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BISC 421 > Lecture 4 - Somatosensation > Flashcards

Lecture 4 - Somatosensation Flashcards

1
Q

Where are the cell bodies of sensory neurons located?

A

in the DRG or dorsal root ganglion which are located along the spinal cord

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2
Q

Where are the cell bodies of sensory neurons that innervate the face?

A

-trigeminal ganglia

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3
Q

What are the cells of these sensory neurons like?

A

pseudo unipolar - meaning they have two axons and no dendrite

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4
Q

What is the basic circuit for somatosensation?

A

the cell bodies for somatosensory neurons are in the DRG and they send an axon to you skin and an AP is initiated at the nerve endings and the information is then transmitted to the dorsal horn or goes up the spinal cord

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5
Q

What is a dermatome?

A

the specific region of the body innervated by a sensory ganglia

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6
Q

Why is knowledge of dermatomes important?

A

doctors can determine the location of a spinal cord lesion

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7
Q

What are some dermatomes?

A

trigeminal - face
cervical - shoulder, arms
thoracic- trunk
-lumbar - legs
-sacral - genitals, legs

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8
Q

What does the skin contain a variety of?

A

morphologically distant mechanoreceptors

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9
Q

What are the five types of nerve endings in the skin?

A

meissner corpuscle
pacinian corpuscle
ruffini’s corpuscles
merkel’s disks
free nerve endings

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10
Q

What is the pacinian corpuscle involved in and what is its location in the skin?

A

deep within the skin and is a big ball so when you sit down and feel the chair that nerve ending is able to not keep responding to stimuli so you can ignore it once something is etched

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11
Q

What is the merkel cell involved in?

A

higher up in skin so will be in tactile sensation

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12
Q

What are free nerve endings involved in?

A

temp and pain

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13
Q

What are the three things that can be used to characterize somatosensory fibers?

A

speed of nerve conduction
adapting or non adapting
receptive field size

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14
Q

What causes greater conduction velocity?

A

axon diameter; myelination

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15
Q

Why is touch (merkel, meissner, pacinian, and ruffini cells) have faster conduction velocity than pain?

A

-greater axonal diameter and myelination
-inflammatory pain has been going on for a while so we do not need to register it as fast as a touch stimulus

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16
Q

What are tough merkel, meissner, pacinian, and ruffini cell fibers called?

A

AB (big axonal diameter, myelinated)

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17
Q

What are muscle spindle fibers called?

A

Ia, II (big axonal diameter, myelinated)

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18
Q

What are free nerve endings called that respond to pain and temperature only?

A

A(delta) (smaller axonal diameter, myelinated)

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19
Q

What are free nerve endings called that respond to pain and temperature and itch?

A

C (smaller axonal diameter, unmyelinated)

20
Q

How was conduction velocity of different fibers measured?

A

a probe held against the skin injects a small current which stimulates the nerve and another electrode affixed at various nerve locations measure the speed of the impulse and other properties

21
Q

What is characteristic of rapidly adapting responses and what are they ideal?

A

they will go away quickly and they are ideal for detecting a change in stimulus intensity and ignoring a constant stimulus

22
Q

What somatosensory afferent is slowly adapting?

A

Merkel cell

23
Q

What somatosensory afferent is rapidly adapting?

A

pacinian corpuscle

24
Q

What is the receptive field?

A

the nerve bifurcates and barbarizes over a certain area and this area is the receptive field

25
Q

What is the two point discrimination and what does it test?

A

-it tests the receptive field size and it is to tell wether two points are felt separately or if only one point is felt

26
Q

Where is the smallest receptive field and what does it provide us?

A

-in the fingers
-gives us fine discrimination

27
Q

What have large receptive fields?

A

pacinian and ruffini corpuscles

28
Q

What activates the pacinian corpuscle?

A

vibration when you sit down; vibratory cues cane be transmitted by the body when you grasp an object

29
Q

What activates merkel cell neurite complex?

A

indentation depth, fine tactile discrimination form and texture perception

30
Q

What activates mechano-nociceptor?

A

activates on injurious forces in respond to tissue damage or injury
-skin injury, pain

31
Q

What does a merkel cell mediate?

A

fine touch like braille; merkel cells were recorded from the afferent nerve fibers of a monkey and the monkey as reading braille and the merkel cell was slowly adapting
-pacinian corpuscle empty cause does not encode that info

32
Q

What do proprioceptors do?

A

detect the body position

33
Q

What are the two proprioceptors?

A

muscle spindles and Golgi tendon organs; information comes from sensory neurons goes into spinal cord and then goes to these to cause a reflex you also gave projections that go to the cortex to increase your awareness of these things
-muscle spindle fiber - changes in muscle length
-GTO - tension on muscle

34
Q

What is the basic idea behind mechanosensory transduction?

A

ion channel in mechanosensory neuron opens in response to stretch which leads to the membrane to depolarize and APs to generate

35
Q

What were identified as the mechanically activated ion channels?

A

Piezo 1 and Piezo 2

36
Q

How were Piezo 1 and 2 identified?

A
  1. found cell line that has a mechanically activated current and used a patch electrode and a blunt probe to poke the cell and record electrical activity
  2. screened 72 candidate genes by the RNAi which is able to knock down the expression of was gene and from this Piezo one was identified since when it was KO the electrical activity when poked by a blunt probe stopped
  3. also found Piezo 2 which is similar in amino acid sequence to Piezo 1
37
Q

Do Piezo 2 and 2 alone encode mechanically activated ion channels and how was this found?

A
  1. transfected cDNA encoding ion channel into tissue culture cells that are not normally sensitive to touch
  2. see large inward current in response to poking the cell indicating that it Is a mechanically gated ion channel and that it is excitatory

so yes both are sufficient on their own to induce mechanosensitivity

38
Q

How many transmembrane domains per monomer do Piezo 1 and 2 have and what do they assemble as (i.e. monomer, dimer, trimer, etc.)?

A

38 transmembrane domains and they assemble as trimer

39
Q

What aspect of the piezo channels allows them to detect stretch on the membrane?

A

the proteins has wings so when the protein is stretched the wings flatten out when it is relaxed they are up

40
Q

Is Piezo 2 the mechanoreceptor in sensory cells and how was that determined?

A
  1. It was found in the DRG via in situ hybridization (piezo 1 is found in nonsensory cells)
  2. fusion of Piezo 2 to GFPO showed expression in the skin
  3. was found to be required in mechanosensory responses in sensory cells
  4. and is in fact required for behavior (done using a KO and tested bouts in mice)
41
Q

What was found in humans that have a Piezo knockout?

A

their eyes compensate but when they are closed they are not able to detect

42
Q

What is the pathway for touch?

A

the dorsal column-medial lemniscal system

-info comes in through the sensory neurons in the DRG which then exits via the dorsal horn
-the axons of these mechanosensory neurons then ascend ipsilaterally through dorsal columns up the spinal cord
-they then synapse and tract cross the midline near the brain (gracile and cuneate nucleus)
-they then extend through the medial lemniscus to the thalamus and then to the cortex

43
Q

What is the central pathway for proprioception?

A
  1. proprioceptive axons travel in the spinal cord with axons containing cutaneous information
  2. axon collaterals synapse in the dorsal horn and this circuit underlies reflexes such as knee-jerk (local circuit)
    3.its central projection is the cerebellum
44
Q

What does somatotopic mean?

A

there are areas near each other on the body maps neat each other on the brain

45
Q

What is the size of cortical representation proportional to?

A

degree of sensory innervation

46
Q

What is homunculus?

A

human drawn to reflect the relative space body parts occupy in somatosensory cortex

47
Q
A

BISC 421 (23 decks)

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