APA Dictionary of Psychology

a myelinated nerve fiber (axon) of the somatosensory system. A fibers are subdivided by diameter, ranging from largest to smallest: A-alpha fibers are 13 to 20 μm in diameter and transmit information from proprioceptors of skeletal muscles, A-beta fibers are 6 to 12 μm and transmit information from mechanoreceptors of the skin, and A-delta fibers are 1 to 5 μm and transmit temperature and sharp pain information. See also B fiber; C fiber.