Neurophysiology of Nerve Conduction Studies

Abstract

The methodology for performing standard nerve conduction studies has been established by identifying the most helpful and consistent physiological data obtainable while being constrained by a variety of technical and practical limitations. Nerve stimulation occurs underneath the negatively charged anode of the applied stimulator and simultaneous hyperpolarization of the nerve occurs beneath the positively charged cathode. Referential or bipolar recording techniques are used for all types of measurements. Sensory conduction studies can be performed either antidromically or orthodromically, although, for technical reasons, the former are usually preferred; the recorded sensory nerve action potential is made up of the simultaneous depolarization of all of the cutaneous sensory axons. In motor studies, the compound motor action potential is recorded from the motor point of the muscle of interest and represents the depolarization of the underlying muscle fibers rather than the nerve itself and is, thus, of considerably greater amplitude and duration. F-waves and H-reflexes represent the two most commonly evaluated forms of late responses and assist with assessing the entire length of the neurons, from spinal cord to distal muscle.