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