The process involved in hearing a gentle whisper or a loud cry is amazing! Sound waves are collected by the outer part of your ear, the auricle (a receptacle for sound), and funneled into a narrow channel called the ear canal. This all takes place in the outer ear.
Between the outer ear and the middle ear is a thin, tightly-stretched membrane called the tympanic membrane, or eardrum. When sound waves hit this membrane, it begins to vibrate. The three bones in the middle ear, the smallest bones in your body, begin to vibrate as well. These bones, called ossicles, are the hammer-shaped malleous, the anvil-shaped incus, and the stirrup-shaped stapes.
The vibrations caused by sound waves hitting the tympanic membrane are transferred through the ossicles into the cochlea in the inner ear. The cochlea is a small, curled tube, filled with fluid and lined with cells that have tiny hairs. The fluid in the cochlea begins to vibrate from the influence of the ossicles, causing the hairs to move, which in turn sends nerve impulses to the brain, transmitting sounds to the brain in a code that it can read.
The inner ear plays another important role: it helps a person keep his or her balance. Besides the cochlea, there are two other fluid-filled parts, called the semi-circular canals. The fluid in these moves when you bend down, turn your head, or spin around. The hairs that are on the lining of the canals tell your brain what angle your head is at, so it can adjust your muscles accordingly and keep you from falling over. When you get dizzy, the fluid in the canals is swishing back and forth (like water in a cup, if you turn the cup around several times). This causes your brain to think that you are still moving. However, the nerve impulses from your eyes contradict this information, and your brain is temporarily confused, so it tries to adjust the body according to contradictory information.
