The general visceral efferent component of the eighth cranial nerve

Abstract

Study of the brain stem, stato‐acoustic nerve, and inner ear of the mouse by a cholinesterase technique has disclosed that the acetylcholinesterase‐positive centrifugal fibers to the inner ear are part of a general visceral efferent system which supplies fibers to the facial, vestibular and cochlear nerves. This system largely corresponds in its central course to that of the bundle of fibers which has been called “olivocochlear”, but its cells of origin do not appear to lie in the superior olivary complex. Instead, the preganglionic cells of origin are chiefly organized into four nuclei: one medial to the genu of the facial nerve; one lateral to the genu; the superior salivatory nucleus; and a small nucleus lying within the borders of the lateral vestibular nucleus. The fibers to the inner ear synapse, perhaps completely, on postganglionic cells located along their peripheral courses. Additionally, orthosympathetic acetylcholinesterasepositive fibers are present in the cochlear nerve; they arrive via the anterior inferior cerebellar artery. Postganglionic fibers supply not only vascular walls and secretory epithelium in the inner ear but also (1) contact the somata of some acetylcholinesterase‐positive, bipolar cochlear neurons and (2) ramify among, or terminate upon distal, acetylcholinesterase‐positive processes of some sensory neurons at the foramina nervosa. These finding indicate that, on morphological grounds, autonomic nerve activity may influence auditory input at the periphery.