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Neurology > Pain and Thermosensation > Flashcards

Pain and Thermosensation Flashcards

1
Q

What is pain?

A

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 three forms of pain?

A 
Nociceptive = adaptive, short lived, protective
Inflammatory = adaptive, helps healing, lasts days
Pathological = maladaptive, lasts months, no physiological purpose
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3
Q

How can acute mild pain be controlled?

A

NSAIDs, paracetamol and opioids in moderate/severe cases

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4
Q

What are some agents used to control chronic pain?

A

Antidepressants, anticonvulsants and local anaesthetics

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5
Q

What are nociceptors?

A

Specific peripheral primary sensory afferent neurons = normally activated preferentially by intense noxious stimuli

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6
Q

What order neuron are nociceptors?

A

First order neurons = relay info to second order neurons in the CNS by chemical synaptic transmission

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7
Q

What are the subtypes of nociceptors?

A

Comprise of C and Adelta fibres

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8
Q

Where does transduction of nociceptors begin?

A

In free nerve endings = mediated by numerous receptors and channels

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9
Q

What are some features of Adelta fibres?

A

Mechanical/thermal nociceptors
Thinly myelinated
Mediate fast pain

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10
Q

What are some features of C fibres?

A

Unmyelinated nociceptors
Respond to cell noxious stimuli
Mediate slow pain

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11
Q

What are some features of mechanical stimuli?

A

Receptors and channels remain uncertain despite intense investigation

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12
Q

What are some features of thermal stimuli?

A

Member of TRP family = TRPA1, TRPC3, TRPV1

Activated by noxious heat

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13
Q

What are some features of chemical stimuli?

A

H+ activates acid sensing ion channels
ATP activates P2X and P2Y receptors
Bradykinin activates B2 receptors

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14
Q

What are some features of afferent peptidergic polymodal nociceptors?

A

Transmit nociceptive info to the CNS via release of glutamate and peptides within the dorsal horn

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15
Q

What are some features of efferent peptidergic polymodal nociceptors?

A

Release pro-inflammatory from peripheral terminals

Contributes to neurogenic inflammation

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16
Q

What does long term noxious stimulation cause?

A

Increases spinal excitability contributing to hyperalgesia and allodynia

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17
Q

What peptides are released during neurogenic inflammation?

A

SP and CGRP are released from free nerve ending of peptidergic nociceptor due to tissue damage or inflammatory mediators

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18
Q

What effects does SP have?

A

Vasodilation and extravasation of plasma proteins
Release of histamine from mast cells
Sensitises surrounding nociceptors

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19
Q

What effect does CGRP have?

A

Induces vasodilation

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20
Q

What does neurogenic inflammation lead to?

A

Primary and secondary hyperalgesia and allodynia

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21
Q

Where does neurotransmission between primary afferent and the second order neuron occur?

A

Occurs in dorsal horn = AP opens voltage gated Ca2+ channels

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22
Q

What causes glutamate release from neurotransmitters?

A

Ca2+ influx = causes membrane depolarisation and opening of voltage gated Na+ channels which generates AP

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23
Q

How does glutamate produce a fast epsp and neuronal excitation?

A

Activates primary postsynaptic AMPA receptors with NMDA receptor participation

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24
Q

What causes a slow and prolonged epsp?

A

Substance P and CGRP = facilitates activation of NMDA receptors by relieving voltage dependent voltage block by Mg2+

25
Q

Where are primary afferent cell bodies located?

A

In the dorsal root ganglia (except those from trigeminal system)

26
Q

Where do axons terminate?

A

Terminate centrally in the dorsal horn of the spinal cord in various laminae of Rexed

27
Q

Where do nociceptive C and Adelta fibres terminate?

A

Mostly superficially in laminae I and II

Also V for Adelta fibres

28
Q

What are the only fibres that nociceptive specific cells synapse with?

A

C and Adelta fibres

29
Q

What property do cells that receive only Abeta fibres have?

A

Proprioceptive

30
Q

What input do wide dynamic range neurons receive?

A

All three types of fibre (C, Abeta and Adelta) = respond to wide range of stimuli

31
Q

Where does visceral pain originate from?

A

Nociceptors covering tissues or walls of hollow organs = due to stretching, twisting, inflammation and ischaemia

32
Q

What are the characteristics of visceral pain?

A

Poorly localised, dull, aching, throbbing

33
Q

What do visceral afferent from nociceptors follow before they enter the dorsal horn?

A

Sympathetic pathways

34
Q

Can visceral and skin afferents converge upon the same spinothalamic neurons?

A

Yes

35
Q

When does referred pain occur?

A

When the brain interprets the nociceptive info arising from the viscera as originating from an area of skin

36
Q

What are some features of referred pain?

A

Often associated with autonomic features
Area of referral is to single segmental dermatome which may show signs of hyperalgesia
Consistent enough to be of diagnostic value

37
Q

What is the character is viscerosomatic pain?

A

Sharp and well localised

38
Q

What causes viscerosomatic pain?

A

Occurs when inflammatory exudate from a diseased organ contacts a somatic structure

39
Q

Are pain and nociception identical?

A

No = pain is awareness of suffering but nociception may occur in the abscence of pain

40
Q

How is perception of pain variable?

A

For the same degree of nociceptor activity, depending on the level of concurrent non-painful sensory input and behavioural context, more or less pain may be felt

41
Q

How can pain evoked by activity in nociceptors be reduced?

A

By simultaneous activity in low threshold mechanoreceptors

42
Q

What is the gate control theory?

A

Nerve impulses evoked by injury are influenced in the spinal cord by other nerve cells that act like gates = either let them through or stop them entering

43
Q

How do innocuous and nociceptive signals conduct to the spinal cord?

A

Via Abeta and C/Adelta fibres respectively = are in part processed by neuronal circuits of the substantia gelatinosa

44
Q

What happens when Abeta fibre activity exceeds that of C/Adelta fibres?

A

Spinal gate is closed and synaptic transmission of nociceptive signals to the ascending tract is suppressed = pain isn’t perceived

45
Q

When happens when C/Adelta fibre activity exceeds that of Abeta fibres?

A

Spinal gate is open and synaptic transmission of nociceptive signals to the ascending tract is facilitated = pain is perceived

46
Q

What neurons within the substantia gelatinosa project to the spinothalamic tract?

A

P neurons = postulated to be excited by both large diameter sensory axons and unmyelinated nociceptive axons

47
Q

What are projection neurons inhibited by?

A

Interneurons = interneuron is excited by large sensory axons and inhibited by nociceptive axons

48
Q

What is the basis of nociceptive signals arising in the brain?

A

The activity of the nociceptive axon alone maximally exciting the projection neuron

49
Q

How do second order neurons ascend the spinal cord?

A

In the anterolateral system = comprising mainly the spinothalamic and spinoreticular tracts

50
Q

What is required in the spinothalamic tract for pain to be perceived?

A

Simultaneous firing in both pathways

51
Q

Where do projection neurons of the spinothalamic tract arising in laminae I terminate?

A

The posterior nucleus of the thalamus

52
Q

Where do projection neurons of the spinothalamic tract arising in laminae V terminate?

A

The posterior and ventroposterior nucleus of the thalamus

53
Q

What does the spinoreticular tract largely transmit?

A

Slow C fibre pain

54
Q

What does the spinoreticular tract make extensive connections with?

A

The reticular nuclei of the brainstem

55
Q

What is the spinoreticular tract involved in?

A

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

56
Q

What are thermoreceptors?

A

Neurons that are specialised to respond to small changes in temperature

57
Q

Is temperature sensitivity uniform across the body?

A

No = hot sensitive and cold sensitive spots exist

58
Q

Why does thermosensation require separate neurons and their associated receptors/channels?

A

To encode between hot and cold

Neurology (48 decks)

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