2- physiology of pain

Question 1

what are nociceptors?

Answer 1

• they are primary specific sensory afferent neurons
• they’re activated by chemical stimuli (e.g. mechanical, thermal or chemical) and if sufficient intensity then makes pain

Question 2

what are the 4 stages/processes in physiology of pain? (the route from pain on surface of body to effect being made)

Answer 2

1. transduction (pain translated from surface of body to nerve signal)
2. transmission (signal moving as nerve impulse)
3. modulation (adjusting signal to make correct effect e.g. inhibitory neurotransmitters like endogenous opioids)
4. perception (conscious experience of pain, result of pain)

Question 3

describe the 1st order neurons role in nociceptive pathway?

Answer 3

on 1st neuron the nociceptors detect noxious signals and then the neuron carries the signal from periphery to dorsal horn of spinal cord. the central terminal of these neurons release neurotransmitters e.g. glutamate & neuropeptides (substance P & neurokinin A) which act on 2nd order neurons

Question 4

describe the 2nd order neurons role in nociceptive pathway?

Answer 4

• the neurotransmitters released from 1st order neuron cross by chemical synaptic transmission and cause depolarisation & further action potential
• the 2nd order neurons send axons to spinothalamic tract or spinoreticular tract to relay pain signal to higher brain centres

Question 5

where are 2nd order neurons found?

Answer 5

in dorsal horn of spinal cord and ascend the spinal cord in anterolateral system (terminate in thalamus)

Question 6

which type of pain signals does the spinothalamic tract transmit?

Answer 6

sharp, localised pain

Question 7

which type of pain signals does the spinoreticular tract transmit?

Answer 7

dull, achy pain

Question 8

what do the 3rd order neurons do in nociceptive pathway?

Answer 8

they relay sensory information from thalamus to primary sensory cortex

Question 9

what are the 2 subtypes of nociceptos?

Answer 9

A & C fibres

Question 10

what are differences in A & C nociceptor fibres?

Answer 10

A = myelinated, thin, more velocity in conduction, usually sensitive to noxious mechanical & thermal stimuli, mediate fast pain

C = unmyelinated, conduction slower, usually polymodal (sensitive to all noxious stimuli), mediate slow pain

Question 11

what are 4 ways to classify pain?

Answer 11

1. time course (acute or chronic)
2. severity
3. source of origin
4. mechanisms (nociceptive, inflammatory, pathological)

Question 12

what is nociceptive pain?

Answer 12

response to injury from noxious (damaging) stimuli
= it’s only provoked by intense stimulation by noxious stimuli

Question 13

what is adaptive pain?

Answer 13

when the pain is physiologically helpful meaning change in behaviour to promote healing etc

example is nociceptive & inflammatory pain

Question 14

what is inflammatory pain?

Answer 14

pain caused by activation of immune system by tissue injury or infection, the pain’s activated by mediators at site of inflammation

• the pain is hyperalgesia and allodynia

Question 15

what is hyperalgesia?

Answer 15

when increased sensitivity to pain
- involves heightened sensitivity to pain in the damaged area, often due to the release of inflammatory chemicals (like prostaglandins) that sensitize the pain receptors (nociceptors)

Question 16

what is allodynia?

Answer 16

pain sensitivity to innocuous stimuli e.g. touch

(often this means discourages physical contact so adaptive pain)

Question 17

what are the 2 types of pathological pain?

Answer 17

neuropathic and dysfunctional

Question 18

what is neuropathic pain?

Answer 18

pain caused by damage to neural tissue (usually burning, shooting, numbness, may be less localised)

Question 19

what is dysfunctional pain?

Answer 19

no identifiable damage or inflammation e.g. irritable bowel or tension headache

• maladaptive pain
• simple analgesics not effective, more drugs for other pain like anti-depressants or anti-epileptics