Millions of Americans have disorders of balance they describe as dizziness. What can be difficult for both a patient and his or her doctor is that dizziness is what is called "a subjective term." (That means a word like dizziness can be used by people to describe different sensations they are experiencing, but it is hard for anyone but the person experiencing the symptoms to understand or measure the nature or severity of the sensations.) Another difficulty is that people tend to use different terms to describe the same kind of problem. "Balance problems," "dizziness," "imbalance," and "disorders of balance" are all used interchangeably.
What Is a Balance Disorder?
A balance disorder is a disturbance that causes an individual to feel unsteady, giddy, woozy, or have a sensation of movement, spinning, or floating. An organ in our inner ear, the labyrinth, is an important part of our vestibular (balance) system. The labyrinth interacts with other systems in the body, such as the visual (eyes) and skeletal (bones and joints) systems, to maintain the body's position. These systems, along with the brain and the nervous system, can be the source of balance problems.
Three structures of the labyrinth, the semicircular canals, let us know when we are in a rotary (circular) motion. The semicircular canals, the superior, posterior, and horizontal, are fluid-filled. Motion of the fluid tells us if we are moving. The semicircular canals and the visual and skeletal systems have specific functions that determine an individual's orientation. The vestibule is the region of the inner ear where the semicircular canals converge, close to the cochlea (the hearing organ). The vestibular system works with the visual system to keep objects in focus when the head is moving. Joint and muscle receptors also are important in maintaining balance. The brain receives, interprets, and processes the information from these systems that control our balance.
How Does the Balance System Work?
Movement of fluid in the semicircular canals signals the brain about the direction and speed of rotation of the head--for example, whether we are nodding our head up and down or looking from right to left. Each semicircular canal has a bulbed end, or enlarged portion, that contains hair cells. Rotation of the head causes a flow of fluid, which in turn causes displacement of the top portion of the hair cells that are embedded in the jelly-like cupula. Two other organs that are part of the vestibular system are the utricle and saccule. These are called the otolithic organs and are responsible for detecting linear acceleration, or movement in a straight line. The hair cells of the otolithic organs are blanketed with a jelly-like layer studded with tiny calcium stones called otoconia. When the head is tilted or the body position is changed with respect to gravity, the displacement of the stones causes the hair cells to bend.
The balance system works with the visual and skeletal systems (the muscles and joints and their sensors) to maintain orientation or balance. For example, visual signals are sent to the brain about the body's position in relation to its surroundings. These signals are processed by the brain, and compared to information from the vestibular and the skeletal systems. An example of interaction between the visual and vestibular systems is called the vestibular-ocular reflex. The nystagmus (an involuntary rhythmic eye movement) that occurs when a person is spun around and then suddenly stops is an example of a vestibular-ocular reflex.
(Information provided by the National Institutes of Health)
Page updated 2/11/09