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What Are the Three Bones of the Middle Ear?

By Vaishali Mehta ; Updated August 14, 2017

The smallest bones in the human body are the middle ear bones. There are three tiny bones that stretch across the middle ear. They are the malleus, incus and stapes. They're also called ossicles. Only one bone is seen in birds, amphibians and reptiles The function of the ear bones is to help in hearing. They transfer sound from the eardrum to the inner ear.

Function

Sound enters the outer ear. This strikes against the eardrum and makes it vibrate. These vibrations go via the eardrum to the ossicles. Hinges connect the bones. They form a lever system, and the sound is transmitted to the stapes. This pushes like a piston against the membrane in the oval window of the inner ear. Thus, the sound vibrations from the drum are carried to the inner ear. The lever is actually adjustable by the muscles in the middle ear and may actually dampen very loud sounds to protect the inner ear.

Malleus

This is the largest bone in the middle ear. It's attached to the inner side of the eardrum and shaped like a mallet or hammer (the word "malleus" is Latin for "mallet.") This bone transmits the sound from the eardrum to the second bone, called the incus. The malleus can be seen through the eardrum with a special instrument called the otoscope.

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Incus

The sound from malleus is transferred to the incus. This bone is between the malleus and stapes. The incus is shaped like an anvil.

Stapes

This is the smallest bone in the human body. This bone is shaped like a stirrup (the word "stapes" is Latin for "stirrup"). The stapes fits into the oval window of the inner ear. It transmits sound from the incus to the inner ear through the oval window. In a condition called otosclerosis, this bone is immobilized and there are hearing loss and noises in the ear. Your doctor can suggest surgery or a hearing aid to improve hearing.

Damaged Ossicles

Damage to the ossicles may occur by birth defects, due to infections and trauma. There is hearing loss. Babies can be born with fused or absent ossicles. Head injuries or trauma to the eardrum can dislocate the bones. The joint between the incus and stapes is often affected. To treat this, an operation may be required to repair or replace the damaged bone. This reconstruction of the ossicle can be done with an artificial bone or cartilage taken from the ear, according to Baylor College of Medicine reports.

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