[The action of a short inhibitory volley on human firing motoneurons (an experiment and a model)].

The influence of a short inhibitory volley on firing motoneurons of soleus and ext. carpi uln. was studied in human experiments and the results obtained were used as a basis for simulation. An increase of the interspike interval (ISI) depended on the timing of inhibitory volley arrival and silent period (SP) duration was studied. The ability of the individual motoneuron to respond to inhibitory volley by prolongation of ISI influenced the SP duration. Two parameters were crucial: the duration of the part of ISI where the inhibition was efficient in increasing the ISI (d) and the maximal increase of ISI (delta x max). The latter corresponded to the inhibitory volley arrival at the very end of ISI. If d less than delta x max the SP = d; if d greater than delta x max the SP = delta x max. In the case of variable ISIs those relations should be applied to the smallest ISI among the ISI distribution. Therefore the SP duration depended not only on the mean ISI of a motoneuron, but on ISI variability as well.