BIOLOGICAL EQUILIBRIUM

Balance in Body System

Equilibrium is the maintenance of the body’s balance. Balance is controlled by three interacting parts of the nerve system; the visual organs, the vestibular apparatus of the ear, and the mid brain. The vestibular system is the most important, but even without it, body orientation in space could still be maintained through information supplied to the brain from visual cues and nerve endings and position of the body.

The vestibular system consists of a membranous labyrinth of delicate structure containing sensory and supporting cells. There are two saclike structures –the utricle and the saccule - and tree semicircular canals. These structures are filled with a specialized fluid. this labyrinth is encased within a larger, bony labrint that also is filled with fluid.

Utricle and Saccule

Two types of sensory hair cells are found in a section of the wall, called a macula, in both the utricle and saccule. Vestibular hair cells, which a contain a single motile hair, the kinocilium, and multiple stereocilia, are embedded in a gelatinous material, called a cupula, that contains a mass of calcium carbonate crystal, called a otolith. An otolith forms a weighted mass above the sensory cells; movements of the mass deflect the sensory hairs and thus trigger neural activity.

The utricle is particularly sensitive to linear acceleration such as vertical or horizontal movement. The saccule’s function is not completely understood.