| Abstract: | The pattern of motor unit activity of the rectus femoris muscle during isometric contraction was studied. Interspike interval sequences were analyzed. At frequencies below 8–10/sec the interval histograms were asymmetrical (long intervals predominated), the standard deviation was high and depended on the mean interval, and adjacent intervals were independent. At frequencies above 10–13/sec the interval distribution became normal in type, the standard deviation was low and independent of the mean interval duration, and negative correlation was found between adjacent intervals. During brief contraction specific for this particular (fast) muscle the activity of most neurons was of the second type, while during prolonged contraction it was of the first type. The change from activity of the first to the second type took place approximately when, with an increase in frequency, spikes began to appear against the background of after-hyperpolarization. A hypothesis is put forward to the effect that after-hyperpolarization creates the rhythm of activity (low variability of the intervals), and that the duration of after-hyperpolarization is correlated with the lower limit of working frequencies of the motoneurons. The motoneuron is regarded as performing not only a summating, but also a damping function, reducing the effect of random fluctuations of the synaptic inflow and coding information for transmission as a mean frequency.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 609–619, November–December, 1971. |
