Somatosensory System Flashcards
Transduce energy=?
Make action potentials in response to a stimulus
How do we classify receptors?
Modality (e.g. mechano, thermo, nociceptors)
Morphology
Axon diameter
What are the four encapsulated types of “touch” receptors?
Whats the fifth nonencapsulated type?
Four encapsulated types: Meissner, Merkel, Pacini, Ruffini
A fifth type “free nerve endings” is not encapsulated
Position sense relies on receptors in what? (3 things)
Receptive field
Size varies with what?
Density varies with what?
On the back, two points have to be farther and close together than on the hand?
Farther
What does a 2 point discrimination test, test?
At what distance on the skin are 2 points perceived as 2 separate points. Different body regions have different distances.
DCML pathway lower body:
Wheres the location of the 1st order cell body? (above or below what vertebral level?)
Divided into what 2 general branches?
Axon travels in what?
Where will it synapse?
DRG below T6
Synapse in in more medial nucleus gracilis in dorsal aspect of medulla
In DCML pathway: lower body, where is the 2nd order neuron cell body?
What happens to the axons, which forms what?
Where are they headed?
Headed to VPL of thalamus
In DCML lower body, Where are the 3rd order neuron cell bodies?
Where do the axons go?
How do they get there?
DCML upper body: Where are the cell bodies (vertebral level as well)
What 2 branches?
Axons travel in what?
DCML: Upper Body
Where are cell bodies for 2nd order
What happens to axons? To form what?
DCML upper body:
Where are the 3rd order neurons cell bodies?
Axons travel to what via what?
Originally nucleus gracilis is on the medial side and nu cuneatus is on the lateral side (at the 2nd order cell body in medulla). But what happens to this relationship in the 3rd vpl and why?
What happens at cortex?
In the 3rd order VPL, the cunneatus (arm neurons) are on the medial side, and the gracilis neurons are on the more lateral side. This happens because when the axons cross midline, the lateral becomes the medial and the medial becomes the lateral.
At cortex it flips back to the way it was at spinal cord (gracilis medial, and cuneatus lateral)
If you damage the posterior columns in DCML what deficit do you expect?
If you damage the left medial lemniscus (or above) you would expect to see deficits in what?
Deficits in discrimitive touch, propioception, vibration on right side (contralateral)
What is the hand dermatome?
c6-8
What is the nipple dermatome?
T4
What is the umbilicus dermatome?
t10
What is the feet dermatome?
L5-S1
What is the sacrum dermatome?
S2-4
How can you differentiate between a peripheral nerve issue and a dermatome issue?
If you have something that matches an entire dermatome, vs portions of a dermatome, then thats a CNS issue, like C5 for example. Injury is at neck etc.
If your injury is in a peripheral nerve (ex lateral cutaneous), then you may have patches of dermatomes, for example a patch of c6, patch of c5, but not a whole dermatome.
What is stocking and glove effect?
Stocking and glove you get deficits in just the hands or just the feet and not the arms or legs. Damage to the axons, example of a condition that doesnt fit dermatome or peripheral nerve
example of a peripheral neuropathy
DCML Dorsal column or root damage will produce what effects?
If you had damage all the way from L5 to S1, where would that show on the dermatome map?
What would that mean in terms of damage?
The whole front leg. Lesion of the spinal cord from L2
Damage to the brain stem or cerebral cortex presents…
contralateral deficits that match dermatomal distribution
Peripheral nerve damage will present as
Deficits in portions of adjacent dermatomes
Peripheral neuropathies
Often begin in distal extermities
For higher order processing the cortext does what?
Where would this higher processing occur?
Posterior parietal cortex
What are the two pain perceptions, and what fibers are they carried by?
What are the 3 ascending pain pathways?
Spinothalamic, spinoreticular, and spinomesencephalic
Spinothalamic: Fast pain
Location of cell bodies for 1st order neuron?
What kind of fibers?
Synapse where?
Spinothalamic: Fast pain
2nd order neuron:
location of cell bodies?
What happens to axons, where do they cross, and what do they form?
Spinothalamic: Fast pain
3rd order Cell bodies located?
Axon travels in what? To where?
Explain whats happening in this photo as the fibers come in from top right.
Also explain the significance of the regions of the pain and temp axons and their relationship to midline
A deltas and C fibers coming in the dorsal root of the spinal cord, synapse in the area of nucleus proprius or substania gelatinosa. Axon of 2nd order neuron will cross midline and coalesce out in ventral lateral funiculus of spinal cord
Unlike dorsal column where lower body is most medial, its reversed for pain and temp. Lower body is most lateral
If you damaged the whole left side of the spinal cord (including dorsal column and anterolateral), where and what kind of effects would you expect?
Deficits in fine touch and vibratory touch on the left side, while deficits in pain and temperature on right side, below the level of the lesion
Explain how there can be a difference in the level that is affected below a lesion in DCML vs spinothalamic
When the axons come in, they can go up or down a couple levels (in Lissauer’s tract) before they synapse, so sometimes what happens is if you have damage at T1, then you will have deficits in fine touch all the way below T1, but contralaterally may only have deficits in pain and temp starting at t3
What would you expect to see with a right spinal cord Hemisection?
What condition is this called?
Hemisection of right upper brain stem or cortex?
Two pathways of spinocerebellar
Dorsal spinocerebellar (lower body) and cuneocerebellar (upper body)
Dorsal spinocerebellar tract: Trunk and legs
1st order neuron- Location of cell bodies? Synapse?
Dorsal spinocerebellar tract: Trunk and legs
2nd order neuron cell body?
Which vertebral levels of axons syanpse directly on Clark’s nucleus? Which have to ascend in fasiculus grasciculus?
Axons ascend ipsilateral or contralaterally?
Dorsal nucleus of Clark is only present in what verterbal level?
How do axons below this level get up there?
Thoracic
They use fasiculus gracilis
Cuneocerebellar Tract: Arm and neck
1st order neuron cell body
axon ascends in what? Ips or contra?
Cuneocerebellar tract: Arm and neck
2nd order neuron cell body in where?
Axon ascends (ips or contra) to reach what? Via what
Where is the 3rd order neuron?
What is Friedreich’s Ataxia?
Initially the spinocerebellar tracts degenerate, not involving other tracts, but then it will evolve into other tracts
Damage here, what do you expect?
Damage here, what do you expect?
What level cut is this?
What happens if we lose PICA?
Damage here, what do you expect?
This was damage to the medial lemniscus
What part of the brain is this? What happens if we lesion both the spinothalamic tract and medial lemniscus?
Pons, contralateral analgesia for the body. Both fine touch and pain/temp lost
Basilar artery (circumfrential branches)
Damage here, what do we expect?
Left side
Proximal PCA
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