Nocitseptor

Nocitseptor, commonly spelled nociceptor in scientific literature, refers to sensory neurons that detect noxious stimuli and initiate the perception of pain. They are free nerve endings of primary afferent neurons located in peripheral tissues such as the skin, mucosa, joints, and visceral organs.

Two main fiber classes convey nociceptive signals: A-delta fibers, which are thinly myelinated and transmit fast, sharp pain; and C fibers, which are unmyelinated and convey slow, dull pain. Nocitseptors express a range of receptors and ion channels, including TRPV1, TRPA1, ASICs, and P2X3, that respond to thermal, mechanical, and chemical stimuli.

Activation occurs through mechanical damage, extreme temperatures, and chemical mediators such as bradykinin, prostaglandins, serotonin, lactic acid, and capsaicin. Transduction converts these stimuli into electrical signals that travel to the central nervous system.

Signals are carried to the dorsal root ganglion, synapse in the dorsal horn of the spinal cord (lamina I and II), and ascend via the spinothalamic tract to the thalamus and then to the somatosensory cortex. Additional pathways include the spinomesencephalic and spinoreticular tracts that mediate affective and autonomic aspects of pain. Nociceptors participate in inflammatory and neuropathic pain through peripheral and central sensitization, lowering activation thresholds and increasing responsiveness to stimuli.

Clinical relevance: analgesic strategies often target nociceptor signaling, such as capsaicin-induced desensitization of TRPV1-expressing fibers and CGRP inhibitors for specific pain syndromes. See also Nociception, Pain, TRP channels, and Pain pathways.