The Effect of Repetitive Stimulation on Firing Motoneurons. Computer Simulation Based on a Motor Unit Study
A computer model for the repetitive stimulation of firing motoneurons (background activity) was based on experimental data derived from the response characteristics of human triceps surae motoneurons to single stimuli. Extrapolated data of response probability in the interspike interval were used in the model. The parameters of motoneuronal firing (firing rate and standard deviation of interspike interval duration) were based on experimental data.
The results of this simulation make it possible to extend our knowledge about the control of motoneuronal firing rate in the low firing-rate range observed during voluntary contraction of human muscles. In the model, stimulation at a mean frequency of 200 st/s shifted the motoneuronal firing rate from 3–12 imp/s to 11–16 imp/s. With decreasing background firing rates below 6–7 imp/s, the excitability of firing motoneurons depending on the mean firing rate increment increased. The mean decrement of interspike intervals decreased with the increase in background firing rate within the whole range of firing rates studied. The data obtained in the experiments and by simulation may help to clarify the controversy about the ramp slopes of membrane potential trajectories of firing motoneurons. Our results suggest that these slopes increase with the firing rate in the range investigated.
KeywordsFiring Rate Motor Unit Single Stimulus Interspike Interval Repetitive Stimulation
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