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NS13 - Mechanism of Pain Perception (ii) (Endocannabinoids (R =…
NS13 - Mechanism of Pain Perception (ii)
Endocannabinoids
= anandamide (NT, bliss molecule) + related mediators
R = tetrahydrocannabinol (THC)
CB1
CB2
in brain, cord, immune cells, dorsal root ganglion neurons
Gate Theory
Melzack + Wall
somatic non-painful signals can act as analgesia in cord
inhibit pain transmission
e.g. touch/pressure/vibration/temp signals serve as distraction
A alpha + beta fibres carry these to substantia gelatinosa, where interneurons (i.e. the gates) can inhibit synapse between 1st + 2nd oder A delta/C fibres using GABA + opioids
descending analgesic pathways
1) from periaqueductal gret matter (in midbrain) -> reticular formation (opiate release) -> pain transmission blocked to thal
2) rostroventral medulla (raphe nuclei)
NTs used: serotonin + NA
visual analogue scale
0: no pain
10: unbearable
pain treatment
use knowledge of pain modulation mechanisms
paresthesia: pins + needles
dysesthesia: burning sensation
hyperalgesia: decreased pain threshold, exaggerated response
allodynia: pain in response to non-noxious stimulus
deafferentation pain: peripheral N lesions
e.g. phantom limb pain
psychogenic pain: disproportionate, no organic cause