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3rd Year - Neurology > Peter's Physiology 7 - Pain and Thermosensation > Flashcards

Peter's Physiology 7 - Pain and Thermosensation Flashcards

1
Q

What is pain?

A

An unpleasant sensory and emotional experience, associated with actual tissue damage or described in terms of such damage (although pain may be perceived in the absence of tissue/ organ damage)

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2
Q

What type of pain is a pin prick and visceral distension examples of?

A

Nociceptive (acute) pain

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3
Q

What type of pain is sunburn and an inflamed wound examples of?

A

inflammatory (prolonged) pain

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4
Q

What type of pain is IBS, fibromyalgia, arthritis, cancer and AIDs examples of?

A

Pathological (neurogenic) pain

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5
Q

What are the specific peripheral primary sensory afferent neurones that are normally activated preferentially by intense stimuli (e.g. thermal, mechanical, chemical) that are noxious, or damaging?

A

Nociceptors

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6
Q

Where are nociceptor cell bodies located?

A

in the dorsal root ganglia and trigeminal ganglia

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7
Q

What type of primary afferent fibres are nociceptors?

A

A delta and C fibres (NB not all A delta and C fibres are nociceptors)

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8
Q

What type of noxious stimuli do A delta fibres respond to?

What type of pain does this mediate?

A

Mechanical and thermal stimuli

First/ fast pain

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9
Q

Which of A delta and C fibres are unmyelinated?

A

C fibres

A delta fibres are thinly myelinated

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10
Q

what type of noxious stimuli do C fibres respond to?

What type of pain does this mediate?

A

All types of noxious stimuli - polymodal

Second/ slow pain

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11
Q

What is the phrased used to describe the fact the rate of action potential discharge from nociceptors correlates with the intensity of the applied stimulus ?

A

Frequency coding

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12
Q

What is another name for type I A delta fibres?

A

High threshold mechanoreceptors

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13
Q

What are type 1 A delta fibres activated by?

A

Strong mechanical stimuli/ noxious heat (threshold >53 degrees C)

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14
Q

What happens to type I A delta fibres in response to prolonged stimuli?

A

Sensitisation occurs - threshold for activation by heat or mechanical stimuli falls

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15
Q

What do type II A delta fibres respond to?

A

Noxious mechanical stimuli and also noxious heat (threshold of 43-47 degrees C), sensitive to capsaicin

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16
Q

Which type of A delta fibres mediate first pain to intense mechanical stimuli?

A

Type I

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17
Q

Which type of A delta fibres mediate first pain to heat?

A

Type II

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18
Q

What are the 4 sub-classes of C fibres?

A

C - MH
C - M
C - H
C - MiHi (silent)

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19
Q

What do C - MH fibres respond to?

A 
Noxious mechanical stimuli
Noxious heat (threshold 39 - 51 degrees C)
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20
Q

What type of C fibres are sensitive to capsicain?

A

C-MH
C-H
C-MiHi

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21
Q

Do C-MH fibres show sensitisation to repeated stimuli?

A

Yes

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22
Q

What functions does C-MH fibres have?

A

Contributes to heat pain

Location of stimulus

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23
Q

What type of stimuli do C-M fibres respond to?

A

Noxious mechanical stimuli

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24
Q

What type of stimuli do C-H fibres respond to?

A

Noxious heat (threshold 42 - 48 degrees C)

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25
Q

What function does C-H fibres mediate?

A

Heat hyperalgesia

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26
Q

What does C-H fibres acquire in the context of inflammation?

A

Sensitivity to mechanical stimuli

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27
Q

Describe the function of C - MiHi fibres?

A

Normally insensitive to both mechanical and heat stimuli but acquires sensitivity following sensitisation by inflammatory mediators

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28
Q

What is released from the peripheral terminal of nociceptors?

A

Molecules that influence local tissue environment e.g. substance P causing vasodilation and extravasation of plasma proteins, calcitonin gene related peptide causing vasodilation)

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29
Q

Where are primary afferent cell bodies located (apart from in the trigeminal system)?

A

In the dorsal root ganglia

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30
Q

What is the name for the 10 layers of grey matter in the spinal cord which are defined by their cellular structure?

A

Laminae of rexed

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31
Q

Which laminae of rexed do the primary afferent axons terminate in?

A

I - V

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32
Q

What laminae of Rexed do nociceptive C- and A-delta fibres mostly terminate in?

A

Superficially in laminae I and II (also V for A-delta fibres

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33
Q

What do nociceptive specific cells synapse only with in the spinal cord?

A

C and A-delta fibres

34
Q

What is the input to proprioeceptive cells in the spinal cord?

A

Only A-beta fibres

35
Q

What do wide dynamic range neurones receive input from in the spinal cord?

A

All 3 types of fibres (thus respond to a wide range of stimuli)

36
Q

Name the 3 divisions of the trigeminal nerve?

A 
V1 = ophthalmic
V2 = maxillary
V3 = mandibular
37
Q

Where are soma of the trigeminal nerves located?

A

Trigeminal sensory ganglion

38
Q

Where do trigeminal nerve fibres carrying info about general tactile stimuli synapse onto second order neurones?

A

In the chief sensory nucleus

39
Q

Where do trigeminal nerve fibres carrying info about pain and temperature synapse onto second order neurones?

A

Spinal nucelus

40
Q

Where do second order neurones in the trigeminal system project to in the thalamus and via what?

A

Decussate and project via the trigeminal lemniscus to the ventroposteriomedial (VPM) nucleus of the thalamus

41
Q

Describe the route of third order trigeminal neurones from the thalamus?

A

Project via thalamocortical neurones to the cortex

42
Q

Primary neurotransmitter used in the neurotransmission between the primary afferent and second order neurone in the dorsal horn (or spinal nucleus of the TG system)?

A

Glutmate

43
Q

In the dorsal horn (or spinal nucleus of the TG system) what does activation of glutamate receptors on second order neurones cause?

A

Membrane depolarisation (fast e.p.s.p.), opening of voltage-gated Na+ channels, action potential

44
Q

In the dorsal horn (or spinal nucleus of the TG system) what the of receptors are activated by glutamate?

A

Primary postynapti AMPA receptors with NMDA receptor participation

45
Q

In the dorsal horn (or spinal nucleus of the TG system), apart from glutamate, what other neurotransmitters are involved? (particularly during high frequency stimulation)

A

Peptides (substance P and CGRP)

46
Q

In the dorsal horn (or spinal nucleus of the TG system) what does peptide release cause?

A

A slow and prolonged e.p.s.p.facilitating activation of NMDA receptors be relieving voltage-dependent block by Mg2+

47
Q

What are the names of the 2 distinct types of sensitisation of the nociceptive pathway following tissue damage?

A

Peripheral sensitisation

Central sensitisation

48
Q

What mediates peripheral sensitisation?

A

Nociceptors at the site of injury/ tissue inflammation

49
Q

What mediates central sensitisation?

A

An increase in CNS neurone activity and propeties

50
Q

What does peripheral sensitisation cause?

How? (2)

A

Primary hyperalgesia

Reduced threshold
Amplified response

51
Q

What does central sensitisation cause?

How? (2)

A

Secondary hyperalgesia and allodynia
Recruitment of novel inputs to nociceptive pathways
Abnormal processing of sensory input

52
Q

What is required for maintenance of peripheral sensitisation?

A

Ongoing peripheral pathology

53
Q

What type of sensitisation causes pain that persists after tissue healing?

A

Central sensitisation

54
Q

What type of sensitisation is the main cause of heat sensitivity?

A

Peripheral sensitisation

55
Q

What type of sensitisation is the main cause of mechanical sensitivity?

A

Central sensitisation

56
Q

Where does visceral pain originate from?

A

Nociceptors covering tissues or walls of hollow organs

57
Q

What type of stimulus cause visceral pain? (4)

What type of stimulus do not cause visceral pain? (2)

A

Stretching, twisting, inflammation and ischaemia

Not cutting or burning

58
Q

Describe visceral pain?

A

Poorly localised

Dull, aching, throbbing character

59
Q

What pathways do visceral afferents follow before entering the dorsal horn?

A

Sympathetic pathways

60
Q

What type of neurones do visceral afferents converge on in the spinal cord?

A

Spinothalamic neurones

61
Q

Along with visceral afferents, what also converges onto spinothalamic neurones in the spinal cord?
What does this describe?

A

Skin afferents

Referred pain

62
Q

What laminae do visceral nocicpetors terminate in?

A

Laminae I and V

63
Q

What is referred visceral pain often associated with?

A

Autonomic features e.g. nausea, vomiting, sweating, pallor

64
Q

Dermatome of referred pain from gallbladder?

A

C4

65
Q

Dermatomes of referred pain from heart?

A

T1-5

66
Q

Character of viscerosomatic pain?

A

Sharp and well localised

67
Q

How does viscerosomatic pain occur?

A

When inflammatory exudate from a diseased organ contacts a somatic (body wall) structure e.g. parietal peritoneum

68
Q

What 2 tracts does the anterolateral system comprise of?

A 
Spinothalamic tract (STT)
Spinoreticular tract (SRT)
69
Q

How do second order nociceptor neurones ascend the spinal cord?

A

In the anterolateral system

70
Q

What type of nociceptive neurones are transmitted by the spinothalamic tract?

A

Fast fibre A-delta

WDR neurones

71
Q

Where do nociceptive projection neurones originating from lamina I (fast fibre Adelta pain) terminate?

A

Posterior nucleus of the thalamus

72
Q

Where do protection neurones originating from lamina V (WDR neurones) terminate?

A

Posterior and ventroposterior nucleus of the thalamus

73
Q

For pain perception (location, intesity) from the spinothalamic tract, what must occur?

A

Simultaneous firing in both pathways

74
Q

What type of neurones does the spinoreticular tract mostly transmit?

A

Slow C-fibre pain

75
Q

What do second order neurones within the spinoreticular tract connect with?

A

Reticular nuclei in the brainstem

76
Q

What are signals int he spinoreticular tract responsible for?

A

Autonomic responses to apin, arousal, emotional responses, fear of pain

77
Q

Which out of the spinothalamic pathway and the spinoreticular pathway are classified as slow and fast?

A 
STT = fast
SRT = slow
78
Q

In the spinothalamic tract, where are signals from the thalamus relayed to?
By what?

A

Relayed by thalamuocrotical neurones to the primary sensorimotor cortices

79
Q

What does the spinothalamic tract act as? By doing what?

A

Acts as a warning system by signalling the exact location and severity of the injury and duration of pain
Also analyses the features of the pain

80
Q

Where does the spinoreticular pathway signal to?

Via what?

A

Intralaminar nuclei of the thalamus indirectly through the brainstem reticular formation via reticulothalamic tracts
Signals from the thalamus are then relayed by the thalamuocrotical neurones to limbic areas of the forebrain

81
Q

Is pain and nociception the same?

A

No - pain is awareness of suffering -> nociception may occur in the absence of pain and vice versa

82
Q

How can pain evoked by activity in nociceptors be reduced?

A

By simultaneous activity in LTMs (Abeta-fibres)

3rd Year - Neurology (17 decks)

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