L27 - pain Flashcards
1st pain fibres
Alpha delta fibres
examples of 1st pain receptors
mechanic/thermoreceptors
localisation of 1st pain receptors
easily localised
type of pain in first pain receptors
sharp or prickling
speed and duration of first pain receptors
occurs rapidly
short duration
2nd pain fibres
slow C fibres
examples of 2nd pain receptors
Polymodal nociceptors
localisation of 2nd pain receptors
poorly localised
speed and duration of 2nd pain receptors
slow onset
persistent
type of pain in 2nd pain receptors
dull ache, burning
purinergic ligand-gated channels
specific ATP channels which respond to tissue damage
peripheral sensitisation
Peripheral nerve fibres become over-sensitive
peripheral sensitisation due to inflammatory pain
- Cytokines and other inflammatory mediators released to coordinate immune response at site of inflammation
- A lot of these inflammatory mediators also act on peripheral nerve endings
types of inflammatory mediators
- Act to directly activate ligand-gated ion channels
- Act via activation of G-protein-coupled receptors
- Act via activation of receptor tyrosine kinases
- ‘Gasotransmitters’
examples of inflammatory mediators which activate ligand-gated ion channels
ATP
H+
examples of inflammatory mediators which activate G-protein-coupled receptors
prostaglandins bradykinin proteases histamine substance P
examples of inflammatory mediators which activate receptor tyrosine kinases
NGF
BDNF
examples of inflammatory mediates which are gasotransmitters
CO
NO
N2S
signalling cascades of inflammatory nociception
- activation / sensitisation of sensory channels
- modulation of ion channels through intracellular signalling cascades
- modulation of gene expression
activation / sensitisation of sensory channels in the cascade of inflammatory nociception
- Ligands to ion channels such as protons and ATP
- Acute excitation of primary somatosensory nerve terminal
modulation of ion channels through intracellular signalling cascades in the cascade of inflammatory nociception
- G-protein couple receptors
- Triggers signalling cascade which leads to action on the ion channels in the somatosensory terminals
Modulation of gene expression in the cascade of inflammatory nociception
- Receptor tyrosine kinase
- Phosphorylation of TP1 responses
- Often lead to change in gene expression
role of amygdala in pain
important for perception of pain
dissociation of amygdala in pain
can paradoxically preserve the sensation of pain but reduce the suffering
from where do inhibitory neurones receive information
mechanoreceptors
descending inhibitory pathway
descending inhibitory neurone
shuts down perception neurone
role of mechanoreceptors in inhibition
e.g., rubbing a sore shoulder produces a degree of inhibitions
role of inhibitory neurones
gate keepers - decide how much sensation from receptors reach the thalamus
central sensitisation
Refers to the process through which a state of hyperexcitability is established in the central nervous system, leading to enhanced processing of nociceptive (pain) messages
- second order neurones become more responsive
how does central sensitisation response occurs
Same degree input creates more pain
- More Glu, Sp, CGRP and ATP in spinal cord leading to increased calcium = increased response = PAIN
Microglia
- Increased input from peripheral terminals activates microglia in the spinal cord
- Uses chemical factors to trigger the activation stimulation of remodelling of second order neurones
- Similar to peripheral inflammatory pain
Familial hemiplegic migraine (FHM)
autosomal dominant subtype of severe migraine accompanied by visual disturbances known as aura
aura
cortical spreading depression - a slowly advancing wave of tissue depolarisation in the cortex
cause of >50% FHM
- mutation within voltage gated calcium channels
- increased flow of Ca2+ into dendrites
- excessive release of excitatory neurone glutamate
- increasing likelihood that K+ will reach CSD (cortical spreading depression) threshold
- K+ causes vasodilation followed by vasoconstriction
- vasoconstriction weakens blood brain barrier
- release of things which activate trigeminal afferents = triggers migraine attack