Principles of Pain

The Common Vein Copyright 2008

Introduction

Pain is a symptom caused by irritation of a structurewith functional consequences. The cause of the irritation is any one of many diseases and the treatment varies from palliative to direct intervention.

Pain is a symptom and as such reflects a derangement of either the external or internal environment. All sensations start by stimulating a receptor of  a nerve that conducts the impulse to the spinal cord where low level control and discrimination occurs, and transfers  the stimulus to the brain, where higher centers process the stimulus and react to it.  The structures in the brain include the thalamus, somatosensorycortex, limbic system, and autonomic systems and they are involved in  perception, localization and integration.  They send out a stimulus with instructions of how to react which is excecuted by muscle contraction or tissue secretion.

Functionally, pain is protective. The physiology and pathophysiology relate to changing the mechanical stimulus into an electrical impulse, and then through a series of complex synapses the stimulus is transmitted with the intent of  protecting the person from further damage.

The causes of pain are innumerable and exist within the full spectrum of human diseases. Pain may result from pain receptors sensitive to pain, (pricking, cutting, tearing) extreme temperatures, pressure, or aberrant chemical environments. A myriad of processes then occur in response to tissue injury causing either irritation of a somatic nerve or distension and pressure on a visceral sensory nerve. Inflammation is one of the most common of these injurious processes that is classically and universally expressed with  pain – a concept first described by the second century philosopher Celsus.

The result of a pain impulse is usually withdrawal from the insulting stimulus, resting of the injured part, or seeking the help of a medical practitioner if the pain is unbearable and arises from an internal disorder.

Diagnosis of pain disorders should proceed with careful history taking and clinical examination, followed by appropriate laboratory tests, and imaging if necessary.

Pain is a very common symptom and most instances are treated with an analgesic or antiinflammatory agent.   For more serious pains, treatment is directed at the cause of the pain.