Physiology and Pathophysiology of Pain

Question 1

What is pain?

Answer 1

An unpleasant sensory and emotional experience associated with, or resembling that association with, actual or potential tissue damage

Question 2

What are the key notes for pain?

Answer 2

Is always a personal experience, pain and nociception are different phenomena, learn the concept of pain, may have adverse effects and can use verbal description to express

Question 3

Describe nociception

Answer 3

Physiological process by which noxious stimulation is communicated through the peripheral and CNS

Question 4

Where does perception of pain occur?

Answer 4

Somatosensory cortex

Question 5

What neural pathways are involved in pain?

Answer 5

PNS - detection and transmission
Spinal cord - processing ang transmission to brain (thalamus)
Brain - perception, learning and response
Modulation by descending tracts

Question 6

Describe nociceptors

Answer 6

Free nerve endings of A delta (faster pain as myelinated) and C fibres (slower)
Respond to thermal, chemical and mechanical noxious stimuli

Question 7

Describe primary afferents

Answer 7

Cell body in dorsal root ganglion
First order neurons
Synapse at spinal cord

Question 8

Where do the 1st order neurons synapse and what neurons receive this?

Answer 8

In Rexed lamina 1 and 2
Input to nociceptive specific, low threshold mechanoreceptive and wide dynamic range
After this axons continue as tracts

Question 9

What is the main ascending tract for nociception?

Answer 9

Spinothalamic tract - arises in Rexed lamina 1,2 and 5, then becomes lateral spinothalamic tract
Also have spinoreticular, spinomesencephalic and spinohypothalamic tracts

Question 10

What are the 2 systems of the thalamus?

Answer 10

Lateral and medial systems

Question 11

What communicates with the thalamus?

Answer 11

Somatosensory cortex, spinal cord and basal ganglia in lateral system
Insula, brainstem and cingulate in medial system

Question 12

Describe descending pathways for pain

Answer 12

Periaqueductal grey in midbrain assimilates the info
Effective via rosteroventral medulla
Usually decreases pain signals - DNIC
Noradrenergic system

Question 13

What is the outcome of sensitisation?

Answer 13

Leftward shift of stimulus intensity curve towards innocuous (not harmful)

Question 14

What causes spontaneous pain?

Answer 14

Spontaneous activity in nerve fibres

Question 15

What are the changes in nociceptor to cause allodynia?

Answer 15

This is pain from stimulus which is not usually painful
There is decreased threshold for that response

Question 16

What are the changes in nociceptor to cause hyperalgesia?

Answer 16

This is abnormally heightened sensitivity to pain
There is exaggerated response to normal and supra-normal stimuli

Question 17

What can influence the primary afferent neuron?

Answer 17

Interneurons and descending neurons

Question 18

What is central sensitisation?

Answer 18

Response of second order neurons in the CNS to both noxious and non-noxious stimuli

Question 19

What are the 3 main components of central sensitisation?

Answer 19

Wind up
Classical
Long term potentiation

Question 20

Describe wind up - central sensitisation

Answer 20

Involves only activated synapses
homosynaptic activity dependant progressive increase in response of neurons
Manifests over course of stimuli and terminates with stimuli

Question 21

What is included in wind up?

Answer 21

Substance P and CGRP

Question 22

Describe classical central sensitisation

Answer 22

Involves opening up of new synapses
Hetero-synaptic activity dependant plasticity
Immediate onset with appropriate stimuli and outlasts the initial stimuli

Question 23

What receptors does classical sensitisation involve?

Answer 23

NDMA receptors

Question 24

Describe long term potentiation

Answer 24

Involves mainly activated synapses
Occurs primarily for very intense stimuli
Involves NMDA and AMPA receptors

Question 25

What are the mechanisms for pain?

Answer 25

Nociceptive
Neuropathic
Nociplastic

Question 26

Describe acute pain

Answer 26

Physiological
Presence of noxious stimuli
Serves protective function
Usually nociceptive

Question 27

Describe chronic pain

Answer 27

Pathological
No presence of noxious stimuli
Does not serve any purpose
Nociceptive, neuropathic and nociplastic

Question 28

What is nociceptive pain?

Answer 28

A sensory experience that occurs when specific peripheral sensory neurons respond to noxious stimuli

Question 29

Where is nociceptive pain and how long does it last?

Answer 29

Painful region is typically localised at site of injury
Usually time limited and resolves when damaged tissue heals
Can also be chronic

Question 30

What does nociceptive pain usually respond to?

Answer 30

Conventional analgesics

Question 31

What is neuropathic pain?

Answer 31

Pain caused by a lesion or disease of the somatosensory nervous system

Question 32

What is neuropathic pain?

Answer 32

Painful region may not be the same as site of injury - in in neurological territory of affected structure - nerve, root, spinal cord, brain
Usually chronic

Question 33

Describe nociplastic pain

Answer 33

Pain that arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing activation of peripheral nociceptors or disease or lesion in somatosensory system

Question 34

What can cause nociplastic pain?

Answer 34

Fibromyalgia
Chronic widespread pain
Painful physical symptoms of depression and anxiety

Question 35

What are the characteristics of nociplastic pain?

Answer 35

Stimulus independent, no inflammation or injury, no structural neuronal damage
Due to central plasticity, no protective or adaptive function and pathological pain