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Neurology > The Somatosensory System 1 > Flashcards

The Somatosensory System 1 Flashcards

1
Q

What does the somatosensory system not mediate?

A

Special senses

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2
Q

What does the somatosensory system include the modalities of?

A 
Touch, pressure, vibration
Joint and muscle position 
Temperature
Pain
Itch
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3
Q

Mechanosensation is?

A

Touch
Pressure
Vibration

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4
Q

Proprioception is?

A

Joint and muscle position

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5
Q

Thermosensation is ?

A

Temperature

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6
Q

Nocioception is?

A

Pain

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7
Q

Pruriception is?

A

Vibration

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8
Q

What does stimuli do to the nerve terminal?

A

Opens CATION selective ion channels to elicit a depolarising receptor potential

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9
Q

Describe the amplitude of generator potential.

A

GRADED
+
Proportional to stimulus intensity

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10
Q

What triggers ‘all or none’ action potentials? What is the frequency of these action potentials proportional to?

A

Low current flow

At a frequency proportional to the amplitude of the receptor potential

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11
Q

Sensory neurones transduce a stimulus into ……… activity?

A

ELECTRICAL

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12
Q

What is a muscle spindle?

A

A sensory structure in skeletal muscle

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13
Q

What are muscle spindles activated by?

A

STRETCH

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14
Q

Outline the process through which a spindle is transduce into electrical activity.

A
  1. Graded receptor potential
  2. Triggers ‘all or none’ AP
  3. AP
  4. Output graded release of neurotransmitter
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15
Q

What is the neurotransmitter?

A

Glutamate

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16
Q

What is meant by ‘modality’?

A

The principle type of adequate stimulus that is transduce into an electrical signal by a primary afferent neurone

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17
Q

What do low threshold units respond to?

A

Low intensity stimuli
(non damaging and non painful)
e.g low threshold mechanoreceptors and low threshold thermosensors

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18
Q

Give an example of what low threshold mechanoreceptors sense?

A

Mediate touch, vibration and pressure

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19
Q

Give an example of what low threshold thermosensors sense?

A

Cold, cool, indifferent, warm and hot

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20
Q

What do high threshold units mediate?

A

High intensity stimuli

Noxious and potentially damaging

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21
Q

What is another name for high threshold units?

A

Mechanical nociceptors

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22
Q

What do thermal nociceptors respond to?

A

Extreme degrees of heat (>45°C), or cold (< 10-15°C)

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23
Q

What do chemical nociceptors respond to?

A

Substances in tissue (as found in inflammation) e.g. prostaglandins, bradykinin, serotonin, histamine, K+, H+ and ATP and many others

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24
Q

What do polymodal nociceptors respond to?

A

At least 2 of the above types

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25
Q

What is adaptation?

A

A feature of primary sensory neurones that determines whether they change their firing rate only in response to a stimulus of changing intensity, or fire continuously throughout a constant stimulus

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26
Q

Slowly Adapting (SA) Tonic/Static Response is?

A

Continuous information to the CNS while terminal deformed

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27
Q

What does SA respond give information about? Give an example.

A

Position, degree of stretch or force

e.g stretch receptors

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28
Q

Rapidly Adapting (RA) Phasic/Dynamic Response detects changes in?

A

Stimulus strength e.g rate of movement

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29
Q

What is the number of impulses proportional to? Give examples.

A

Rate of change of stimulus

e.g Some muscle spindle afferents, hair follicle afferents

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30
Q

Very Rapidly Adapting (very RA) Very Phasic/Dynamic Response responds to?

A

Only very fast movements

e.g rapid vibration

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31
Q

Give an example of very RA.

A

Pacinian corpuscles

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32
Q

Aa

A

THICK myelination

e.g proprioceptors of skeletal muscle

33
Q

C

A

NO myelination

e.g temperature, pain, itch

34
Q

What is the receptive field of an afferent neurone?

A

The region that when stimulated with an adequate stimulus causes a response in that neurone

35
Q

For primary afferent neurones, the RF is the site of?

A

The peripheral terminal

36
Q

A patch of skin contains many overlapping RF’s innervated by individual primary afferent fibres

37
Q

There is wide differences in two point discrimination

38
Q

How do most peripheral nerves communicate with the CNS?

A

Via the spinal cord

39
Q

What is the innervation of the anterior head by?

A

The trigeminal system

40
Q

If a single dorsal root is cut, why does the corresponding dermatome not lose all sensation?

A

Because of the degree of overlap with the region of adjacent dorsal roots

41
Q

Where does shingles infect?

A

Dorsal root ganglion neurones

42
Q

What virus causes shingles?

A

Varicella zoster

43
Q

What does VZV also cause?

A

Chickenpox

44
Q

What does the VZV do in adulthood?

A

REACTIVATES in a single ganglion

45
Q

What is grey matter of the spinal cord divided into?

A

Dorsal horns
Ventral horns
10 distinct laminae of rexed

46
Q

Name the 3 broad categories that the somatosensory system can be divided into?

A

Exteroceptive
Proprioceptive
Enteroceptive

47
Q

Exteroceptive division is?

A

(cutaneous senses) registers information from the surface of the body by numerous receptors

48
Q

Proprioceptive division is?

A

Monitors posture and movement (sensors in muscle and tendons and joints)

49
Q

Exteroceptive division is?

A

Reports upon the internal state of the body and is closely related to autonomic function

50
Q

Describe the pathway of neurones in the somatosensory system.

A
  1. 1st order neurone
  2. 2nd order neurone
  3. 3rd order neurone
  4. Somatosensory cortex
51
Q

Describe the 1st order neurone and its location.

A

Primary sensory afferent

Cell body located in dorsal root ganglion

52
Q

Describe the 2nd order neurone and its location.

A

Projection neurone

Cell body located in dorsal horn of spinal cord or brainstem nuclei

53
Q

Describe the 3rd order neurone.

A

Projection neurone

Cell body located in thalamic nuclei

54
Q

What is ‘modality’?

A

Primary afferent neurons are especially ‘tuned’ to respond to a specific type of energy (the adequate stimulus) that normally excites them underlying the sensation that they subserve

55
Q

How is two point discrimination tested?

A

applying simultaneously two sharp point stimuli, separated by a variable distance, at different sites on the body surface and get person to close eyes and say if they feel one or two points

56
Q

Name the 4 cell types of hairless skin.

A 
Merkel cell neutrite complexes (SA1)
Meissner corpuscle (FA1)
Ruffini endings (SA2)
Pacinian corpuscles (FA2)
57
Q

Describe merkel cell neutrite complexes.

A

Formed from many expanded nerve terminals, each closely associated with a Merkel cell as a ‘synapse-like’ structure

58
Q

Where are SA1’s located?

A

Basal epithelium

59
Q

SA1’s have …. sensory acuity

60
Q

What are SA1’s sensitive to?

A

Pressure, texture, and are extremely sensitive to the edges of objects

61
Q

SA1’ are….

A

MECHANOSENSITIVE

62
Q

Describe Messiener corpuscles

A

Formed from a capsule in which several axons zigzag between modified Schwann cells (teloglia)

63
Q

Where is FA1’s located?

A

Close to the basal epithelium

64
Q

FA1’s have HIGH sensory acuity

65
Q

What are FA1’s sensitive to?

A

Sensitive to stroking, flutter, low frequency vibration

66
Q

What allows for the detection of textured surfaces of FA1’s?

A

Small RF and high density

67
Q

Describe Ruffini endings.

A

Collagenous core in which axons branch

68
Q

Located in dermis (also joint capsules) of both glabrous and hairy skin describes what cell type?

A

Ruffini endings

69
Q

What are ruffini endings sensitive to?

A

Drag (shearing forces)

70
Q

Describe pacinian corpuscles.

A

Large ‘onion-like’ structures

71
Q

Where are pacinian corpuscles located?

A

In SC tissue close to the periosteum of bone

72
Q

What are pacinian corpuscles sensitive to?

A

Very sensitive to vibration over frequency range higher (approx. 200 – 300 Hz) than Meissner corpuscle

73
Q

What do pacinian corpuscles act as?

A

‘event detectors’

during the manipulation of an object

74
Q

Hairy skin contains all receptors except? What are they replaced by?

A

Meissner corpuscles

Hair units

75
Q

What is a ‘hair unit’?

A

Comprise follicular (free) nerve endings that either wrap around the follicle (circumferential fibres), or parallel to it (palisade fibres)

76
Q

A single afferent fibre innervates many follicles

77
Q

Units are responsive to the bending of hairs, which increases, or decreases their firing when the hair is in motion, but not when static

78
Q

Sensory units may be slowly, or fast, adapting

Neurology (42 decks)

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