Jaw-Closing Muscle Activities with the Mandible in Rest Position

Abstract

The electromyogram [EMG] of the jaw muscles during the resting state of the mandible were analyzed in human and cat. In human, the spontaneous EMG activity of the superficial belly of the masseter was mostly recorded from the medial and lower areas of the frontal part, and from the lower area of the posterior part of the muscle. In cat, 4 different types of the spontaneous EMG activity of the masseter and temporalis were observed. The 1st type activity was regular and continuous, the 2nd type activity was irregular and intermittent discharges and the 3rd type activity discharged only during the expiratory phase. The 4th type was a long lasting and low amplitude burst discharges. In addition, there were reciprocal relationships in the spontaneous muscle activity between the anterior and posterior bellies of the temporalis.