the puzzle of pain the reverend dr. david cm taylor dcmt/painpuz.ppt
TRANSCRIPT
The Puzzle of PainThe Reverend Dr. David CM Taylor
http://pcwww.liv.ac.uk/~dcmt/painpuz.ppt
“The Puzzle of Pain”
“Tell me where it hurts…”
There is more than one ....
First SecondAdequatestimulus
pin prick, heat tissue damage
Sensory unit A mechanicalmechanical/heat
C and Apolymodal
Pathway spinothalamic spinoreticularintralaminar
thalamicDistribution Body Surface Most tissues
Reflex Phasiccontraction
Tonic contraction
Gate Control Theory
Melzack and Wall in 1968rubbing injured region decreases pain sensation
detail wrong but useful
G a tec e ll
Tra nsm issio nc e ll
Pa in fib re
To uc h fib re
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De sc e nd ingc o ntro l
Descending InhibitionTouch
cortico-thalamic pathways
why we don’t feel clothes
Painbattle and sporting injuries, ecstasy
children, animals, elderly/suffering
Descending control of painmicroinjection of opiates into discrete regions of the CNS (PAG,limbic
system, SG) produces analgesiaMicrostimulation there also produces analgesia Opioid peptides are present thereElectrical stimulation of the PAG or NRM produces analgesia
Just for re-orientation
Proposed mechanism
limbic system
periaqueductal grey
nucleus raphe magnus
interneurones in lamina II of spinal cord
Scratch pad if needed
Presynaptic hypothesis
from brain
to brainsubstance P fibre
5HT
enkephalin
pioneered by Leslie Iversen
How might control work?
Electrical (“Sherringtonian or…”)Shorter action potentials,
Altered levels of “second messengers”less Ca2+, less transmitter release, less activity
ChemicalAlter gene expression
Change level or type of transmitter released or
Receptors on post synaptic cells
Post-synaptic hypothesis
from brain
to brainc-fibre “pain”
A fibre touch
This is the currently accepted “gate control” theory