Lecture 14 - Pain

Question 1

what are pain receptors?

Answer 1

receptors with axon endings without obvious anatomical specialisations

Question 2

where are pain receptors found?

Answer 2

found everywhere in the body except the brain

Question 3

what do pain receptors respond to?

Answer 3

respond to strong mechanical stimuli and/or high temperatures and chemicals released in damaged tissues

Question 4

what are the exogenous chemicals released that pain receptors respond to?

Answer 4

capsaicin and menthol

Question 5

how do capsaicin and menthol chemicals activate pain receptors?

Answer 5

activate receptors directly by internalising receptors by over activating pain fibres till the receptors eventually stop responding

Question 6

what are the 4 things pain is useful for?

Answer 6

to avoid injury
alert us to local infection
aid in recovery
indicate further disease

Question 7

what are the 2 types of nerve fibres that carry pain?

Answer 7

“c” fibres and “A-delta” fibres

Question 8

what are “c” pain nerve fibres?

Answer 8

smallest diameter fibres (in relation to A-delta fibres) myelinated axons

Question 9

what is the conduction velocity of “c” pain nerve fibres?

Answer 9

slow conduction velocity

Question 10

what do “c” pain nerve fibres signal to?

Answer 10

signal to sustained and ongoing damage (or potential damage)

Question 11

what are “A-delta” pain nerve fibres?

Answer 11

a subtype of A fibres that are small diameter myelinated axons

Question 12

what is the conduction velocity of “A-delta” pain nerve fibres?

Answer 12

fast conduction velocity

Question 13

what do “A-delta”pain nerve fibres signal to?

Answer 13

signal the acute onset of a painful stimulus

Question 14

what is hyperalgesia?

Answer 14

increasing sensitivity of pain pathways following an injury or an inflammatory disease (e.g arthritis)
–> the tenderness of an area

Question 15

how does hyperalgesia occur?

Answer 15

occurs as the injury site and area around the injury become ‘tender’

Question 16

why does the injury site and area around the injury become ‘tender’?

Answer 16

this is due to the sensation of sensory endings by locally released factors and changes at the CNS synapses

Question 17

what are the local factors that might be released if we damage an area of the skin?

Answer 17

K+
bradykinins
5-HT (serotonin)
prostaglandins

Question 18

what is the effect of the release of K+ in a damaged area of the skin?

Answer 18

an increase of K+ from the high concentration of K+ inside the cell will generate more AP’s in response to tissue damage

Question 19

what is the function of prostaglandins?

Answer 19

platelet aggregation for cloating

activation of pain fibres

Question 20

what is the relationship between increasing sensitivity of a damaged area and the anterolateral pathway?

Answer 20

another way to increase sensitivity is to increase synapse efficiency in the anterolateral pathway in the spinal cord to the CNS

Question 21

what do pain fibres release once activated?

Answer 21

release substance P and CGRP

Question 22

what is the effect of the release of local factors?

Answer 22

local factors will activate mast cells to release histamine which will give positive feedback on to nerve terminals

Question 23

what is the effect of histamine?

Answer 23

histamine spreading out from mast cells recruits neighbouring axons to bring them closer to threshold

Question 24

what is the hyperalgesic area?

Answer 24

the area sensitised by neighbouring axons

Question 25

what causes the itch sensation?

Answer 25

histamine

Question 26

what is the function of asprin?

Answer 26

inhibitor of prostaglandin synthesis which are involved in blood clotting

Question 27

what is asprin?

Answer 27

both an anti-blood clotting agent and a pain reliever

Question 28

what is sensation in pain pathways modulated by?

Answer 28

modulated by descending pathways

Question 29

what is the inhibition of pain pathways?

Answer 29

the "gating" of pain impulses by non-painful stimuli of nearby nerves. Inputs from nearby non-pain nerves inhibits the response of ascending pain fibres which is a non-chemical innervation to pain relief)

Question 30

what are the methods of non-chemical innervation to pain relief?

Answer 30

methods include rubbing the affected area or trans-epidermal nerve stimulation (TENS) through an electronic skin rubber

Question 31

what is the function of endogenous opiates?

Answer 31

decrease the post synaptic excitability of axons taking pain information to the CNS

Question 32

where are endogenous opiates released?

Answer 32

released at synapses on pain-pathway neurons

Question 33

what are endogenous opiates?

Answer 33

the site of action to 'centrally acting' painkillers of morphine and codeine

Question 34

what is the function of endocannabinoids?

Answer 34

decrease long-term sensitivity to pain. They are involved in - arousal - placebo - anxiety - association - suggestion

Question 35

what is atonic modulation?

Answer 35

long term retrograde signalling thats released by the post synaptic neuron to effect the amount of neurotransmitter that the terminal releases on to it

Question 36

what is the relationship between the level of arousal and pain?

Answer 36

the level of arousal tunes out pain fibre sensation level of conciousness

Question 37

what are the symptoms of diabetic neuropathy?

Answer 37

- tingling or burning (in toes, legs, fingers, hands or arms) - "pins and needles" - pain/cramping - loss of sensation - insensitivity to heat/cold - extreme sensitivity to light touch - muscle weakness in hands or feet - loss of coordination - multiple autonomic dysfunctions

Question 38

what do all of the symptoms of diabetic neuropathy result in?

Answer 38

result in loss of sensation, including loss of pain and this leads to tissue damage

Question 39

why does tingling occur?

Answer 39

because AP's are not occurring in the correct sequence to be interpreted

Question 40

where does loss of sensation start?

Answer 40

starts way out in the periphery where the nerve endings are further away from the cell body in the spinal cord that is providing them their metabolic support

Question 41

why is dental pain poorly localised?

Answer 41

dental pain could be located in the mouth but could also be referred pain from a sinus/ear infection or migraine

Question 42

what is pulpitis?

Answer 42

a cavity in the tooth

Question 43

what is referred pain?

Answer 43

pain feelings from the viscera referred to a body surface | e.g heart pain to the neck and arm

Question 44

what causes referred pain?

Answer 44

the presumed "cross-talk" of visceral and somatic sensory pathways that is activated by stretch and ischemia

Question 45

what is neurogenic pain?

Answer 45

nerve compression that can cause pain to be felt in the region of nerve termination e.g pain in the leg from the compression of a nerve in the back by a slipped disc (herniated intervertebral disc)

Question 46

what are the 2 causes of phantom limb pain?

Answer 46

1) ongoing activity in nerves that used to come from that limb 2) invasion of corticol representation for that part of intact body regions that cause spare neurons to invade regions that no longer exist e. g cortex representation of amputated hand may become activated by inputs from the face