[Rapid adaptation of the response to static stretching of the primary endings of the elementary dynamic type of muscle spindles].

The elementary dynamic (ED) type receptors reveal a peculiar combination of high--frequency discharges in response to dynamic component of mechanical stimulus with fast disappearance of responses to static stretching of the muscle as well as post--activational discharges. 29 ED receptors were observed in stretching of isolated m. soleus, semi--isolated and intact m. triceps in anesthetized cats. Other 185 spindle afferents revealed stable static discharges. ED receptors constituted 5% of 570 units under study. When recording the responses of ED receptors to stretching and fisimotor stimulation, the muscle fiber and the afferent fiber were in a good functional condition. The property of fast adaptation of some primary endings of the muscle spindle seems to depend on connection of the afferent's sensitive terminals only with the nuclear--bag intrafusal fibers.