Lab 6 - Auditory, Vestibular, Gustatory and Olfaction Systems

Central Auditory Pathway - The Medulla

This is a section near the pontomedullary junction: the level of entry of the vestibulocochlear nerve. Locate the pyramidal tract, preolivary sulcus, inferior olivary complex, postolivary sulcus, and glossopharyngeal rootlets. In the floor of the fourth ventricle, note that the median eminence has replaced the hypoglossal trigone and that the sulcus limitans separates it from a large sensory area (vestibular in this case).

The ventral trigeminal lemniscus (also known as the ventral trigeminothalamic tract) has not formed a single tract at this point and is distributed medial and superior to the inferior olivary complex and laterally and medially on the posterior part of the central tegmental tract.

Locate the following somatosensory structures: the medial lemniscus, spinothalamic tract, ventral trigeminal lemniscus, and spinal trigeminal nucleus and tract.

The dorsal and ventral cochlear nuclei (also called the cochlear nuclear complex) contain the cell somata of the 2° auditory afferents. They are located along the lateral and posterolateral surfaces of the inferior cerebellar peduncle. The central processes of the 1° afferents (the auditory nerve) terminate in an orderly fashion within these nuclei forming the anatomical basis for the tonotopic organization of the cochlear nuclear complex. The axons of the 2° afferents pass to the superior olivary complex of the lower pons.