[Reflex response in the masseter muscle after tapping the chin in healthy persons--an electromyographic study]

In a group of healthy subjects the author evoked reflex responses in both masseters by percussion of the chin with a reflex hammer. The reflexes were evoked during relaxation, slight or intense contraction of the masseters with the mouth open or closed. By percussion of the chin from above extension reflexes were evoked and by percussion of the chin from below contracting reflexes. The response was recorded by means of an electromyographic apparatus. The short-term stretch responses were evoked from the relaxed and slightly contracted masseters with the mouth open or closed. During intense contraction of the masseters the short-latency reflex stretch response was not evoked. In that case at first a short-latency inhibition of the basal activity of the masseter was observed followed by a medium and late-latency excitation response. With the masseters relaxed a long-latency stretch response was observed only with the mouth open. Percussion of the chin from beneath with slight contraction of the masseter caused initial inhibition of its basal activity followed then by a short-latency excitation response. Based on the assembled results the author analyzed the mechanism of the reflex control of the masseters.