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Neurology > An introduction to pain and thermosensation > Flashcards

An introduction to pain and thermosensation Flashcards

1
Q

What are the three forms of pain?

A

Nociceptive
Inflammatory
Pathological

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2
Q

What activates nociceptors?

A

Intense stimuli (thermal, mechanical, chemical)

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3
Q

Nociceptors are _____ ____ ______ that relay information to _____ ____ ______ in the CNS by ________ synaptic transmission

A

Nociceptors are first order neurones that relay information to second order neurones in the CNS by chemical synaptic transmission

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4
Q

What fibres are found within nociceptors?

A

Aδ- and C-fibres

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5
Q

What kind of fibres are Aδ?

A

Mechanical/thermal nociceptors

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6
Q

Describe the structure and speed of conduction of Aδ fibres?

A

Thinly myelinated, conduction velocity of 6-30ms-1

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7
Q

What kind of fibres are C?

A

Respond to all noxious stimuli

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8
Q

Describe the structure and speed of conduction of C fibres?

A

0.5-2ms-1

unmyelinated

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9
Q

C fibres mediate ____ or ____ pain and Aδ fibres mediate _____ or ____ pain

A

C fibres mediate second or slow pain and Aδ fibres mediate first or fast pain

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10
Q

Give examples of first pain stimuli?

A

Lancinating, stabbing, pricking

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11
Q

Give examples of second pain stimuli?

A

Burning, throbbing, cramping, aching

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12
Q

Thermal stimuli activates which nociceptors?

A

Transient Receptor potential family, particularly TRPA1, TRPC3, TRPV1

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13
Q

Chemical stimuli activates which nociceptors

A

H+ activates acid sensing ion channels (ASICs)

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14
Q

What nociceptors does ATP activate

A

P2X and P2Y

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15
Q

What nociceptors does bradykinin activate?

A

bradykinin activates B2 receptors

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16
Q

Describe the nociceptive pathway

A

Noxious stimulation of free nerve ending —> action potential in axon of nociceptor –> enters dorsal horn of spinal cord —> projects to second order neurone —> spinothalamic and spinoreticulothalamic tracts

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17
Q

What are the subsets of peptidergic polymodal nociceptors (subset of C fibres)

A

Afferent and efferent

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18
Q

Describe the function of afferent nociceptors

A

Transmit nociceptive info to the CNS via release of glutamate and peptides (substance P, neurokinin A) within the dorsal horn

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19
Q

Describe the function of efferent nociceptors

A

Release pro-inflammatory mediators e.g. calcitonin gene-related peptide or substance p, from peripheral terminals contributing to neurogenic inflammation

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20
Q

Noxious stimulation in the long term causes what?

A

Increased spinal excitability contributing to hyperalgesia and allodynia

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21
Q

What does substance P cause in neurogenic inflammation?

A

Vasodilation and extravasation of plasma proteins (promotes formation of bradykinin and prostaglandins)

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22
Q

What is the role of histamine in neurogenic inflammation?

A

Sensitises surrounding nociceptors

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23
Q

What does CGRP cause in neurogenic inflammation?

A

Vasodilation

24
Q

What facilitates neurotransmission between the primary afferent and second order neurone in the dorsal horn

A
  • glutamate : fast e.p.s.p and neuronal excitation by activating postsynaptic AMPA receptors with NMDA receptor participation
  • peptides (substance P and GCRP): slow e.p.s.p that facilitates activation of NMDA receptors
25
Q

How does a slow and prolonged e.p.s.p by peptide facilitate activation of NMDA receptors?

A

By relieving voltage-dependent block by Mg2+

26
Q

Primary afferent cell bodies (apart from the trigeminal system) are located in the ______ ____ ______ (___). Axon terminates centrally in the dorsal horn of the spinal cord in various ______ of _____

A

Primary afferent cell bodies (apart from the trigeminal system) are located in the dorsal root ganglia (DRG). Axon terminates centrally in the dorsal horn of the spinal cord in various laminae of Rexed

27
Q

Nociceptive C- and Aδ-fibres mostly terminate superficially in laminae _ and __ (and also V for __-fibres)

A

Nociceptive C- and Aδ-fibres mostly terminate superficially in laminae I and II (and also V for Aδ-fibres)

28
Q

Nociceptive specific (NS) cells synapse only with _- and __-fibres

A

Nociceptive specific (NS) cells synapse only with C- and Aδ-fibres

29
Q

Cells that receive input from only Aβ-fibres are ___________?

A

Cells that receive input from only Aβ-fibres are proprioceptive

30
Q

Wide dynamic range (WDR) neurones receive input from all _____ types of fibre and thus respond to a wide range of stimuli

A

Wide dynamic range (WDR) neurones receive input from all three types of fibre and thus respond to a wide range of stimuli

31
Q

What structures does visceral pain originate from?

A

Nociceptors covering tissues (peritoneum or pleura), or walls of hollow organs.

32
Q

What events does visceral pain originate from?

A

Stretching, twisting, inflammation and ischaemia- not cutting or burning

33
Q

What does visceral pain tend to present as?

A

Poorly localised, dull, aching, throbbing

34
Q

Visceral afferents from nociceptors follow __________ pathways before entering the ______ horn

A

Visceral afferents from nociceptors follow sympathetic pathways before entering the dorsal horn

35
Q

Terminals of visceral nociceptors terminate in laminae _ and _, but not _

A

Terminals of visceral nociceptors terminate in laminae I and V, but not II

36
Q

What is referred pain?

A

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 – the phenomenon of referred pain

37
Q

Where is visceral pain perceived?

A

At a distance from the affected organ

38
Q

What is visceral pain associated with?

A

Autonomic features

-nausea, vomiting, sweating, pallor

39
Q

The area of pain referral is to where?

A

The segmental dermatome e.g. heart T1-5, Gallbladder C4

40
Q

What may be seen in the segmental dermatome of pain referral?

A

Hyperalgesia

41
Q

When does viscerosomatic pain occur?

A

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

42
Q

Pain evoked by activity in nociceptors (C and Aδ fibres) can be reduced by what?

A

Simultaneous activity in low threshold mechanoreceptors Aβ-fibres

43
Q

Signals from Aβ-fibres, and C/Aδ fibres are processed by neuronal circuits of the?

A

Substantia gelatinosa

44
Q

When Aβ-fibre activity is greater than that of C/Aδ fibres what happens?

A

The spinal gate is closed and synaptic transmission of nociceptive signals to the ascending tracts is suppressed and pain is not perceived

45
Q

When C/Aδ-fibre activity is greater than that of Aβ fibres what happens?

A

The spinal gate is open and synaptic transmission of nociceptive signals to the ascending traces is facilitated and pain is perceived

46
Q

In gate control theory; Certain neurones (_) within the _______ ________ project to the _________ tract and are postulated to be excited by both large diameter (__) sensory axons and unmyelinated (___) nociceptive axons

A

Certain neurones (P) within the substantial gelatinosa project to the spinothalamic tract and are postulated to be excited by both large diameter (Aβ) sensory axons and unmyelinated (C/Aδ) nociceptive axons

47
Q

In gate control theory;
The projection neurone (P) inputs are inhibited by an _________ (_) and the ________ is excited by the large sensory axon and inhibited by the _______ axon

A

The projection neurone (P) inputs are inhibited by an interneurone (I) and the interneurone is excited by the large sensory axon and inhibited by the nociceptive axon

48
Q

In gate control theory;
activity in the _______ axon alone maximally excites the projection neurone, allowing nociceptive signals to arise to the _____

A

activity in the nociceptive axon alone maximally excites the projection neurone, allowing nociceptive signals to arise to the brain

49
Q

Second order neurones ascend the spinal cord in the anterolateral system comprising mainly;
The ________ tract (S__)
The ________ tract (S__)

A

Second order neurones ascend the spinal cord in the anterolateral system comprising mainly;
The spinothalamic tract (STT)
The spinoreticular tract (SRT)

50
Q

In the spinothalamic tract projection neurones originating from lamina _ (fast fibre __ pain) terminate in the ______ _______ of the _______

A

In the spinothalamic tract projection neurones originating from lamina I (fast fibre Aδ pain) terminate in the posterior nucleus of the thalamus

51
Q

In the spinothalamic tract projection neurones originating from lamina _ (WDR neurones) terminate in _______ and __________ ______ of the ______

A

In the spinothalamic tract projection neurones originating from lamina V (WDR neurones) terminate in posterior and ventroposterior nucleus of the thalamus

52
Q

In the spinothalamic tract what is required for pain perception to occur?

A

Stimulus firing in both pathways (Fast fibre Aδ and WDR)

53
Q

The spinoreticular tract largely transmits ____ _ fibre pain

A

The spinoreticular tract largely transmits slow C fibre pain

54
Q

What does the spinoreticular tract make extensive connections with?

A

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

55
Q

The spinoreticular tract is involved in ______ responses to pain, _____, _______ responses, ____ of pain

A

The spinoreticular tract is involved in autonomic responses to pain, arousal, emotional responses, fear of pain

Neurology (41 decks)

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