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Treatment of Hearing
Cochlear Implants
The cochlear implant is a device that uses special technology
to help deaf people hear. In order for you to understand what
a cochlear implant does, it helps to discuss how the normal
ear works. Hearing occurs through a series of events:
1. Sounds
waves enter into the ear canal.
2. The
sound waves hit the eardrum and set it into vibration.
3. The
vibration sets the three tiny bones in the middle ear into motion.
4. The
bones then pass the vibration to the fluids in the cochlea (inner
ear).
5. The
fluids move the tiny hairs on the sensory cells (hair cells)
in the cochlea.
6. The
movements of the hair cells, which are connected with the auditory/hearing
nerve, send electrical impulses along the nerve.
7. The
hearing nerve carries the message to the brain.
8. The
brain interprets the message as sound.
For patients with some kinds of hearing loss, the sensory
hair cells no longer send the electrical impulses along the
hearing nerve. The cells may have been absent or malfunctioning
from birth, or they may have been damaged by an illness, medication,
or noise. In some cases even the most powerful hearing aids
may not help enough and the patient will benefit more with
a cochlear implant.
A cochlear implant bypasses the sensory hair cells in the
cochlea to activate the hearing nerve directly. Because of
the direct stimulation to the nerve, people with profound
hearing impairment may be able to experience hearing sensations
that they could not hear with a hearing aid. Even though
the sound will not be like that for normal hearing individuals,
cochlear implant patients may communicate much better than
they could with little or no sound at all. In adults, the
stimulation provided by a cochlear implant helps them to hear
and identify environmental sounds as well as improves the
recognition of speech with lip-reading. Clearly, the results
differ from patient to patient, and it is important to understand
that a cochlear implant does not restore an individual’s hearing
to normal levels. Unfortunately, it is difficult to predict
how much speech understanding any one individual will receive.
The cochlear implant cannot help all people with a severe
to profound hearing loss and will help some patients more
than others. The full benefit of the cochlear implant is
not seen overnight—it does take time, training, and experience.
Factors that influence success with an implant:
1. Extent
of hearing impairment
2. Duration
of deafness
3. Cause
of deafness
4. Method
of communication
5. Appropriate
expectations
Dr. Thedinger places the implanted parts into the cochlea and
under the skin behind the ear. Once the area has healed and
the hair has grown back, the internal parts are not visible
from the outside. The implanted parts include an electronics
package called the receiver/stimulator. Extending from this
package is a narrow length of tubing called an electrode array.
This very narrow electrode is threaded into the cochlea and
positioned near the nerve endings. This is what allows the
stimulation needed for hearing.
The external parts of the implant system include a headset (which
contains the microphone and transmitter coil) and the speech
processor. They provide information about sound to the implanted
parts. The patient wears a transmitting coil behind the ear
on the implanted side with the microphone fitted over the ear
just like a hearing aid. The transmitting coil contains a small
magnet. The magnet, in combination with a similar magnet in
the implanted receiver/stimulator, holds the transmitter securely
in place above or behind the ear. The microphone and speech
processor are both housed inside of the behind the ear type
casing.
1. The
microphone picks up sound waves and sends them through the speech
processor (both housed in the behind the ear device)
2. The
speech processor breaks down the sounds and “codes” them and
sends them to the external transmitter coil
3. The
coil emits a radio signal which is picked up through the skin
by the implanted receivers
4. The
receiver/stimulator sends the appropriate electrical signals
to the electrodes in the cochlea
5. The
electrodes then stimulate the remaining nerve fibers there
6. The
hearing nerve carries the resulting nerve impulses to the brain,
which interprets them as sounds.
Amazingly, this entire process happens almost instantaneously,
just like it does for a normal-hearing person.
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