Complete model for the statistical composition of the end-plate potential

Abstract

A statistical model for the composition of end-plate potentials has been designed and used for detailed study of end-plate potential's amplitude distribution function. The model is based on the present knowledge of synaptic function and takes into account the miniature end-plate potential's amplitude distribution, pulse shape and latency fluctuation as well as the residual potential difference across the membrane, non-linear summation of unit quanta and the mean quantum content. The building up of end-plate potentials is a stochastic process in which all of the above factors have significant influence. The computer model for statistical building of end-plate potentials is designed on the basis of the Monte Carlo technique. The end-plate potentials' distribution is not calculated, but is built up in the same way as in a living neuromuscular junction through the addition of miniature end-plate potentials which have random amplitudes and random times of arrival. Large numbers of experiments have been performed with the model with the mean quantum content in the range from 2 to 200, mean amplitudes of miniature end-plate potentials in the range of 0·2 to 0·8 mv, coefficient of variation of miniature end-plate potentials in the range of 0·1 to 0·2, number of depolarizations per experiment up to 25,000. Latency fluctuation and pulse shape have been taken according to the measurements by Katz & Miledi (1965). Very good agreement between results produced by the theoretical model and real experiments was obtained. Coefficients of variation of end-plate potentials produced by the model are in good agreement with experimental results for all values of mean quantum content. This is due partly to the fact that not only non-linear summation but also the latency fluctuation diminishes the coefficient of variation.