Algesia

Algesia is the sensory perception of pain or heightened sensitivity to painful stimuli. The term derives from Greek algos meaning pain and gesia meaning sensation. In medical usage, algesia refers to the functional state of nociception and pain processing, and is distinct from analgesia, which denotes the reduction or absence of pain, and from algia, a less precise term sometimes used to denote pain itself.

Nociception is the neural encoding of noxious stimuli by specialized receptors called nociceptors. Peripheral fibers include A-delta fibers, which typically convey fast, sharp pain, and C fibers, which convey slower, throbbing pain. Signals travel to the dorsal horn of the spinal cord and ascend via the spinothalamic tract to the thalamus and cerebral cortex, where the pain experience is generated. Algesia is modulated at multiple levels, including peripheral sensitization after inflammation and central sensitization within the spinal cord and brain. Descending inhibitory pathways from regions such as the periaqueductal gray and other brainstem nuclei can amplify or dampen algesic signaling, contributing to analgesia.

Clinically relevant terms related to algesia include hyperalgesia (increased pain from a painful stimulus), hypoalgesia (decreased pain sensitivity), and allodynia (pain in response to non-painful stimuli). Assessment of algesia often employs pain scales and quantitative sensory testing to determine pain thresholds and patterns of sensitization.