Brad Ingrao Articles

The Middle Ear

You'll recall from the October column, the external ear canal collects

sound. The border of the outer and middle ear is the eardrum (A), or

tympanic membrane. This very thin structure vibrates in response to

sounds traveling down the ear canal. The eardrum also has a resonance and

further amplifies the speech sounds. Like the ear canal, the eardrum acts to

protect the middle ear from foreign bodies and bacteria. For the eardrum to

work properly, it must vibrate freely. Even minor changes in air pressure can

limit the eardrum's movement enough to affect hearing temporarily.

Attached to the inside of the eardrum are three tiny bones called the

Ossicles. These are commonly know as the hammer (B), anvil (C) and

stirrup (D). Like the ear canal and eardrum, the Ossicles resonate, further

enhancing the sounds of speech. The third bone, the stapes, vibrates in

the oval window and passes the airborne sound vibrations into the fluid of

the inner ear, known as the cochlea

A tube at the bottom of the middle ear space, called the Eustachian

tube (E) connects to the back of the nose to control the air pressure of the

middle ear. Swollen tonsils or adenoids are common causes of Eustachian

tube blockage. If left untreated, a blocked Eustachian tube can lead to a

buildup of fluid in the middle ear space. While this fluid may become

infected, it is usually sterile. Even after an ear infection has cleared, the

fluid may persist, causing a temporary hearing loss.

Brad Ingrao is the audiologist with Tobias & Battite, Inc. Hearing

Healthcare Centers of Boston

www.tobias-battite.com