Physiology of Pain and Thermosensation Flashcards
What are the 3 types of pain?
nociceptive
inflammatory
pathological
Describe nociceptive pain?
immediate short lived protective response
adaptive
Describe inflammatory pain?
assists in healing, persists over days - weeks
adaptive
Describe pathological pain?
persists over lots of time
no physiological purpose
may be maladaptive
What fibres make up nociceptors?
A gamma and C fibres
What are the characteristics of A gamma fibres?
mechanical/thermal nociceptors
thinly myelinated
mediate fast/first pain
What are the characteristics of C fibres?
respond to all noxious stimuli
unmyelinated
mediate second/slow pain
What two peptides are released in inflammatory pain?
substance P
CGRP
What is the role of Substance P?
causes vasodilation and extraction of plasma proteins (promotes formation of bradykinin and prostaglandins) causes release of histamine
sensitises surrounding nociceptors
What is the role of CGRP?
induces vasodilation
What do substance P and CGRP cause?
slow and prolonged epsp that activate NMDA receptors by relieving voltage dependant block by Mg
What is the primary transmitter and what are its receptors?
glutamate
AMPA and NMDA receptors
Where are primary afferent cell bodies located?
dorsal root ganglia
Where do primary afferent cell bodies terminate?
laminae of Rexed
Which laminae do nociceptive C and A gamma dibres terminate?
laminae I and II
V also for A gamma
What fibre input do proprioceptive cells receive?
A beta fibres
What does visceral pain result from?
nociceptors covering tissues of hollow organs - follow sympathetic pathways before entering the dorsal horn
What causes referred pain?
some afferents converge upon the same spinothalamic neurones - but all cells with visceral receptive fields also have separate cutaneous receptive fields
What is referred pain?
pain percieved at a distance from the affected organ
area of referral is to the segmental dermatome
often associated with autonomic features
What is viscerosomatic pain?
sharp and well localised pain
What causes viscerosomatic pain?
occurs when inflammatory exudate from a diseased organ contacts a somatic (body wall structure)
What are Abeta fibres?
mechanoreceptors
What are Agamma and C fibres?
pain perceivers
Where are Agamma, C and Abeta fibres processed?
substantia gelatinosa
What does the gate control theory relate to?
synaptic transmission of nociceptive signals
What happens to the gate control theory when Abeta activity > Agamma/C activity?
gate is CLOSED, synaptic transmission of nociceptive signals is SURPRESSED
SO PAIN IS NOT PERCIEVED
What happens to the gate control theory when Agamma/C activity > Abeta activity?
gate is OPEN, synaptic transmission of nociceptive signals happens
PAIN IS PERCIEVED
In the Spinothalamic tract, where do Agamma projection neurones originate?
lamina 1
In the Spinothalamic tract, where do WDR projection neurones originate?
lamina V
Where do projection neurones from lamina 1 terminate?
posterior nucleus of the thalamus
Where do projection neurones from lamina V terminate?
posterior and ventroposterior nucleus of the thalamus
What fibres does the spinoreticular tract transmit?
slow C fibre pain
What fibres respond to cold? C or Agamma?
C fibres
What fibres respond to warm? C or Agamma?
C fibres or Agamma fibres
What are more common C or Agamma fibres?
C fibres
What is the presentation of chronic regional pain syndrome?
allodynia - sore to stimulus that shouldnt be painful eg cotton wool
hyperalgesia - increased sensitivity to pain
swelling
hair and nail changes
osteopenia
What is neuropathic pain?
pain generated from within the nervous system - does not respond to NSAIDs or paracetemol
What is the presentation of neuropathic pain?
allodynia
hyperalgesia
burning, shooting, tingling pain
What can cause neuropathic pain?
shingles surgery trauma diabetic neuropathy amputation
What can be used to treat neuropathic pain?
tricyclic antidepressants - amytryptilline anticonvulsants - gabapentin capsicin GABA agonists NMDA agonists Na channel blockers opioids
