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Ossicles

Timothy C. Hain, MD Page last modified: May 6, 2017

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The ossicles are tiny bones in the middle ear, that form a chain connecting the ear drum (Tympanic membrane, TM) and the inner ear. When airborne sound vibrates the TM, the ossicles perform an "impedance match" allowing sound energy to be transferred into the fluid filled inner ear, rather than just bouncing off.

Stapedius and Tensor Tympani Muscles
Cartoon of the middle ear showing muscles that attach to ossicles (ear bones), and ear drum. The stapedius is attached to the stapes (of course -- horseshoe object above), while the tensor tympani is attached to the ear drum. While useful, be aware that there are multiple errors in this illustration from Loyola Medical School. With permission, from: http://www.meddean.luc.edu/lumen/meded/grossanatomy/dissector/mml/images/stap.jpg Image showing middle ear and tensor tympani from Gray's anatomy http://upload.wikimedia.org/wikipedia/commons/2/24/Musculustensortympani.png

There are 3 ossicles -- the malleus, incus and stapes. There are two muscles that attach to the ossicles -- the tensor tympani, and the stapedius. These muscles work (without much effect) to tighten up the ossicular chain to reduce the impact of loud noise. These muscles can be a source of tinnitus.

The cavity that contains the ossicles (middle ear) is connected to the throat through the Eustachian tube, and to the mastoid sinus.

When the ossicles are broken, missing, or otherwise not functional, hearing can be reduced by a large amount for "air" conduction, but hearing through the bone is unaffected. This type of hearing loss is called a "conductive" hearing loss. As a general rule, conductive hearing loss can be surgically fixed, as the ossicles can be replaced with a prosthesis. In addition, bone-conduction type hearing devices can bypass the middle ear and also "fix" a conductive hearing loss, although these require some sort of device to be attached to the head.

Disorders of the ossicles include

As a general rule, ossicular problems are not associated with dizziness, but rather are associated with hearing loss or tinnitus.

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Copyright May 6, 2017 , Timothy C. Hain, M.D. All rights reserved. Last saved on May 6, 2017