Anaesthesia | Pain | Modulation and Plasticity in the Nociceptive System

Modulation and Plasticity in the Nociceptive System
Session Overview
Description
This session describes the mechanisms by which the pain signal is subject to modulation, from induction to perception.

Learning Objectives
By the end of this session you will be able to:

• Critically appraise the ‘classical’, Cartesian model of a hard-wired pain pathway
• Explain how a TENS machine works
• Account for the phenomenon of the painless battlefield injury
• Explain the analgesic effect of tricyclic antidepressants and opioids
• Account for the effect of emotion on pain perception
• Define the concept of neuroplasticity within the nociceptive system

Prerequisites
Before commencing this session you should:

• Module 05a/Anatomy of Nociceptive Pathway/Anatomy of the Ascending Pain Pathway (001-0496)
• Module 05a/Anatomy of Nociceptive Pathway/Physiology of Pain Transmission (001-0497)

In previous sessions we have looked at the anatomy and physiology of the nociceptive system. It is tempting to think of the nociceptive system as a simple conduit for the pain signal, from transduction of a noxious stimulus to perception, rather like Descartes’ famous model, published in 1664 (Fig 1a).

However, everyday experience tells us that pain transmission is more complex than this. A sprained ankle should be more painful than having a blood test, yet under certain conditions (e.g. running a marathon) an ankle injury might go unnoticed, while anticipation of pain can make straightforward phlebotomy an exquisitely painful experience.

The reason for these inconsistencies is that the pain signal is modulated at many levels between induction and perception (Fig 1b). In this session we will look at the major ways in which the nociceptive signal undergoes modulation, from nociceptor to brain.