Kenyon-Somatic Sensory System Flashcards by michelle granstrom

When sensory info gets to the CNS it can take 2 main pathways. What are they? Which brain structures do they target to drop off their info?

They target the thalamus & the cortex.
They can go as TVP or P&T
TVP (touch, vibration, proprioception)
P&T (pain & temp & coarse touch)

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What is the largest sensory organ in your body?

the skin!

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T/F The primary afferent neurons for TVP & P&T are vastly different.

False. They are generally similar.

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What do PANs do?

they receive stimuli (mechanical, chemical, thermal) & generate a generator potential. If this generator potential reaches the threshold it will conduct AP via its axons into the spinal cord

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What is another name for generator potentials? What are their characteristics?

Receptor Potentials.

small (few mV)
graded (amplitude varies w/ strength of stimulus)
NOT conducted–can only be detected in endings of the nerve (of skin, muscle, viscera)

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Generator potentials are similar to _______.

EPSP

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If a generator potential arches the threshold what do you get?

you get a spike potential & propagation of AP along the axon.

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What are the characteristics of APs?

large depolarization
all or none
CONDUCTED–>the AP at the end of the axon will look the same as the one at the beginning of the axon.

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T/F The generator potential looks like the same at the end of an axon as it does at the beginning.

False. It lowers in amplitude. If it doesn’t reach threshold–>it won’t even conduct along the axon.

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On a smaller level, what causes a generator potential?

the opening of ion channels that respond to stretch, chemicals, temp. Note: it is tough to study stretch ion channels.

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Where are the receptors of PANs located? Some of this are specialized–what does this mean?

in the periphery (skin, muscle, blood vessel)

sometimes inserted into a capsule that is important in encoding the stimulus. These are called specializations.

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What are some examples of specializations of PAN receptors?

Meissner's
Ruffini's
Pacinian Corpuscles
Merkel's disks
**these are mechanoreceptor examples. There are other examples for pain & temp

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Where are the cell bodies of PANs located?

DRG**
or spinal ganglia,
or brainstem ganglia

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What makes DRGs unique from autonomic ganglia?

there are no dendrites or synapses.

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What happens to the terminal ends of the PANs?

they are presynaptic & enter the spinal cord

from there they go up & down the cord & synapse at different levels.

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What is the actual size of the cell body & axon of a neuron?

the cell body is super small!
the axon is really thick & long
it doesn’t really make sense, but he says that the cell body is 50 micrometers across & the axon is 5 micrometers across.

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T/F As a conducting cell gets bigger, its conduction rate gets slower.

False. As it gets bigger it gets faster.

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Which fibers conduct messages the most rapidly? Which type of PAN does this correspond with? Are these thick or thin fibers?

Thick fibers
A fibers
A beta
These correspond with TVP

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Which fibers conduct messages least rapidly? What type of PAN does this correspond with? Are these thick or thin fibers?

Thin fibers
C fibers
Adelta fibers
These correspond with pain & temp PANs

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Rank these from slowest to fastest:

Aalpha, Adelta, Abeta

Slowest: Adelta
Middle: A alpha
Fastest: Abeta

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What is a receptive field?

somatic sensory neuron receptive field:

**place where tactile stimulus evokes sensory response

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What is 2 pt discrimination?

the ability to distinguish one or two tactile stimuli varies over the body.

How far apart do the calipers have to be on the face for you to do 2 pt discrimination? How about on the thigh & leg?

Face: 2mm

Thigh & Leg: 40 mm

Which structures in the brain ultimately do the 2 pt discrimination?

the thalamus & the cortex

What is a dermatome? What is its most important clinical correlation?

area of innervation of a spinal nerve | herpes zoster flare

What are the 2 main pathways to get sensory info from the body back into the brain?

Pathway #1: Body & back of head-->Dorsal column/Medial Lemniscus Pathway #2: Face & Teeth-->Trigeminal Nerve

Describe pathway #2 from the face & teeth.

Info from the face & teeth is collected by neurons. their cell bodies are in the trigeminal ganglion they ultimately enter the brainstem via the trigeminal nerve

Describe pathway #1 from the body & back of neck.

info from these areas is collected by neurons. their cell bodies are in the DRG they enter the spinal cord via dorsal roots

What uses the dorsal column/medial lemniscus?

TVP

What are the 2 pathways within the dorsal column/medial lemniscus pathway?

there is pathway A: no synapse in the dorsal horn (gracile & cuneate tracts)-->ascending up the dorsal horn to the medulla there is pathway B: branches enter dorsal horn & synapse in various Rexed's levels-->important in spinal reflexes

Which pathway are gracile tracts a part of? Which part of the body do they apply to?

``` Dorsal Column/Medial Lemniscus Pathway Pathway A (no synapses in dorsal horn) Applies to TVP Applies to Lower limbs Found in the medial part of the dorsal column ```

Which pathway are cuneate tracts a part of? Which part of the body do they apply to?

``` Dorsal Column/Medial Lemniscus Pathway Pathway A (no synapses in dorsal horn) Applies to TVP Applies to upper limbs, trunk, neck Found in lateral part of the dorsal column ```

In the gracile fascicle which part is most medial? | Trunk, Lower limb

Lower limb is more medial

In the cuneate fascicle which part is more medial?

Upper limb is more medial | Neck & occiput is more lateral

Where do you find the face in the dorsal column?

Trick Q you don't! Test question. This is found in the trigeminal pathway

What clinical problem can cause you to lose some of your dorsal column function & TVP info? What effect would this have?

syphilis this would have modest effects on your ability to perform simple tactile tasks loss of proprioception & ability to detect speed of stimulus **wouldn't completely destroy your TVP tho b/c there are pathways that bear some of this burden.

T/F The only pathway for TVP is the dorsal column/ medial lemniscus pathway.

False. there are others...but this is def the major one!

Where do the axons in the dorsal column synapse?

NOT in the dorsal horn or spinal cord | their first synapse is at either the gracile or cuneate nucleus in the lower medulla.

What happens during their synapse in the nuclei of the brainstem?

It is not a simple pass thru. | Info is mixed around, descending inputs are added, processing occurs.

What is the internal arcuate tract?

this is a tract in the brainstem where the tracts of the dorsal horn flip sides & become the medial lemniscus. They also become ventral

The axons for the lower limbs are medial in the dorsal horn. Where would these inputs end up in the brainstem after the internal arcuate tract?

they would end up ventral & lateral to the cuneate & on the other side of the brainstem

What happens to the axons in the medial lemniscus?

they synapse with 3rd order neurons in the VPL (ventral posterior lateral) nucleus of the thalamus. they then continue to the post central gyrus or primary sensory cortex.

T/F The VPL of the thalamus contains a complete representation of the somatic sensory periphery.

True. The thalamus knows everything!

Describe the trigeminal pathway.

* *Somatic sensation from face & mouth come in thru trigeminal nerve & synapse onto secondary neurons in the principal nucleus of the trigeminal complex * *these secondary sensory axons cross over & join their TVP buddies on the medial lemniscus. * *it then deviates to form the trigeminal lemniscus * *this goes to the VPM of the thalamus * *it then projects to the primary sensory cortex

Where is the principal nucleus of the trigeminal complex found?

in the mid-pons

What is the order of body parts on the cortex, according to the homunculus man? Medial-->Lateral

``` Medial Genitalia Toes Feet Leg Trunk Neck Head Shoulder Arm Hand Digits Thumb Neck Eyes Nose Face Lips Jaw Tongue Throat Lateral ```

Based on knowing which parts of the cortex the anterior & middle cerebral arteries supply...if you had a stroke & lost the area supplied by your anterior cerebral artery-->which parts of your body would you lose TVP to?

Trunk & Legs

Based on knowing which parts of the cortex the anterior & middle cerebral arteries supply...if you had a stroke & lost the area supplied by your middle cerebral artery-->which parts of your body would you lose TVP to?

arms & face

What happens to the neurons after they are in the primary sensory cortex?

they go to secondary somatosensory cortex

What happens to neurons after they are in the secondary somatosensory cortex?

they project to the limbic system, amygdala, & hippocampus | **this helps mediate tactile learning, memory etc

When you are thinking about a lecture & not about your feet you don't think about how your feet feel. Not until you start thinking about them. What explain this phenomenon?

descending pathways from sensory cortex-->thalamus-->brainstem-->spinal cord **these modulate the flow of sensory information upwards

T/F Ascending pathways outnumber descending pathways.

False. There are more descending pathways.

If you are taking a lab practical & looking @ a slice of spinal cord...which side is from the patient's left side? If you are looking at this slice...how can you tell which side of the spinal cord a touch on the pt's left arm would go thru?

It is the same as if you are looking at the patient. The pt's left side is your right side. If you touch the pt's left arm-->it goes to the left side of the slice of spinal cord.