Hearing Loss - Description
Hearing is a complex process that consists of many steps. It begins when sound waves strike the outside of the ear. Sound waves are vibrations that occur in air. When sound waves hit the ear, they cause tissue in the ear to start vibrating.
The ear consists of three major sections: the external ear, the middle ear, and the inner ear. The external ear acts like a small sound-collecting tube. Sound waves enter the ear and pass down a narrow canal called the auditory canal. At the end of the canal, the sound waves strike a thin membrane called the tympanic (pronounced tim-PA-nik) membrane, or ear drum. They cause the tympanic membrane to begin vibrating.
- Audiometer:
- An instrument for testing a person's hearing.
- Auditory canal:
- A tube that leads from the outside of the ear to the tympanic membrane.
- Auditory nerve:
- A bunch of nerve fibers that carries sound from the inner ear to the brain.
- Conductive hearing loss:
- Hearing loss that occurs in the external or middle ear.
- Eustachian tube:
- A passageway that connects the middle ear with the back of the throat.
- Ossicles:
- A set of tiny bones in the middle ear responsible for transmitting sound vibrations from the outer ear to the inner ear.
- Otosclerosis:
- A disorder in which the bones of the middle ear become joined to each other.
- Sensory hearing loss:
- Hearing loss that occurs in the inner ear, auditory nerve, or brain.
- Tympanic membrane:
- A thin piece of tissue between the external ear and the middle ear.
Just beyond the tympanic membrane is the middle ear. The middle ear contains three bones called ossicles (pronounced AH-sih-kulls). Vibration of the tympanic membrane is passed along to the ossicles. They too begin to vibrate.
The ossicles are connected to the inner ear. The inner ear is filled with a clear, watery fluid. As the ossicles vibrate, they create another wave inside the watery fluid in the inner ear. This wave is similar to a water wave on a lake or the ocean.
In the last stage of hearing, the water wave in the inner ear collides with the auditory nerve. The auditory nerve picks up these vibrations and transmits them to the brain. The brain "reads" these vibrations as a sound.
Hearing loss can occur at any stage of this process. For example, sound waves may be blocked as they try to pass down the auditory canal. Or they may not be able to pass through the ossicles in the middle ear. Or they may not be transmitted through the liquid of the middle ear or along the auditory nerve. Finally, the brain may lose its ability to make sense out of the vibrations it receives from the auditory nerve.
Hearing loss is usually defined as being either conductive or sensory hearing loss. Conductive hearing loss is caused by damage to the external or middle ear. Sound vibrations are unable to pass down the auditory canal, across the tympanic membrane, and through the ossicles. Sensory hearing loss occurs in the inner ear and the auditory nerve. Sound waves may reach the inner ear, but they are not transmitted successfully to the brain.
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