Organ of Corti

The Body's Microphone

DiscussionArrangement of hair cellsSingle hair cell
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Organ of Corti

The organ of Corti is the sensitive element in the inner ear and can be thought of as the body's microphone. It is situated on the basilar membrane in one of the three compartments of the Cochlea. It contains four rows of hair cells which protrude from its surface. Above them is the tectoral membrane which can move in response to pressure variations in the fluid- filled tympanic and vestibular canals. There are some 16,000 -20,000 of the hair cells distributed along the basilar membrane which follows the spiral of the cochlea.

The place along the basilar membrane where maximum excitation of the hair cells occurs determines the perception of pitch according to the place theory. The perception of loudness is also connected with this organ.

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Arrangement of Hair Cells

The hair cells of the organ of Corti are arranged in four rows along the length of the basilar membrane. Individual hair cells have multiple strands called stereocilia. There may be 16,000 - 20,000 such cells. The place theory of pitch perception suggests that pitch is determined by the place along this collection at which excitation occurs. The pitch resolution of the ear suggests a collection of hair cells like this associated with each distinguishable pitch.


This is another conception of the arrangement of the outer three rows of hair cells, consistent with the above picture, but showing that a cluster of the cilia is associated with a single hair cell. It is drawn roughly from the work of McGutin. I think that the best that we know about the cilia arrangements comes from electron micrographs like those of Hudspeth.

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McGutin
 
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Single Hair Cell Structure

The sensitive hair cells of the organ of Corti may have about 100 tiny stereocilia which in the resting state are leaning on each other in a conical bundle. In response to the pressure variations in the Cochlea produced by sound, the stereocilia may dance about wildly and send electrical impulses to the brain.


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