INHIBITION OF ANTIDROMIC RESPONSES OF MOTONEURONES

Abstract

An afferent volley in a muscle or cutaneous nerve that inhibits the reflex response of a motoneurone may also cause blockage of antidromic propagation from the axon into the soma, but 3 dissimilarities show the inhibitory actions are not identical: the latent period of the antidromic depression is longer; no antidromic depression has been observed to be associated with the direct inhibitory action of group I muscle proprioceptor impulses and even with the secondary inhibitory action exerted by impulses in smaller afferent fibers the antidromic inhibition may be slight while the reflex inhibition is total; and deep anesthesia abolishes the antidromic inhibitory action but leaves the monosynaptic facilitatory action much less affected. The effect of inhibitory volleys on the facilitation curve of the antidromic impulse was studied. The mechanism of antidromic propagation into a motoneurone is discussed and it is shown that the Golgi-cell hyopthesis of inhibition offers plausible explanations of the above 3 dissimilarities between reflex and antidromic inhibition. The importance of this inhibitory mechanism to postural coordination is discussed.