Anatomy + Physiology of Pain

Question 1

Transduction

Answer 1

Noxious stimuli translated into electrical activity at sensory nerve endings

Question 2

Transmission

Answer 2

Propagation of impulses along pain pathway

Question 3

Perception

Answer 3

Discrimination/affect/motivation

Question 4

Pain

Answer 4

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

Question 5

Signal transduction

Answer 5

Receptor proteins in membrane of nociceptors that allow response to tissue-damaging stimuli

Question 6

ASIC3

Answer 6

Skeletal and cardiac muscle
Acid sensing
Detects pH change with ischaemia

Question 7

TRPV1

Answer 7

Heat

Acid

Question 8

TRPM8

Answer 8

Cold

Question 9

Loss of transduction/transmission genetic defect

Answer 9

Loss of NaV1.7

Congenital indifference to pain

Question 10

Loss of C fibres

Answer 10

trkA-NGF receptor mutation

Congenital insensitivity to pain with anhidrosis CIPA

Question 11

A Delta nociceptors

Answer 11

MYELINATED
Sharp, pricking, fast pain
Thermal + mechanical nociception
Precise location of insult/stimulus
Reflex withdrawal

Question 12

C fibres

Answer 12

Non-myelinated
Slow burning pain
Peptidergic C fibres
Peptide poor C fibres

Question 13

Peptidergic C fibres

Answer 13

Release peptides peripherally, e.g. substance P/CGRP
Thermal nociception
Vasoactive, promote inflammatory responses + healing

Question 14

Peptide poor C fibres

Answer 14

Have distinct receptors e.g. P2X3 ATP receptors

Mechanical nociception

Question 15

Lamina I- dorsal horn

Answer 15

A delta nociceptors

Question 16

Lamina I-IIo

Answer 16

A delta/C peptidergic fibres

Question 17

Lamina II

Answer 17

C non-peptidergic fibres

Question 18

Lamina IIi-III

Answer 18

A delta hair follicle afferents

Question 19

Lamina IIi-V

Answer 19

A beta hair follicle and tactile afferents

Question 20

C fibres innervate lamina..

Answer 20

Lamina I
Interneurones in Lamina II
Lamina V through interneurones in lamina II

Question 21

A delta fibres innervate lamina…

Answer 21

Lamina I and V projection neurones

Question 22

Lamina V

Answer 22

A delta
A beta fibres- touch
C fibres- indirectly through interneurones

Question 23

Lateral spinothalamic tract

Answer 23

Pain and Temp

Question 24

Limbic system

Answer 24

Projections to here from lateral spinothalamic tract mediate unpleasant (painful) character of pain

Question 25

Anterior "neo" spinothalamic tract

Answer 25

Primary afferent- A delta as well as C and A Beta Innervate projection neurones in lamina C --> after decussating, axons travel in anterior spinothalamic tract Innervate VPL and VPM in somatosensory thalamus Innervate VPI and CL nuclei in reticular + limbic associated areas

Question 26

Anterior spinothalamic- projections to cortex

Answer 26

VPI --> secondary somatosensory cortex | CL --> anterior cingulate cortex, prefrontal cortex + striatum

Question 27

Anterior spinothalamic function summary

Answer 27

Subserves the first, discriminative aspects of pain

Question 28

Lateral spinothalamic tract

Answer 28

Primary afferent- C fibres but some A Delta Innervate projection neurones in lamina 1 --> after decussating, axons travel in lateral spinothalamic tract Innervate more posterior/medial parts of thalamus --> mediodorsal nucleus, posterior and ventral medial nuclei

Question 29

Lateral spinothalamic- projections to cortex

Answer 29

MDvc --> ACC (amotion, motivation) | POm/VMpo --> anterior and rostral insula (emotion, quality i.e. pain

Question 30

Lateral spinothalamic function summary

Answer 30

Subserves second, punishing aspects of pain

Question 31

Primary sensory cortex

Answer 31

Somatosensory discrimination- location, intensity

Question 32

Anterior cingulate cortex

Answer 32

Emotional reaction/motivation

Question 33

Pre-frontal cortex

Answer 33

Evaluation | Cognition

Question 34

insula

Answer 34

Pain map, interoception, homeostatic adjustment, emotion

Question 35

Amygdala

Answer 35

Aversion, emotional memory + response

Question 36

Peripheral sensitisation

Answer 36

Sensitisation of area of injury Due to effects of inflammatory receptors --> reduction in activation threshold --> increase in responsiveness - Na channels change thresholds for opening, K channels close, TRPV1 channels increases sensitivity to heat, some nociceptors become tonically active

Question 37

Hyperalgesia/allodynia/spontaneous pain

Answer 37

Enables protection + facilitates healing | Resolves with healing of underlying cause

Question 38

4 Cardinal signs of inflammation

Answer 38

Calor Rubor Dolor Tumor

Question 39

Prostaglandin synthesis

Answer 39

Phospholipase A2 releases arachidonic acid from cell membranes COX1 and COX 2 use it as substrate for PG synthesis

Question 40

COX 1

Answer 40

Present in tissue at low levels

Question 41

COX 2

Answer 41

Induced during inflammation

Question 42

Central sensitisation

Answer 42

Prolonged nociceptor input onto dorsal horn neurone projection neurones Nociceptor afferents release glutamate and peptides --> increased dorsal horn nociceptive second order neurones to inputs sensitivity

Question 43

Primary thermal hyperalgesia

Answer 43

Increased sensitivity to heat induced pain

Question 44

Primary mechanical hyperalgesia

Answer 44

Increased sensitivity to pressure pain

Question 45

Chronic pain

Answer 45

Pain of more than 12 weeks

Question 46

Maladaptive pain

Answer 46

Abnormal activity in NS - neuropathic pain, dysfunctional pain Characterised by hyperalgesia, allodynia, spontaneous pain

Question 47

Endogenous modulation

Answer 47

Innocuous stimuli lessen pain- rubbing an acute injury | Pain can inhibit pain

Question 48

Acupuncture

Answer 48

Activate A delta fibres | Stimulates through PAG mediated Diffuse Noxious Inhibitory control "DNIC" of pain

Question 49

Analgesia through stimulation of non-noxious afferents

Answer 49

Non-noxious inputs also stimulate lamina II interneurones | Basis of TENS