Maintenance of Balance

The human balance system is made up of four parts, the eye, inner ear, muscles and central nervous system. The brain acts as a central computer receiving information in the form of nerve impulses (messages) from its three input terminals: the eyes, the inner ear, and the muscles and joints of the body. There is a constant stream of impulses arriving at the brain from these input terminals. All three systems work independently and yet work together to keep the body in balance.

The eyes receive visual clues from light receptors that give the brain information as to the position of the body relative to its surroundings. The receptors in the muscles and joints are called proprioceptors. The most important ones are in the head and neck (head position relative to the rest of the body) and the ankles and joints (body sway relative to the ground).

The inner ear balance mechanism has two main parts: three semicircular canals and the vestibule. Together they are called the vestibular labyrinth and are filled with fluid. When the head moves, fluid within the labyrinth moves and stimulates nerve endings that send impulses along the balance nerve to the brain. Those impulses are sent to the brain in equal amounts from both the right and left inner ear. Nerve impulses may be started by the semicircular canals when turning suddenly, or the impulses may come from the vestibule, which responds to changes of position, such as lying down, turning over or getting out of bed.

When the inner ear is not functioning correctly the brain receives nerve impulses that are no longer equal, causing it to perceive this information as distorted or off balance. The brain sends messages to the eyes, causing them to move back and forth, making the surroundings appear to spin. It is this eye movement (called nystagmus) that creates a sensation of things spinning.

Remember to think of the brain as a computer with three input terminals feeding it constant up-to-date information from the eye, inner ear and muscles and joints (proprioceptors). The brain itself is divided into several different parts. The most primitive area is known as the brainstem, and it is here that processing of the input from the three sensory terminals occurs. The brainstem is affected by two other parts of the brain, the cerebral cortex and the cerebellum.

The cerebral cortex is where past information and memories are stored. The cerebellum, on the other hand, provides automatic (involuntary) information from activities, which have been repeated often.

The brainstem receives all these nerve impulses: sensory from the eyes, inner ear, muscles and joints; regulatory from the cerebellum; and voluntary from the cerebral cortex. The information is then processed and fed back to the muscles of the body to help maintain a sense of balance.

Because the cortex, cerebellum and brainstem can eventually become used to (ignore) abnormal or unequal impulses from the inner ear, exercise may be helpful. Exercise often helps the brain to habituate the dizziness problem so that is does not respond in an abnormal way and does not result in the individual feeling dizzy. An example of habituation is seen with the ice skaters who twirl around, stop suddenly, and do not apparently have any balance disturbance.