What Does the Nose Do?

A big batch of cookies coming out of the oven. Your gym bag full of dirty clothes. How do you smell these smells and thousands more? It's your nose, of course.

Your nose lets you smell and it's a big part of why you are able to taste things. The nose is also the main gate to the respiratory system, your body's system for breathing. Let's be nosy and find out some more about the nose.

What Are the Parts of the Nose?

The nose has two holes called nostrils. The nostrils and the nasal passages are separated by a wall called the septum (say: SEP-tum). Deep inside your nose, close to your skull, your septum is made of very thin pieces of bone.

Closer to the tip of your nose, the septum is made of cartilage (say: KAR-tel-ij), which is flexible material that's firmer than skin or muscle. It's not as hard as bone, and if you push on the tip of your nose, you can feel how wiggly it is.

Behind your nose, in the middle of your face, is a space called the nasal cavity. It connects with the back of the throat. The nasal cavity is separated from the inside of your mouth by the palate (roof of your mouth).

What's the Trachea Do?

When you inhale air through your nostrils, the air enters the nasal passages and travels into your nasal cavity. The air then passes down the back of your throat into the trachea (say: TRAY-kee-uh), or windpipe, on its way to the lungs.

Your nose is also a two-way street. When you exhale the old air from your lungs, the nose is the main way for the air to leave your body. But your nose is more than a passageway for air. The nose also warms, moistens, and filters the air before it goes to the lungs.

What's the Mucous Membrane?

The inside of your nose is lined with a moist, thin layer of tissue called a mucous membrane (say: MYOO-kus MEM-brayne). This membrane warms up the air and moistens it. The mucous membrane makes mucus, that sticky stuff in your nose you might call snot. Mucus captures dust, germs, and other small particles that could irritate your lungs. If you look inside your nose, you will also see hairs that can trap large particles, like dirt or pollen.

If something does get trapped in there, you can probably guess what happens next. You sneeze. Sneezes can send those unwelcome particles speeding out of your nose at 100 mph!

Further back in your nose are even smaller hairs called cilia (say: SILL-ee-uh) that you can see only with a microscope. The cilia move back and forth to move the mucus out of the sinuses and back of the nose. Cilia can also be found lining the air passages, where they help move mucus out of the lungs.

How Does Smelling Work?

The nose allows you to make scents of what's going on in the world around you. Just as your eyes give you information by seeing and your ears help you out by hearing, the nose lets you figure out what's happening by smelling. It does this with help from many parts hidden deep inside your nasal cavity and head.

Up on the roof of the nasal cavity (the space behind your nose) is the olfactory epithelium (say: ol-FAK-tuh-ree eh-puh-THEE-lee-um). Olfactory is a fancy word that has to do with smelling. The olfactory epithelium contains special receptors that are sensitive to odor molecules that travel through the air.

These receptors are very small — there are about 10 million of them in your nose! There are hundreds of different odor receptors, each with the ability to sense certain odor molecules. Research has shown that an odor can stimulate several different kinds of receptors. The brain interprets the combination of receptors to recognize any one of about 10,000 different smells.

How Does the Brain Recognize Smells?

When the smell receptors are stimulated, signals travel along the olfactory nerve to the olfactory bulb. The olfactory bulb is underneath the front of your brain just above the nasal cavity. Signals are sent from the olfactory bulb to other parts of the brain to be interpreted as a smell you may recognize, like apple pie fresh from the oven. Yum!

Identifying smells is your brain's way of telling you about your environment. Have you ever smelled your toast burning? In an instant, your brain interpreted the smell and a problem and you knew to check on your toast.

You learned to associate a certain smell with burning and now your brain remembers that smell so you recognize it. Your sense of smell also can help you keep safe. For example, it can warn you not to eat something that smells rotten or help you detect smoke before you see a fire.

How Does the Nose Help With Taste?

Most people just think of the tongue when they think about taste. But you couldn't taste anything without some help from the nose! The ability to smell and taste go together because odors from foods allow us to taste more fully.

Take a bite of food and think about how it tastes. Then pinch your nose and take another bite. Notice the difference? It's just another reason to appreciate your knockout of a nose!

Your Eyes

Which part of your body lets you read the back of a cereal box, check out a rainbow, and see a softball heading your way? Which part lets you cry when you're sad and makes tears to protect itself? Which part has muscles that adjust to let you focus on things that are close up or far away? If you guessed the eye, you're right!

Your eyes are at work from the moment you wake up to the moment you close them to go to sleep. They take in tons of information about the world around you — shapes, colors, movements, and more. Then they send the information to your brain for processing so the brain knows what's going on outside of your body.

You can see that the eye's pretty amazing. So, come on — let's take a tour of its many parts.

What Are the Parts of the Eye?

You can check out different parts of the eye by looking at your own eye in the mirror or by looking at (but not touching) a friend's eye. Some of the eye's parts are easy to see, so most friends will say OK. Most friends won't say OK if you ask to see their liver!

How Big Is the Eye?

The eye is about as big as a ping-pong ball and sits in a little hollow area (the eye socket) in the skull.

What Do Eyelids and Eyelashes Do?

The eyelid protects the front part of the eye. The lid helps keep the eye clean and moist by opening and shutting several times a minute. This is called blinking, and it's both a voluntary and involuntary action, meaning you can blink whenever you want to, but it also happens without you even thinking about it.

The eyelid also has great reflexes, which are automatic body responses, that protect the eye. When you step into bright light, for example, the eyelids squeeze together tightly to protect your eyes until they can adjust to the light. And if you flutter your fingers close (but not too close!) to your friend's eyes, you'll be sure to see your friend's eyes blink. Your friend's eyelids shut automatically to protect the eye from possible danger. And speaking of fluttering, don't forget eyelashes. They work with the eyelids to keep dirt and other unwanted stuff out of your eyes.

What's the Sclera?

The white part of the eyeball is called the sclera (say: SKLAIR-uh). The sclera is made of a tough material and has the important job of covering most of the eyeball. Think of the sclera as your eyeball's outer coat. Look very closely at the white of the eye, and you'll see lines that look like tiny pink threads. These are blood vessels, the tiny tubes that deliver blood, to the sclera.

What's the Cornea?

The cornea (say: KOR-nee-uh), a transparent dome, sits in front of the colored part of the eye. The cornea helps the eye focus as light makes its way through. It is a very important part of the eye, but you can hardly see it because it's made of clear tissue. Like clear glass, the cornea gives your eye a clear window to view the world through.

What's the Iris?

Behind the cornea are the iris, the pupil, and the anterior chamber. The iris (say: EYE-riss) is the colorful part of the eye. When we say a person has blue eyes, we really mean the person has blue irises! The iris has muscles attached to it that change its shape. This allows the iris to control how much light goes through the pupil (say: PYOO-pul).

What's the Pupil?

The pupil is the black circle in the center of the iris, which is really an opening in the iris, and it lets light enter the eye. To see how this works, use a small flashlight to see how your eyes or a friend's eyes respond to changes in brightness. The pupils will get smaller when the light shines near them and they'll open wider when the light is gone.

What's the Anterior Chamber?

The anterior (say: AN-teer-ee-ur) chamber is the space between the cornea and the iris. This space is filled with a special transparent fluid that nourishes the eye and keeps it healthy.

What's the Lens?

These next parts are really cool, but you can't see them with just your own eyes! Doctors use special microscopes to look at these inner parts of the eye, such as the lens. After light enters the pupil, it hits the lens. The lens sits behind the iris and is clear and colorless.

The lens' job is to focus light rays on the back of the eyeball — a part called the retina (say: RET-i-nuh).

The lens works much like the lens of a movie projector at the movies. Next time you sit in the dark theater, look behind you at the stream of light coming from the projection booth. This light goes through a powerful lens, which is focusing the images onto the screen, so you can see the movie clearly. In the eye's case, however, the film screen is your retina.

What Does the Retina Do?

Your retina is in the very back of the eye. It holds millions of cells that are sensitive to light. The retina takes the light the eye receives and changes it into nerve signals so the brain can understand what the eye is seeing.

What's the Ciliary Body?

The lens is suspended in the eye by a bunch of fibers. These fibers are attached to a muscle called the ciliary (say: SIL-ee-air-ee) body. It has the amazing job of changing the shape of the lens. That's right — the lens actually changes shape right inside your eye! Try looking away from your computer and focusing on something way across the room. Even though you didn't feel a thing, the shape of your lenses changed. When you look at things up close, the lens becomes thicker to focus the correct image onto the retina. When you look at things far away, the lens becomes thinner.

What's the Vitreous Body? And What's Vitreous Humor?

The biggest part of the eye sits behind the lens and is called the vitreous (say: VIH-tree-us) body. The vitreous body forms two thirds of the eye's volume and gives the eye its shape. It's filled with a clear, jelly-like material called the vitreous humor. Ever touch toy eyeballs in a store? Sometimes they're kind of squishy — that's because they're made to feel like they're filled with vitreous humor. In a real eye, after light passes through the lens, it shines straight through the vitreous humor to the back of the eye.

What Do Rods and Cones Do?

The retina uses special cells called rods and cones to process light. Just how many rods and cones does your retina have? How about 120 million rods and 7 million cones — in each eye!

• Rods see in black, white, and shades of gray and tell us the form or shape that something has. Rods can't tell the difference between colors, but they are super-sensitive, allowing us to see when it's very dark.

• Cones sense color and they need more light than rods to work well. Cones are most helpful in normal or bright light. The retina has three types of cones. Each cone type is sensitive to one of three different colors — red, green, or blue — to help you see different ranges of color. Together, these cones can sense combinations of light waves that let our eyes to see millions of colors.

Rods and cones process the light to give you the total picture. You're able to see that your friend has brown skin and is wearing a blue hat while he tosses an orange basketball.

                             What Are the Lacrimal Glands? And Why Do Eyes Need Tears?

For crying out loud, the eye has its own special bathing system — tears! Above the outer corner of each eye are the lacrimal (say: LAK-ruh-mul) glands, which make tears. Every time you blink your eye, a tiny bit of tear fluid comes out of your upper eyelid. It helps wash away germs, dust, or other particles that don't belong in your eye.

Tears also keep your eye from drying out. Then the fluid drains out of your eye by going into the lacrimal duct (this is also called the tear duct). You can see the opening of your tear duct if you very gently pull down the inside corner of your eye. When you see a tiny little hole, you've found the tear duct.

Your eyes sometimes make more tear fluid than normal to protect themselves. This may have happened to you if you've been poked in the eye, if you've been in a dusty or smoking area, or if you've been near someone who's cutting onions.

And how about the last time you felt sad, scared, or upset? Your eyes got a message from your brain to make you cry, and the lacrimal glands made many, many tears.

How Can I Protect My Eyes?

Your eyes do some great things for you, so take these steps to protect them:

• Wear protective goggles in classes where debris or chemicals could go flying, such as wood shop, metal shop, science lab, or art.

• Wear eye protection when playing racquetball, hockey, skiing, or other sports that could injure your eyes.

• Wear sunglasses. Too much light can damage your eyes and cause vision problems later in life. For instance, a lens could get cloudy, causing a cataract. A cataract prevents light from reaching the retina and makes it difficult to see.

The eyes you have will be yours forever — treat them right and they'll never be out of sight!