somatosensation I Flashcards

1
Q

what does the somatosensory system do?

A

connects the body to the CNS via peripheral nerves

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2
Q

what sensations does the somatosensory system convert from the body?

A
  • heat, cold
  • pain, itch
  • proprioception
  • touch
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3
Q

what is proprioception?

A

being aware of the position of the body (like sixth sense)

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4
Q

what types of peripheral nerves exist?

A

spinal and cranial

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5
Q

structure of peripheral nerves?

A

a nerve is a bundle of axons, covered in a connective sheath called an epineurium

  • the nerve consists of several fascicles, all separate by connective tissue called perineurium
  • the fascicles contain axons, and individually myelinated axons are wrapped in endoneurium
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6
Q

what does the dorsal root contain?

A

cell bodies of incoming sensory neurones

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7
Q

what does the ventral root contain?

A

cell bodies of outgoing motor neurones

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8
Q

what us the dorsal root ganglion?

A

occurs just as the dorsal and ventral roots fuse, located just outside of the spinal cord
-contain cell bodies of the sensory neurones that are part of the somatosensory system

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9
Q

dorsal and ventral root reunite to form what?

A

spinal nerve

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10
Q

white matter

A

ascending and descending axons tracks

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11
Q

grey matter

A

cell bodies, dendrites, synapses, glial cells

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12
Q

what is the spinal cord divided into

A

incoming sensory info and outgoing motor info

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13
Q

what are dorsal root ganglion cells?

A

sensory receptors of the somatosensory system

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14
Q

explain the 2 functionally distinct systems of the somatosensory system

A

2 different white matter tracts

  1. (DCML)
    - mechanosensory afferent fibres
    - a-beta and a-alpha afferent fibres
    - large fibres, large diameter, myelinated, fast conduction
    - touch, vibration, tactile, proprioception
    - enter the spinal cord and enter the medulla and then cross
  2. (STT)
  • thin fibres
  • a-delta and C fibres
  • small diameter, thinly myelinated/unmyelinated, medium/slow conducting
  • pain, itch, crude touch coarse, temperature
  • enter the spinal cord, make contact with second order neurones in the spinal cord - these cross to the other side, then ascend up to the brain
  • the receptor endings/axon terminals are in areas of the body eg. the fingers
  • the axon travels centrally via the dorsal root
  • axon can then terminate or they may ascend the spinal cord all the way to the brainstem
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15
Q

crude touch

A

crude touch is touch without knowing the location

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16
Q

what does the quality of sensation depend upon?

A

the afferent fibre type

17
Q

if the afferent fibre is a member of the small class of fibre what will the sensation be?

A

temperature related, pain or crude touch

18
Q

if the afferent fibre is a member of the large class of fibre what will the sensation be?

A

proprioception

19
Q

cutaneous receptors of the somatosensory system?

A

larger diameter afferents - 4 major classes in the skin:

2 are cutaneous, receptor endings between the dermis and epidermis - tactile afferents, sensitive to light touch - Meissners Corpuscle and Merkels discs

2 are deeper in the dermis, or between dermis and hypodermic - Ruffini’s and Pacinian corpuscles

also there are free nerve endings

20
Q

proprioceptors of the somatosensory system?

A

group 1 and 3 afferent axons detect changes in length

  • muscle spindles are stretched and increase their firing rate
  • muscle spindle itself can be made to contract by the gamma motor neurone - recalibration of muscle spindle length
21
Q

what are muscle spindles?

A

specialised muscle fibres, detect changes in muscle length

22
Q

receptors of the somatosensory system?

A
  1. proprioception
    - muscle spindles, A-alpha afferent fibres, large diameter, fastest conduction
  2. tactile afferents - A-beta afferent fibres, large diameter, second fastest conduction
    a) superficial
    Meissners Corpuscle and Merkels discs
    b) deep
    Ruffini’s and Pacinian corpuscles
  3. free nerve endings
    - end in the dermis/epidermis
    - A delta fibres - thin, myelinated, moderate conduction
    - C fibres - thin, unmyelinated, slow conduction
23
Q

what do Pacinian Corpuscles detect?

24
Q

what do Ruffini Corpuscles detect?

25
what are small receptive field needed for?
precise detail
26
having a large receptive field mean?
the stimulus cannot be localised apart from the fact that its within that large receptive field
27
larger areas of the cortex are devoted to?
areas of the body where receptive fields are small