How We Hear
Hearing depends on a series of events that change sound waves in the air into electrical signals. Your auditory nerve then carries these signals to your brain through a complex series of steps.
1. Sound waves enter your outer ear and travel through a narrow passageway called the ear canal, which leads to your eardrum.
2. Your eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in your middle ear. These bones are called the malleus, incus, and stapes.
3. The bones in your middle ear amplify, or increase, the sound vibrations and send them to your inner ear, also called the cochlea, which is shaped like a snail and filled with fluid. An elastic membrane runs from the beginning to the end of the cochlea, splitting it into an upper part and a lower part.
4. The sound vibrations cause the fluid inside your cochlea to ripple, and a traveling wave forms along the membrane. Hair cells — sensory cells sitting on top of the membrane —“ride the wave.” (Hair cells have nothing to do with hair. They get their name from bristly structures that look like hair jutting from their tops.)
5. As the hair cells move up and down, their bristly structures bump up against an overlying membrane and tilt to one side. This tilting action causes pore-like channels on the surface of the bristles to open up. When that happens, certain chemicals rush in, creating an electrical signal.
6. Your auditory nerve carries this electrical signal to your brain, which translates it into a “sound” that you recognize and understand.
Hair cells near the wide end of the snail-shaped cochlea detect higher-pitched sounds, such as a cell phone ringing. Those closer to the center detect lower-pitched sounds, such as a large dog barking.
Extent of Hearing Loss
Hearing loss is the THIRD most common chronic health problem in the United States. Over 16% of American adults suffer hearing loss in the speech range. Nearly 2/3 of Americans with hearing loss are UNDER retirement age and hearing loss is one of the most common conditions affecting older adults.
Approximately 17 percent, or 36 million, of American adults say that they have some degree of hearing loss. Roughly one-third of Americans 65 to 74 years of age and 47 percent of those 75 and older have hearing loss. Men are more likely to experience hearing loss than women.
Forms of Hearing Loss
Hearing loss comes in many forms. It can range from a mild loss to a total loss of hearing. It can be hereditary or it can result from disease, trauma, certain medications, or long-term exposure to loud noises.