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2nd Year - MSK > Physiology and Pharmacology 5 - Pain > Flashcards

Physiology and Pharmacology 5 - Pain 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

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2
Q

What are the 3 forms of pain?

A

Nociceptive pain
Inflammatory pain
Pathological pain

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3
Q

What of the 3 forms of pain are adaptive?

A

Nociceptive and inflammatory pain = adaptive

Pathological pain = maladaptive

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4
Q

What are nociceptors?

A

Specific peripheral primary sensory afferent enrolees normally activated preferentially by intense stimuli e.g. thermal, mechanical, chemical, that are noxious

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5
Q

Are nociceptors first or second order neurones?

A

First order neurones (they relay information to second order neurones in the CNS by chemical synaptic transmission)

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6
Q

What are first order neurones?

A

Neurones that conduct impulses from receptors of the skin and from proprioceptors, to the spinal cord or brain stem, where they synapse with second order neurones

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7
Q

What is adaptive pain?

A

Helpful pain that produces behaviour that promotes healing and recovery (compared with maladaptive pain)

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8
Q

Why can nociceptive pain be described as adaptive?

A

It serves as an early warning system to detect and minimise contact with damaging stimuli (noxious events)

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9
Q

Threshold of nociceptive pain?

A

High threshold - provoked only by intense stimuli that activate nociceptors

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10
Q

Features of nociceptive pain? (5)

A

Overrides most other ongoing activities of the nervous system
Initiates a withdrawal reflex
Extremely unpleasant
Engages adverse emotional components
Serves to inscribe memories that allow avoidance of harm in the future

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11
Q

What causes inflammatory pain?

A

Activation of the immune system in injury, or infection

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12
Q

what does activation of the immune system in injury, or infection, cause in terms of inflammatory pain? (2)

A 
Pain hypersensitivity (heightened sensitivity to noxious stimuli)
Allodynia (innocuous stimuli now elicit pain)
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13
Q

How is inflammatory pain protective and adaptive?

A

Assists in the healing of a damaged body part by:
Discouraging physical contact e.g. a wound
Discouraging movement e.g. an inflamed joint

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14
Q

What causes pathological pain?

A

Abnormal nervous system function

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15
Q

2 types of pathological pain?

A

Neuropathic

Dysfunctional

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16
Q

What causes neuropathic pain?

A

peripheral nerve damage

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17
Q

What causes dysfunctional pain?

A

No identified cause

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18
Q

What type of fibres are nociceptors either?

A

Aδ- and C-fibres (not all Aδ- and C-fibres are nociceptors)

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19
Q

What type of nociceptors are Aδ- fibres?

A

Mechanical/ thermal nociceptors

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20
Q

Myelination of Aδ- fibres?

A

Thinly myelinated

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21
Q

What type of stimuli do Aδ- fibres respond to?

A

Noxious mechanical and thermal stimuli

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22
Q

What type of pain do Aδ-fibres mediate?

A

First/ fast pain

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23
Q

Myelination of C-fibres?

A

Unmyelinated

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24
Q

What type of stimuli do C-fibres respond to?

A

All noxious stimuli

25
Q

What type of pain do C-fibres cause?

A

Second/ slow pain

26
Q

4 examples of receptors that pick up chemical stimuli on polymodal nociceptors?

A

ASIC
P2X
P2
B2 receptors

27
Q

Example of a thermal receptor that is activated by noxious heat?
What happens to this in inflammation?

A

Members of the transit receptor potential (TRP) family - particularly TRPV1
Greatly sensitised in inflammation to become active at body temperature

28
Q

What ion channel (chemical receptor) does H+ activate?

A

Acid sensing ion channel (ASICs)

29
Q

What ion channel (chemical receptor) does ATP activate?

A

P2X and P2Y receptors

30
Q

What ion channel (chemical receptors) does bradykinin activate?

A

B2 receptors

31
Q

What happens when a stimulus (mechanical, thermal or chemical) activates a receptor?

A

It open ion channels (cation selective) in nerve terminal to elicit a depolarisaiton receptor (or generatory) potnetial

32
Q

What is amplitude of generator potential proportional to?

A

Stimulus intensity (it is graded)

33
Q

What does local current flow (hermann currents) in a sensory neurone terminal trigger?

A

all or none action potentials at a frequency proportion to the amplitude of the receptor potential

34
Q

What type of signals do c-polymodal nociceptors pick up?

A

Thermal, chemical and mechanical stimuli

35
Q

What temperature stimulates c-polymodal fibres?

A

43 degrees C

36
Q

What temperature stimulates type I Aδ-fibres?

A

53 degrees C

37
Q

What temperature stimulates type II Aδ-fibres?

A

43 degrees C

38
Q

Where does the first order and second order neurone synapse in the nociceptive pathway?

A

in the dorsal (posterior) horn of the spinal cord

39
Q

What is the name of the subset of C-fibres that have both afferent and efferent functions?

A

Peptidergic polymodal nociceptors

40
Q

How do afferent peptidergic polymodal nociceptors transmit nociceptive information to the CNS?

A

Via release of glutamate and peptides (substance p, Neurokinin A) within the dorsal horn

41
Q

What do efferent peptidergic polymodal nociceptors do?

A

Release pro-inflammatory mediators e.g. substance P, calcitonin gene-related peptide (CGRP) from peripheral terminals - contributes to neurogenic inflammation

42
Q

What does noxious stimulation of peptidergic polymodal nociceptors do in the long term?

A

Increases spinal excitability contributing to hyperalgesia and allodynia

43
Q

What are released from free nerve endings of peptidergic nociceptor due to tissue damage?

A

Peptides (SP and CGRP) or inflammatory mediators

44
Q

What does substance P (released from peptidergic nociceptors due to tissue damage) cause?

A

Vasodilation and extravasation of plasma proteins (promotes formation of bradykinin and prostaglandins)
Release of histamine from mast cells
Sensitised surrounding nociceptors

45
Q

What does CGRP released from free nerve endings of peptidergic nociceptors cause?

A

Vasodilation

46
Q

What does the release of SP and CGRP, or inflammatory mediators, from peptidergic nociceptors due to tissue damage cause? (neurogenic inflammation)

A

primary and secondary hyperalgesia and allodynia

47
Q

What happens when the action potential arrives at the terminal of the primary afferent neurone?

A

Opening of voltage-gated Ca2+ channels occurs
Ca2+ influx
glutamate release

48
Q

What happens to glutamate released by the primary afferent neurone in the dorsal horn?

A

It activates glutamate receptors on the projection neurone in the distal horn causing membrane depolarisation
This leads to the opening of voltage-gated Na+ channels and the production of the action potential

49
Q

Aside from glutamate, what else is involved in neurotransmission between the primary afferent and second order neurone in the dorsal horn?

A

petides - substance P and CGRP (cause a slow prolonged e.p.s.p. that facilitates activation of NMDA receptors by relieving voltage-dependent block by Mg2+

50
Q

Where are primary afferent cell bodies located?

What is the exception to this?

A

Dorsal root ganglia

Apart from the trigeminal syste

51
Q

Where do primary afferent axons terminate?

A

Centrally in the dorsal horn of the spinal cord in various laminae of Rexed

52
Q

What laminae in the spinal cord do nociceptive C and Aδ fibres terminate?

A

Superficially in laminae I and II (also V for Aδ fibres)

53
Q

What do nociceptive specific cells only synapse with?

A

C and Aδ fibres

54
Q

What type of cells are those that only receive input from Aβ-fibres?

A

Proprioceptive

55
Q

What do wide dynamic range neurones receive input from?

A

All 3 types of fibre - therefore respond to a wide range of stimuli

56
Q

Second order nociceptive neurones ascend the spinal cord in the anterolateral system comprising mainly of?

A 
Spinothalamic tract (STT)
Spinoreticular tract (SRT)
57
Q

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

A

Posterior nucleus of the thalamus

58
Q

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

A

Posterior and ventroposterior nucleus of the thalamus

59
Q

What type of pain does the spinoreticular tract largely transmit?

A

Slow C-fibre pain

2nd Year - MSK (23 decks)

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