Vestibular influences on primary afferents in the spinal cord.

Abstract

In the decerebrate cat, repetitive stimulation of the VIII th cranial nerve elicits dorsal root potentials in the lumbar cord at the same threshold frequency responsible for extrafusal contraction of extensor muscles. Excitability measurements indicate that presynaptic depolarization of Group I fibers from both flexor and extensor muscles as well large cutaneous afferents contribute to these dorsal root potentials. These findings suggest that the vestibular system can depress the orthodromic transmission of somatic afferent impulses to spinal motoneurons at presynaptic level just at the time descending vestibular volleys elicit motoneuronal discharge.