Mechanisms of Physiologic Pain

Abstract

Detection of environmental threats and noxious stimuli is vital to an organism’s survival and well-being. Without this ability, protective behaviors could not be formed against potentially harmful situations, which may become life threatening. The role of nociceptors as specialized sensory neurons is to detect the environmental threats presented as intense stimuli and relay the information to neural circuits to formulate a reaction to avoid them. Nociceptive pain serves as an alarm system. Acute nociceptive pain serves not only to trigger early withdrawal responses and enhance wound healing but also to initiate affective responses and modify future behaviors. Perception of pain is a complex experience, involving transduction of various noxious environmental stimuli (thermal, mechanical, environmental, and chemical) through polymodal peripheral receptors; action potentials ensue and relay the signal to the central nervous system to be processed into cognitive and emotional experiences by the brain. Noxious stimuli generating nociceptive pain are generally temporary. However, persistent pain beyond the resolution of initial stimuli and tissue healing is maladaptive and could lead to chronic pain. Intense and prolonged pain transmission associated with chronic pain is associated with sensory neuronal plasticity which results in changes in pain transmission pathways of both the peripheral and central nervous systems. This chapter focuses on the neurophysiology of pain transmission and processing. Particular emphasis is directed to receptors, sensory neurons, and mechanisms modulating noxious stimulation.