We donít just hear with our ears Ė we hear with our brains. How does it work? Find out how simple vibration becomes a birdcall, a rock lyric or the blast of a jackhammer.

While the outer ear is a great place to display jewelry, itís specifically designed to transmit sound. Sound begins as motion. When objects vibrate, molecules of air are set in motion and transmitted as sound waves. The outer earís bell-like contours guide and focus these sound waves into the ear canal, where theyíre aided and amplified by its spiraling shape. This natural phenomenon works so well we copy it to hear even better: a radio announcer cups his hand around his ear, simultaneously gathering sound in and blocking background noise out. Once inside the ear canal, sound waves travel on until they reach the eardrum, the dividing point between the outer and middle ear.

When sound waves hit the eardrum, they cause it to vibrate, sending the sound on to the delicate machinery of the middle ear. Here, the bodyís three tiniest bones - commonly referred to as the hammer, anvil and stirrup - mechanically advance and organize the sound to further amplify it and facilitate its passage into the inner ear. The middle ear also contains the eustachian tube, which equalizes air pressure between the outer and inner ear.

The fluid-filled inner ear is where the action takes place. Here, microscopic hair cells reside within the spiral-shaped cochlea. These hair cells are stimulated by the sound wave moving through the fluid and convert that movement into nerve impulses that are sent to the brain.


Our brain interprets the signals and tells us in turn that the doorbell rang, or that words are being spoken. Many things help determine just exactly what it is you hear, but itís the combination of frequencies that give different sounds their distinctive qualities. Source and direction of the sound and loudness are other clues the brain uses to decipher messages.

Hearing loss occurs when hair cells are damaged or die, a common occurrence as we age. And hair cells, like brain cells, do not regenerate. Thatís why most hearing loss is irreversible.


The ear is a very complex organ comprising three parts: the outer ear, the middle ear and the inner ear. From the inner ear the auditory nerve transmits information to the brain for processing.

The outer ear includes the auricle, the auditory canal and the eardrum. It funnels sounds from the surrounding environment into the hearing system. The auricle helps to gather the sound waves, and the auditory canal then directs them to the eardrum.

The middle ear is an air-filled cavity which contains the smallest bones in the human body - the malleus, incus and stapes. These are connected to the eardrum on one side, and on the other side to a thin membrane-covered opening on the wall of the inner ear. The middle ear is also connected to the throat via the Eustachian tube which keeps the air pressure in the middle ear equal to that of the surrounding environment.

In the inner ear the auditory input is processed by the cochlea, while information affecting balance is processed by the semicircular canals. Along the entire length of the fluid filled cochlea there are tiny hair cells. These hair cells are bent when the fluid is displaced by sound waves passed on by the middle ear bones. This triggers a chemical response which activates the corresponding nerve endings. These then transmit the message to the area of the brain in charge of interpreting auditory input.


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