The Cochlear Implant Center at Stanford University

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Cochlear Implant Glossary


What are the Functions of the Normal Ear?

The ear is divided into 3 parts: the external ear, the middle ear, and the inner ear.

The external ear includes the visible part of the ear (the auricle) and the ear canal. This system allows the air vibrations of sounds to pass from the environment to the ear drum.

The middle ear includes the eardrum (tympanic membrane) and the air-filled chamber behind it. The middle ear space contains the three bones of hearing, the malleus ("hammer"), incus ("anvil") and stapes ("stirrup"). In the normal ear, the tympanic membrane vibrates from sound, the three bones (or ossicles) move as a unit to transmit the sound energy to the inner ear. The middle ear space is connected to the back of the nose through the eustachian tube, this allows air to enter the middle ear and equalize pressures with the outside environment.

The inner ear consists of the cochlea (organ of hearing), the vestibular system (organ of balance), and the nerves that travel to the brain. The cochlea converts mechanical sound vibrations to electrical nerve impulses. Within the cochlea there are about 16,000 "hair cells" embedded in a system of flexible membranes. When sound vibrations cause the membranes to move, the microscopic hairs on these hair cells bend. This bending causes an electrical signal to be sent to the hearing nerve. The electrical signal from the hearing nerve is then processed in the brain, where the sound is perceived.


What is Hearing Loss?

An alteration of any part of the hearing system can result in hearing loss. Most people who lose their hearing have difficulty converting sound vibrations into electrical signals. This type of hearing loss is often referred to as "nerve deafness". Despite this term, the injury to the system usually occurs in the inner ear (or cochlea) itself, and not primarily in the nerve of hearing. Often the microscopic hair cells in the inner ear are lost, thereby interrupting the normal conversion of vibrations to electrical signals. Without the cochlea to provide electrical signals, the hearing nerve has no sound information to send to the brain.

The great majority of individuals with mild or moderate hearing loss do well with conventional hearing aids. Simply turning up the sound volume, and vibrating the remaining inner ear structures with more sound can provide better understanding. However, the hearing loss may be so severe that simply amplifying the sound no longer helps. People with such severe or profound hearing loss caused by inner ear injury are potential candidates for cochlear implantation.


What is a Cochlear Implant?

A cochlear implant is an electronic device that bypasses the non-functioning inner ear to stimulate the nerve of hearing directly. In doing so, an implant can potentially restore useful hearing and significantly increase an individual's ability to communicate

Cochlear implants are made up of both an internal and external component. The internal component (also known as the "receiver" or "stimulator") is placed surgically under the skin behind the ear. A tiny electrode is threaded into the curved inner ear, where it comes in close contact with the ends of the hearing nerve. The external component consists of a headpiece that communicates with the internal component, and a sound processor that modifies the sound information so it can be best understood by the individual. The external components also contain the battery that powers the implant.

First, an external microphone receives the sound. The sound is next converted into a digital signal by the processor. This digital electronic signal is sent to the headpiece, which is held in place on the skin over the internal receiver by a strong magnet. The sound information is transmitted from the headpiece to the receiver through the skin as a radio wave.

The receiver sends the sound signal to the electrode. The electrode is actually made up of a number of small electrical "contacts" that are each in a different position within the cochlea. Depending on which contact is stimulated, different parts of the hearing nerve will be stimulated, and a different pitch can be perceived. By stimulating the hearing nerve in the right way, meaningful sound information can be transmitted to the brain, and heard.


Who is an Implant Candidate?

Anyone with severe or profound inner ear hearing loss in both ears can be considered for cochlear implantation. Children as young as one year of age, and adults of any age can potentially benefit from this procedure. The determination of whether an individual can benefit from a cochlear implant requires specialized medical and hearing evaluations.

A cochlear implant is not for everyone with hearing loss. Each individual and family needs consider what this technology has to offer for them.


How Well do Cochlear Implants Work?

Cochlear implants can provide useful sound perception to the great majority of people who receive them. The quality of sound a person perceives is variable, and depends on many factors, including the timing of implantation, the duration of hearing loss, the cause of the hearing loss, and the individual's ability to communicate verbally before the procedure. It is impossible to tell any given individual just how well he or she will do with the device. It is also essential that a person receiving a cochlear implant be willing and able to undergo hearing rehabilitation. Learning to hear with a cochlear implant can be require patience and effort. However, the benefits from this effort are well worth the investment.

Many children who are born deaf can grow up with a cochlear implant using spoken language as their method of communication. Many attend hearing schools, and develop language and reading at an age-appropriate rate. The majority of adults who lost their hearing after learning to speak can use the telephone with a cochlear implant. Most regain some appreciation for music, and almost all gain a new awareness of environmental sounds. Even adults who were born without hearing can gain significant new sound perception through cochlear implantation.


The Otolaryngology - Head and Neck Surgery Department offers an extensive online resource of general health information. Please do not substitute information on this website for professional advice, a diagnosis of your condition, or a recommendation about the course of treatment for your particular circumstances. This information is not intended to be, and should not be used as, a substitute for medical treatment by a health care professional.