How Do 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.
   
   Illustration showing the sound pathway
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.
   
   Cochlea
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.)
   
   Hair cells
   
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.

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