[Proprioceptive reflexes and the regulation of movement].

Apart from the direct influences of muscle spindle sensory endings on skeletomotor neurones a great deal of their reflex drive is provided indirectly via the gamma-loop. Fusimotor neurones modulate their discharge rate in parallel with that of the skeletomotor neurones during the rising phase, as well as during the maintained reflex tension in m.triceps surae of decerebrated cat, when small tension oscillations are present in the muscle. However, under other conditions of spinal reflex activities either skeletomotor or fusimotor neurones could be activated independently by impulses from muscle receptors. On the ground of the presented results, it can be supposed that fusimotor firing, together with the afferent firing from muscle spindles, does not provide the main stimulus for the reflex activity of skeletomotor neurones but serves as an indicator of the deviations from the expected or planned movement representing, in this way, its model.