VENTRAL ROOT DISCHARGE IN RESPONSE TO VESTIBULAR AND PROPRIOCEPTIVE STIMULATION

Abstract

A method was used for microdissection of certain peripheral afferent nerve branches from the vestibular organ. Responses to electrical stimulation of these nerves were recorded either from thin filaments isolated from lower ventral roots or from single cells in the ventral pool. The descending stream of impulses occurring in response to vestibular stimulation will have an effect upon the ventral horn cells which is either excitory or inhibitory or excitatory and inhibitory in parallel. Differences between the activity of alpha fibers and gamma fibers in reponse to vestibular stimulation are described. The small gamma efferents were activated at low strength while a somewhat stronger shock also elicited large spikes in alpha fibers. The gamma fibers showed a higher output frequency during vestibular stimulation than the alpha fibers. Results obtained indicate that the discharge in the gamma fibers is not controlled by an inhibitory feed-back mechanism of their own as are impulses in the alpha fibers. In studying the effect of the proprioceptive impulses upon the efferent discharge elicited by vestibular stimulation, it became obvious how strongly and dominatingly it is under proprioceptive control. The effect of the inhibitory impulses from the Golgi tendon organs will dominate when strong muscular contractions are induced. The vestibular response, however strong it may be, will be inhibited. A complete redistribution of the activity in the fibers of a filament could thus be noted.