Exteroceptive suppression and motor control of the masseter and temporalis muscles in normal man.

Single electrical stimuli to the gums and mucosa inside the mouth elicit two successive exteroceptive suppressions (ES1 and ES2) in the voluntary electromyogram of the masseter and temporalis muscles in normal man. The same afferent axons appear to be involved in the two effects, as indicated by the intensity function, the electrical excitability, the afferent conduction velocity and the lack of differential effect of Xylocaine infiltration of the inferior alveolar nerve. Two similar phases of inhibition involve the monosynaptic masseter reflex and the synchronized electromyographical spikes induced by jaw vibration. Exteroceptive suppression is thought to be mediated, in the brain stem, by both an oligosynaptic (ES1) and a multisynaptic (ES2) mechanism.