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Pain and Thermosensation Flashcards

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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?

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A

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

25
Where are primary afferent cell bodies located?
In the dorsal root ganglia (except those from trigeminal system)
26
Where do axons terminate?
Terminate centrally in the dorsal horn of the spinal cord in various laminae of Rexed
27
Where do nociceptive C and Adelta fibres terminate?
Mostly superficially in laminae I and II | Also V for Adelta fibres
28
What are the only fibres that nociceptive specific cells synapse with?
C and Adelta fibres
29
What property do cells that receive only Abeta fibres have?
Proprioceptive
30
What input do wide dynamic range neurons receive?
All three types of fibre (C, Abeta and Adelta) = respond to wide range of stimuli
31
Where does visceral pain originate from?
Nociceptors covering tissues or walls of hollow organs = due to stretching, twisting, inflammation and ischaemia
32
What are the characteristics of visceral pain?
Poorly localised, dull, aching, throbbing
33
What do visceral afferent from nociceptors follow before they enter the dorsal horn?
Sympathetic pathways
34
Can visceral and skin afferents converge upon the same spinothalamic neurons?
Yes
35
When does referred pain occur?
When the brain interprets the nociceptive info arising from the viscera as originating from an area of skin
36
What are some features of referred pain?
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
What is the character is viscerosomatic pain?
Sharp and well localised
38
What causes viscerosomatic pain?
Occurs when inflammatory exudate from a diseased organ contacts a somatic structure
39
Are pain and nociception identical?
No = pain is awareness of suffering but nociception may occur in the abscence of pain
40
How is perception of pain variable?
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
How can pain evoked by activity in nociceptors be reduced?
By simultaneous activity in low threshold mechanoreceptors
42
What is the gate control theory?
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
How do innocuous and nociceptive signals conduct to the spinal cord?
Via Abeta and C/Adelta fibres respectively = are in part processed by neuronal circuits of the substantia gelatinosa
44
What happens when Abeta fibre activity exceeds that of C/Adelta fibres?
Spinal gate is closed and synaptic transmission of nociceptive signals to the ascending tract is suppressed = pain isn't perceived
45
When happens when C/Adelta fibre activity exceeds that of Abeta fibres?
Spinal gate is open and synaptic transmission of nociceptive signals to the ascending tract is facilitated = pain is perceived
46
What neurons within the substantia gelatinosa project to the spinothalamic tract?
P neurons = postulated to be excited by both large diameter sensory axons and unmyelinated nociceptive axons
47
What are projection neurons inhibited by?
Interneurons = interneuron is excited by large sensory axons and inhibited by nociceptive axons
48
What is the basis of nociceptive signals arising in the brain?
The activity of the nociceptive axon alone maximally exciting the projection neuron
49
How do second order neurons ascend the spinal cord?
In the anterolateral system = comprising mainly the spinothalamic and spinoreticular tracts
50
What is required in the spinothalamic tract for pain to be perceived?
Simultaneous firing in both pathways
51
Where do projection neurons of the spinothalamic tract arising in laminae I terminate?
The posterior nucleus of the thalamus
52
Where do projection neurons of the spinothalamic tract arising in laminae V terminate?
The posterior and ventroposterior nucleus of the thalamus
53
What does the spinoreticular tract largely transmit?
Slow C fibre pain
54
What does the spinoreticular tract make extensive connections with?
The reticular nuclei of the brainstem
55
What is the spinoreticular tract involved in?
Autonomic responses to pain, arousal, emotional responses and fear of pain
56
What are thermoreceptors?
Neurons that are specialised to respond to small changes in temperature
57
Is temperature sensitivity uniform across the body?
No = hot sensitive and cold sensitive spots exist
58
Why does thermosensation require separate neurons and their associated receptors/channels?
To encode between hot and cold

Neurology (48 decks)

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