Multidimensional Nature of Pain

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Define acute and chronic pain terms of a multidimensional pain experience.

• Anatomical, physiological, and psychological basis of pain and pain relief, including pain as an 'output' from the brain
• Definition of pain and evidence of the multidimensional nature of the pain experience e.g. social and psychological infleuncing factors

Original Editor - Alberto Bertaggia.

Top Contributors - Alberto Bertaggia, Nina Myburg, Admin, Kim Jackson, Michelle Lee, Vidya Acharya, 127.0.0.1, WikiSysop, Lauren Lopez, Jo Etherton and Jess Bell  

Introduction

A definition of pain is provided by the International association for the Study of Pain (IASP) as follows:

"An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage"

Pain is always subjective and everyone learns the use of this word through experiences related to injury in early life.

It is a sensation in a part or parts of the body, but it is also always unpleasant and therefore also emotional. 

Even in the absence of tissue damage or any likely pathophysiological cause, people still report pain; usually this happens for psychological reasons. In these cases, it is challenging to distinguish whether their experience arise from a damaged tissue or not, based only upon the subjective report.

It is important to underline that activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always the output of a widely distributed neural network in the brain rather than one coming directly by sensory input evoked by injury, inflammation, or other pathology.

In the following video Karen D. Davis tries to explain why do some people react to the same painful stimulus in different ways.

Relevant anatomy and physiology

Nociceptors

Nociceptors (from the latin nocere = to hurt) are sensory receptors which detect signals from damaged tissue or the threat of damage and indirectly also respond to chemicals released from the damaged tissue. There are free nerve endings present in many types of tissues,  and cell bodies located in the dorsal root ganglions or in the cranial nerve ganglia.

(A) Somatosensory neurons are located in peripheral ganglia (trigeminal and dorsal root ganglia) located alongside the spinal column and medulla. Afferent neurons project centrally to the brainstem (Vc) and dorsal horn of the spinal cord and peripherally to the skin and other organs. Vc, trigeminal brainstem sensory subnucleus caudalis. (B) Most nociceptors are unmyelinated with small diameter axons (C-fibers, red). Their peripheral afferent innervates the skin (dermis and/or epidermis) and central process projects to superficial laminae I and II of the dorsal horn. (C) A-fiber nociceptors are myelinated and usually have conduction velocities in the Aδ range (red). A-fiber nociceptors project to superficial laminae I and V. from: Dubin AE, Patapoutian A. Nociceptors: the sensors of the pain pathway. J Clin Invest. 2010 Nov 1;120(11):3760–72.

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