How You Hear
When an object makes a noise, it sends vibrations (better known as sound waves) speeding through the air. These vibrations are then funneled into your ear canal by your outer ear. As the vibrations move into your middle ear, they hit your eardrum and cause it to vibrate as well. This sets off a chain reaction of vibrations. Your eardrum, which is smaller and thinner than the nail on your pinky finger, vibrates the three smallest bones in your body: first, the hammer, then the anvil, and finally, the stirrup. The stirrup passes the vibrations into a coiled tube in the inner ear called the cochlea.
 
 

The fluid-filled cochlea contains thousands of hair-like nerve endings called cilia. When the stirrup causes the fluid in the cochlea to vibrate, the cilia move. The cilia change the vibrations into messages that are sent to the brain via the auditory nerve. The auditory nerve carries messages from 25,000 receptors in your ear to your brain. Your brain then makes sense of the messages and tells you what sounds you are hearing.

 How You Keep Your Balance
Near the top of the cochlea are three loops called the semi-circular canals. The canals are full of liquid also. When you move your head, the liquid moves. It pushes against hairlike nerve endings, which send messages to your brain. From these messages, your brain can tell whether or how your body is moving.

 If you have ever felt dizzy after having spun around on a carnival ride, it was probably because the liquid inside the semicircular canals swirled around inside your ears. This makes the hairs of the sensory cells bend in all different directions, so the cells' signals confuse your brain.

 What Did You Say?
Did you know that some people have trouble hearing and others cannot hear at all? Well it's true. When a person can't hear well, a hearing aide can sometimes help them hear better. However, people who are entirely deaf have to rely on all their other senses to help process all of the information from the world around them. They are deaf because of an illness or they were born that way. You can also lose your ability to hear at an early age by listening to things that are very loud. Scientists measure loudness in decibels. Below is a table of various noises and their decibel level.
 
 

	Babies can get earaches because of milk backing up in the Eustachian tube, which causes bacteria to grow and may cause hearing problems later in life.
	When you go up to high elevations, the change in pressure causes your ears to pop.
	Children have more sensitive ears than adults. They can recognize a wider variety of noises.
	Dolphins have the best sense of hearing among animals. They are able to hear 14 times better than humans.
	Animals hear more sounds than humans.
	An earache is caused by too much fluid putting pressure on your eardrum. Earaches are often the result of an infection, allergies or a virus.

	Hearing Experiment - An experiment you can do to test your sense of hearing.
	Anatomy Of The Ear - Great page that describes the anatomy of the ear!
	How Your Hearing Works - Another good page that explain how you hear sounds. Also has a coool Quicktime movie of the ear.
	Hearing Animation - Cool animation of how vibrations travel through the ear!
	Your Gross and Cool Body - General information on the sense of hearing.
	Minutes From ME - Another good site with information and activities on the sense of hearing.