Cochlear Implant.

Hearing Mechanism and Problems Related to It:

Before going into the subject I think it would be helpful that, if we quickly refresh our theories of the working mechanism of human ear as short as we can. Then you can easily understand the functions of the Cochlear implants and the Hearing Aids 👈(My previous article. If you like to read those, please click this link).

Diagram of the Human Ear.

Working Mechanism of Human Ear:

There are three anatomical parts in ear which are:

     1. Outer Ear.

         The outer ear consists of the pinna (also called auricle), ear canal and eardrum

     2. Middle Ear.

         The middle ear consists of three ossicles (tiny ear bones) which are 

• Malleus [hammer]  
• Incus [anvil] 
• Stapes [stirrup]) 

         and the ear drum is at last (which is connected to the Stapes).

     3. Inner Ear.

        The inner ear, which contents the cochlea. (‘Cochlea’ means ‘snail’ in Latin; the cochlea gets its          name from its distinctive coiled up shape). Apart from Cochlea the inner ear consists of the the            auditory (hearing) nerves which connects with the brain.

Sound waves from the environment enter the ear canal with the help of the Pinna which is the only visible part of the entire anatomy of the ear and it helps to focus all the sound waves to go into the ear canal and make the ear drum vibrate. This action moves the tiny chain of bones (ossicles – malleus, incus, stapes) in the middle ear. The last bone in this chain ‘knocks’ on the membrane window of the cochlea and makes the fluid in the cochlea move.  When the cochlea's hair cells which are inside of the cochlea, are stimulated by the fluid waves a neurochemical event takes place which excites the nerves of hearing. The physical characteristics of the original acoustic signal are preserved at every energy change along the way until this code becomes one that the central auditory pathways can direct to the temporal lobe of the brain for sound recognition and processing.

What Happens Internally when We Have Hearing Problems?

When the ear is working normally, information is being passed through the different parts of the ear to the brain.

The type of hearing problems we face, are depended on which part of the ear is not responding or functioning well.

1. Conductive Hearing Loss:

Outer ear or middle ear problems lead to inefficient transfer of sound. The cochlea is still working but may not receive enough information through the previous two regions. This type of hearing loss is called conductive hearing loss. The problem is that the sound is not being conducted (transferred) well enough. Conductive deafness can be caused by things such as an ear infection, a hole in the eardrum, otosclerosis (It’s a disease of the bones of the middle and inner ear), etc…

2. Sensorineural Hearing Loss:

An inner ear (cochlear) problem means that sound arrives at the cochlea, but is then not fully passed on to the hearing nerve. Also it is possible that the hearing nerve itself is not passing on information well, or fails to pass on the sound at all. A cochlear or neural hearing loss is called a sensorineural hearing loss. Sensorineural hearing loss can be caused by things such as old age, loud noise, Ménière’s Disease (It’s a disorder of the inner ear that causes episodes in which you feel as if you're spinning (vertigo), and you have fluctuating hearing loss with a progressive, ultimately permanent loss of hearing, ringing in the ear (tinnitus), and sometimes a feeling of fullness or pressure in your ear), etc…

Note:- It is possible to have a mixed hearing loss with both a conductive and sensorineural element.

Type of hearing problems.

Introducing the Cochlear Implant:

While most people with hearing loss are quite successful with hearing aids, there are some individuals with severe to profound hearing loss for which hearing aids do not provide enough benefit. For these people with severe damage to the sensory cells in the inner ear, a cochlear implant is often the best option for better hearing.

A cochlear implant is an electronic device which is also considered as a prosthetic substitute which directly stimulates the cochlea that partially restores hearing. It can be an option for people who have severe hearing loss from inner-ear (cochlea) damage and who receive limited benefit from hearing aids by providing sound signals to the brain.

Cochlear Implant.

These tiny, complex medical devices work differently than hearing aids. Rather than amplifying sound, which helps an individual with residual hearing ability; a cochlear implant provides the sense of sound by stimulating the auditory nerve directly. Cochlear implants do not cure hearing loss or restore hearing, but they do provide an opportunity for the severely hard of hearing or deaf to perceive the sensation of sound by bypassing the damaged inner ear.

Note:-

• Many people have cochlear implants in both ears (bilateral). Listening with two ears can improve the ability to identify the direction of sound and separate the sounds we want to hear from those we don’t.
• It takes time and training to learn to interpret the signals received from a cochlear implant. Within a year of use, most people with cochlear implants make considerable gains in understanding speech.

Parts and Its functions of a Cochlear Implant:

A cochlear implant operates using two main components which are coupled using a powerful magnet: 

1. External part that hooks over the ear:

The external component of a cochlear implant contains a microphone, a speech processor and a transmitter. The microphone and speech processor are housed in a small unit that looks like a behind-the-ear hearing aid. A small wire usually links them to the transmitter, which is positioned over the internal part of the device. The microphone picks up acoustic sounds and sends it to the speech processor. The processor analyzes and digitizes the signal before sending it to the transmitter. The transmitter then codes the signals and sends them to the implanted receiver via the magnetic coupling.

External Part.

2. Surgically implanted internal part:

The internal part of a cochlear implant includes a receiver, which is located under the skin on the temporal bone, and one or more electrode arrays. The receiver collects the signals from the transmitter and converts them to electrical pulses. It then dispatches the pulses to the electrodes that have been inserted deeply into the inner ear. These electrodes directly stimulate the auditory nerve throughout a portion of the cochlea and the brain then interprets these signals as sound.

Internal Part.

Note:-  All cochlear implant systems have the same broad characteristics and design principles and are all well engineered. Variations arise in styling, accessories and battery type. Particular differences exist in electrode design, MRI compatibility and speech processing strategies which encode the external sound frequency details into digital signals.

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References:

• Cochlear Implants | Hearing Loss Treatments | Cochlear™ AU/NZ. 2018. Cochlear Implants | Hearing Loss Treatments | Cochlear™ AU/NZ. [ONLINE] Available at: https://www.cochlear.com/au/home/understand/hearing-and-hl/hl-treatments/cochlear-implant. [Accessed 13 July 2018].
• Cochlear implants. 2018. - Mayo Clinic. [ONLINE] Available at: https://www.mayoclinic.org/tests-procedures/cochlear-implants/about/pac-20385021. [Accessed 13 July 2018].
• Healthy Hearing. 2018. Cochlear implants: Who, how and why?. [ONLINE] Available at: https://www.healthyhearing.com/help/hearing-aids/cochlear-implants. [Accessed 13 July 2018].
• Hearing Link. 2018. Cochlear implants - Hearing Link. [ONLINE] Available at: https://www.hearinglink.org/your-hearing/implants/cochlear-implants/. [Accessed 13 July 2018].
• Hearing Link. 2018. Understanding how the ear works - Hearing Link. [ONLINE] Available at: https://www.hearinglink.org/your-hearing/how-the-ear-works/. [Accessed 13 July 2018].
• How We Hear | The Process of Hearing & How the Ear Works. 2018. How We Hear | The Process of Hearing & How the Ear Works. [ONLINE] Available at: http://www.betterhearing.org/hearingpedia/how-we-hear. [Accessed 13 July 2018].
• NIDCD. 2018. Cochlear Implants | NIDCD. [ONLINE] Available at: https://www.nidcd.nih.gov/health/cochlear-implants. [Accessed 13 July 2018].