Vestibulocochlear Nerve

What is the vestibulocochlear nerve?

Your vestibulocochlear nerve is a two-part structure that sends sensory information from your inner ear to your brain. Nerves are like cables that carry information (in the form of electrical impulses or signals) between your organs and brain to coordinate body functions.

Your vestibulocochlear nerve transports information from organs in your inner ear that help you hear and maintain your sense of balance.

The vestibulocochlear nerve is one of 12 cranial nerves that help with processes that allow you to use senses (like hearing, smell, taste and touch) and make facial expressions. It’s the eighth cranial nerve, which is involved in hearing and balance, specifically. Other names for the vestibulocochlear nerve include:

• Auditory vestibular nerve.
• Cranial nerve VIII (CN VIII).

What is the function of the vestibulocochlear nerve?

The name “vestibulo-cochlear” provides clues about the two parts of CN VIII, including how they function in your body:

• The vestibular nerve (the “vestibulo” part) sends information from your vestibular system organs to your brain. The vestibular organs detect information about your head position and movement. Your brain uses this information to help you maintain your sense of balance.
• The cochlear nerve (the “cochlear” part) sends sound information from your cochlea (the spiral-shaped structure and innermost part of your hearing system) to your brain. Your brain uses this information to help you hear.

These two nerves join to form a single nerve — CN VIII. But each maintains its separate role as messenger for either your balance or hearing system.

Vestibular nerve

Your vestibular nerve carries information from your vestibular system organs to your brainstem. Your vestibular organs include two otolith organs (utricle and saccule) and three semicircular canals. All five organs are filled with fluid lined with sensory cells that shift in response to head movements.

Here’s how your vestibular nerve works within your vestibular system:

• The signal activates. When your head moves, fluid inside your vestibular organs shift, moving the sensory cells inside. The shift creates a signal about your body’s position and movement.
• Nerve cells carry the signal along the vestibular nerve. The nerve cells (neurons) carry the signal until the message arrives at a structure called the vestibular nuclei complex in your brainstem. The complex contains four nuclei. Each nucleus (singular “nuclei”) in your brain is responsible for directing the signal to various parts of your body so you can maintain your balance.
• Your brain processes balance information. Some nuclei send sensory signals about your body’s position to parts of your brain, like your cerebral cortex and cerebellum. Other nuclei send sensory signals to your neck or legs to help you adjust your position. Some nuclei send sensory signals to your eye muscles to help them remain focused even when your body’s in motion. This is called the vestibulo-ocular reflex (VOR).

Cochlear nerve

Your cochlear (auditory) nerve carries information from your cochlea to your brainstem. Like your vestibular system organs, your cochlea is fluid-filled and lined with sensory hair cells. The fluid and cells shift in response to sound waves.

Here’s how your cochlear nerve works within your hearing system:

• The signal activates. When sound waves reach your cochlea, they vibrate a membrane inside called the Basilar membrane. The vibrations cause sensory hair cells on the membrane to shift. The shifting creates a signal about the sound quality. This includes the frequency of the sound waves (how high or low the pitch is) and loudness.
• Nerve cells carry the signal along the auditory nerve. The neurons carry the signal until the message arrives at the cochlear nuclei in your brainstem. The cochlear nuclei have three divisions. Each division receives different types of information about the sound. For example, some receive information about lower sounds (low frequencies). Others receive information about higher sounds (high frequencies).
• Your brain processes sound information. The cochlear nuclei send sensory signals about the sound to the auditory cortex in your temporal lobe. This is the part of your brain that processes sound information.

Where is the vestibulocochlear nerve located?

The vestibulocochlear nerve passes through a bony passage called the internal auditory canal (IAC). This passage connects your inner ear to the lower part of your skull:

• The vestibular nerve extends from a collection of nerves called the vestibular (Scarpa’s) ganglion, located near the vestibular organs. It joins with the cochlear nerve inside the IAC to form CN VIII. The vestibular nerve separates from the cochlear nerve once it reaches the vestibular nuclei complex in your brainstem.
• The cochlear nerve extends from a collection of nerves called the spiral ganglion, near the cochlea. It joins with the vestibular nerve inside the IAC to form CN VIII. It separates from the vestibular nerve once it reaches its corresponding nuclei in your brainstem.

What is the vestibulocochlear nerve made of?

The vestibulocochlear nerve consists entirely of afferent, or sensory, neurons. This means that their only purpose is to carry signals that help the brain process information based on your senses, like your hearing and perception of your body’s position.

What are the common conditions that may affect your vestibulocochlear nerve?

Conditions that may damage your vestibulocochlear nerve include:

• Injuries, especially to the parts of your skull that house your inner ear.
• Congenital conditions that cause CN VIII to develop incorrectly.
• Tumors, including benign (noncancerous) growths like acoustic neuromas.
• Infections, like vestibular neuritis or labyrinthitis.

Common signs or symptoms of an issue

When your vestibulocochlear nerve is damaged, you may experience symptoms that impact your hearing and ability to maintain your sense of balance. Symptoms include:

• Sensorineural (inner ear) hearing loss.
• Tinnitus (ringing in your ears).
• Dizziness (feeling woozy or off-balance).
• Vertigo (feeling as if you’re spinning when you’re not).
• Nystagmus (rapid, uncontrollable eye movements).

Common tests to check CN VIII

Tests to check the health of your vestibulocochlear nerve include:

• Hearing tests: You may need hearing tests that check for hearing loss involving your inner ear. Examples include Rinne’s test and Weber’s test. During these tests, a healthcare provider positions a vibrating tuning fork at various locations near your skull and ear to check whether you can hear the sound.
• Vestibular tests: You may need tests to check the health of your vestibular system. Tests that check your eye movements for nystagmus are especially useful for identifying issues with cranial nerve VIII.
• Imaging tests: CT scans (computed tomography scans) or MRIs (magnetic resonance imaging) can reveal unusual growths in your ear. An MRI can show signs of an injury to your vestibulocochlear nerve, like bleeding within your inner ear.

How do you treat vestibulocochlear nerve conditions?

Treatments may include:

• Medications: Most infections that affect your vestibulocochlear nerve are viral and get better on their own. But sometimes, your provider may prescribe antivirals to help you get better faster. They may prescribe corticosteroids to ease inflammation in CN VIII.
• Surgery: You may need surgery to remove acoustic neuromas that are causing problems with your hearing or balance. If you’re not a candidate for surgery, your healthcare provider may use stereotactic radiotherapy to shrink tumors.
• Vestibular rehabilitation therapy: You may need to learn exercises that can help you improve your balance if you’re experiencing long-lasting issues with your vestibular system. The type of therapy you need depends on the type of condition that’s causing problems with your vestibulocochlear nerve.

How can I keep my vestibulocochlear nerve healthy?

You can’t always prevent conditions that may damage your vestibulocochlear nerve, like injuries or growths. But you can take steps to protect your inner ear.

For example, you can be mindful about protecting your ears from loud sounds that can damage the sensitive sensory hair cells inside. You can see your healthcare provider at the first sign of a problem like an infection. Caring for your inner ear helps your balance and hearing systems in general. It provides a clearer originating message for your vestibulocochlear nerve to carry to your brain.