Cerebellar Control of the Vestibular Pathways to Spinal Motoneurons and Primary Afferents

Abstract

Publisher Summary This chapter shows that stimulation of the fastigial nucleus produces not only contraction of the extensor muscles, but also negative dorsal root potentials (DRPs) in the lumbar cord. These DRPs are because of depolarization of the terminal arborizations of the primary afferents and involve the group Ia pathway from both extensor and flexor muscles and the cutaneous afferents. The fastigial influence on the extensor muscles is mediated via the lateral vestibular nucleus, which is known to exert a facilitatory influence on the extensor motoneurons. On the other hand, the medial vestibular nucleus is in the transmission of the fastigial influence on primary afferents. Stimulation of the vermal cortex of the cerebellar anterior lobe with the same intensities, which inhibit the decerebrate rigidity, may evoke positive DRPs in the lumbar cord. The same stimulation is also able to suppress the depolarization in the group Ia muscle and the cutaneous afferents elicited by stimulation of the VIII nerve. It appears that neurons in the lateral and the medial vestibular nuclei influence the motoneurons and the primary afferents respectively, therefore, it is concluded that the cerebellar inhibitory control of the vestibular reflex path to motoneurons is exerted through the lateral vestibular nucleus, while the cerebellar inhibitory control of the vestibular reflex path to primary afferents is exerted through the medial vestibular nucleus.