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Mariko Misono

Balance and equilibrium help us stay upright when standing and know where we are in relation to gravity. Our balance system also helps us walk, run, and move without falling. Balance is controlled through signals to the brain from your eyes, the inner ear, and the sensory systems of the body (such as the skin, muscles, and joints). This balance system is also known as the vestibular system.

In the inner ear, the balance system consists of three semicircular canals that contain fluid and “sensors” that detect rotational movement of the head. Each of the semicircular canals lies at a different angle and is situated at a right angle to each other. The semicircular canals deal with different movement: up-and-down, side-to-side, and tilting from one side to the other. All contain sensory hair cells that are activated by movement of inner ear fluid (endolymph). As the head moves, hair cells in the semicircular canals send nerve impulses to the brain by way of the acoustic nerve. The nerve impulses are processed in the brain to help us know where we are in space or if we are moving.

Located near the semicircular canals are the utricle and the saccule. The ends of the semicircular canals connect with the utricle, and the utricle connects with the saccule. The semicircular canals provide information about movement of the head. The sensory hair cells of the utricle and saccule provide information to the brain about head position when it is not moving. The utricle is sensitive to change in horizontal movement. The saccule is sensitive to the change in vertical acceleration (such as going up in an elevator).