The Vestibular System

Lab 6, Page 19 of 38

The 1° vestibular afferents enter the brain stem, bifurcate and ascend and descend the brain stem to terminate within the four nuclei of the vestibular nuclear complex. This complex consists of the inferior, medial, lateral & superior vestibular nuclei. Their names describe their relative locations in the brain stem. The major outflow from the vestibular nuclei is not to the thalamus: That is, most of the axons of the vestibular nuclei travel to

1. Visceromotor nuclei via the reticular formation
2. The extraocular motor nuclei via the medial longitudinal fasciculus,
3. The cerebellum via the inferior cerebellar peduncle, and
4. The spinal cord via the medial longitudinal fasciculus and lateral vestibulospinal tract.

The 2° afferents ascending to the thalamus appear to travel either with the lateral lemniscus or near the medial longitudinal fasciculus. The 2° afferents end in the ventral posterior inferior nucleus of the thalamus. The VPI axons travel in the posterior limb of the internal capsule to terminate in the inferior parietal lobule, posterior part of the insula near auditory cortex, and central sulcus near the face representation.

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