The eyes, the joints and muscles and the vestibular organs in the inner ears control a body's balance by sending nerve signals to the brain. Dysfunction in any one of these systems can result in loss of balance.
Light-sensitive nerve endings, or sensory receptors, in the retina send nerve impulses to the brain. These visual sensory signals are used by the brain to help maintain balance.
Sensory input provided by muscles and joints, the sense of proprioception, is received by the brain. The muscles and joints are surrounded by sensory receptors sensitive to pressure or stretch, and these sensory impulses tell the brain what the body is doing at any instant. The impulses that come from the neck, which indicate the head's direction, and the impulses that come from the ankles, which determine the body's movement or sway, are the most important.
The complex series of passageways and chambers within the bony skull of the inner ear are called the vestibular system. These chambers are filled with and surrounded by fluid. Identical yet independent systems are located in both ears. Each inner ear has a hearing component called the cochlea and a balance component called the vestibular apparatus, consisting of otolith organs and three semicircular canals. There is also a sensory receptor that reacts to head movement. When the head alters direction, there is fluid lag, causing the sensory receptor to bend. This creates an impulse that tells the brain about movement. When these vestibular apparatus function properly, symmetrical impulses are sent to the brain. So, the impulses coming from the right side agree with the impulses coming from the left side and a person remains balanced. When impulses disagree, or are asymmetrical, an individual can lose balance and become dizzy.