Muscle stretch and chemical muscle spindle excitation: effects on Renshaw cells and efficiency of recurrent inhibition.

Publisher Summary This chapter analyzes the aspects of the functional role of the Renshaw mechanism in the stretch reflex and focuses on the stabilizing function of the Renshaw mechanism that could be sufficiently demonstrated by the behavior of individual tonic α-motoneurones (α-MNs) and Renshaw cells (RCs), under natural stretch conditions. The chapter also discusses the property of the Renshaw feedback—namely, its selecting, functionally focussing action on an entire α-MN pool. For this purpose, many single α units are investigated, interacting together with their RCs in the control of the muscle under study. Reliable stretch response data of numerous α-motor units can be easily collected and compared by means of the conventional recording technique from ventral rootlet filaments. Studies show that the response type of individual α-MNs within the same pool, submitted to identical stretch tests, can differ widely from purely phasic to extremely tonic behavior. There are many transitions between the two extremes, and the same cell can be brought from phasic to tonic behavior or vice versa, by suitable means. The focus is on the fact that a person frequently finds either one or the other of two different decerebrate preparation types, with respect to their overall stretch reflex behavior.

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