The Relative Sensitivity of Renshaw Cells to Static and Dynamic Changes in Muscle Length

Abstract

Publisher Summary This chapter discusses that Renshaw cells, which belong to the monosynaptic reflex pathway made by the Ia afferents from the gastrocnemius-soleus (GS) muscle on the homonymous motoneurons, may respond to both static stretch and vibration of the homonymous muscle. However, the Renshaw cell discharge induced by vibration of the GS muscle is much higher than that elicited during static stretch of the same muscle for comparable frequencies of discharge of the primary endings of the muscle spindles. The possible factors responsible for this difference are considered at length in the chapter. The experiments are performed on precollicular decerebrate cats, operated under ether anesthesia. Results show that Renshaw cells disynaptically excited by the orthodromic group I volleys induced by low-threshold electrical stimulation of the intact GS nerve responds to vibration applied longitudinally to the de-efferented GS muscle. Even in this instance, the Renshaw cells fire with a latency that is compatible with the disynaptic origin of the response, indicating that excitation of the Renshaw cells depend upon monosynaptic reflex discharge of the GS motoneurons following the stimulation of the Ia afferents. An analysis of the stimulus-response relationship, evaluated by measuring the discharge rate of the Renshaw cells as a function of the amplitude of vibration, clearly indicates that this response depends upon the activation of the primary endings of the muscle spindles.