Auditory System Vestibular System

The body’s sense of balance and orientation is governed by several systems. One of these is called the vestibular system, whose structures are housed in the inner ear. Both hearing and balance information are transmitted from the inner ear to the brain via the same nerve, the auditory nerve. The vestibular system is constantly sending information to the brain that helps keep the body in balance. It also helps us to know unconsciously where the head is in space.

Vestibular System - Hearing Disorders - Vertigo

Anatomy of the Vestibular System

The vestibular system is housed in the inner ear. The cochlea, the inner ear’s organ of hearing, is connected to three other bony structures called the semicircular canals, which extend from a central chamber called the vestibule. The semicircular canals consist of membranous tubes inside of bony exterior tubes. The utricle and saccule (containing the otoliths) are housed in the vestibule. The vestibule and the semicircular canals are filled with fluid. As in the cochlea for hearing, the movement of this fluid triggers nerve impulses that send information to the brain. The semicircular canals and the otoliths aid the balance system in perceiving motion.

How Does the Vestibular System Work?

The vestibular system helps to send proprioceptive feedback to the brain. Proprioception is the awareness of one’s own body location and movements in space, and contributes to the body’s sense of balance. Vestibular system structures perceive two types of movement:

  • Angular acceleration, or rotational movement
  • Linear acceleration, or motion along a straight line, both up and down and side to side.

Information transmitted from the vestibular structures to the brain also helps the brain to execute necessary motor movements to adjust the body’s position.

Components and Functions of the Vestibular System

The semicircular canals detect rotational movement. The canals are placed at three different angles, corresponding to different directions of movement. Like the cochlea, the semicircular canals contain hair cells that detect movement of the fluid inside the structures. However, whereas the cochlea has hair cells throughout the structure, the hair cells in the canals are located only at the base of the canal. When fluid is displaced by movement in a particular direction, the fluid moves the cilia, triggering nerve impulses that send information about rotational movement to the brain.

The utricle and saccule detect linear acceleration. Together, these are known as the “otolithic organs.” Like the semicircular canals, they also contain a single group of hair cells, which are stimulated when movement of the head causes the fluid inside the structures to move. This stimulation triggers nerve impulses, which send proprioceptive information to the brain. When you are moving laterally for extended periods of time, such as when you are riding on a train, the movement in the utricle and saccule equalize, so that you eventually feel as if you are sitting still. In detecting both rotational and lateral movement, the vestibular sensory system is an important component of the body’s system of balance and equilibrium.

Resources

Hain, T. (2002). Otoliths. Retrieved January 30, 2010, from TCHain.com Web site: http://www.tchain.com/otoneurology/disorders/bppv/otoliths.html.

Martin, F.M.