REFLEX SELF-REGULATION OF MUSCLE CONTRACTION AND AUTOGENETIC INHIBITION

Abstract

The problem of reflex self-regulation of muscle contraction has been re-opened by using the monosynaptic reflex (cat) as a test of the excitability of the motoneurones during contraction and stretch of the muscles they supply. By this technic the complicating efferent supply is removed by de-efferentation so that the size of the monosynaptic response, recorded from the cut root, directly gauges motoneurone excitability. In stretch and contraction there is first a period of facilitation which is succeeded by depression (inhibition). Both are seen in the muscle activated as well as in synergists. The depression does not require the period of facilitation which can be removed selectively by various means without effect on the inhibition. The latter increases with an increase of initial tension of the muscle and is also augmented by increasing the degree of stretch. Thus muscle operates aided by a central mechanism which first accelerates it by facilitation and then damps it,inputting on the brakes (inhibition) the more effectively the greater the amt. of tensile stress. The results have been discussed in reference to muscle end organs, to "lengthening reaction" and "silent period.".