REFLEX DISCHARGES IN BRANCHES OF THE CRURAL NERVE

Abstract

The sartorius and the vastus internus are 2 muscles of different function which are supplied by motor axons originating in the same and adjacent segments of the spinal cord and passing together peripherally in the crural nerve. In cats under pentobarbital sodium anesthesia, reflex discharges were evoked into the motor nerves of these muscles by the stimulation of dorsal roots. The discharges had a constancy from prep. to prep., which stands in contrast with the variability observed in ventral root discharges similarly evoked in comparable preparations. In spite of the topographical association of the 2 groups of motoneurons, the reflex discharges in the motor branches supplying the sartorius differed considerably from those in branches to the vastus internus, and the reflex discharges to the 2 muscles were conditioned differently by antecedent stimulation of the same groups of sensory axons. An L6 dorsal root volley evoked in the nerve to the vastus internus a nearly synchronous discharge having a central latency of only 0.9 to 1.6 msec, and in the nerve to the sartorius a dispersed discharge of relatively long central latency. An L7 dorsal root volley produced no conspicuous discharge of vastus internus motoneurons and had a profound and prolonged inhibitory effect on discharges set up by L6 dorsal root stimulation. The inhibitory action was already present when the conditioning volley arrived at the L6 segment of the cord only 1.0-1.1 msec. before the firing of the tested motoneurons. In contrast an L7 volley produced in the branches to the sartorius a discharge similar to that produced by an L6 volley. The discharge to an L6 volley was facilitated by an L7 volley proceeding at intervals up to ca. 15 msec; at longer intervals the discharge to the L6 volley was inhibited.