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Why does loose tensor tympani cause hypoacusis?

  1. Oct 20, 2013 #1
    If the tensor tympany is loose, the ear drum is also loose. But then, the ear drum will vibrate even by weak sound waves, which will cause increased vibration of malleus, incus, and stapes. Isn't that supposed to cause hyperacusis instead?
  2. jcsd
  3. Oct 20, 2013 #2
    The primary purpose of the tensor tympani muscle (TTM) is to damp loud noises and adjust for low frequency sound waves. If it is flaccid, the middle and inner ear is subject to injury. The results of injurious loud noises or acoustic shock (AS) can be either hypoacusis (hearing loss) or hyperacusis. CNS involvement may play a role as to which it is. Clearly, in the absence of protection against loud noises, the tympanic membrane (ear drum or TM) and possibly the middle ear bones and cochlea are subject to injury which can lead to hearing loss.

    As far as I know, the TTM does not significantly impinge on hearing directly, but primarily acts in a protective role. By relaxing, it serves to augment lower frequencies in conjunction with the stapedius muscle. However, this apparent effect is due to the fact that contraction of the TTM primarily decreases acuity in the lower frequencies.


    EDIT: In theory, a loose TTM would result in a flaccid TM resulting in a high frequency hearing loss at least, but that doesn't seem to happen. The TM quickly regains its proper level of tension.

    http://books.google.com/books?id=HS...epage&q=flaccid tensor tympani muscle&f=false
    Last edited: Oct 21, 2013
  4. Oct 24, 2013 #3
    Thank you very much for your answer, and the links. And sorry about the belated reply.
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