Nociceptoreiden

Nociceptors are specialized sensory neurons that detect tissue damage or potentially harmful stimuli and initiate nociception, the neural process that leads to the perception of pain. They are found in the skin, joints, muscles, viscera, and other tissues, often as free nerve endings that respond to different noxious modalities.

Nociceptors can be classified by the type of stimulus they primarily detect: mechanical (high-intensity pressure or distortion), thermal (extreme temperatures), chemical (irritants and inflammatory mediators), and polymodal (responding to several types). They are carried by different fiber types, notably A-delta fibers, which are thinly myelinated and convey fast, sharp pain, and C fibers, which are unmyelinated and transmit slower, duller pain.

When activated, nociceptors generate receptor potentials that trigger action potentials traveling along peripheral nerves to the dorsal horn of the spinal cord. From there, signals are transmitted via ascending pathways such as the spinothalamic tract to the thalamus and cerebral cortex, where pain is perceived and localized. Some nociceptive information also reaches brainstem and limbic regions, contributing to reflex responses and the emotional aspects of pain.

Nociceptor signaling can be modulated by inflammatory mediators (e.g., bradykinin, histamine, prostaglandins) that sensitize nociceptors, a process known as peripheral sensitization. Central sensitization may occur within the spinal cord, enhancing pain sensitivity. Nociceptors can release neuropeptides such as substance P and CGRP, promoting inflammation and vasodilation in the affected area.

Clinical relevance: altered nociception underlies many pain conditions, including hyperalgesia, allodynia, and chronic pain. Treatments target various levels of the pathway, from peripheral transduction (anti-inflammatory drugs) to central processing (certain antidepressants, anticonvulsants, and opioids).