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The electromyographic silent period can be observed preceding a reaction movement. It has been suggested that the electrical silence was attributable to the supraspinal influences. Since the electrical activities of the muscle are related to the excitability of the motoneurons in the spinal cord, the excitability of the motoneurons might be changed in the period corresponding to the appearance of the silent period. The present study has been designed to investigate variability of the excitability of the motoneurons prior to a reaction movement by means of the H-wave.<BR>It has been observed that the change of the H-wave amplitude began with a slight decrease, and progressive increase.followed the depression period. The depression period of the H-wave appeared from 150 msec to 90 msec before the onset of the phasic discharge under the condition of the preparatory phase without the sustained contraction. Under the other condition with the sustained contraction, the depression period appeared from 120 msec to 85 msec. Thus, by application of the sustained contraction, the onset of the depression period was delayed and the duration was shortened. The results suggested that the depression period was closely related to the silent period. In other words, when the excitability of the motoneurons was lowered below the level of the EMG appearance, the silent period could be observed.
一般社団法人日本生体医工学会の論文