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Concept
Nerve conduction velocity
Résumé
In neuroscience, nerve conduction velocity (CV) is the speed at which an electrochemical impulse propagates down a neural pathway. Conduction velocities are affected by a wide array of factors, which include age, sex, and various medical conditions. Studies allow for better diagnoses of various neuropathies, especially demyelinating diseases as these conditions result in reduced or non-existent conduction velocities. CV is an important aspect of nerve conduction studies.
Ultimately, conduction velocities are specific to each individual and depend largely on an axon's diameter and the degree to which that axon is myelinated, but the majority of 'normal' individuals fall within defined ranges.
Nerve impulses are extremely slow compared to the speed of electricity, where the electric field can propagate with a speed on the order of 50–99% of the speed of light; however, it is very fast compared to the speed of blood flow, with some myelinated neurons conducting at speeds up to 120 m/s (432 km/h or 275 mph).
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.
Normal impulses in peripheral nerves of the legs travel at 40–45 m/s, and those in peripheral nerves of the arms at 50–65 m/s.
Largely generalized, normal conduction velocities for any given nerve will be in the range of 50–60 m/s.
Nerve conduction velocity is just one of many measurements commonly made during a nerve conduction study (NCS). The purpose of these studies is to determine whether nerve damage is present and how severe that damage may be.
Nerve conduction studies are performed as follows:
Two electrodes are attached to the subject's skin over the nerve being tested.
Electrical impulses are sent through one electrode to stimulate the nerve.
The second electrode records the impulse sent through the nerve as a result of stimulation.
Source officielle
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