2.3.7: Nerve Fiber Types

Nerve fibers can be categorized into three types according to their diameter. Type A fibers possess a substantial diameter, are myelinated, and exhibit the swiftest conduction velocity among all nerves within the body. Both afferent (sensory) and efferent (motor) nerve fibers fall within type A, which are further classified into their subtypes. On the other hand, type B fibers, though myelinated, possess a smaller diameter and predominantly function as preganglionic neurons within the ANS. Type C fibers, unmyelinated and featuring a modest diameter, operate with a comparably slower conduction velocity. These fibers function as postganglionic neurons within the ANS (Table 1). ²⁵

Table 1 | Peripheral Nerve Fiber Types and Their Functions |

Fiber Type	Fiber Size (\(\mu \mathrm{m}\))	Location/ Function
A\(\alpha\)	12-20	Neurons associated with proprioception
A\(\beta\)	5-12	Neurons associated with touch and pressure
A\(\gamma\)	3-6	Part of the muscle spindle detecting stretch
A\(\delta\)	2-5	Neurons dealing with pain and temperature
B	<3	Preganglionic autonomic neurons
C	0.2-1.5 (unmyelinated)	Postganglionic autonomic neurons and neurons associated with pain and temperature

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