Electrogenesis of muscular fibers in the rat masseter muscle proper

It was established by the method of intracellular lead of membrane rest potentials (MRP) and action potentials (AP) that fibers with high MRP and little overshot are mainly located in superficial layers of the rat masseter muscle proper whereas those with low MRP and high overshot principally in deep layers. Excitability of the cytoplasmic membrane of muscular fibers of both types proved to be related in electrical properties (critical level of depolarization, current threshold). It is suggested that the rat masseter muscle contains a great number of rapid phasic fibers in superficial layers and slow ones in deep layers.