The vestibular nuclei are structures in the brains of mammals that are part of the vestibular system, which provides the organism with its sense of balance and awareness of the body's orientation in space. They are associated with the vestibular nerve, which carries sensory data from the ear canals. These structures are located in the brainstem, an area in the lower rear part of the brain connected to the spinal cord.
There are four vestibular nuclei in total, and they are located in the fourth ventricle, a cavity in the brainstem filled with cerebrospinal fluid. Three of them, the inferior vestibular nucleus, lateral vestibular nucleus, and medial vestibular nucleus, are in the medulla oblongata, the lowest part of the brainstem. The fourth, the superior vestibular nucleus, is in a structure immediately above the the medulla oblongata called the pons. They are joined to the vestibular system by the vestibular nerve, a branch of the larger vestibulocochlear nerve that carries signals from the ears to the brain.
The vestibular system is located in the inner ear, and is made up of two parts, the otoliths and the semicircular canals. The semicircular canals are small fluid-filled passages lined with extremely sensitive hair cells, similar to the ones used to detect sound. These structures can sense the movement of fluid in the semicircular canals caused by rotational motion when the head's orientation changes.
The otoliths contain small, dense crystals that lie in a less dense gel. When the organism's body is subjected to a linear acceleration, the crystals become slightly displaced, which hair cells in the otoliths detect. This information then travels from the inner ear along the vestibular nerves to the vestibular nuclei.
This sensory data helps the organism to track its own position and movements in three-dimensional space. It is why, for example, it is possible for people riding in a car or elevator to sense when it is in motion even when they cannot see anything outside. It also coordinates with the organism's sense of sight to provide context to help interpret visual data, for instance, determining whether the movement of objects in the organism's visual field is the result of the objects moving, the organism itself moving, or the organism's head shifting orientation while it stands in place.
The functioning of the vestibular nuclei is essential to an organism's ability to maintain it's balance and stay up while standing or walking. Consequently, damage to it causes vertigo, nausea, and problems with motor control due to the brain's diminished ability to track the body's position and motion. The vestibular nuclei are also important to vision, since information from the vestibular system that tells the brain when the orientation of the head has changed allows the eyes to quickly move to compensate so that they remain focused on the object they were looking at.