Molecular components of itch, pain, and touch sensation

Article By:

Mishra, Santosh K. Department of Molecular Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina.

Wheeler, Joshua Department of Molecular Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina.

Last reviewed:2016

DOI:https://doi.org/10.1036/1097-8542.YB160504

Touch, itch, and pain are parts of the somatosensory system and are triggered by the stimulation of sensory receptors present in the skin. These sensory receptors are expressed in the neurons of the sensory ganglia (groups of nerve cell bodies), whose cell bodies lie adjacent to the spinal cord in the form of beads known as the dorsal root ganglia (DRG), as well as at the base of the skull [trigeminal ganglia (TG)]. The signals from the periphery are conveyed by the DRG neurons and then transmitted to the spinal cord, where they synapse or make contact with other neurons, which in turn send messages to the brain for further processing. Although the cell bodies in the ganglia are commingled, they are specialized to detect different stimuli, such as pain, itch, and touch. Therefore, the somatosensory system is divided into various subsystems. Typically, the somatosensory system has been classified based on various parameters, including cell size, myelination (accumulation of myelin around nerve cells), expression of molecular markers, specialization of the nerve endings, projection of afferents (which carry nerve impulses from sensory receptors toward the central nervous system) in the spinal cord, and action potentials. With further advances in molecular biology techniques, researchers have found specific ion channels that are known to be G protein–coupled receptors (GPCRs); these are expressed in a specific subtype population of sensory neurons, where they perform specific functions involved in the detection of itch, pain, and touch (see illustration). This article will focus on the cellular and molecular components of touch, itch, and pain neurons and receptors involved at the periphery in the DRG. See also: Brain; Cognition; Cutaneous sensation; Ganglion; Ion channels (genetics); Ion transport; Nerve; Nervous system (vertebrate); Neurobiology; Neuron; Pain; Perception; Sensation; Sense organ; Skin; Somesthesis; Spinal cord

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