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

Central Vestibular Pathway - Medulla (continued)

View and identify the structures in the illustration.

Figure 1, layer a is a section through the open or rostral medulla near the obex. Locate the pyramids, preolivary sulcus, inferior olive, and postolivary sulcus. In the floor of the fourth ventricle locate the sensory (vestibular) area, sulcus limitans, vagal trigone and hypoglossal trigone. Within the medulla tegmentum, locate the medial lemniscus and spinal trigeminal nucleus and tract, and the approximate location of the spinothalamic tract. You may see rootlets of the hypoglossal nerve emerging at the preolivary sulcus and rootlets of the vagal nerve emerging at the postolivary sulcus.

The medial vestibular nucleus forms the sensory area lateral to the sulcus limitans. The inferior vestibular nucleus is wedged between the medial vestibular nucleus and the inferior cerebellar peduncle. These two vestibular nuclei extend from caudal pontine levels through most of the rostral (open) medulla. Fibers from the medial vestibular nucleus join the medial longitudinal fasciculus to ascend to the extraocular motor nuclei and thalamus and to descend into the spinal cord as the medial vestibulospinal tract. Most of the axons of the inferior vestibular nucleus and some from the medial vestibular nucleus travel in the inferior cerebellar peduncle to terminate in the cerebellum.

Figure 1, layer b has the medial vestibular nucleus continuing to form the bulge called the sensory area in the floor of the fourth ventricle. The inferior vestibular nucleus continues to be wedged between the medial vestibular nucleus and the inferior cerebellar peduncle. The inferior cerebellar peduncle is moving posteriorly to enter the cerebellum and, at this level, is covered by the fibers of the middle cerebellar peduncle. Locate the medial longitudinal fasciculus. The axons of the medial vestibular nucleus enter this tract to ascend to the Extraocular motor nuclei and thalamus and to descend to the spinal cord. A large bundle of fibers, the vestibulocochlear nerve (VIII), may be seen entering the brain stem at the cerebellopontine angle.