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Background about middle ear muscles from Encyclopædia Britannica
Two minuscule muscles are located in the middle ear. The longer muscle, called the tensor tympani, emerges from a bony canal just above the opening of the eustachian tube and runs backward then outward as it changes direction in passing over a pulleylike projection of bone. The tendon of this muscle is attached to the upper part of the handle of the malleus. When contracted, the tensor tympani tends to pull the malleus inward and thus maintains or increases the tension of the tympanic membrane. The shorter, stouter muscle, called the stapedius, arises from the back wall of the middle-ear cavity and extends forward and attaches to the neck of the head of the stapes. Its reflex contractions tend to tip the stapes backward, as if to pull it out of the oval window. Thus it selectively reduces the intensity of sounds entering the inner ear, especially those of lower frequency.
Another piece of information
There are two small muscles in the middle
ear: the tensor tympani and the stapedius muscles. The former pulls the manubrium of the malleus inward, while the latter is attached to the stapes and pulls the stapes in a direction that is perpendicular to its pistonlike motion. The stapedius muscle is the smallest striated muscle in the body, and it contracts in response to an intense sound (of about 85 dB above the threshold of hearing). This is known as the acoustic middle-ear reflex. The muscle's contraction reduces sound transmission through the middle
ear and thus acts as a regulator of input to the cochlea. Perhaps a more important function of the stapedius muscle is that it contracts immediately before and during a person's own vocalization, reducing the sensitivity of the speaker's ears to his or her own voice and possibly reducing the masking effect of an individual's own voice. The role of the tensor tympani muscle is less well understood, but it is thought that contraction of the tensor tympani muscle facilitates proper ventilation of the middle-ear cavity. |
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