Neuro - PHYSIOLOGY AND PATHOLOGY OF PAIN Flashcards
what is the area over which a receptor can respond to a stimulus?
receptive field
what sensation does Meissner’s corpuscule detect?
light touch
what sensation do Merkle’s corpuscules detect?
touch
what sensation do free nerve ending detect?
pain
what sensation do Pacinian corpuscules detect?
deep pressure
what sensation does Ruffini corpuscule detect?
warmth
is it axons or dendrites which transmit to CNS?
axons
which primary afferent fibres mediate cutaneous sensation of touch, pressure, vibration at a speed of 30-70 ms^-1? what do these fibres look like in terms of myelination and size?
A beta, large myelinated fibres
which primary afferent fibres mediate cutaneous sensation of cold, “fast” pain and pressure at a speed of 5-30 ms^-1? what do these fibres look like in terms of myelination and size?
A gamma, small myelinated fibres
which primary afferent fibres mediate cutaneous sensation of warmth and “slow” pain at a speed of 0,5-2 ms^-1? what do these fibres look like in terms of myelination?
C, non-myelinated
what 2 primary afferent fibres mediate proprioception?
A alpha and A beta (ex: muscle spindles, golgi tendon organ…)
where do primary afferent fibres enter the spinal cord? where do primary afferent fibres in the head enter the CNS?
dorsal root ganglia for the spinal cord, cranial nerve ganglia for the head
what fibres are considered mechanoreceptive?
A alpha fibres and A beta fibres
how do the mechanoreceptive fibres travel up the spinal cord?
dorsal columns on ipsilateral side
where do the mechanoreceptive fibres synapse?
cuneate and gracile nuclei
where do the 2nd order fibres carrying mechanoreceptive decussate? where do they project after this?
decussate in brain stem, then project to reticular formation, thalamus and cortex
what fibres are thermoreceptive & nociceptive?
A gamma fibres and C fibres
how do thermoreceptive & nociceptive fibres travel up the spinal cord?
spinothalamic tract on anterolateral side
where do thermoreceptive and nociceptive fibres synapse?
dorsal horn of spinal cord
where do the 2nd order fibres carrying thermoreceptive and nociceptive fibres decussate? where do the project after this?
decussate in midline in the spinal cord, then project to reticular formation, thalamus and cortex
damage to dorsal columns causes loss of touch, vibration, proprioception below lesion on which side?
ipsilateral side
damage to anterolateral quadrant causes loss of nociceptor & temperature sensation below lesion on which side?
contralateral side
what is the ultimate termination of sensory information?
sometosensory cortex (S1) of the postcentral gyrus
what local chemical mediators activate pain receptors?
bradykinin, histamine, prostaglandins
what do inhibitory interneurones release? what do these do?
opioid peptides (endorphins), they inhibit neurotransmitter release from A gamma fibres/ C fibres to their respective 2nd order neurones
which neurones do inhibitory interneurones attach from?
A beta primary afferent neurones
what way does the cortex have of exciting the inhibitory interneurone?
descending pathways from PAG (peri-aqueductal grey matter) and NRM (nucleus raphe magnus)
how do NSAIDS work as a analgesic?
prostaglandins sensitise nociceptors to bradykinin and prostaglandin production is inhibited (inhibition of cyclo-oxygenase which converts arachidonic acid to prostaglandins)
how do local anaesthetics work as analgesics?
block Na+ AP and therefore all axonal transmission
how do opiates work as analgesics?
reduce sensitivity of nociceptors, block transmitter release in dorsal horn, activate descending inhibitory pathways
what other way is there to block pain using the fact that activation A beta fibres will activate the inhibitory interneurone inhibiting A gamma fibres and C fibres?
Trans cutaneous electric nerve stimulation (TENS)
