C fiber

Group C nerve fiber
C fiber not labeled, but substantia gelatinosa of Rolando is Rexed lamina II, labeled at upper left.
Anatomical terminology []

Group C nerve fibers are one of three classes of nerve fiber in the central nervous system and peripheral nervous system. The C group fibers are unmyelinated and have a small diameter and low conduction velocity. They include Postganglionic fibers in the autonomic nervous system (ANS), and nerve fibers at the dorsal roots (IV fiber). These fibers carry sensory information.

Damage or injury to nerve fibers causes neuropathic pain. Capsaicin activates C fibers Vanilloid receptors, giving chili peppers a hot sensation.

C fibers are one class of nerve fiber found in the nerves of the somatic sensory system. They are afferent fibers, conveying input signals from the periphery to the central nervous system.

C fibers are unmyelinated unlike most other fibers in the nervous system. This lack of myelination is the cause of their slow conduction velocity, which is on the order of no more than 7000200000000000000♠2 m/s. C fibers are on average 0.2-1.5 μm in diameter.

C fiber axons are grouped together into what is known as Remak bundles. These occur when an unmyelinated Schwann cell bundles the axons close together by surrounding them. The Schwann cell keeps them from touching each other by squeezing its cytoplasm between the axons. The condition of Remak bundles varies with age. The number of C fiber axons in each Remak bundle varies with location. For example, in a rat model, large bundles of greater than 20 axons are found exiting the L5 dorsal root ganglion, while smaller bundles of average 3 axons are found in distal nerve segments. Multiple neurons contribute axons to the Remak bundle with an average ratio of about 2 axons contributed per bundle. The cross sectional area of a Remak bundle is proportional to the number of axons found inside it. Remak bundles in the distal peripheral nerve are clustered with other Remak bundles. The Remak Schwann cells have been shown to be electrochemically responsive to action potentials of the axons contained within them.