Nerve Conduction, Electromyography and Evoked Potentials

Nerve conduction studies (NCS) involve the application of a small harmless (0.1–0.2 ms duration 5–80 m amp) depolarizing square wave electrical current to the skin over a peripheral nerve. This stimulation results in generation of a nerve action potential (NAP) recorded at a distant point on the same nerve as well as a compound muscle action potential (CMAP) due to the activation of muscle fibres in a target muscle supplied by the nerve. In both cases, these may be recorded with surface or needle electrodes. Nerve conduction studies (NCS) are extremely useful for the following: