nerve fiber, a slender process, the axon of a neuron. Each fiber is classified as myelinated or unmyelinated. Myelinated fibers are further designated as A or B fibers. C fibers are unmyelinated. The A fibers are somatic. A alpha fibers are large fibers and transport impulses at a velocity of 60 to 100 meters per second; A beta fibers are smaller and transmit pressure and temperature impulses at a velocity of 30 to 70 meters per second. A gamma fibers transmit touch and pressure impulses. A delta fibers are the smallest and transmit impulses associated with sharp pain sensation. B fibers are more finely myelinated than A fibers. They are both afferent and efferent and are mainly associated with visceral innervation. The unmyelinated C fibers are efferent postganglionic autonomic and afferent fibers that conduct impulses of prolonged, burning pain sensation from the viscera and periphery.
