Lab 7 (ƒ6) - Auditory, Vestibular, Gustatory and Olfaction Systems

Central Gustatory Pathway - Medulla

This section shows microscopic slides from the medulla. Figure 1, layer a is more caudal. At this level of the medulla, the solitary tract contains visceral afferent fibers from the glossopharyngeal and vagus nerves and gustatory 1° afferents of the vagus nerve. The solitary nucleus and tract first appear in the lower (closed) medulla near the caudal limit of the inferior olivary complex. They extend the length of the medulla to end in the caudal pons. Only the rostral part of the solitary nucleus is concerned with gustatory information. The more caudal regions of the solitary nucleus are concerned with viscerosensory and visceroafferent pathways.

Figure 1, layer b is more rostral. Some of the rootlets of the glossopharyngeal nerve are 1° afferents which enter the solitary tract to terminate in the solitary nucleus. Those carrying gustatory information innervate taste receptors in the posterior one-third of the tongue. This marks the rostral extent of the solitary nucleus. The axons of the gustatory portion of the solitary nucleus are believed to ascend uncrossed in the central tegmental tract. At this level of the brain stem, the central tegmental tract is a flattened band of fibers located along the posterolateral margin of the inferior olivary complex.