HOW HEARING WORKS
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.
FROM SOUND WAVES TO
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.
FUNCTION OF THE EAR
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
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.
B) THE MIDDLE EAR
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.
C) THE INNER EAR
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.