[Comparative analysis of discharge regularity and position sensitivity of the primary endings of passive muscle spindles].

In 75 primary endings of passive muscle spindles with high dynamic sensitivity, static thresholds, position sensitivity and discharge regularity were studied on stepwise stretching of the m. triceps surde in anesthetized cats. Receptors with more regular discharges revealed low static thresholds, high static responses, monotonously rising curve "the length of muscle -- the mean firing rate" and oftener displays of spontaneous activity. Receptors with less regular discharges revealed high static thresholds and low static responses; the probability of mean firing rate increment for each "step" of muscle stretching is rather small in them. Low dispersion of interspike intervals seems to characterize is rather small in them. Low dispersion of interspike intervals seems to characterize discharges of those primary endings whose large terminal branch makes contact mainly with the chain intrafusal fibers.