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Y3 Neurology > Physiology - The Somatosensory System > Flashcards

Physiology - The Somatosensory System Flashcards

1
Q

where are receptors for the somatosensory system located?

A

throughout the body

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2
Q

what are the receptors for the somatosensory system?

A

peripheral nerve endings and their associated specialisations

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3
Q

what five sensory modalities are mediated by the somatosensory system?

A 
fine touch 
proprioception 
temperature 
pain 
itch
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4
Q

what five things come under fine discriminatory touch?

A 
light touch
pressure
vibration 
flutter 
stretch
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5
Q

what is another name for mediating fine touch?

A

mechanosensation

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6
Q

what is another name for mediating temperature?

A

thermosensation

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7
Q

what is another name for mediating pain?

A

nociception

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8
Q

what is another name for mediating itch?

A

pruriception

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9
Q

how many neurones usually make up a somatosensory pathway?

A

three

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10
Q

where is the first order neurone of a somatosensory pathway found?

A

the PNS

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11
Q

what type of neurone is the first order order neurone of a somatosensory pathway?

A

primary sensory afferent

pseudounipolar

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12
Q

where is the cell body of the first order order neurone of a somatosensory pathway found?

A

dorsal root ganglia if innervating limbs/trunk/posterior head

cranial ganglia if innervating the anterior head

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13
Q

what type of neurone is the second order neurone of a somatosensory pathway?

A

projection neurone

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14
Q

where is the cell body of the second order neurone of a somatosensory pathway found?

A

dorsal horn of the spinal cord or a brainstem nuclei

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15
Q

what type of neurone is the third order neurone of a somatosensory pathway?

A

projection

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16
Q

where is the cell body of the third order order neurone of a somatosensory pathway found?

A

thalamic nuclei

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17
Q

where are the cell bodies located in the somatosensory cortex?

A

parietal and posterior parietal cortex

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18
Q

what do sensory neurone terminals do?

A

transduce a stimulus into electrical activity

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19
Q

what effect does a stimulus have when it reaches a sensory neurone terminal?

A

opens cation selective ion channels, eliciting a depolarising receptor potential

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20
Q

what determines the amplitude of the sensory receptor potential produced in response to a stimulus?

A

the intensity of the stimulus

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21
Q

when a sensory receptor potential is produced what does it do?

A

if over threshold, triggers an AP which then causes the graded release of neurotransmitters onto the second order neurones

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22
Q

what is modality?

A

the type of stimulus that excites the sensory receptor

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23
Q

what is the adequate stimulus?

A

the specific type and intensity of energy that excites a primary afferent neurone

24
Q

what is the stimulus and sensory unit for the modality of touch, pressure and vibration?

A

stimulus = mechanical forces acting on the skin

unit = skin mechanoreceptors

25
Q

what is the stimulus and sensory unit for the modality of proprioception?

A

stimulus = mechanical forces acting on joints and muscles

unit = joint and muscle mechanoreceptors

26
Q

what is the stimulus and sensory unit for the modality of temperature?

A

stimulus = heat

unit = thermoreceptors

27
Q

what is the stimulus and sensory unit for the modality of pain?

A

stimulus = strong mechanical force or heat

unit = mechanical, thermal and polymodal nociceptors

28
Q

what is the stimulus and sensory unit for the modality of itch?

A

stimulus = irritant on the skin/mucous membranes

unit = itch receptors

29
Q

what does threshold mean?

A

the intensity of the stimulus required for excitation of the receptor

30
Q

what do low threshold units respond to?

A

low intensity/non-damaging stimuli

31
Q

what do low threshold mechanoreceptors mediate?

A

fine discriminatory touch

32
Q

what do low threshold thermoreceptors mediate?

A

cold through to hot temperatures

33
Q

what do high threshold units respond to and what is another name for these units?

A

high intensity potentially damaging stimuli

aka nociceptors

34
Q

what do high threshold mechanoreceptors (HTMs) respond to?

A

high intensity mechanical stimuli

aka mechanical nociceptors

35
Q

what do thermal nociceptors respond to?

A

extreme degrees of heat or cold

36
Q

what do chemical nociceptors respond to?

A

substances in tissue that are harmful

37
Q

what do polymodal nociceptors respond to?

A

at least two types of noxious stimuli

38
Q

what does adaptation rate?

A

whether a sensory unit discharges AP’s continuously during the stimulus or does it respond preferentially to a changing stimulus

39
Q

what are the three possible adaptation rates that a sensory unit can have?

A 
slowly adapting (SA)
fast adapting (FA) 
very fast adapting (very FA)
40
Q

what is another name for the slowly adapting response?

A

tonic/static response

41
Q

describe an SA adaptation rate

A

AP’s are released in relation to when and how the stimulus is present - either step or ramp

42
Q

describe a step SA adaptation rate

A

stimulus present at all times at the same amplitude

action potentials released at even intervals

43
Q

describe a ramp SA adaptation rate

A

stimulus varies until it reaches a maximum

action potentials released proportionally to the stimulus present - reaches a peak

44
Q

name a receptor that shows SA adaptation

A

stretch receptors

45
Q

describe a FA adaptation response

A

generates a burst of action potentials and then no more

number of impulses proportional to the rate of change of the stimulus

46
Q

describe a very FA adaptation response

A

responds only to very fast movement

produces one AP at the start of the stimulus

47
Q

what is conduction velocity?

A

how rapidly the sensory unit conducts AP’s along its axons

48
Q

what is the receptive field (RF)?

A

the target territory from which a sensory unit can be excited

49
Q

what determines the RF?

A

innervation density - inverse relationship

50
Q

describe the relationship between RF size and sensory acuity

A

small RF = high acuity (+ high density of innervation)

large RF = low acuity (+low density of innervation)

51
Q

what is another name for two point discrimination?

A

spatial acuity

52
Q

how can spacial acuity be tested clinically?

A

applying two sharp point stimuli at two different sites simultaneously

patient reports whether one or two points are felt

53
Q

what is a dermatome?

A

the area of skin innervated by the bilateral dorsal roots of a single spinal segment

54
Q

what forms the dorsal columns?

A

medial gracile tract = fasiculus gracilis

lateral cuneate tract = fasciculus cuneatus

55
Q

what do the dorsal and ventral spinocerebellar tracts convey?

A

unconscious proprioceptive information to the cerebellum

Y3 Neurology (31 decks)

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