Spread of Excitation in Skeletal Muscle: Some Factors Contributing to the Form of the Electromyogram

Abstract

When studied by means of a mapping technic, the form of the action potential of the anterior gracilis muscle of the rat, elicited in response to indirect electrical stimulation, varied with the position of the recording electrodes. Factors shown to be concerned in these variations were: the location of end plates in 2 restricted zones; the occasional occurrence of doubly-innervated fibers; and variations in conduction rates of 3.4 to 5 m./sec. in different fibers. Histological prepns. confirmed the location of the end plates and the existence of doubly-innervated fibers. Variations in length and diam. of the muscle fibers were demonstrated. The effect of these variations on the form of the potentials is discussed.