Anatomy of the vestibular component

The vestibular component of cranial nerve VIII begins with the peripheral processes of bipolar neurones which synapse with movement transducers in the vestibular and semicircular canals. The processes project centrally to as the vestibular nerve to enter the brainstem at the cerebellopontine angle.

The nerve splits within the medulla to supply four nuclei in the floor of the fourth ventricle: the medial, lateral, inferior and superior vestibular nuclei. Some fibres bypass this area to enter the cerebellum directly via its inferior peduncle; the vestibular nuclei receive input from the cerebellum via the cerebellar cortex and fastigial nucleus.

Fibres from the vestibular nuclei have diffusely-sited targets:

• the oculomotor, trochlear and abducens nuclei via the medial longitudinal fasciculus
• the reticular formation
• the vestibulospinal tract to facilitate extensor tone
• the vestibular area in the postcentral gyrus of the cortex via the thalamus