The A-beta fibers originate from hair follicles, Meissner's corpuscles, Pacinian corpuscles, Merkle cell endings, and Ruffini endings. These fibers transmit sensory information regarding touch, vibration, and hair deflection. They are large-diameter, myelinated nerves, these characteristics make the A-beta fiber a fast-conducting nerve fiber. The A-beta fiber has a relatively low threshold. making it easily stimulated.
The A-delta fibers transmit information from warm and cold receptors, a few hair receptors, and free nerve endings, thus transmitting pain. The free nerve endings supplied by A-delta fibers primarily respond to noxious mechanical stimulation such as pinching, pricking, and crushing. The A-beta fibers are myelinated, but are smaller than A-beta fibers and thus have a slower conduction velocity.
The "C" fibers are the smallest afferent peripheral nerves that are associated with pain. They are unmyelinated and also include the efferent postganglionic fibers of the sympathetic nervous system. Those fibers that originate at deep receptors are primarily mechanoreceptors and nociceptors. A few type C afferents are themoreceptors. The C fibers are the slowest of the sensory nerve fibers in conduction and require a greater stimulation than the others to elicit a response.
