THE QUESTION OF LOCALIZING ACTION CURRENTS IN MUSCLE BY NEEDLE ELECTRODES

Abstract

A study, with full discussion, relating to the validity of investigations in which the rhythm of the electromyogram has been employed as an indication of the frequency of the discharge of impulses from the motor neurons. A number of workers have assumed that the change of electrical potential measured through needle electrodes inserted into the muscle is influenced only by the activity of muscle fibers in close proximity to them. In the present experiments on the tibialis anticus and gastrocnemius muscles of the cat, needle electrodes inserted in either one of these antagonistic muscles have been shown to lead off a considerable action current arising from the activity of the opposite muscle, amounting to 13-40% of that obtained when the muscle containing the electrodes contracts. This result shows that conclusions based on the assumption that the influence of neighboring fibers or muscles is negligible are unwarranted.