Abstract:

Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage. For more than a century, views on the nature of pain sensation have been dominated by three major theories – the Specificity theory by Frey, the Intensivity theory by Goldscheider and the Gate-Control theory by Melzack and Wall. There are various types of somatic and visceral nociceptors that can activate a somatic or visceral pain pathway. Neurochemical reactions at the site of injury activate the nociceptors which initiate an afferent impulse that enters the spinal cord, traverses specific ascending spinal tracts and reaches cerebral centers for interpretation. Nociceptive information is transmitted from the spinal cord to the thalamus and cerebral cortex along five ascending pathways. The intensity of pain sensation can be modulated at the periphery, the spinal cord, midbrain, and cerebral cortex, by various mechanisms such as the Gate control theory, neurotransmitter substances such as enkephalin and endorphins, and descending pain modulatory systems. This article summarizes the theories of pain, somatic and visceral pain, its pathways, viscero-somatic convergence, neurotransmitters of pain, pain syndromes and therapeutic modalities used for pain control.

Keywords: pain pathway, neurotransmitters of pain, pain receptors, pain syndromes