Vestibular nerve


The vestibular nerve is one of the two branches of the vestibulocochlear nerve. In humans the vestibular nerve transmits sensory information transmitted by vestibular hair cells located in the two otolith organs and the three semicircular canals via the vestibular ganglion of Scarpa. Information from the otolith organs reflects gravity 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 in the pons 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 :
The primary role of the vestibular nerve is to transform vestibular information 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 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 and some rare autoimmune disorders. Typically, patients with a damaged nerve suffer from acute attacks of vertigo 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.

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