1. The Ear Introduction Lecture

2. Your Ears & Hearing Your ears are exceedingly well-designed organs with two roles -- they enable you to hear and to keep your balance. Your outer ear gathers the sound waves or vibrations that reach it and funnels them into the ear canal. As vibrations travel through the middle ear, they hit your ear drum, a membrane smaller and thinner than the nail on your pinky finger. This causes your ear drum to vibrate like the skin of a drum.

3. Your Ears & Hearing The vibrations of the ear drum are then passed along a series of three tiny bones, the hammer, the anvil, and the stirrup. Each, in turn, vibrates. The last bone, the stirrup, passes the vibrations on into the inner ear to a fluid-filled curled tube called the cochlea.

4. Your Ears & Hearing Inside the cochlea thousands of tiny sensitive hairs called cilia begin to move and turn these vibrations into nerve messages that travel to your brain. There, your brain analyzes and makes sense of "sounds" -- and you "hear."

5. What are sounds, anyway? Sound is made by vibrations. If you hit a gong, the hammer hits the metal causing the molecules that make up the metal to vibrate in a particular pattern, back and forth, back and forth. As they vibrate, they push the air molecules around them back and forth, as well. And that vibrating continues, traveling outward from the gong in every direction like the circular ripples from a splash in water. Sound vibrations travel through almost anything -- metal, air -- even water!

6. But what do ears have to do with balance? Not only do your ears provide you with a rich and bountiful array of sounds to hear, they are sensitive instruments which help keep your sense of balance in a variety of ways.

7. First, there are three small curved tubes called semi- circular canals above the cochlea. Each is filled with fluid and lies at right angles to the next. As you move, the fluid inside each one moves, bending microscopic hairs that are also inside these tubes. When these hairs, which rest in a layer of jelly, bend they send messages to your brain about whether or how your body is moving.

8. But what do ears have to do with balance? At the same time, there are minute crystals balancing on these hairs. When you tilt your head, gravity causes these crystals to tumble off their perch, bending the tops of the hairs, and sending another type of message to your brain. This message tells your brain where "up" and "down" are. So thank goodness for your inner ear and all its tubes and hairs! Without them, your brain wouldn't know how to hold your head and how to adjust your body to stay balanced.

9. Why do you feel dizzy for a moment after getting off of an amusement ride? Have you ever been moving and when you stop you still feel like you're moving? Sometimes, it's your brain which is telling you that you're moving when you're not. But, sometimes, for a brief moment, it may be your inner ear which is giving out the wrong information.

10. Why do you feel dizzy for a moment after getting off of an amusement ride? To see what we mean, take a jar half- filled with water and spin it around. When you stop moving the jar, what happens? It takes a moment before the water stops moving. The same holds true for the liquid inside your semi-circular canals.

11. What causes earaches? Although earaches are not often serious, they are painful and, unfortunately, all too common. What causes them? Generally, you experience pain in your ears because of pressure on your eardrum. What causes the pressure? Too much fluid which can be the result of infection, allergies, or a virus.

12. Do you know anyone who has had surgery to put tubes in their ears? It's a common procedure in which a doctor inserts a small artificial tube into the middle ear to help drain excess fluid and keep the ear earache-free.

13. Are there people who can not hear at all? Yes. As a result of illness or a birth defect, some people don't hear well, and some don't hear at all. If they don't hear well, sometimes hearing aides can help them hear better. People who are entirely deaf, however, have to rely on their other senses even more to provide them with information about the world around them.

14. Did you know? Most humans can distinguish over 1500 tones. A piano, meanwhile, has only 88 tones! Many animals lack ears altogether. Fish don't have ears. They have a ridge that goes down the length of their body and allows them to "hear" pressure changes through their body. How loud is a whisper? 20 decibels. How loud is a rock concert? Over 100 db. A road drill? 115 decibels. A gunshot? 140 decibels.

15. Beware of sounds at the upper end of the human hearing spectrum. Hearing them without having ear phones to dampen the sound can cause permanent injury to your eardrums!