What do you hear?

Sirens! Music! Whistling! A friend's laughter! Much of the information you take in during the day comes in through your ears, even when you are not aware of it. How do your ears turn sounds into information?

Vibrations in the air are collected by the part of the ear you can see, called the pinna (PIN-a). These vibrations, or sound waves, enter the ear canal and strike a thin membrane stretched across the end of the ear canal called the eardrum.

The eardrum vibrates as each sound wave hits it. These vibrations are magnified by three of the body's tiniest bones, the hammer, anvil, and stirrup. They are located in an air-filled chamber known as the middle ear.

As the eardrum vibrates, it moves the hammer. This causes the anvil to vibrate and push the stirrup. The stirrup is connected to the oval window, which is a membrane covering an opening to the inner ear. The stirrup moves in and out, causing vibrations in a fluid-filled portion of the inner ear called the cochlea (KOK-le-a).

Inside the cochlea, special cells turn the vibrations into coded electrical signals. These signals are picked up and sent to the brain by large nerves. Once inside the brain, the signals are compared with other sounds already stored in your memory to see if the new sound should be ignored, stored, or acted upon.

Not all creatures have ears on the sides of their heads. Some actually have them on their legs! Grasshoppers have ears on their first pair of legs. Spiders' ears are on the last joint of some of their legs.