[Tremor. Mechanical effect of the discharge behavior of motor neurons]

From the accordance of the discharge and recruitment behaviour of motor units with the Fourier-analysis of the tremor ripples it is shown that the action tremor originates from any muscle innervation and is equivalent to the mechanical effect of the discharges of all motoneurones of a particular muscle. The power spectrum of tremor is mainly caused by the twitch contractions between recruitment (7--8/sec) and total fusion (25/sec) of the discharging motoneurones. The maximum of the frequency spectrum, which represents the dominant tremor rate, corresponds to the discharge frequency just after recruitment of each motoneurone. The twitch contractions of these newly recruited motor units are mechanically least fused. The power spectrum of the tremor in patients with motor disturbaces parallels the changes in the discharge and recruitment behaviour of motoneurones during voluntary contraction. The correlation between the discharges of two simultaneously recorded motor units shows a tendency to synchronization of all discharge rates the extent of which corresponds to the individual tremor intensity.