The balance organ (labyrinth) is an integral part of the inner ear and consists of a series of very small fluid-filled soft tissue tubes connected to a main cavity (vestibule) and embedded in very hard bone. The 3 semi-circular canals lie at right angles to each other and detect angular acceleration such as rotation of the head. Each canal contains hair cells which are embedded in a jelly-like substance in the cupola. Angular motion moves the fluid and cupola bending the cilia hairs and stimulating the hair cell, resulting in the propogation of an electrical discharge in the vestibular nerves. Inside the vestibule the hair cells of the utricle and saccule are embedded in a dense calcium membrane (otolithic membrane). The utricle detects acceleration in a straight line either forwards and backwards and the saccule up and down motion, such as gravity.
Two vestibular nerves convey information as electrical nerve impulses from each balance organ to the balance centre in the brain. The brain balance centre acts like a complex computer server. It is connected to a wide range of other body systems which are also essential for normal orientation and balance. These include the eyes and cerebellum, whilst nerve connections in the spinal cord link to various types of sensory and pressure receptors in the muscles of the neck, trunk, legs and feet. Automatic vestibular reflexes help maintain posture and muscle tone, and also contribute to eye stability and equilibrium when a person is moving.