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Table 2.    Size and conduction velocity of nerve fibers

Name and function of type of fiber. (Letters are used for any nerve; Roman numerals are for sensory fibers in dorsal spinal roots.) External
diameter

(micrometres)
Conduction
velocity

(metres/second)
Myelinated fibers
   A-alpha or IA Motor to skeletal muscle; sensory from muscle spindle proprioceptive endings (phasic, annulospiral type) 12-20 70-120
   A-beta or IB Sensory from tendons (tension); also Ruffini endings in skin 10-15 60-80
   II Sensory from Meissner's and pacinian corpuscles and similar endings in skin and connective tissue; from large hair follicles, and tonic proprioceptive endings (flower-spray type) of muscle spindles 5-15 30-80
   A-gamma Motor to intrafusal fibers of muscle spindles 3-8 15-40
   A-delta or III Sensory from small hair follicles and from free nerve endings for temperature and pain sensations 3-8 10-30
   B Preganglionic autonomic (white rami and cranial nerves 3, 7, 9, 10) 1-3 5-15
Unmyelinated fibers
   C or IV Pain & temperature; Olfaction; Postganglionic autonomic 0.2-1.5 0.5-2.5


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Last updated: January 2003