Physiology of Pain

Question 1

why is pain difficult to assess?

Answer 1

very subjective as pain perception and tolerance varies between different people

Question 2

define chronic pain?

Answer 2

lasting over 3 months

Question 3

how does chronic pain prevalence change with age?

Answer 3

more common in elderly

Question 4

what is pain?

Answer 4

unpleasant sensory and emotional experience associated with actual tissue damage or described in terms of such damage
(not all pain related to actual damage)

Question 5

what are the 4 processes in the physiology of pain?

Answer 5

transduction
transmission
modulation
perception

Question 6

what is transduction?

Answer 6

translation of noxious/damaging stimulus into electrical activity at the peripheral nociceptor (receptor)
how body conveys stimulus to CNS

Question 7

what is transmission?

Answer 7

propagation of pain signal as a nerve impulse through the nervous system

Question 8

what is modulation?

Answer 8

modification/hindering of pain transmission in the nervous system (e.g by inhibitory neurotransmitters like endogenous opioids)

Question 9

what is perception?

Answer 9

conscious experience of pain

causes physiological and behavioural responses

Question 10

what are nociceptors?

Answer 10

free nerve endings
primary sensory afferent neurons
normally activated by intense noxious stimuli (Mechanical, thermal or chemical)
- must be severe stimuli

Question 11

what do nociceptors do?

Answer 11

first order neurons that relay information to second order neurons in the CNS by chemical synaptic transmission

Question 12

describe what happens in nociceptors

Answer 12

free nerve ending (e.g in skin, or organ etc) depolarizes due to noxious stimuli which elicits AP that propagate to the CNS
central terminal is in CNS and releases neurotramsmitters that excite second order neurones

Question 13

where is the cell body (soma) in nociceptors?

Answer 13

within dorsal root ganglion or trigeminal ganglion

pseudounipolar - one side = free nerve endings, other side = central terminal

Question 14

what are the neurotransmitters in the nociceptive pathway?

Answer 14

glutamate and peptides (substance P, neurokin A)

Question 15

through what system do the second order neurones ascend the spinal cord?

Answer 15

anterolateral system terminating in the thalamus

Question 16

what are the 2 parts of the anterolateral system used by second order neurons?

Answer 16

spinothalmic tract (STT)
spinoreticular tract (SRT)

Question 17

what is the spinothalmic tract?

Answer 17

involved in pain perception

goes to thalamus

Question 18

what is the spinoreticular tract?

Answer 18

involved in autonomic response to pain, arousal, emotional responses, fear of pain
also goes to thalamus

Question 19

where does the pain go after the thalamus?

Answer 19

sensory information is relayed (third order neurones) to the primary sensory cortex

Question 20

what are the 2 subtypes of nociceptors?

Answer 20

A delta fibres

C fibres

Question 21

what are A gamma fibres?

Answer 21

mechanical/thermal nociceptos
thinly myelinated so very fast
respond to noxious mechanical and thermal stimuli
mediate first/fast pain (stabbing pain)

Question 22

what are C fibres?

Answer 22

nociceptors that are unmyelinated (slow conduction)
respond to all noxious stimuli (polymodal)
mediate second/slow pain (burning, throbbing pain)

Question 23

how can pain be classified?

Answer 23

mechanisms (e.g nociceptive, inflammatory, neuropathic, dysfunctional etc)
Time course (acute/chronic etc)
Severity
Source of origin (somatic vs visceral)

Question 24

what is nociceptive pain?

Answer 24

normal response to injury of tissue by noxious stimuli

Question 25

what causes nociceptive pain?

Answer 25

intense stimulation of nociceptors by noxious stimuli adaptive acts as warning to protect body

Question 26

what causes inflammatory pain?

Answer 26

activation of the immune system by tissue injury/infection | pain activated by mediators released at site of inflammation by leukocytes, vascular epithelium and mast cells

Question 27

what does inflammatory pain cause?

Answer 27

heightened pain sensitivity to noxious stimuli (hyperalgesia) and pain sensitivity to innocuous (harmless) stimuli (allodynia)

Question 28

why can inflammatory pain be useful?

Answer 28

discourages physical contact and movement of the area while it heals

Question 29

is inflammatory pain adaptive?

Answer 29

yes

Question 30

name 2 types of neuropathic pain

Answer 30

neuropathic | dysfunctional

Question 31

what is neuropathic pain?

Answer 31

pain caused by damage to neural tissue can be burning, shooting, numbness, pins and needles can be less localised

Question 32

give some examples of neuropathic pain

Answer 32

``` compression neuropathy peripheral neuropathy central pain (after stroke/spinal injury) postherpatic neuralgia trigeminal neuralgia phantom limb ```

Question 33

is neuropathic pain protective?

Answer 33

no

Question 34

what is dysfunctional pain?

Answer 34

no identifiable damage or inflammation | not protective and maladaptive

Question 35

give some examples of dysfunctional pain

Answer 35

fibromyalgia irritable bowel tension headache

Question 36

how is pathological pain treated?

Answer 36

simple analgesics usually not effective | sometimes treated with non pain relieving drugs (anti-depressants or anti-epileptics)

Question 37

what is referred pain?

Answer 37

pain developed in one part of the body is felt in another part

Question 38

which types of pain is usually referred?

Answer 38

deep pain | superficial pain usually not referred

Question 39

what causes referred pain?

Answer 39

convergence of nociceptive visceral and skin afferents upon the same spinothalmic neurons at same spinal level

Question 40

give some examples of sites of referred pain?

Answer 40

``` heart = left arm diaphragm = left shoulder/neck liver = right side of neck stomach/pancreas = epigastric appendix = middle abdomen gall bladder = right shoulder/neck ```