The vestibular nerve is one of the two branches of the vestibulocochlear nerve (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 transmitted by vestibular hair cells located in the two

otolith organs An otolith ( grc-gre, ὠτο-, ' ear + , ', a stone), also called statoconium or otoconium or statolith, is a calcium carbonate structure in the saccule or utricle of the inner ear, specifically in the vestibular system of vertebrates. The s ...

(the utricle and the

saccule The saccule is a bed of sensory cells in the inner ear. It translates head movements into neural impulses for the brain to interpret. The saccule detects linear accelerations and head tilts in the vertical plane. When the head moves verticall ...

) and the three

semicircular canal In mathematics (and more specifically geometry), a semicircle is a one-dimensional locus of points that forms half of a circle. The full arc of a semicircle always measures 180° (equivalently, radians, or a half-turn). It has only one line o ...

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

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

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 The vestibular nuclei (VN) are the cranial nuclei for the vestibular nerve located in the brainstem. In Terminologia Anatomica they are grouped in both the pons and the medulla in the brainstem. Structure Path The fibers of the vestibular nerve ...

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 ve ...

in the

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds 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 Va ...

and medulla. It arises from

bipolar cells A bipolar neuron, or bipolar cell, is a type of neuron that has two extensions (one axon and one dendrite). Many bipolar cells are specialized sensory neurons for the transmission of sense. As such, they are part of the sensory pathways for smell, ...

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 transform vestibular information (related to balance) into an egocentric frame of reference based on the position 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 Ménière's disease (MD) is a disease of the inner ear that is characterized by potentially severe and incapacitating episodes of vertigo, tinnitus, hearing loss, and a feeling of fullness in the ear. Typically, only one ear is affected initi ...

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

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

vertigo Vertigo is a condition where a person has the sensation of movement or of surrounding objects moving when they are not. Often it feels like a spinning or swaying movement. This may be associated with nausea, vomiting, sweating, or difficulties w ...

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

nystagmus Nystagmus is a condition of involuntary (or voluntary, in some cases) eye movement. Infants can be born with it but more commonly acquire it in infancy or later in life. In many cases it may result in reduced or limited vision. Due to the invol ...

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