Human Ear is divided into three sections ;

Outer Ear, Middle Ear and

Inner Ear.

Each section plays an important and a unique part in

decomposing and translating acoustical waves into electrical impulse signals that are used by the Brain.

Sound waves travel through the Pinna along the external canal of the Outer Ear and cause the Tympanic Membrane (Ear Drum) to vibrate,

then this motion is transferred to the Middle Ear.

The Stapes (Stirrup) is connected to the ear drum by the other middle ear bones, the Incus (Anvil)

and the Malleus (Hammer).

A difference in the pressure causes the stapes to move and it stimulates the perception of sound.

The three bones carry the vibrations to the Cochlea of the Inner Ear.

The Cochlea is the part of the Inner Ear where mechanical

motion of the auditory vibration is converted to

electrical impulses ,so it considers the

Sensory Organ of Hearing.

Cochlea is composed of three fluid filled chambers that extend

along the length of the structure and help to maintain

the Body Balance. The cochlear duct contains the Basilar Membrane upon which lies the Organ of Corti. This

organ has ten thousands of sensory Hair Cells which are connected to the nerve endings

of the Auditory Nerve.

Sound

efferent signals

Fast Open Hair Cells Loop

efferent signals ( from both ears )

Middle Ear Ossicles

other Ear

cross section of the Cochlea

Three main chambers:

• Scala Vestibuli• Scala Media• Scala Tympani

Organ of Corti

Hearing Loss can be rated on a scale based on the

threshold of hearing.

Severe hearing loss is defined as a bilateral hearing threshold

of 70-90 dB and profound hearing is defined as a

hearing threshold of 90 dB and above.

Hearing Loss is divided primarily into

two general categories :Conductive and Sensorineural.

Conductive hearing loss results from diseases or disorders that limit the transmission of sound through the outer or middle ear. This loss can usually be treated medically or

surgically. In some cases, a hearing aid can provide sufficient hearing improvement .

Sensorineural hearing loss affects the auditory nerve and hair cells inside the cochlea that excite it. In this case, sound is transmitted normally through the outer and

middle ears, but the inner ear is less efficient in transmitting the sound. The result is an impaired ability

to hear sound and to understand speech .

This loss is usually treated with a cochlear implant which amplifies sound to overcome the decrease in sensitivity

of the fine nerve endings within the cochlea.

ConductiveOtosclerosis = Stiff Ossicles

Torn EardrumWax Otitis Media = Fluid in middle ear

Sensorineural

Damaged Hair Cells

Damaged Nerve

The Bionic Ear

bypasses damaged parts of

the inner ear and electronically stimulates the nerve of

hearing that converts sound into electrical impulses.

Part of the device is

surgically implanted in the Skull behind the ear

and tiny wires are inserted

into the cochlea.

The other part

of the device is external, and battery powered.

Cochlear Implant is a type of neural prosthetic device that can restore the lost hearing sensation for the severe hearing disabled and profound deaf.

All devices have the following features in common: A microphone that picks up the sound,

A speech processor that converts the sound into electrical signal,

A transmission system that transmits the electrical signals to the implanted electrodes with

transcutaneous RF link, And an intra-cochlear electrodes array that is

inserted in the cochlea by surgery.

1 -Sounds are detected by the Microphone.

2 -The information from the microphone is sent to the Speech Processor.

3 -The speech processor analyses the information and converts it into an electrical code.

4 -The coded signal travels via a cable to the transmitting coil in the headset. Radio waves from the transmitter coil carry the

coded signal through the skin to the implant inside.

5 -The implant package decodes the signal. This signal contains information that determines how much electrical current

will be sent to the different electrodes array.

6 -The appropriate amount of electrical current passes down the appropriate lead wire to the chosen electrodes.

7 -The position of stimulating electrodes within the cochlea will determine the frequency of the sounds. The amount of

electrical current will determine the loudness of the sounds.

8 -Once the nerve endings in the cochlea are stimulated, the message is sent up to the Brain along the auditory nerve. The Brain

can then try to interpret the stimulation as a meaningful sound .

Electrodes Array is inserted in the cochlea so that different auditory nerve fibers can be stimulated at different places .Electrodes stimulation is depending on the signal frequency.

Electrodes near the base of cochlea are stimulated with high frequency signals, while electrodes near the apex

are stimulated with low frequency signals .

The signal processing strategy consists of band pass filters that divide the acoustic wave into four channels .

The envelopes of the band-passed waveforms are then detected by rectification and low pass filtering.

The generated pulses are delivered to the appropriate electrodes through a radio frequency link.

For centuries, people believed that only a miracle could

restore hearing to the Deaf. It was not until fifty years ago

that scientists first attempted to restore normal hearing to the

deaf by electrical stimulation of the impaired auditory nerve.