Anatomy of the Two Vestibulo-oculomotor Projection Systems

Abstract

Publisher Summary Two separate, direct, and somatotopically organized vestibulo-oculoniotor fiber projection systems have been demonstrated in this chapter. One of these arises in the superior vestibular nucleus and ascends in lateral portions of the ipsilateral medial longitudinal fasciculus (MLF). The other arises in rostral portions of the medial vestibular nucleus and ascends in medial portions of the contralateral MLF. The sites of origin of these vestibulo-oculomotor projection systems are the regions where primary vestibular afferents from the ganglia of the semicircular canals have previously been shown to project. The two vestibulo-oculomotor fiber projection systems each have extensive bilateral projections among the extraocular motoneurons, and are widely distributed among motoneurons of both synergistic and antagonistic muscles. Evidence for functional differences in the projection systems from the superior and medial vestibular nuclei in relation to excitation and inhibition of extraocular muscle motoneurons is discussed. The complex and delicate balance of influences necessary in the fine coordination of head and extraocular movements must depend on such highly organized pathways.