Cochlear Nucleus: Anatomy and Physiology

Abstract

The cochlear nucleus (CN) has traditionally been divided into dorsal and ventral divisions (DCN and VCN), the latter region being further subdivided into anterior and posterior divisions (AVCN and PVCN, respectively) by the entering auditory nerve (AN) root. All AN fibers terminate in CN (Ramon y Cajal 1909; Jones and Casseday 1979a; Lorente de Nó 1933 a, b; Osen 1970; Powell and Cowan 1962)⁸, and each fiber bifurcates after entering the CN, sending an ascending branch to AVCN and a descending branch which traverses PVCN and terminates in DCN. The bifurcation is beautifully illustrated in Ramon y Cajal’s drawing of AN fibers in the dog (Fig. 13A). The classical descriptions of the central projections of AN fibers in the cat were based on Golgi material from kittens (Lorente de Nó 1933a; Ramon y Cajal 1909). Recent studies of the central processes of individual type I ganglion cells intracellularly labeled with HRP in adult cats (Fekete et al. 1984) have confirmed many features of the traditional account, but have also revealed some departures from it. Most notably, the descending branches of a significant proportion (16%) of fibers labeled by Fekete et al. did not project into DCN. These authors, and Lorente de Nó (1981) in his most recent account of the Golgi material, have also described different groups of fibers distinguished by the morphology of the ascending branches.