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PRESENTER: Sound waves[br]entering the ear travel

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through the external[br]auditory canal

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before striking the eardrum[br]and causing it to vibrate.

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The eardrum is connected[br]to the malleus,

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one of three small[br]bones of the middle ear,

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also called the hammer.

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It transmits sound vibrations[br]to the incus, which

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passes them to the stapes.

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The stapes pushes in and[br]out against the structure

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called the oval window.

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This action is passed[br]on to the cochlea,

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a fluid-filled,[br]snail-like structure that

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contains the organ of Corti,[br]the organ for hearing.

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It consists of tiny hair[br]cells that line the cochlea.

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These cells translate vibrations[br]into electrical impulses

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that are carried to the[br]brain by sensory nerves.

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In this cut view, you can[br]see the organ of Corti

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with its four rows[br]of hair cells.

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There is an inner[br]row on the left

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and three outer[br]rows on the right.

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Let's watch this[br]process in action.

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First, the stapes rocks[br]against the oval window.

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This transmits waves of sound[br]through the cochlear fluid,

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sending the organ of[br]Corti into motion.

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Fibers near the upper[br]end of the cochlea

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resonate to lower[br]frequency sound.

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Those near the oval window[br]respond to higher frequencies.