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Conduction velocity

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Conduction velocity

For the test used to evaluate nerve function in humans, see Nerve conduction study.

Nerve conduction velocity is the speed at which an electrochemical signal propagates down a neural pathway. Many things can affect this, including axon diameter, myelination, the internal resistance of the axon, and temperature. Nerve conduction velocity differs from species to species, and to a lesser degree, from individual to individual.

These impulses are extremely fast, with some myelinated neurons conducting at speeds up to 120 m/s (432 km/h)

Motor fiber types
Type Erlanger-Gasser
Classification
Diameter Myelin Conduction velocity Associated muscle fibers
α 13-20 µm Yes 80–120 m/s Extrafusal muscle fibers
γ 5-8 µm Yes 4–24 m/s [1][2] Intrafusal muscle fibers

Different sensory receptors are innervated by different types of nerve fibers. Proprioceptors are innervated by type Ia, Ib and II sensory fibers, mechanoreceptors by type II and III sensory fibers and nociceptors and thermoreceptors by type III and IV sensory fibers.

Sensory fiber types
Type Erlanger-Gasser
Classification
Diameter Myelin Conduction velocity Associated sensory receptors
Ia 13-20 µm Yes 80–120 m/s[3] Responsible for proprioception
Ib 13-20 µm Yes 80–120 m/s Golgi tendon organ
II 6-12 µm Yes 33–75 m/s Secondary receptors of muscle spindle
All cutaneous mechanoreceptors
III 1-5 µm Thin 3–30 m/s Free nerve endings of touch and pressure
Nociceptors of neospinothalamic tract
Cold thermoreceptors
IV C 0.2-1.5 µm No 0.5-2.0 m/s Nociceptors of paleospinothalamic tract
Warmth receptors
Fiber types
Type Erlanger-Gasser
Classification
Diameter Myelin Conduction velocity
preganglionic fibers B 1-5 µm Yes 3–15 m/s
postganglionic fibers C 0.2-1.5 µm No 0.5-2.0 m/s

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