Nerve
Vestibulocochlear nerve (CN VIII)
Auditory and vestibular connections with the brainstem
High-yield
VIII connects the inner ear with the posterior cranial fossa through the internal acoustic canal; it does not end at the canal. Vestibular schwannoma commonly causes asymmetric sensorineural hearing loss or tinnitus and may affect neighboring nerves as it enlarges, without a fixed sequence of deficits.
Overview
Cochlear and vestibular divisions bring inner-ear information to the brainstem. Bipolar sensory neurons lie in spiral and vestibular ganglia. Their central axons traverse the internal acoustic canal beside VII and labyrinthine vessels, then cross the cerebellopontine angle. Cochlear fibers reach cochlear nuclei; vestibular fibers reach vestibular nuclei and, in part, the cerebellum directly.
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Reference facts
- Origin
- Spiral-ganglion neurons in the cochlea and vestibular-ganglion neurons in the internal acoustic canal. Central targets include cochlear and vestibular nuclei near the pontomedullary region.
- Skull exit
- The internal acoustic canal provides passage between posterior cranial fossa and inner ear; there is no separate extracranial exit.
- Course
- Peripheral processes connect to cochlear hair cells and vestibular maculae/cristae. Central processes reach brainstem nuclei; auditory processing then uses bilateral brainstem relays, inferior colliculus, medial geniculate and auditory cortex. Vestibular connections reach cerebellar, ocular and spinal motor systems.
- Motor
- No skeletal-muscle motor supply. Efferent fibers traveling toward the inner ear, including olivocochlear fibers, modulate sensory processing, so not every accompanying axon is afferent.
- Sensory
- Hearing, with cochlear frequency organization; head tilt and linear acceleration from otolith organs, and rotational acceleration from semicircular ducts. These inputs support stable gaze and posture.
Clinical correlation
In typical asymmetric sensorineural loss, air conduction exceeds bone conduction on Rinne testing and Weber lateralizes to the better ear; conductive loss often reverses those patterns. Profound unilateral sensorineural loss can give a misleading Rinne result. Vestibular neuritis often causes sustained vertigo without hearing loss, but that pattern alone does not exclude a central cause.
Frequently asked questions
Where does the vestibulocochlear nerve (CN VIII) arise?
Spiral-ganglion neurons in the cochlea and vestibular-ganglion neurons in the internal acoustic canal. Central targets include cochlear and vestibular nuclei near the pontomedullary region.
What muscles does the vestibulocochlear nerve (CN VIII) supply?
No skeletal-muscle motor supply. Efferent fibers traveling toward the inner ear, including olivocochlear fibers, modulate sensory processing, so not every accompanying axon is afferent.
What is the sensory distribution of the vestibulocochlear nerve (CN VIII)?
Hearing, with cochlear frequency organization; head tilt and linear acceleration from otolith organs, and rotational acceleration from semicircular ducts. These inputs support stable gaze and posture.
Where does the vestibulocochlear nerve (CN VIII) leave the skull?
The internal acoustic canal provides passage between posterior cranial fossa and inner ear; there is no separate extracranial exit.