Physiology of Pain

Question 1

what is pain

Answer 1

an unpleasant sensory and emotional experience, associated with actual tissue damage or describe in terms of such damage

Question 2

what are the four processes of pain

Answer 2

transduction, transmission, modulation, perception

Question 3

what is transduction

Answer 3

translation of noxious stimulus into electrical activity at the peripheral nociceptor

Question 4

what is transmission

Answer 4

propagation of pain signals as nerve impulses through the nervous system

Question 5

what is modulation

Answer 5

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

Question 6

what is perception

Answer 6

conscious experience of pain, causes physiological and behavioural responses

Question 7

what are nociceptors and what activates them

Answer 7

specific primary sensory afferent neurones normally activated by intense noxious stimuli (mechanical, thermal or chemical)

Question 8

what is a soma

Answer 8

nerve cell body

Question 9

what is the path of pain in nerve

Answer 9

nociceptor (free nerve ending)- axon of nociceptor- soma- central terminal in CNS (dorsal posterior horn of spinal chord)- axon of projection (second order neurone)- spinothalamic and spinoreticulothalamic tracts

Question 10

what does the central terminal do

Answer 10

releases neurotransmitters that excite second order neurones

Question 11

what order of neurones are nociceptors

Answer 11

first order (relay information to second order neurones in CNS by chemical synaptic transmission)

Question 12

where are nociceptor soma

Answer 12

within dorsal (posterior) root ganglion (DRG) (or terminal ganglion)

Question 13

what are the neurotransmitters release by central terminal nociceptors

Answer 13

glutamate and peptides

Question 14

what is the path of second order neurones

Answer 14

ascend the spinal chord in the anterolateral system to terminate in the thalamus

Question 15

what tracts mainly make up the anterolateral system of the spinal chord and what do they do

Answer 15

the spinothalamic tract (STT) - involved in pain perception (intensity and location)

spinoreticular tract (SRT)- involved in automated response to pain, arousal, emotional response, fear of pain

Question 16

what do third order neurons do

Answer 16

replay sensory information from the thalamus to the primary sensory cortex

Question 17

what fibres make up nociceptors

Answer 17

Aδ and C fibres

Question 18

describe Aδ fibres

Answer 18

mechanical/thermal nociceptors that are thinly myelinated

respond to noxious mechanical and thermal stimuli

conduct fast (lancinating, stabbing, prickling sensations)

Question 19

describe C fibres

Answer 19

nociceptors that are unmyelinated

respond to all stimuli (are polymodal)

slow conduction (burning, throbbing, cramping, aching)

Question 20

how can you classify pain

Answer 20

mechanisms (e.g. nociceptive, inflammatory, pathological

time course (acute, chronic, breakthrough pain)

severity

source of origin (somatic- skin, muscle, joints or visceral- internal organs)

Question 21

what is nociceptive pain

Answer 21

normal response to injury of tissues by noxious damaging stimuli

only provoked by intense stimulation of nociceptors by noxious stimuli (chemical, mechanical, thermal)

Question 22

why is nociceptive pain adaptive

Answer 22

is protective- acts as early warning physiological protection system to detect and avoid noxious stimuli

Question 23

what causes inflammatory pain

Answer 23

activation of the immune system by tissue injury of infection

pain activates by variety of mediators released at the site of inflammation by leukocytes, vascular endothelium and tissue resident mast cells

Question 24

how is inflammatory pain characterised

Answer 24

heightened sensitivity to noxious stimuli (hyperalgesia) and pain sensitivity to innoculus (non harmful) stimuli (allodynia)

Question 25

how is inflammatory pain adaptive

Answer 25

discourages physical contact and movement which promotes repair until healing occurs

Question 26

what is neuropathic pain

Answer 26

pain caused by damage to neural tissue

Question 27

give 6 examples of neuropathic pain

Answer 27

compression neuropathies, peripheral neuropathies, central pain (following stroke/ spinal injury), postherpetic neuralgua, trigeminal neuralgia, phantom limb

Question 28

how can neuropathic pain be perceived

Answer 28

burning, shooting, numbness, pins and needles

can be less localised

Question 29

is pathological pain adaptive

Answer 29

no, is maladaptive

Question 30

what are the types of pathological pain

Answer 30

neuropathic, dysfunctional

Question 31

what is dysfunctional pain

Answer 31

pain where there is no identifiable damage or inflammation

Question 32

give 5 examples of dysfunctional pain

Answer 32

fibromyalgia, irritable bowel syndrome, tension headache, temporomandibular joint disease, interstitial cystitis

Question 33

how can pathological pain be treated

Answer 33

simple analgesics not usually effective, sometimes treated with antidepressants or anti-epileptics

Question 34

what is referred pain

Answer 34

pain developed in one part of the body felt in another structure away from the place of its development

Question 35

where is the most likely origin site of referred pain

Answer 35

deep or visceral pain- superficial structures don’t usually have referred pain

Question 36

what causes referred pain

Answer 36

convergence of nociceptive visceral and skin afferents upon the same spinothalamic neurones at the same spinal level

Question 37

name the common referred pain sites of the:
liver
gallbladder
diaphragm 
lungs
heart
stomach/pancreas
appendix

Answer 37

liver- right side of neck
gall bladder- left shoulder
diaphragm/ lungs- right shoulder
heart- left side jaw, arm
appendix- belly button