PAIN-TRANSDUCTION
SUMMARY
1. The principal receptors for pain are the unmyelinated, 'free', branched endings of C and Aδ (delta) fibers in the skin, muscles & joints.
2. Damaging (or potentially damaging) energy in the cellular environment impacts the free nerve endings leading to signal transduction.
Aδ FIBERS (2-5 µm)
3. Subdivided into: type 1 (high-threshold, responds to heat > 50oC & noxious mechanical stimuli) & 2 (low-threshold, responds to heat > 43oC & noxious mechanical stimuli).
4. Transduces & transmits acute, first pain sensation.
C FIBERS (2 µm)
5. Subdivided into: peptidergic & non-peptidergic; responds to mechanical, thermal & chemical noxious stimuli.
6. Transduces & transmits a dull, more diffuse second pain sensation.
7. Peptidergic fibers contain substance P, CGRP; express tyrosine kinase receptors are key players in neurogenic inflammation.
Reference(s)
Cifu, D.X. (2020). Braddom’s physical medicine and rehabilitation. Elsevier. Get it on Amazon.
Cuccurullo, S. (2019). Physical medicine and rehabilitation board review. New York: Demosmedical. Get it on Amazon.
O’Young, B., Young, M.A. and Stiens, S.A. (2008). Physical Medicine and Rehabilitation Secrets. Mosby. Get it on Amazon.
