The vestibular nerve is one of the two branches of the

vestibulocochlear nerve The vestibulocochlear nerve or auditory vestibular nerve, also known as the eighth cranial nerve, cranial nerve VIII, or simply CN VIII, is a cranial nerve that transmits sound and equilibrium (balance) information from the inner ear to the br ...

(the

cochlear nerve The cochlear nerve (also auditory nerve or acoustic nerve) is one of two parts of the vestibulocochlear nerve, a cranial nerve present in amniotes, the other part being the vestibular nerve. The cochlear nerve carries auditory sensory information ...

being the other). In humans the vestibular nerve transmits sensory information from vestibular hair cells located in the two otolith organs (the utricle and the saccule) and the three

semicircular canal The semicircular canals are three semicircular interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the lateral, anterior and posterior semicircular canals. They are the part of the bony labyrinth, ...

s via the vestibular ganglion of Scarpa. Information from the otolith organs reflects

gravity In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

and linear accelerations of the head. Information from the semicircular canals reflects rotational movement of the head. Both are necessary for the sensation of body position and gaze stability in relation to a moving environment. Axons of the vestibular nerve synapse in the vestibular nucleus are found on the lateral floor and wall of the

fourth ventricle The fourth ventricle is one of the four connected fluid-filled cavities within the human brain. These cavities, known collectively as the ventricular system, consist of the left and right lateral ventricles, the third ventricle, and the fourth ...

in the

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other mammals, lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of ...

and medulla. It arises from bipolar cells in the vestibular ganglion which is situated in the upper part of the outer end of the internal auditory meatus.

Structure

The peripheral fibers divide into three branches (some sources list two): * the ''superior branch'' passes through the foramina in the area vestibularis superior and ends in the utricle and in the osseous ampullae of the superior and lateral semicircular ducts; * the fibers of the ''inferior branch'' traverse the foramina in the area vestibularis inferior and end in the saccule; * the ''posterior branch'' runs through the foramen singulare and supplies the ampulla of the posterior semicircular duct.

Function

The primary role of the vestibular nerve is to transmit information about balance of the head in relation to the body. The vestibular nerve dynamically updates the frame of reference of motor movement based on the orientation of the head in relation to the body. As an example, when standing upright and facing forward, if you wished to tilt your head to the right you would need to perform a slight leftward motor movement (shifting more of your weight to your left side) to maintain balance. While the head is still in motion, the response magnitude of alteration to motor coordinates is significantly reduced when compared to when the head is fixated in one position.

Clinical significance

Damage

Due to its role in transforming motor coordinates, the vestibular nerve implicitly plays a role in maintaining stable blood pressure during movement, maintaining balance control, spatial memory and spatial navigation. The most common causes of damage to the vestibular nerve are exposure to ototoxic antibiotics, Ménière's disease,

encephalitis Encephalitis is inflammation of the Human brain, brain. The severity can be variable with symptoms including reduction or alteration in consciousness, aphasia, headache, fever, confusion, a stiff neck, and vomiting. Complications may include se ...

and some rare autoimmune disorders. Typically, patients with a damaged nerve suffer from acute attacks of

vertigo Vertigo is a condition in which a person has the sensation that they are moving, or that objects around them are moving, when they are not. Often it feels like a spinning or swaying movement. It may be associated with nausea, vomiting, perspira ...

accompanied by nausea/vomiting, inability to maintain posture and horizontal nystagmus.

Rehabilitation

Rapid compensation to damage of the vestibular nerve occurs within seven to ten days of receiving the damage. A small percentage of patients with damage to the vestibular nerve experience recurrent symptoms. These patients have not been able to undergo vestibular compensation and are left with long-term attacks of vertigo. By administering betahistine to the damaged nerve over a long period of time, the process of vestibular compensation can be accelerated to alleviate symptoms. Patients can also learn strategies to recover their balance through physical therapy.

Additional images

File:Bigotolith.jpg, Illustration of otolith organs

References

External links

Illustration at dizziness-and-balance.com
{{DEFAULTSORT:Vestibular Nerve * Vestibular system