Physiology of Pain

Question 1

What are nociceptors?

Answer 1

Nociceptors are specific peripheral primary sensory afferent neurones normally activated preferentially by intense stimuli (e.g. thermal, mechanical, chemical) that are noxious
Comprose Adelta and C-fibres.

Question 2

what type of neurones are nociceptors?

Answer 2

First order neurones

Question 3

What are the 3 forms of pain? Are they adaptive or maladaptive?

Answer 3

Nociceptive pain - adaptive
Inflammatory pain - adaptive
Pathological pain - maladaptive

Question 4

Why is pain essential to the protection of the organsim?

Answer 4

Discourages physical contact and movement thus promoting tissue repair

Question 5

Describe first and second pain noting the nociceptors involved in these processes.

Answer 5

First pain - immediately after the insult – know exactly where it’s coming from – lancinating, stabbing, pricking
Second pain - throbbing, cramping, aching, burning, not as well localised - mediated by C-fibres

Question 6

Describe the nociceptive pathway from a peripheral site to the dorsal horn of the spinal cord and the projection pathways from the spinal cord to the brain

Answer 6

• Free nerve ending is stimulated by noxious componeent
• Axon of nociceptor (1st order neurone)
• dorsal (posterior) horn of spinal cord
  !Crosses over spinal cord!
• Axon of projection (2nd order) neurone
• Anterior (neo)- and posterior (paleo)-spinothalamic and spinoreticulothalamic tracts on opposite side of body – contra-laterally
• Pain

Question 7

What kind of functions do peptidergic C-fibres have?

Answer 7

efferent and afferent functions

Question 8

Describe the development of neurogenic inflammation

Answer 8

CGRP released from branches of free nerve endings can propagate around other free nerve endings giving efferent signal away from CNS – sets up special kind of inflammation = neurogenic inflammation

Question 9

Give examples of stimuli that can cause nociceptor sensitization.

Answer 9

extreme temperatre
chemicals
mechanical injury

Question 10

What is hyperalgesia? Primary and secondary

Answer 10

Increased sensitivity to pain caused by damage to nociceptors or peripheral nerves
Primary hyperalgesia describes pain sensitivity that occurs directly in the damaged tissues.
Secondary hyperalgesia describes pain sensitivity that occurs in surrounding undamaged tissues.

Question 11

What is allodynia?

Answer 11

innoculus stimuli now elici pain

Question 12

What is pain hypersensitivity?

Answer 12

heightened sensitivity to noxious stimuli

Question 13

What causes inflammatory pain?

Answer 13

activation of the immune system to injury or infectop

Question 14

What causes pathological pain?

Answer 14

results from abnormal nervous system function - may be neuropathic or dysfunctional.

Question 15

Does pathological pain have a protective function?

Answer 15

No

Question 16

what is the purpose of nociceptive pain?

Answer 16

Serves as an early warning system to detect and minimise contact with damaged stimuli (noxious events)

Question 17

Why is nociceptive pain high threshold?

Answer 17

It is provoked only by intense stimuli that activate nociceptors

Question 18

How does nociceptive pain override most other ongoing activities of the nervous system?

Answer 18

• initiates a withdrawl reflex
• extremely unpleasant
• engages adverse emotional components
• serves to inscribe memories that allow avoidance of harm in the future

Question 19

What happens in the absence of pain?

Answer 19

Gross damage to the body occurs and goes undetected

Question 20

What are Adelta fibres?

Answer 20

mechanical/thermal nociceptors that are thinly myelinated (conduction velocity of 6 – 30 ms-1 ) - respond to noxious mechanical and thermal stimuli. Mediate ‘first pain’

Question 21

What are C-fibres?

Answer 21

nociceptors that are unmyelinated (conduction velocity of 0.5 – 2.0 ms-1) – collectively they respond to all noxious stimuli (e.g. they are polymodal). Mediate ‘second pain’

Question 22

Where do dorsal root ganglia lie?

Answer 22

Lateral to the spinal column – project centrally to the dorsal horn of the spinal cord and peripherally to the skin, muscle, tendons, joints, internal organs

Question 23

Where do Trigeminal ganglia project?

Answer 23

centrally to brainstem trigeminal nucleus

Question 24

Where do Nodose (iferior vagal) ganglia go?

Answer 24

Project centraly to the floor of the 4th ventricle to innervate the viscera

Question 25

What do selective NSAIDs inhibit?

Answer 25

COX2 (to inhibit the synthesis and accumulation of prostaglandins)

Question 26

Give examples of non-selective NSAIDs.

Answer 26

aspirin, ibuprofen, indometacin, naproxen and diclofenac – prescription drugs not OTC drugs

Question 27

Peptidergic Polymodal Nociceptors are what and have what?

Answer 27

Subset of C-fibres

afferent and efferent functions

Question 28

Is COX 1 or COX 2 constitutively active?

Answer 28

COX1 - COX2 is induced by inflammation