Balance is an internal sense and relies on sensory receptors that monitor the position of the head and body. Whether we are still or moving, balance is essential for maintaining our posture and stopping us falling over. The vestibule and semicircular canals of the inner ear provide information on the position and movements of the head. Combined with signals from the eyes, this helps us balance.
Turning movements of the head are picked up by sensory hair cells embedded in structures called cupulae in the semicircular canals. Tilting movements of the head, and its position, are monitored by hair cells within structures in the vestibule.
These tiny crystals, called otoliths, are attached to sensory hair cells in the vestibule. When the head tilts, the otoliths move, causing the hair cells to bend and nerve signals to be sent to the brain.