抄録
Location of the neuromuscular junction, end plate, of the masseter muscle was estimated from surface electromyograms (EMGs). The EMGs in response to clenching action were recorded from eight sites over the masseter muscle in a monopolar manner where the reference electrode was put on the tip of the nose. Base lines of the EMGs deflected either negatively or positively depending on the recording sites during clenching action, and these occurrences coincided with the action potential bursts. Slow wave and action potential components were separated from the raw EMG with digital filters. Deflection of the slow wave component was most negative over the inferior masseter muscle close to the mandibular ramus, while the polarity of the deflection shifted to positive over the superior part. The magnitude of the action potential component was largest at almost the same site as the most negative deflection of the slow wave component. The phase of the action potential component with reference to the signals for the channel that showed the most negative deflection of the slow wave also reversed at almost the same site as the polarity change of the slow wave component. All of these findings indicated that the slow wave detected by this method is the externally recorded synaptic potential originating at the meuromuscular junction, and that of the masseter muscle is located on the inferior part close to the mandibular ramus. [Jpn J Physiol 54 Suppl:S158 (2004)]
