RESPONSES OF SINGLE HUMAN MOTOR UNITS TO ELECTRICAL STIMULATION

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Abstract
Clinical electro-myography has usually been limited to studies of voluntary contractions, while systematic analysis utilizing electrical stimulation of motor nerves has been less common. The paper describes a method for recording the activity of in-dividual human motor units to electrical stimulation with currents of different gradients. Single unit responses showing all or none reaction at threshold strength and the characteristic repetitive responses to stimuli of supra threshold strength are illustrated. Accommodation curves with the electrical response of a single motor unit as index were detd. and compared with those given by a muscle twitch. The former ones have a smaller slope value than those obtained by using the muscle contraction as index. The repetitive responses of single units to stimulation with constant currents were also studied. Significant differences were found to exist for the proximal and distal parts of the same motor fibre in the ulnar nerve, the former showing longer adaptation time and, consequently, less accommodation. The pathophysiologie significance of this result is discussed.

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