Nerve conduction velocity

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). The speed of nerve impulse transmission ranges from about 0.5 m/s to over 120 m/s 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. ==Testing methods==

Nerve conduction studies 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: To address these problems, new devices are being developed, such as 3-dimensional electrode arrays. These are MEMS devices that consist of arrays of metal micro-towers capable of penetrating the outer layers of skin, thus reducing impedance. Compared with traditional wet electrodes, multi-electrode arrays offer the following: • Electrodes are about 1/10 the size of standard wet surface electrodes • Arrays of electrodes can be created and scaled to cover areas of almost any size • Reduced impedance • Improved signal power • Higher amplitude signals • Allow better real-time nerve impulse tracking ==Causes of conduction velocity deviations==

Anthropometric and other individualized factors Baseline nerve conduction measurements are different for everyone, as they are dependent upon the individual's age, sex, local temperatures, and other anthropometric factors such as hand size and height. It is important to understand the effect of these various factors on the normal values for nerve conduction measurements to aid in identifying abnormal nerve conduction study results. The ability to predict normal values in the context of an individual's anthropometric characteristics increases the sensitivities and specificities of electrodiagnostic procedures. Because ALS shares many symptoms with other neurodegenerative diseases, it can be difficult to diagnose properly. The best method of establishing a confident diagnosis is via electrodiagnostic evaluation. To be specific, motor nerve conduction studies of the Median, Ulnar, and peroneal muscles should be performed, as well as sensory nerve conduction studies of the Ulnar and Sural nerves. CTS is another condition for which electrodiagnostic testing is valuable. However, before subjecting a patient to nerve conduction studies, both Tinel's test and Phalen's test should be performed. If both results are negative, it is very unlikely that the patient has CTS, and further testing is unnecessary. These levels of severity are categorized as: This degeneration is due to an autoimmune response typically initiated by various infections. Two primary classifications exist: demyelinating (Schwann cell damage) and axonal (direct nerve fiber damage). Each of these then branches into additional sub-classifications depending on the exact manifestation. In all cases, however, the condition results in weakness or paralysis of limbs, the potentially fatal paralysis of respiratory muscles, or a combination of these effects. Nerve conduction studies performed on the Ulnar motor and sensory, Median motor and sensory, Tibial motor, and Peroneal motor nerves in patients with LEMS have shown that the conduction velocity across these nerves is actually normal. However, the amplitudes of the compound motor action potentials may be reduced by up to 55%, and the duration of these action potentials decreased by up to 47%. Studies have shown that the Rho/Rho-kinase signaling pathway is more active in individuals with diabetes and that this signaling activity occurs mainly in the nodes of Ranvier and Schmidt-Lanterman incisures. Therefore, over-activity of the Rho/Rho-kinase signaling pathway may inhibit nerve conduction. Motor nerve conduction velocity studies revealed that conductance in diabetic rats was about 30% lower than that of the non-diabetic control group. In addition, activity along the Schmidt-Lanterman incisures was non-continuous and non-linear in the diabetic group, but linear and continuous in the control. These deficiencies were eliminated after the administration of Fasudil to the diabetic group, implying that it may be a potential treatment. ==See also==