Gary Garcia, age 12, of Reno, Nev., for his question:
HOW DOES THE EAR WORK?
The organ you use for hearing is the ear. It is made up of three parts: the outer ear, the middle ear and the inner ear.
Sound reaches your ear as sound waves. The outer ear, or auricle, is formed in such a way as to catch these sound waves, which are then changed to messages that the nerves carry to your brain.
Sound waves travel down the outer ear's canal and reach a thin skin that is tightly stretched across a tube. This skin is called the eardrum and it separates the outer ear from the middle ear. It acts like a drum membrane and the sound waves make it vibrate.
Behind the eardrum is the middle ear that includes three bones: the hammer, anvil and stirrup. They touch both the eardrum and the inner ear. Sound waves travel down the canal, hit the eardrum and start the three bones vibrating. These bones in turn set up a series of vibrations in the fluid of the shell shaped inner ear.
The shell or cochlea is called the organ of Corti. It is made up of tiny cells that transfer the sound waves to the auditory nerves. These nerves carry them to the center of hearing in the brain. There a person has the reaction that is called hearing. In the inner side of the eardrum is a canal called the Eustachian tube. It leads to the throat. Enough air is in this tube to keep the air pressure equal on either side of the eardrum. The equal air pressure makes it easier for the eardrum to move with entering sound waves.
Three semicircular canals form part of the inner ear where the organ of Corti is located. Their function has nothing to do with hearing, however. These canals give the body its sense of balance. Each canal is filled with a fluid and contains sensory cells that end in hairs. These hairs respond to changes in the position of the body.
Germs can cause problems in the outer, middle or inner ear. A cold will often cause an infection to spread from the nose to the ears and such an infection can cause a temporary loss of hearing as well as injury to the sense of balance.
The delicate eardrum can sometimes be harmed by a force such as an explosion that causes great pressure. Also, there are disturbances that can occur in the inner ear mechanism that cause vertigo or dizziness, and this is often accompanied by nausea.
Deafness or a loss of hearing can be caused by a malfunction of some part of the ear or it can be caused by hereditary factors.
Conduction deafness is caused when the passage of sound waves through the middle ear is stopped. Deafness caused when the auditory nerves don't carry the sound waves to the brain's hearing center is called nerve deafness.