Maxine Snyder, age 14, of Camden, N. J., for her question:

HOW DO WE HEAR?

Hearing is one of your five senses. You can hear because your ears are able to feel vibrations in the air that are called sound. Your ears allow the vibrations to pass from outside your head to the part of your brain that controls hearing.

In the vestibule section of your inner ear is a small division shaped like a snail's shell called the cochlea. Within it is the actual sense organ for hearing, the organ of Corti.

For you to hear, the sound vibrations must reach the organ of Corti. They can reach the inner ear by three routes.

First, sound waves can make the eardrum vibrate. The vibrations of the eardrum are then carried across the middle ear by the auditory ossicles to the round window, an opening between the middle and inner ears. Sound vibrations then cause the footplate of the bone called the stapes to move like a plunger in and out of the oval window. This causes the fluid in the cochlea to move.

A second way in which sound waves can reach your inner ear is by traveling through air from the eardrum to the secondary eardrum, a membrane that covers the round window.

A third way is for sound waves to travel directly through the bones of your skull. The bones then send the sound vibrations to the inner ear. This is a method used in some hearing aids to carry sound waves.

Within the cochlea, sound waves move through about 25,000 fibers and then cause a vibration in the specialized sense cells, called hair cells, of the organ of Corti. The vibrations of the hair cells stimulate nerves attached to them and messages are sent to the temporal lobe, which is the brain's hearing center.

The fibers of the cochlea vary in length, and because of this they are able to tell the difference between sounds of different pitch. The shortest fibers respond to the high pitched sounds.

Your vocal cords start sound waves when you start to speak. These are actually vibrations in the air.

There are many differences in sound waves, the most important of which is frequency, or the speed of the vibrations. A low sound has a low speed of vibration or a low pitch. A high sound has a high pitch.

You era able to hear sounds that range from about 15 to about 20,000 vibrations per second.

As a person grows older, he loses some ability to hear high frequency sounds. A young person usually has the best hearing ability.

Poor hearing brings many problems. But even the deaf are able to solve many of the problems.

It is difficult for deaf children to learn to speak because most children learn to speak by listening to adults and than imitating them. If you can't hear the sound, you can't very well imitate it.