The neck, the labyrinth, the cerebellum and posture.

Abstract

Neuronal organizations between the labyrinth, the neck, and vestibulo-cerebellum were investigated in the cat. Disynaptic excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) were recorded in dorsal neck extensor motoneurons in response to stimulation of individual ampullary nerves. Stimulation of the saccular nerve usually evoked IPSPs in contralateral and EPSPs in ipsilateral neck motoneurons. Many potentials probably were trisynaptic. The predominant pattern produced by utricular nerve stimulation consisted of ipsilateral inhibition and contralateral excitation and many potentials were disynaptic. Afferent volleys from the neck joint ascend ipsilaterally in the spinal cord, cross to the contralateral side in the brain stem, and project to the vestibular nuclei interacting with the vestibulo-ocular reflex activity. EPSPs or IPSPs were evoked in abducens motoneurons by stimulation of contralateral or ipsilateral neck joint, respectively. Stimulation of neck afferents causes activity in the flocculus by a climbing fiber (CF) and also by a mossy fiber (MF) route. In the rostral half of the flocculus, field potentials were recorded in response to stimulation of the neck, vestibular and optic nerves. Neck afferents project also to the nodulus. With regard to MF pathways, neck activity arises, at least in part, in joint receptors and the relay is located in Brodal and Pompeiano's group X.