Pain

Question 1

What is the difference between nociception and pain?

Answer 1

Pain is the perception of nociception and requires its relay to the cortex

Question 2

What are the 2 broad classifications of pain? Give 2 specific examples of each type

Answer 2

Adaptive/protective (e.g. nociceptive pain, inflammatory pain)
Maladaptive/pathological (e.g. neuropathic pain, functional pain syndromes)

Question 3

Describe the pathway for transmission of nociceptive pain

Answer 3

Input from noxious stimuli (e.g. heat, cold, intense mechanical force, chemical irritants) is carried to the spinal cord via unmyelinated C fibres or myelinated AD fibres
Fibres synapse with 2nd-order neurons in different layers of the dorsal horn dependent on the type of fibre type
~5-10% of 2nd-order neurons cross via the anterior white commissure to project to the brain in the anterolateral tract; others form circuits ipsilaterally (e.g. for spinal reflexes)
May produce pain, autonomic response and withdrawal reflex

Question 4

What is TRPV1?

Answer 4

A nociceptive transducer and the receptor for capsaicin

Question 5

What is the mechanism underlying nociception in inflammatory states?

Answer 5

Inflamed or damaged tissues release nociceptor sensitisers (e.g.IL-6, TNF-A, H+), resulting in a pain response to low- and high-intensity stimuli

Question 6

What are the different effects of peripheral and central sensitisation?

Answer 6

Peripheral sensitisation results in any stimulation of the peripheral nociceptor (innocuous or noxious) producing primary allodynia or primary hyperalgesia, due to the sensitivity of the receptor
Central sensitisation produces secondary allodynia where an innocuous stimulus stimulates a low-threshold neuron, and secondary hyperalgesia where a noxious stimulus stimulates a nociceptor, due to the sensitivity of the central pathway

Question 7

Name 4 different types of nociceptor. How do they differ?

Answer 7

Heat
Cold
Peptidergic (secrete proteins; polymodal)
Non-peptidergic (polymodal)

Question 8

Distinguish between allodynia and hyperalgesia

Answer 8

Allodynia: a painful response to a normally innocuous stimulus
Hyperalgesia: an increased response to a normally painful stimulus (in secondary hyperalgesia the area of sensitivity may expand outside the damaged region)

Question 9

What is the abnormality in neuropathic pain?

Answer 9

Peripheral or central neural lesion or disease

Question 10

Describe 5 ways peripheral neural lesions may cause maladaptive, low-threshold pain

Answer 10

Increased axonal sensitivity to stimuli, producing ectopic transduction
Sympathetic-sensory neuron coupling
Ectopic action potential generation
Neuronal cell death
Altered synaptic transmission and central sprouting

Question 11

Give some examples of peripheral and central causes of neuropathic pain

Answer 11

PNS: nerve trauma, toxic and metabolic neuropathies, HZV, AIDS
CNS: stroke, spinal cord injury, MS

Question 12

List 3 conditions causing dysfunctional, maladaptive pain due to abnormalities in central processing

Answer 12

Migraine, pelvic pain conditions, fibromyalgia

Question 13

List 7 drugs which can induce analgesia

Answer 13

Opioids
NSAIDs
Anti-convulsants
Cannabinoids
TCAs
A2-adrenergic agonists
SNRIs

Question 14

How do analgesic drugs work?

Answer 14

By activating the periaqueductal grey pathway (projects to dorsal horn of spinal cord to inhibit the transfer of pain-related information)

Question 15

How does the spinal cord modulate pain?

Answer 15

Inflammation produces negative feedback which modulates transmission of nociceptive information in the spinal cord

Question 16

How does the fear response induce hypoalgesia? What cortical areas are involved?

Answer 16

Via the top-down psychological modulation of pain

Involving the anterior cingulate, PFC and insula

Question 17

What is the effect of expectation of pain on pain perception?

Answer 17

Produce nocebo hyperalgesia