A radiographic and electromyographic study of snapping and biting in the oppossum

Abstract

The attacking bite of the oppossum was studied using cinefluorographic, electromyographic (EMG) and bite gauge techniques. The activities recorded were divided into two broad groups: the first exemplified by a large initial gape, a high rate of jaw closure, a short duration bite and a low peak force; the second was typified by the opposite traits. Two separate patterns of EMG activity were found: in one, both the elevator and the depressor muscles of the jaw were activated simultaneously (synchronous EMG): in the other the muscles were activated in the classical reciprocal manner (asynchronous EMG). The synchronous EMG pattern was often associated with high levels of elevator activation and the asynchronous with low levels of elevator activation. The EMG pattern of the classic jaw opening reflex only occurred after weak elevator EMG activity and never after EMG activity indicative of a powerful bite. The rapid rebound of the jaw following tooth contact, classically associated with the jaw opening reflex, was never seen. We conclude that the different patterns of activity in jaw closure seen in the fast snap and the slower bite probably reflect different mechanisms of control.