vestibulocochlear

The vestibulocochlear nerve, also known as cranial nerve VIII, is a purely sensory nerve that carries information related to hearing and balance. It consists of two functionally independent divisions: the cochlear nerve, which transmits auditory information from the cochlea to the brain, and the vestibular nerve, which conveys information about head position and movement from the vestibular apparatus.

Anatomy and connections: The cell bodies for the cochlear fibers reside in the spiral ganglion, while the vestibular fibers originate in Scarpa’s (vestibular) ganglion. The fibers join to form the vestibulocochlear nerve, exit the brainstem at the pontomedullary junction, and pass through the internal acoustic meatus, accompanying the facial nerve and the labyrinthine artery. Cochlear afferents project to the cochlear nuclei in the caudal pons and rostral medulla; vestibular afferents project to the vestibular nuclei.

Pathways and functions: Auditory information proceeds from the cochlear nuclei through central auditory pathways to the inferior colliculus, then to the medial geniculate body, and finally to the auditory cortex. Vestibular information reaches the vestibular nuclei, with connections to the cerebellum, the oculomotor system (via the vestibulo-ocular reflex), and the spinal cord (via the vestibulospinal tracts). The nerve supports hearing, balance, spatial orientation, and reflexes that stabilize vision and posture.

Clinical relevance: Lesions can cause sensorineural hearing loss, vertigo, and imbalance on the affected side. Vestibular schwannoma (acoustic neuroma) is a common tumor arising from this nerve. Evaluation relies on audiometry, vestibular testing, and magnetic resonance imaging with contrast.