Superior Olivary Complex: Anatomy and Physiology

Abstract

In all mammals, the superior olivary complex (SOC) comprises a number of closely grouped nuclei in the lateral part of the ventral pons (see Fig. 1). The three most distinctive nuclei in the cat are commonly designated the lateral superior olivary nucleus (LSO), the medial superior olivary nucleus (MSO), and the medial nucleus of the trapezoid body (MNTB; see Figs. 1 and 23). These major nuclei are clearly defined in the drawing of the afferent axonal plexus in SOC by Ramon y Cajal (1909) (Fig. 22 A), by whom they were termed the superior olive, the accessory superior olive, and the nucleus of the trapezoid body, respectively. Surrounding the major nuclei are a number of smaller and less clearly defined aggregations of cells which have been given a variety of names. Ventral to MNTB and LSO, respectively, are situated what Ramon y Cajal (1909) termed the internal and external preolivary nuclei (Fig. 22A). They are now more commonly known either as the medial and lateral preolivary nuclei, or as the ventral and lateral nuclei of the trapezoid body (VNTB and LNTB; Fig. 1; Morest 1968 a, 1973). The latter terms will be used here as they more accurately describe the location of the nuclei and have the further advantage of avoiding confusion with the terms used to describe the final group of SOC neurons. These consist of scattered groups of neurons at the margins of the SOC (corresponding in part to Ramon y Cajal’s retro-olivary region), which together comprise the periolivary region.