Amazing Facts

Inner ear








The inner ear consists of the cochlea and the semicircular canals. The
cochlea serves to permit hearing

Sound waves
entering the ear set up a chain of vibrations, starting with the
eardrum. The vibrations are then transferred via the middle ear bones
(ossicles) to the cochlea. One of these bones (the stapes) moves up and
down in the oval window causing fluid waves in the cochlea that are
dependent on both the frequency of the sound, and its amplitude
(volume). The response of the hair cells to these waves is dependent on
their location within the cochlea.


The cochlea is designed so the hair cells
right near the oval window
move in response to high frequency sounds while those furthest from the
oval window move in response to low frequency sounds. There is a very
smooth gradient between the two extremes. The brain
is thus able to tell what frequency a sound is by which of the hair
cells in the cochlea are moving and sending out sound signals.


As noted above, the
semicircular canals are necessary for balance.
There are three of these canals that are positioned at right angles to
one another. Like the cochlea, they contain fluid and specialized hair
cells. They are different, however, because they contain small crystals
that move freely in the fluid when the head moves. These crystals brush
against the hair cells to indicate that the head has changed position.
If one spins around and around, the fluid and the crystals continue to
move even after the head has stopped moving. This explains why a person
becomes dizzy and may fall down from too much spinning.



   
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