axon type (alt name) | 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
proprioception | muscle spindle | Aα (Ia + Ib), **myelinated** | 13–20 | 80–120
touch | Merkel, Meissner, Pacinian, and Ruffini cells | A𝛽 (II), **myelinated** | 6–12 | 35–75
pain, temperature | free nerve endings | Aδ (III), **myelinated** | 1–5 | 5–30
pain, temperature, itch | free nerve endings | C, **unmyelinated** | 0.2–1.5 | 0.5–2
</div>
@@ -109,15 +111,25 @@ The slowest ones are…
Tab. 1 after Rosenzweig 2005
--
## Slowly adapting and rapidly adapting mechanoreceptors respond differently to stimulation
<figure><img src="figs/Neuroscience5e-Fig-09.04-0_b85b14e.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 9.4</figcaption></figure>
Note:
Another type of somatosensory afferent variability I mentioned was rate of adaptation– this figure highlights this difference where if we were performing extracellular electrode recordings close to somatic sensory we find that some types adapt slowly, with sustained spiking as a stimulus stays on, whereas others adapt rapidly with their spiking activity strong at the beginning of the stimulus but quiet as the stimulus is maintained.
---
## Proprioception
* The function of some sensory receptors is to relay information about **self**. Where are my limbs and other body parts?
* Muscle spindles– are located in most muscles. Contain specialized muscle fibers encapsulated by connective tissue
* Axons from sensory neurons wrap around this connective tissue and fire depending on muscle length
* Feeds back to γ motor neurons that change spindle length to compensate as needed
* Golgi tendon organs do a similar thing but with tendons
* Sensory feedback information about **self**. Where are my limbs and other body parts?
* Muscle spindles– sensory organ inside muscles. Consists of 'intrafusal' muscle fibers enveloped by fast Group Aα (Ia) sensory neuron afferents. Signals present muscle stretch.
* Golgi tendon organs– sensory organ between muscle fiber and tendon. Consists of connnective tissue enveloped by fast Group Aα (Ib) sensory neuron afferents. Signals present muscle force.
Note:
@@ -125,6 +137,8 @@ Proprioception are stimuli that are produced and perceived within an organism, s
proprioceptive and vestibular system input is integrated within the brain to cause a perception of body position, movement, and acceleration
Provides feedback to γ motor neurons that change spindle length to compensate as needed
--
## Proprioceptors provide information about the position of body parts
@@ -175,23 +189,18 @@ Piezoelectric Effect
: gas stoves, cigarette lighters
: piezoelectric ceramics (Lead zirconate titanate or PZT Pb[Zr~x Ti~1-x ]O~3 ) and single crystal materials (gallium phosphate, quartz, tourmaline)
---
## Slowly adapting and rapidly adapting mechanoreceptors respond differently to stimulation
- piezo for mechanical stress
- asic for acid/low pH sensing
- TRP for hot/cold
<figure><img src="figs/Neuroscience5e-Fig-09.04-0_b85b14e.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 9.4</figcaption></figure>
Note:
Another type of somatosensory afferent variability I mentioned was rate of adaptation– this figure highlights this difference where if we were performing extracellular electrode recordings close to somatic sensory we find that some types adapt slowly, with sustained spiking as a stimulus stays on, whereas others adapt rapidly with their spiking activity strong at the beginning of the stimulus but quiet as the stimulus is maintained.
---
## Skin harbors morphologically distinct mechanoreceptors
<figure><img src="figs/Neuroscience5e-Fig-09.05-0_41d655d.jpg" height="500px"><figcaption>Neuroscience 5e Fig. 9.5</figcaption></figure>
<figure><img src="figs/Neuroscience5e-Fig-09.05-0_41d655d.jpg" height="450px"><figcaption>Neuroscience 5e Fig. 9.5</figcaption></figure>
Note:
@@ -199,7 +208,7 @@ So here are 5 types of morphologically different somatic sensory receptors—
---
## Low threshold (or high sensitivity) mechanoreceptors
## Mechanoreceptors
* Provide information about touch, pressure, vibration, and cutaneous tension
* Four major types of encapsulated mechanoreceptors:
@@ -215,7 +224,7 @@ Note:
## Properties of mechanoreceptor afferents
<div style="font-size:0.5em;">
<div style="font-size:0.4em;">
<div></div>
| type | Merkel | Meissner | Ruffini | Pacinian |
@@ -334,7 +343,7 @@ pacinian corpuscle
---
## Activity patterns in different mechanosensory afferents as Braille is read
## Activity patterns in different mechanosensory afferents while Braille is read
<figure><img src="figs/Neuroscience5e-Fig-09.06-0_aaf10ad.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 9.6</figcaption></figure>
@@ -363,14 +372,19 @@ Note:
## Receptive field size across the body surface
* Receptive field (RF)– the area in the periphery within which sensory stimulus can modulate the firing of the sensory neuron
<div style="width:500px;float:left">
<div></div>
* **Receptive field** (RF)– the area in the periphery within which sensory stimulus can modulate the firing of the sensory neuron
* Spatial resolution of the RF:
* Size– smaller RF, higher resolution
* Density– higher density, higher resolution
* "Two-point discrimination test"
<div><img src="figs/Neuroscience5e-Fig-09.03-2R_8184af9.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 9.3</figcaption></div>
<div><img src="figs/Neuroscience5e-Fig-09.03-3R_6674a79.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 9.3</figcaption></div>
</div>
<div style="float:left"><img src="figs/Neuroscience5e-Fig-09.03-2R_8184af9.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 9.3</figcaption></div>
<div style="float:left"><img src="figs/Neuroscience5e-Fig-09.03-3R_6674a79.jpg" height="300px"><figcaption>Neuroscience 5e Fig. 9.3</figcaption></div>
<!-- <div><img src="figs/image2_b5039d4.png" height="100px"><figcaption></figcaption></div> -->
@@ -565,7 +579,6 @@ Note:
## Brodmann areas
<div><img src="figs/5892_Fig4_3c30913.png" height="300px"><figcaption>Brodmann 1909</figcaption></div>
<div><img src="figs/brodmann-color-crop_81018e1.png" height="300px"><figcaption>Brodmann 1909 color</figcaption></div>
@@ -623,7 +636,7 @@ Note:
* somatotopy– topographic representation of the body surface
* areas of high receptor density get more cortical space
<div><img src="figs/Neuroscience5e-Fig-09.11-2R_18f72c2.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 9.11</figcaption></div>
<div><img src="figs/Neuroscience5e-Fig-09.11-2R_18f72c2.jpg" height="300px"><figcaption>Neuroscience 5e Fig. 9.11</figcaption></div>
<div><img src="figs/Neuroscience5e-Fig-09.11-3R_0a2e938.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 9.11</figcaption></div>
@@ -631,6 +644,10 @@ Note:
More cortical space for body areas with higher somatic receptor density
topographic
: the arrangement or accurate representation of the physical features of an area
--
## The ‘homunculus’ reflects sensory receptor density
@@ -688,7 +705,8 @@ Note:
* Submodality of the sense of touch, warns of injury and things that should be avoided
* More subjective than the other senses. The same stimulus can produce different responses in different individuals, or in the same individual in different circumstances
<div style="width:430px; float:left;"><iframe src="https://www.youtube.com/embed/s28fCIQKJTA" width="420" height="315"></iframe><figcaption>Congenital insensitivity to pain</figcaption></div>
<!-- <div style="width:430px; float:left;"><iframe src="https://www.youtube.com/embed/s28fCIQKJTA" width="420" height="315"></iframe><figcaption>Congenital insensitivity to pain</figcaption></div> -->
Note:
@@ -709,9 +727,8 @@ Congenital insensitivity to pain
---
## Pain involves specialized neurons not just extrastimulation of touch receptors
## Pain perception involves activation of specialized neurons (not just mechanoreceptors)
* Scheme for transcutaneous nerve recording
* Nociceptor doesn’t fire until pain is felt. Other thermoreceptors fire at all temps and at about the same frequency
<figure><img src="figs/Neuroscience5e-Fig-10.01-0_5b078f2.jpg" height="300px"><figcaption>Neuroscience 5e Fig. 10.1</figcaption></figure>
@@ -719,6 +736,7 @@ Congenital insensitivity to pain
Note:
Scheme for transcutaneous nerve recording
---
@@ -876,7 +894,7 @@ Note:
## Major pathways for pain (and temperature) sensation of the body
<figure><img src="figs/Neuroscience5e-Fig-10.06-1R_15d50f2.jpg" height="500px"><figcaption>Neuroscience 5e Fig. 10.6</figcaption></figure>
<figure><img src="figs/Neuroscience5e-Fig-10.06-1R_15d50f2.jpg" height="450px"><figcaption>Neuroscience 5e Fig. 10.6</figcaption></figure>
Note:
@@ -1104,7 +1122,7 @@ Note:
- mind separate from body. No– this highlights something that neuroscientists already widely accept, that you cannot separate the mind from the body, the mind is body and vice versa
- what is or is not reality philosophers
- highlights descending control and higher order processing of pain
- endogenous opioid
- endogenous opioids
- children are not placebo reactors less than 10 yr old. acupuncture works likely as a placebo (needle can be stuck anywhere). Hypnosis can alter perception (reduce activity in anterior cingulate) without sensory discrimination (Rainville Science 1997). But not sensitive to naloxone, so not through opiate system.
@@ -1112,15 +1130,12 @@ Note:
- 35% of people are placebo reactors
---
<!--
## Phantom limbs and phantom pain
<figure><img src="figs/Neuroscience5e-Box-10D-0_1f5debb.jpg" height="400px"><figcaption>Neuroscience 5e Box 10D</figcaption></figure>
Note:
Phantom limbs can be another fascinating clue to higher order processing of somatic sensation. This stems from the fact that for amputees, almost have an illusion that the missing limb is present.
Phantom limbs can be another fascinating clue to higher order processing of somatic sensation. This stems from the fact that for amputees, almost all have an illusion that the missing limb is present.
It’s been proposed that there is an internal mismatch between the brain’s representation of the body and the pattern of peripheral tactile input that results in the illusory sensation.
@@ -1129,5 +1144,4 @@ R. Melzack 1989 Can Psychol Phantom limbs
TINS 1990
[http://www.youtube.com/watch?v=Esgl1q73wP8](http://www.youtube.com/watch?v=Esgl1q73wP8)
---
-->