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| From Sound Wave to
Hearing |
| Sound plays a very
important part in most people's lives.
It enables us to communicate and receive
information, enjoy the sounds of nature
and listen to music. sound may also
warn us of danger. All sound originates
from movement. When, for example, the
wind blows, it causes the leaves on
trees to move. The leaves push the molecules
in the air, making them vibrate. These
vibrations are called sound waves and
can be perceived by the air.Slow vibrations
(low frequency) are heard as deep tones
(bass), while fast vibrations (high
frequency) are heard as high tones (treble). |
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| The Human Ear |
| The ear is a sophisticated,
sensitive and complex organ, which consists
of three main sections. |
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| The Outer Ear |
| The outer ear is
made up of the external cartilaginous
part of the ear and the ear canal. The
eardrum is located at the end of the
ear canal and forms the boundary of
the middle ear. The outer ear functions
as a kind of satellite dish that picks
up sound waves and conducts them to
the eardrum, causing it to vibrate. |
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| The Middle Ear |
| The middle ear
is an air-filled space that connects
the outer ear canal to the inner ear.
It starts with the Tympanic Membrane
(eardrum) ; it also contains the bones
of the middle ear, and then ends with
the oval window of the cochlea. The
tympanic membrane is a cone shaped layer
of tissue at the end of the ear canal.
Sounds travel down the ear canal and
strike the tympanic membrane causing
it to vibrate. These vibrations are
then transferred to the chain of bones
in the middle ear. The middle ear bones
are the smallest bones in the human
body and are very delicate. Muscles
and ligaments hold this fragile chain
of bones in place and allow them to
vibrate back and forth with sounds.
The first bone in the chain is called
the Malleus (hammer) , the second is
called the Incus (anvil) , and the last
bone is called the Stapes (stirrup)
. The sound vibrations cause the Stapes
to move back and forth. This motion
is thus transferred to the inner ear. |
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| The Inner Ear |
| The inner ear,
or cochlea, is shaped like a snail shell
and filled with fluid. The balance organ
is attached to the cochlear and is made
up of three fluid-filled semicircular
canals. The oval widow connects the
middle ear and the inner ear. The footplate
of the stirrup is attached to the oval
window and functions as a piston moving
the fluid of the inner ear. This movement
of the fluid activates the hair cells
i9n the inner ear (there are about 20,000
of these “sensory cells”).
When the hair cells are activated, they
send impulses via the acoustic nerve
to the brain, which perceives these
impulses as sound. Via these fantastic,
winding ways, the ear is able to pick
up sound waves, transform them to bone
vibrations then to move movements in
fluid and finally to nerve impulses
that can be interpreted by the brain.
Even slightest flaw in this complex
system can compromise hearing ability.
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| Hearing Impairment |
| Millions of people
worldwide are faced with hearing problems
in the form of hearing loss or tinnitus
(ringing or other sounds in the ear)
, but only a minority of them wear hearing
aids. Hearing loss is not just an age-related
problem but affects people of all ages
including, to an increasing extent,
young people. Physiological age-induced
hearing loss is, however, still the
most common type of hearing loss. |
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| Sensorineural Hearing |
Sensorineural hearing
loss is due to:
a problem in the inner ear or cochlea.
The inner ear does not change sound
into the tiny electrical pulses which
the auditory nerve need. The nerve cannot
send sound information to the brain.
A problem in the inner ear can cause
a sensorineural hearing loss.
This can be mild, moderate, severe,
profound or even total hearing loss.
Sensorineural losses are usually permanent.
There is no surgical procedure to cure
problems in this part of the ear; depending
on the cause, medication may be helpful
in some cases. Conventional hearing
aids can usually help in mild to severe
hearing loss. Cochlear implants can
be a very effective option for those
with severe, profound or total hearing
loss, meaning those people who are not
able to gain sufficient speech information
even with the most powerful hearing
aids. |
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| Neural Hearing Loss |
Neural hearing
loss is due to:
a problem in the nerve pathway The auditory
nerve being damaged or missing so that
signals cannot pass to the brain. In
very rare cases hearing loss may be
caused by the absence of or damage to
the auditory nerve, resulting in a neural
hearing loss. Conventional hearing aids
will give little benefit because the
nerve is not able to pass on enough
information to the brain. A cochlear
implant will not help unless there is
some auditory nerve function. |
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| Conductive Hearing
Loss |
Conductive hearing
loss is due to:
a problem in the outer or middle ear
blocking the sound. Making it harder
to hear. Ear drum and bones cannot vibrate.
Any problem in the outer or middle ear
can block sound to the ear and cause
a conductive hearing loss (so called
as it stops the ear from conducting
sound properly). Conductive losses are
usually mild or moderate in nature,
i.e. causing hearing loss of up to about
60 or 70 decibels. Conductive hearing
losses can be temporary in some cases.
In many cases medication or surgery
can help, depending on the cause of
the problem. Hearing loss does not only
mean the inability to hear loudly enough.
Some people may have great difficulty
in hearing within a specific and narrow
frequency region. The may result in
a “discrimination loss”
, whereby one can hear speech but not
understand speech. If not detected and
treated in time, hearing loss in a child
can have a very adverse effect on the
child’s language development and
learning ability. With children as well
as adults, untreated hearing loss can
have broad-reaching effects. Hearing
problems often make it difficult to
“keep up” , which can lead
to a sense of isolation, fatigue and
loneliness. As hearing is often associated
with old age - and frequently interpreted
as a lack of intelligence – it
may affect life at school and work,
as well as social interaction and general
quality of life. It is therefore important
to do something about hearing problems
as soon as possible. |
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| Treating Hearing Loss |
| Conductive hearing
losses can sometimes be helped through
surgical or medical treatment. In most
cases, however, hearing aids are the
only means of helping hearing loss.
This is especially true with sensorineural
hearing losses. There is a wide variety
of hearing aids available today in which
sound reproduction can be tailored to
the user’s own unique hearing
loss and needs. It is important to note
that, while hearing aids may not restore
normal hearing, they can significantly
improve hearing ability in all situations
– allowing for a fuller life in
many ways. For further information on
hearing aids, please click here. |
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