nociceptorer

Nociceptors are specialized sensory neurons in the peripheral nervous system that detect potentially damaging or noxious stimuli. They are found in the skin and mucosa as well as in joints, muscles, and some internal organs. Their peripheral endings are typically free nerve endings, which makes them sensitive to a range of injurious stimuli rather than to normal touch or pressure.

Signals travel from nociceptors along primary afferent fibers to the spinal cord or brainstem. A-delta fibers are thinly myelinated and convey fast, sharp pain, while C fibers are unmyelinated and transmit slower, dull or burning pain. Nociceptors can be mechanical, thermal, or chemical, and many are polymodal, responding to multiple noxious modalities.

Transduction is mediated by ion channels and receptors on the sensory endings. Important players include TRPV1 for heat and chemical irritants, TRPA1 for chemical stimuli, ASICs for acidity, and various receptor systems that respond to inflammatory mediators. Activation leads to depolarization and release of neurotransmitters such as glutamate and neuropeptides like substance P and calcitonin gene-related peptide (CGRP) at central synapses.

Inflammation or tissue injury can sensitize nociceptors, lowering their activation threshold and increasing responsiveness. This peripheral sensitization contributes to hyperalgesia (increased pain from a noxious stimulus) and, in some cases, allodynia (pain from non-noxious stimuli). Silent nociceptors, which are typically inactive, may become responsive during inflammation.

Understanding nociceptors informs approaches to pain management. Therapies target nociceptor signaling or central processing, including nonsteroidal anti-inflammatory drugs, opioid analgesics, and emerging strategies aimed at ion channels, neuropeptide signaling, or nerve-gate modulation. Ongoing research seeks to reduce pain while preserving protective sensory function.