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Learn About
Hearing... |
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The ear is an advanced and very sensitive
organ of the human body. The major task of the ear is to
detect and analyse noises by transduction. |
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Another very important function is to
maintain the sense of balance. |
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The ear is divided into three different
parts: |
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*The
outer ear |
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*The middle ear |
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*The inner ear |
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1-
The Outer Ear: |
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The only visible part of the ear is
the pinna (the auricle) which - with its special helical
shape - is the first part of the ear that reacts with
sound. The pinna acts as a kind of funnel which assists in
directing the sound further into the ear. |
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Without this funnel the sound waves would
take a more direct route into the auditory canal. This would
be both difficult and wasteful as much of the sound would be
lost making it harder to hear and understand the sounds. |
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Once the sound waves have passed the
pinna, they move two to three centimeters into the auditory
canal before hitting the eardrum. |
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2- The Middle
Ear: |
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The eardrum (tympanic membrane), which
marks the beginning of the middle ear, is extremely
sensitive. In order to protect the eardrum, the auditory
canal is slightly curved making it more difficult for
insects, for example, to reach the eardrum. At the same
time, earwax (cerumen) in the auditory canal also helps to
keep unwanted materials like dirt, dust and insects out of
the ear. |
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In addition to protecting the eardrum, the
auditory canal also functions as a natural hearing aid which
automatically amplifies low and less penetrating sounds of the
human voice. In this way the ear compensates for some of the
weaknesses of the human voice, and makes it easier to hear and
understand ordinary conversation. |
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3- The Inner
Ear: |
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Once the vibrations of the eardrum
have been transmitted to the oval window, the sound waves
continue their journey into the inner ear. The inner ear
is a maze of tubes and passages, referred to as the
labyrinth. In the labyrinth can be found the vestibular
and the cochlea. |
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The cochlea
In the cochlea, sound waves are transformed into electrical
impulses which are sent on to the brain. The brain then
translates the impulses into sounds that we know and
understand.
The cochlea resembles a snail shell or a wound-up hose. The
cochlea is filled with a fluid called perilymph and contains
two closely positioned membranes. These membranes form a type
of partition wall in the cochlea. However, in order for the
fluid to move freely in the cochlea from one side of the
partition wall to the other, the wall has a little hole in it
(the helicotrema). This hole is necessary, in ensuring that
the vibrations from the oval window are transmitted to all the
fluid in the cochlea.
When the fluid moves inside the cochlea, thousands of
microscopic hair fibres inside the partition wall are put into
motion. There are approximately 24,000 of these hair fibres,
arranged in four long rows.
The hair fibres are all connected to the auditory nerve and,
depending on the nature of the movements in the cochlear
fluid, different hair fibres are put into motion. When the
hair fibres move they send electrical signals to the auditory
nerve which is connected to the auditory centre of the brain.
In the brain the electrical impulses are translated into
sounds which we recognise and understand. As a consequence,
these hair fibres are essential to our hearing ability. Should
these hair fibres become damaged, then our hearing ability
will deteriorate.
The vestibular
Another important part of the inner ear is the organ of
equilibrium, the vestibular. The vestibular registers the
body's movements, thus ensuring that we can keep our balance.
The vestibular consists of three ring-shaped passages,
oriented in three different planes. All three passages are
filled with fluid that moves in accordance with the body's
movements. In addition to the fluid, these passages also
contain thousands of hair fibres which react to the movement
of the fluid sending little impulses to the brain. The brain
then decodes these impulses which are used to help the body
keep its balance.
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