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Block 5; Week 2 > Kenyon-Somatic Sensory System > Flashcards

Kenyon-Somatic Sensory System Flashcards

1
Q

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?

A

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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2
Q

What is the largest sensory organ in your body?

A

the skin!

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3
Q

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

A

False. They are generally similar.

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4
Q

What do PANs do?

A

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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5
Q

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

A

Receptor Potentials.

  1. small (few mV)
  2. graded (amplitude varies w/ strength of stimulus)
  3. NOT conducted–can only be detected in endings of the nerve (of skin, muscle, viscera)
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6
Q

Generator potentials are similar to _______.

A

EPSP

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7
Q

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

A

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

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8
Q

What are the characteristics of APs?

A
  1. large depolarization
  2. all or none
  3. 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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9
Q

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

A

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

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10
Q

On a smaller level, what causes a generator potential?

A

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

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11
Q

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

A

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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12
Q

What are some examples of specializations of PAN receptors?

A 
Meissner's
Ruffini's
Pacinian Corpuscles
Merkel's disks
**these are mechanoreceptor examples. There are other examples for pain & temp
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13
Q

Where are the cell bodies of PANs located?

A

DRG**
or spinal ganglia,
or brainstem ganglia

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14
Q

What makes DRGs unique from autonomic ganglia?

A

there are no dendrites or synapses.

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15
Q

What happens to the terminal ends of the PANs?

A

they are presynaptic & enter the spinal cord

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

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16
Q

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

A

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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17
Q

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

A

False. As it gets bigger it gets faster.

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18
Q

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

A

Thick fibers
A fibers
A beta
These correspond with TVP

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19
Q

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

A

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

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20
Q

Rank these from slowest to fastest:

Aalpha, Adelta, Abeta

A

Slowest: Adelta
Middle: A alpha
Fastest: Abeta

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21
Q

What is a receptive field?

A

somatic sensory neuron receptive field:

**place where tactile stimulus evokes sensory response

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22
Q

What is 2 pt discrimination?

A

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

23
Q

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?

A

Face: 2mm

Thigh & Leg: 40 mm

24
Q

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

A

the thalamus & the cortex

25
Q

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

A

area of innervation of a spinal nerve

herpes zoster flare

26
Q

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

A

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

27
Q

Describe pathway #2 from the face & teeth.

A

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

28
Q

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

A

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

29
Q

What uses the dorsal column/medial lemniscus?

A

TVP

30
Q

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

A

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

31
Q

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

A 
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
32
Q

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

A 
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
33
Q

In the gracile fascicle which part is most medial?

Trunk, Lower limb

A

Lower limb is more medial

34
Q

In the cuneate fascicle which part is more medial?

A

Upper limb is more medial

Neck & occiput is more lateral

35
Q

Where do you find the face in the dorsal column?

A

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

36
Q

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

A

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.

37
Q

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

A

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

38
Q

Where do the axons in the dorsal column synapse?

A

NOT in the dorsal horn or spinal cord

their first synapse is at either the gracile or cuneate nucleus in the lower medulla.

39
Q

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

A

It is not a simple pass thru.

Info is mixed around, descending inputs are added, processing occurs.

40
Q

What is the internal arcuate tract?

A

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

41
Q

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?

A

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

42
Q

What happens to the axons in the medial lemniscus?

A

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.

43
Q

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

A

True. The thalamus knows everything!

44
Q

Describe the trigeminal pathway.

A
  • *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
45
Q

Where is the principal nucleus of the trigeminal complex found?

A

in the mid-pons

46
Q

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

A 
Medial
Genitalia
Toes
Feet
Leg
Trunk
Neck
Head
Shoulder
Arm
Hand
Digits
Thumb
Neck
Eyes
Nose
Face
Lips
Jaw
Tongue
Throat
Lateral
47
Q

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?

A

Trunk & Legs

48
Q

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?

A

arms & face

49
Q

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

A

they go to secondary somatosensory cortex

50
Q

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

A

they project to the limbic system, amygdala, & hippocampus

**this helps mediate tactile learning, memory etc

51
Q

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?

A

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

52
Q

T/F Ascending pathways outnumber descending pathways.

A

False. There are more descending pathways.

53
Q

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?

A

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.

Block 5; Week 2 (8 decks)

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