SYNAPTIC POTENTIALS OF INHIBITED MOTONEURONES

Publisher Website
Google Scholar
Abstract
According to the Golgi-cell hypothesis of inhibition, the spread and fusion of the local responses set up by synaptic excitation of a neurone are limited by anelectrotonic foci generated by current flow in activated Golgi cells. During concurrent inhibition of motoneurones there should be a depression only of that part of the synaptic potential which is attributable to the phase of spread and fusion of local responses. Exptl. observations with both focal and ventral root recorded synaptic potentials have confirmed this prediction. Inhibitory depression of the synaptic potential becomes first observable in the latter part of its rising phase. Likewise, when the synaptic potential is large enough to evoke a reflex discharge, the inhibition depression becomes observable only upon the rapid growth and fusion of the local response which normally occurs to form the propagated impulse. This mechanism of inhibitory action has been demonstrated for both "direct" and "secondary" inhibition. In addition, 2 modes of inhibitory action by blockage of the incoming excitatory volley have been observed: 1) the well-known dorsal root reflex discharge causing a partial block by collision, and 2) a blockage in the immediate presynaptic region of the excitatory fiber may occur. This latter may be attributable to the low safety factor for propagation in this region together with the catelectrotonic depressant action of the dorsal root potential.