The vestibular system is the part of the ear that participates in the control and regulation of the equilibrium of the body (balance).
The semicircular canals of the inner (internal) ear are perpendicularly placed and detect changes in the gravitational position of the head (this is another sensorial function of the inner ear, besides auditory perception). When the head rotates the pressure of the fluid within the canals upon the cilia of specific receptor cells varies and these cells generate action potentials transmitted by the vestibulocochlear nerve. The neural impulse is then interpreted by the brain as information about the gravitational position of the head.