Smärtsignalen

Smärtsignalen, which translates to “pain signal” in English, refers to the complex neurophysiological process by which the nervous system detects and conveys information about tissue damage or potentially harmful stimuli. The pathway begins at specialized nociceptors located in skin, muscles, joints and internal organs. These free‑ending nerve endings respond to mechanical, thermal, or chemical changes that exceed certain thresholds. When activated, nociceptors open ion channels that trigger depolarisation and the generation of action potentials. These electrical impulses travel along peripheral afferent fibers—primarily Aδ and C fibres—toward the dorsal horn of the spinal cord.

Within the dorsal horn, pain signals are synaptically transmitted to second‑order neurons. Here, neurotransmitters such as glutamate, substance P and calcitonin gene‑related peptide (CGRP) mediate the relay. The axons of these second‑order neurons cross to the opposite side of the spinal cord (decussation) and ascend through the spinothalamic tract to the thalamus. The thalamus serves as a relay station, projecting signals to higher cortical centres, including the primary somatosensory cortex, which encodes sensory discrimination, and the limbic system, which processes affective and motivational aspects of pain.

The smärtsignal’s sensitivity and gain can be modulated by descending pathways originating in the brainstem. These descending controls can enhance or inhibit pain perception, and dysregulation can lead to chronic pain conditions. Additionally, the inflammatory milieu can sensitize nociceptors, lowering their activation threshold and contributing to hyperalgesia and allodynia.

Clinically, understanding the mechanics of the smärtsignal underpins diagnostics and treatments for pain, such as pharmacologic modulation of neurotransmitters, nerve block procedures, and neuromodulation techniques. Ongoing research into peripheral and central mechanisms offers prospects for more targeted therapies, aiming to alleviate pain while minimizing adverse effects.