VIII. Vestibulocochlear nerve

Special somatic afferent. The cochlear division conveys sound from the hair cells of the organ of Corti (spiral ganglion). The vestibular division conveys head acceleration and position from the semicircular canals, utricle and saccule (vestibular ganglion of Scarpa).

Dorsal and ventral cochlear nuclei at the pontomedullary junction (then superior olivary complex, lateral lemniscus, inferior colliculus and medial geniculate nucleus to the auditory cortex, Brodmann areas 41 and 42). Four vestibular nuclei (superior, inferior, medial, lateral) in the floor of the fourth ventricle, with connections to the cerebellum, spinal cord and ocular motor nuclei.

Both parts travel with the facial nerve through the internal acoustic meatus of the petrous temporal bone, cross the cerebellopontine angle cistern and enter the brainstem at the pontomedullary junction, lateral to the facial nerve.

Hearing: whisper or finger-rub test, then Rinne and Weber tuning-fork tests to distinguish conductive from sensorineural loss, with audiometry for confirmation. Vestibular: assess nystagmus, the head impulse test, gait and Romberg test, and the Dix-Hallpike manoeuvre for positional vertigo.

Cochlear lesion: sensorineural hearing loss and tinnitus. Vestibular lesion: vertigo, nystagmus (fast phase away from a peripheral lesion), nausea and imbalance. Because central auditory pathways are bilateral, unilateral central lesions rarely cause marked deafness.

Vestibular schwannoma (acoustic neuroma) arises from the vestibular part at the cerebellopontine angle and presents with progressive unilateral sensorineural hearing loss and tinnitus; larger tumours compress CN VII, CN V and the cerebellum. Ototoxic drugs (aminoglycosides, loop diuretics, cisplatin) and Ménière disease are other causes. Bilateral schwannomas suggest neurofibromatosis type 2.

• Cochlear part: hearing; vestibular part: balance. Enters the brainstem at the cerebellopontine angle.
• Travels with CN VII in the internal acoustic meatus.
• Rinne and Weber tests separate conductive from sensorineural hearing loss.
• Vestibular schwannoma: unilateral sensorineural deafness and tinnitus; later CN V and VII involvement.
• Ototoxic drugs include aminoglycosides, loop diuretics and cisplatin.

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2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
3. Haines DE, Mihailoff GA. Fundamental Neuroscience for Basic and Clinical Applications. Elsevier, 5th edition (2018) — Tier 3 (textbook)
4. Kandel ER, Koester JD, Mack SH, Siegelbaum SA. Principles of Neural Science. McGraw-Hill, 6th edition (2021) — Tier 3 (textbook)

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