How an Ear Works - Balance

Balance function and the inner ear
The human inner ear can be divided into several compartments. Inside of the skull there are several bones that merge into one solid structure. The temporal bone houses the ear. Inside the bone is a fluid filled space referred to as the inner ear. It forms early in life well before birth. The inner ear is smaller than a dime and contains less than three drops of fluid. The fluids are composed of differing salt solutions that create an electrical current. Two major divisions of the inner ear are the cochlea for hearing and the vestibule that provides balance information. (See picture of inner ear) (line draw labyrinth.gif) . The balance half of the inner ear is subdivided into three semicircular canals and in the largest opening (called the vestibule) there are two more segments called the utricle and saccule. The utricle and saccule determine your orientation to gravity. They detect linear accelerations in any direction. When a car starts and stops or when an elevator goes up and down, this is the part of the ear that detects that motion and tells the brain how fast you went. The semicircular canals give information about turning. Getting out of bed or bending and twisting are signaled from this part of the inner ear.

Normally both inner ears are always sending signals back to the brain, even when we are not moving. The brain expects to get equal and accurate information from the inner ear. Information from the inner ear is faster and more direct than any other type of signal. If a disease causes the signal to become greater or less than the other side we experience a conflict in sensory perceptions. The brain will verify information with the eyesight and sensation from all of the joints and the muscles attached to those joints. Conflicts in sensory perceptions may be created by amusement park rides where it is done for fun. Amusement park operators understand how to create brief conflicts.  They will flash lights in the wrong direction and wrong speed to create a conflict between eyesight perceptions of position and speed and the inner ear.  They also make flat turns quickly.  These kinds of turns move one ear more than the other ear and therefore briefly create a difference between the inner ears.  In disease, this can result in incapacitation and disabling vertigo (Vertigo - a perception of abnormal rotation that does not correspond to the physical world) and nausea.

The brain cannot adapt to bad information but it will adapt over a long period of time to no signal. If there is no signal, the brain will come to rely on only the good side.  This is called central adaptation.   It is not as well understood as the inner ear itself.  

Eye movement is in part used to control the movement and focus control of the eye.  When you turn quickly the inner ear signals eye muscle controls where you turned and how far.  This enables those centers to recenter the eye and focus on the target more rapidly.  People who have dizziness may not focus clearly or quickly.