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Neurology > Pain and Thermosensation > Flashcards

Pain and Thermosensation Flashcards

1
Q

What is pain?

A

An unpleasant sensory or emotional experience, associated with actual tissue damage or described in terms of such damage

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2
Q

Pain is not a single entity and may be classified in 3 forms. What are these 3 forms?

A
  • Nociceptive
  • Inflammatory
  • Pathological
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3
Q

Describe nociceptive pain.

A

This is acute pain e.g a pin prick or visceral distension

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4
Q

Describe inflammatory pain.

A

This is prolonged pain e.g sunburn or an inflamed wound

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5
Q

Describe pathological pain.

A

This is neurogenic pain e.g IBS, fibromyalgia, arthritis, diabetes, cancer, AIDs

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6
Q

What is chronic pain?

A

When pain arises spontaneously without any underlying pathology

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7
Q

Describe the characteristics of pain that are associated with the skin.

A
  • well localised
  • pricking
  • stabbing
  • burning
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8
Q

Describe the characteristics of pain that are associated with muscle.

A
  • poorly localised
  • aching
  • soreness/tenderness
  • cramping, stabbing, burning
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9
Q

Describe the characteristics of pain that are associated with viscera.

A
  • poorly localised
  • dullness
  • vagueness
  • fullness
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10
Q

Where is visceral pain often referred to?

A

A somatic structure

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11
Q

What are nociceptors?

A

Specific peripheral primary sensory afferent neurones, normally activated preferentially by intense stimuli (ie. thermal, mechanical, chemical) that are noxious, or damaging

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12
Q

First order neurones that relay information to second order neurones in the CNS by chemical synaptic transmission….this described what?

A

Nociceptors

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13
Q

Where are the cell bodies of nociceptors located?

A

In the dorsal root ganglion and trigeminal ganglia

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14
Q

What happens in response to a noxious stimuli?

A

DEPOLARISATION - which elicits an AP to propagate to the CNS

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15
Q

What are the different types of noxious stimuli?

A
  • Chemical
  • Mechanical
  • Thermal
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16
Q

What do nociceptors comprise?

A

Aδ- and C-fibres

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

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17
Q

In nociceptors, where does transduction begin?

A

In free nerve endings

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18
Q

What type of nociceptors are Aδ fibres?

A

Mechanical / Thermal

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19
Q

Describe the myelination of Aδ fibres?

A

Thinly myelinated

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20
Q

What is the conduction velocity of Aδ fibres?

A

Conduction velocity of 6 – 30 ms-1

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21
Q

What do Aδ fibres respond to?

A

Noxious mechanical or thermal stimuli

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22
Q

What do Aδ fibres mediate?

A

‘First’ or fast pain

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23
Q

Describe the myelination of C fibres.

A

Unmyelinated

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24
Q

What is the conduction velocity of C fibres?

A

Conduction velocity of 0.5 – 2.0 ms-1

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25
Q

What do C fibres respond to?

A

ALL noxious stimuli

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26
Q

What term describes the function of C fibres?

A

Polymodal

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27
Q

What do C fibres mediate?

A

‘Second’ or slow pain

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28
Q

Outline the series of events that occur in response to a thermal noxious stimuli.

A
  1. Thermal stimuli
  2. Heat/cold sensitive receptors
  3. Na+/Ca2+ influx
  4. Depolarisation (membrane graded)
  5. Voltage activated Na+ channel activation
  6. AP’s to the CNS
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29
Q

What does noxious stimuli in the long term result in?

A

Increases spinal excitability contributing to hyperalgesia and allodynia
- the synapse becomes more efficient the more it is used

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30
Q

How to afferent C fibres transmit info to the CNS?

A

Via release of glutamate and peptides within the DORSAl horn

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31
Q

Describe the action of efferent C fibres.

A

They release pro-inflammatory mediators from peripheral terminals

32
Q

What do efferent C fibres contribute to?

A

Neurogenic inflammation

33
Q

Name a pro-inflammatory mediator.

A

Calcitonin

34
Q

Describe the 1st step of neurogenic inflammation.

A

Peptides (SP and CGRP) released from free nerve ending of peptidergic nociceptor due to tissue damage, or inflammatory mediators

35
Q

Describe the 2nd step of neurogenic inflammation.

A

SP causes (i) vasodilation and extravasation of plasma proteins (promotes formation of bradykinin and prostaglandins) (ii) release of histamine from mast cells (iii) sensitizes surrounding nociceptors

36
Q

Describe the 3rd step of neurogenic inflammation.

A

CGRP induces vasodilation

37
Q

Describe the 4th step of neurogenic inflammation.

A

Primary and secondary hyperalgesia and allodynia ensue

38
Q

What is the primary neurotransmitter in the dorsal horn?

39
Q

What is the effect of glutamate?

A

Produces a fast e.p.s.p and neuronal excitation by activating primarily post-synaptic AMPA receptors, with NMDA receptor participation (when afferent input is intense)

40
Q

Given 2 examples of peptides that also participate along with glutamate.

A

Substance P

CGRP

41
Q

When do peptides participate?

A

During high frequency stimulation

42
Q

What do peptides cause?

A

A slow and prolonged e.p.s.p that facilitates activation of NDMA receptors by relieving voltage-dependent block by Mg2+

43
Q

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

A

In the dorsal root ganglia (DRG)

44
Q

Where do axons of primary afferents terminate?

A

In the dorsal horn of the spinal cord in various laminae of Rexed (I-V)

45
Q

Where do nociceptive C- and Aδ-fibres mostly terminate?

A

In laminae I and II (and also V from Aδ-fibres

46
Q

What do nociceptive specific (NS) cells synapse with?

A

Only with C- and Aδ-fibres

47
Q

What are cells that receive input from only Aδ-fibres

A

Proprioceptive cells

48
Q

What do wide dynamic range (WDR) neurones receive input from? What is the effect of this??

A

All three types of fibre.

- these therefore respond to a wide range of stimuli

49
Q

What does visceral pain originate from?

A

Nociceptors covering tissues (ie. peritoneum, pleura), or walls of hollow organs.
- originates from stretching, twisting, inflammation and ischaemia

50
Q

What does visceral pain NOT originate from?

A

cutting or burning

51
Q

Describe the typical character of visceral pain.

A

Poorly localised

Dull, aching, throbbing character

52
Q

Before entering the dorsal horn, where do visceral afferents from nociceptors follow?

A

Sympathetic pathways

53
Q

Where do some visceral and skin afferents converge upon?

A

The same spinothalamic neurones (all cells with a visceral receptive field (RF) also have a separate cutaneous RF).

54
Q

Where do terminals of visceral nociceptors terminate?

A

In laminae I and V, but not II

55
Q

Where do terminals of visceral nociceptors NOT terminate?

56
Q

“The brain ‘interprets’ the nociceptive information arising from the viscera as originating from an area of skin that may be distant to the internal organ”, this describes?

A

REFERRED PAIN

57
Q

Visceral pain is pain that is perceived where?

A

At a distance from the affected organ

58
Q

What autonomic features is visceral pain often associated with?

A
  • Nausea
  • Vomiting
  • Sweating
  • Pallor
59
Q

Describe viscera-somatic pain.

A

Sharp and well localised

60
Q

When does viscero-somatic pain occur?

A

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

61
Q

Pain and nociception are identical

A

FALSE - they are not identical

62
Q

What can pain evoked by activity in nociceptors be reduced by?

A

Simultaneous activity in LTMs (Aβ-fibres)

63
Q

What are the projection neurone (P) inputs inhibited by?

A

An interneurone (I)

64
Q

What are project neurones (P) i) exited ii) inhibited by?

A

i) the large sensory axon

ii) the nociceptive axon

65
Q

What does activity in the nociceptive axon alone do?

A

Maximally excites the projection neurone, allowing nociceptive signals to arise to the brain

66
Q

What do second order neurones ascend the spinal cord in?

A

The anterolateral system

67
Q

What is the anterolateral system comprised of?

A
  • The spinothalamic tract (STT)

* The spinoreticular tract (SRT)

68
Q

Where do projection neurones from lamina I of the STT (fast fibre Aδ pain) terminate?

A

In the posterior nucleus of the thalamus

69
Q

Where do projection neurones originating from lamina V of the STT system (WDR neurones) terminate?

A

In the posterior and ventroposterior nucleus of the thalamus

70
Q

What does pain perception (location and intensity) require?

A

Simultaneous firing in both pathways

71
Q

What does the SRT system largely transmit?

A

Slow C-fibre pain

72
Q

What does the SRT system make extensive connections with?

A

Reticular nuclei in the brainstem [e.g. periaqueductal grey (PAG) and parabrachial nucleus (PB)]

73
Q

SRT system is involved in autonomic responses to what?

A

Pain, arousal, emotional responses, fear of pain

74
Q

STT is fast pathway

75
Q

SRT is slow pathway

76
Q

What are thermoreceptors?

A

Neurones that are specialised to respond to small changes in temperature (we can perceive differences as small as 0.01oC)

77
Q

Is temperature sensitivity uniform across the whole body surface?

A

No!

Hot- and cold-sensitive spots exist (and these do not respond to both)

Neurology (42 decks)

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