Animation: Normal Ear, Ear with Hearing Loss, and Cochlear Implant Procedure
This is a animation showing how the cochlear implant works. First, the drawing shows the outer ear, middle ear, and inner ear, along with implanted and external components. The external components are a microphone and a sound processor, placed behind the outer ear, and an external transmitter that is attached to the outside of the skin. Directly opposite the external transmitter is an internal receiver placed beneath the scalp and implanted into the bone behind the ear. From the internal receiver a wire passes into the cochlea and wraps partly around the internal spiral of the cochlea. The cochlea sends impulses through the auditory nerve to the part of the brain that perceives sound.
The animation next shows what you would see if you could view the working ear inside the head. To orient you to the person's head you are viewing, think of the person's head facing you with their right ear on your left. Think of a vertical plane or flat sheet through their head passing through the middle of their right ear toward the middle of their left ear. Now, imagine the front half of the head and face being removed, revealing the inside of the ear. Sound waves enter the external ear, vibrate the flexible surface of the eardrum and the middle ear bones (malleus, incus, and stapes) to convey sound to the oval window of the inner ear or cochlea.
In the animation, sound makes the eardrum wiggle. Since the eardrum is attached to the first of three small bones, the malleus, the malleus moves back and forth. Inside the ear, the malleus connects to the incus, which, in turn, connects to the stapes, which, in turn, connects to the oval window of the cochlea. When the malleus moves back and forth, the incus and stapes move and cause the oval window of the cochlea to move back and forth. The moving oval window sends a pulsating wave to the fluid in the cochlea that stimulates nerves in the cochlea, that, in turn, send hearing impulses to the brain through the auditory nerve.
The animation next shows a similar cutaway drawing enhanced with color to distinguish four regions. It shows sound as a wave in the air outside the head, a vibration in the inner ear bones, a fluid wave inside the cochlea, and a train of impulses in the auditory nerve.
The next part of the animation shows a similar view of the ear, but with lessened transmission of sound from the outer ear to the auditory nerve because of hearing loss. In this ear there are fewer nerve impulses in the auditory nerve, compared to the normal ear described above.
The next series of drawings shows the implanting of the cochlear implant under the skin behind a person's right ear.
The first drawing shows some hair shaved from behind the patient's right ear and a cut or incision in the skin behind the ear. Next, the skin is pulled apart (retracted) at the cut in the skin to reach the bone under the skin. Next, the drawing shows the doctor's drill removing some bone to make room for the implanted receiver. Next, the drawing shows the implanted receiver and wire going into the cochlea. The drilling into the cochlea is not shown. Finally, the drawing shows the cut in the skin closed with some stitches, which ends the surgery
The next part of the animation shows the external components placed on the outside of the head after the surgical wound heals and the implant is adjusted so it works properly.
In this part of the animation, there is an image showing the location of the facial nerve in relationship to the middle ear, cochlea and the cochlear implant electrode. In this drawing, the facial nerve is shown very near and just behind the wire connecting the internal receiver and the cochlea. This shows why very careful placement of the wire is essential so the facial nerve is not accidentally damaged by the surgery.
The final part of the animation shows the working cochlear implant. The animation shows the progression of an external sound wave from the air to the microphone behind the ear. The microphone converts the wave to an electrical signal that goes to the sound processor near the microphone, then to the transmitter attached on the scalp behind the ear, then to the internal receiver in the bony recess created in the head, and then along the wire through a hole in the cochlea where it stimulates nerves to send impulses through the auditory nerve to the brain. This drawing does not show the contribution of hearing through the natural route by way of the eardrum, middle ear bones, and oval window to the cochlea, though in some people this activity continues.