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What are the Bones in the Middle Ear?

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  • Written By: Soo Owens
  • Edited By: Susan Barwick
  • Last Modified Date: 08 November 2016
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    Conjecture Corporation
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There are three bones in the middle ear, collectively referred to as the ossicles. The names of the bones come from Latin and are known as the malleus, incus, and stapes. Their purpose is to enhance the overall function of the middle ear, transmitting sound from the outer ear to the inner ear.

The ossicles are of diminutive size, the smallest bones in the human body with the stapes being the tiniest. Their names reflect each bone's distinctive shape and role. Their common names are the hammer, the anvil, and the stirrup, objects each one visibly resembles.

One end of the middle ear is connected to the tympanic membrane, or the eardrum and the other to the opening of the inner ear. This linked setup from the eardrum to the auditory ossicles to the inner ear allows sound waves that enter the outer ear vibrates fluid in the eardrum. This fluid pushes against the bones in the middle ear which then propagate it to the oval window, the membrane covering the entrance to the inner ear and ultimately to the part of the inner ear known as the cochlea.

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The particular arrangement of the three bones in the middle ear acts as a lever to facilitate sound conduction to the inner ear. The movement of the hammer triggers the anvil, and the anvil displaces the stirrup. The hammer adheres to the part of the eardrum that can move in response to sound wave reception. The anvil is the middle piece, attached to the hammer on one end and the stirrup at the end closer to the inner ear. The stirrup is the last link, pushing against fluid in the inner ear for sound perception.

The hammer and the stirrup are connected to two small muscles that initiate the tympanic reflex, also known as the acoustic reflex, which acts as a protective mechanism to prevent damage to the ear from harmful sounds. The stapedius muscle restricts movement of the stirrup, damping vibrations that might be too forceful or high in amplitude. The tensor tympani muscle tenses the ossicles by pulling on the hammer. This action produces an effect similar to that of the stapedius on the stirrup so that vibrations are reduced, preventing loud noises from harming the ear.

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