Unit 3- Pain & nociception Flashcards

1
Q

what is pain?

A

an unpleasant sensory experience associated with nociception?

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2
Q

what is nociception?

A

information indicating tissue damage

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3
Q

what are the two types of nociceptors?

A

A-delta fibre: simple naked nerve ending
- thin myelination (5-30 m/s)
- first, sharp well localised pain
responds to intense mechanical stimulus
c fibre: polymodal nociceptor - naked nerve ending
- no myelination = slow conduction velocity (0.5 - 3 m/s)
- slow, poorly localised pain (secondary)

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4
Q

why do c fibres respond to capsaicin?

A

opens same non-selective cation channel - Trpv1 as high temperature

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5
Q

what is the consequence of high doses of capsaicin?

A

desensitise pain because of depletion of substance P

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6
Q

what stimulates the release of substance P and what is its effect?

A

axons carry high frequency trains of APs causes neuropeptide release - stimulus perceived as moderate to intense pain
- substance P released peripherally from sensory neurons which induces mast cells to release histamine + inflammatory 5HT (serotonin) - activates nociceptors and causes vasodilation

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7
Q

what molecules increase nociceptor sensitivity?

A

histamine
prostaglandin
bradykinin

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8
Q

what is primary hyperalgesia?

A

increased sensitivity to pain to area of injury

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9
Q

how do painkillers work?

A

block cyclooxygenases that produce prostaglandins

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10
Q

what is the consequence of chronic stimulation of nociceptors due to trauma?

A

accumulation of substance P in dorsal horn leads to increase in neuronal responsiveness - secondary hyperalgesia - pain to area around injury
low threshold nociceptors respond to light touch (non-noxious stimuli) and generate pain responses - allodynia

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11
Q

what is the principle of the gate theory of the pain (melzack and wall 1965)?

A

pain messages travel through the periphery through “nerve gates” in spinal cord and up to brain - gates open - more pain

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12
Q

what factors open nerve gates?

A
  • injury/ inactivity/ poor body mechanics
  • cognitive factors - focussing on pain/ emotional/ stress
  • high frequency APS along spinothalamic interneurones
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13
Q

what factors close nerve gates?

A
  • increasing activity/ pain killers
  • cognitive factors to cope: distraction/ attitude/ emotional state - serotonin act on GABAergic neurons to block signals
  • mechanical stimulation to area of pain
  • blocking release of substance P
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14
Q

why does mechanical stimulation to area of pain help to close the nerve gate?

A

spinothalamic interneurones are contacted by both nociceptive and touch fibres so during painful stimuli, rubbing the region activates touch fibres which inhibits the pain signal

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15
Q

what substances can block the release of substance P?

A

endorphins/ enkephalins - natural opiate-like peptides - analgesic effect

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16
Q

what are the types of pain?

A
  • cutaneous (skin)
  • somatic (within body - bones/muscles/ligaments)
  • visceral (autonomic sensation from organs - spinoreticular tract)
  • referred pain (pain from viscera appears on surface of body)
17
Q

how is a neuroma caused and what is its effect?

A

nerve damage - axons sprout from cut end of nerve so axons become tangled and sensitive to pressure and temperature - large impulse discharges = severe pain