(Intro)

Okay, Squeaks, I think we're ready to start your check-up.  You may have noticed that Squeaks got a few upgrades recently, and I was just getting ready to take a look and make sure everything is working perfectly.  Let's check out your arms first.  Go ahead and move your arm up.  Good.  Now move it down.  Nice.  Squeaks is a robot, so his body moves with motors.  Our bodies work a little differently.  Do you remember what part of our bodies help us move?  It's our muscles.  Let's learn more about how our bodies move while I set up the next test.

I'm sure you know, like Squeeks here does, that exercise is a really important part of keeping your body healthy and strong. And whether you're running a race, playing football, or just doing a whole bunch of jumping jacks, exercise means moving. And one SciShow Kids viewer named Autumn wants to know: How does my body move? Really awesome question Autumn!

Your body is made up of lots of different parts that all have a very special job. To help keep things organized, scientists sometimes group the parts of our bodies into what we call body systems. And all of the parts in a certain body system work together to accomplish a goal. When it comes to making you move it takes three body systems working together to get the job done. They're called the muscular system, the skeletal system, and the nervous system. Ready to check them out?

Lets start with the muscular system. Your muscular system is made of, well, muscles. Muscle is the stuff, what scientists call "tissue," that allows you to move around. Muscles don't just help you to swing a bat, or jump to catch a ball. Some muscles help you chew, wiggle your nose, stick out your tongue, or even blink. And some muscles like the ones in your back and legs just help to hold your body upright so you can walk, run, or simply sit. Muscle tissue is pretty flexible, kind of like thick rubber or elastic, and also like rubber, it can stretch and change shape. Let's see how.

When you bend your arm at the elbow, a muscle called your bicep contracts or squeezes together. When it contracts its shape gets shorter and thicker. When you straighten your arm your bicep relaxes. When a muscle relaxes its shape gets longer and thinner. But muscles contracting and relaxing aren't enough to make us move. They need to be attached to another part of our body to get the job done. And that's where the next system, the skeletal system, comes in.

The main part of your skeletal system, the skeleton, is made of all your hard, sturdy bones. Although we sometimes think of skeletons as dead things, especially around Halloween, that's actually not true. Your bones are very much alive and they have many jobs. One of the most important jobs is to support or hold up the rest of your body, and this includes your muscles. Strong cords called tendons attach your muscles to your bones. When a muscle contracts or relaxes it pulls the bone into a different position, which makes it move.

But how do your muscles know they're supposed to move at all? Well they know because they're under control of your nervous system. The most important part of your nervous system is your brain. Your brain is kind of like your body's command center. When you decide to move, your brain sends signals to your muscles giving them specific instructions on what to do. Say you're trying to pick up a snack. Your brain sends signals to the muscles in your hand and wrist telling some of them to contract. As the muscles contract they pull the bones in your fingers so that you can grab the apple. Then your brain sends more signals to your arm muscles telling them to move the bones in your arm so that you can bring the apple right to your mouth. Snack accomplished!

So it takes the actions of three body systems to help us move. The muscular, skeletal, and nervous systems.

Next up is your vision test.  Go ahead and look at the screen and tell me what you see.  The last line is a little blurry, huh?  Okay, I'll take a look.  In the meantime, remember when we learned about how our eyes see color?

Today is a really special day for me and Squeaks. We’re eating our favorite colors!

Squeaks really loves the color red, and my favorite is green. So we had some green asparagus for dinner… and check out our dessert! Don’t worry, Squeaks; we’ll eat it soon!

But first, take a look at it! When you see a shiny, red apple… the red you see is just how your brain understands the light bouncing off of it. Your brain gets information about colors from a place at the back of your eye called the retina.

The retina has two kinds of parts inside it that help you see: rods, which are mostly for seeing when it’s dark, and cones, which see colors. When the light in the room shines on the apple, some of it bounces off toward your eyes. And then, the millions of cones in your retina get to work!

There are three types of cones: some cones that look for reddish colors, some that look for greenish colors, and some that look for blueish colors. When you look at a red apple, it makes the cones that like red get excited! [Squeaks gets excited. He really loves that apple!

Jessi holds it up again.] Exactly! When the cones get excited, they send a message to your brain – kind of like a secret code. The code from your cones says, “These are the colors I saw!” Most humans can see all the colors in the rainbow pretty easily, using all three types of cones.

But not everybody has three types of cones to work with! Some people are what we call colorblind. That doesn’t mean they’re blind, and it usually doesn’t mean that they don’t see colors at all, either.

It just means that instead of three kinds of cones, only two kinds work properly. People who are red-green colorblind have a problem with some of their cones – either with the ones that look for red, or the ones that look for green. So to them, red and green don’t look as bright as they do to the rest of us.

Both colors look kind of dull, and kind of similar to each other. So red-green colorblind people have trouble telling red and green apart. The other main type of colorblindness is called blue-yellow colorblindness, which means someone has trouble telling apart – you guessed it! – blue and yellow.

Because they have a problem with their blue cones. Other types of animals can have different numbers or types of cones. Dogs, for example, only have two kinds of cones in the first place, so they see the world a little bit like some people with red-green colorblindness do.

Red and green probably look more like shades of blue and yellow and gray to them. So if you’re buying a dog toy … your dog will probably have the most fun with a bright yellow or blue ball. A red ball won’t look so great to a dog.

But what if you had more than three types of cones? A few lucky people see the world through four! We can’t imagine what the world looks like to them, but I’ll bet it’s pretty exciting.

And for some animals, it gets even more exciting that! For example, a flower that looks just looks plain yellow to you might look totally different to a bee! Bees have three kinds of cones to see color, just like us.

But instead of seeing red, green, and blue, their cones look for green, blue … and something called ultraviolet light. That’s a type of light that’s invisible to us, but it is there. And bees can see it!

It’s kind of like a trade … we can’t see ultraviolet, but we can see red, and bees can’t see red, but they can see ultraviolet. And to get bees to land on them, some flowers have not only the pretty colors that we see, but other patterns, too, painted in the ultraviolet light that bees can see, and we can’t. To a bee, some flowers that look plain yellow to us actually look like a big target sign!

Some animals can see even more. A type of animal that lives in the ocean called a mantis shrimp can have not three … not four … but twelve or even sixteen different kinds of cones! A few of those cones are just for seeing ultraviolet light.

We’re still learning what the world looks like to them, but if it looks this colorful to us, with our three kinds of cones, just imagine what the mantis shrimp see when they look at it! Now, I think it’s time to finally eat this apple! 

Now I'm taking a look at Squeaks' temperature.  His body and ours have ways of fighting germs that could make us sick and raising our temperature is one of them.  In the back of our mouths, there's another line of defense against germs: our tonsils.

I just got back from my checkup at the doctor’s office, and I’m happy to report that my doctor says everything is a-okay! [Squeaks squeaks]. Aw, thanks, Squeaks!

I’m really glad, too. Remember when we talked to Dr. Carroll about what the doctor does when you go for a checkup? [Squeaks squeaks].

Well, my doctor did a lot of those things. Like when she asked me to open my mouth wide, stick out my tongue, and say “ah!” … … while she looked inside my mouth and throat with a light. Maybe your doctor has done the same thing at one of your checkups!

One of the reasons the doctor asks you to do that is to see how your tonsils look. Your tonsils are these little lumps that help your body defend itself against the germs that can make you sick. You have a few in different places, like at the back of your nose, that you can’t see very well from the outside.

But the biggest tonsils you have are in the back of your throat — one on each side. Those tonsils are what your doctor is looking for, and with a little help, you can probably see them for yourself! First, stand in front of a mirror.

Then, ask a friend or grownup to shine a flashlight into the back of your throat while you open your mouth wide, stick out your tongue, and say “ah!” If you look carefully, you might be able to see two little lumps deep in the back of your throat. You shouldn’t try to touch them, though, because you could end up hurting yourself. The back of your throat is no place for your fingers!

But it is the perfect place for your tonsils to do their job. Try this: take in a deep breath of air. Whether you took that breath in using your nose or your mouth, the air entered your body through your throat, which means it passed right by your tonsils.

And that’s a good thing! If you could see your tonsils up close, you’d notice that they’re bumpy and kind of sticky on the outside. These sticky bumps trap some of the germs that are mixed with the air you breathe.

So your tonsils keep some germs from getting deeper into your body, where they can make you sick. But that’s not all your tonsils do! After it traps the germs, your tonsils can also destroy them.

But sometimes trapping too many germs, or some especially harmful germs, causes problems for your tonsils! Your tonsils can swell up a little, become red, and make your throat feel pretty sore. That’s called tonsillitis.

If you have tonsillitis, your doctor will probably recommend that you drink lots of liquids and get plenty of rest. Your doctor might also suggest that you eat soft or cold foods, like smoothies or soups, until your throat starts to feel better. But if you get tonsillitis a lot, a doctor may suggest that you have your tonsils taken out.

That’s why some people don’t have their tonsils anymore! [Squeaks squeaks]. Oh, don’t worry — they’re just fine without their tonsils. Even though our tonsils help defend against germs, there are lots of other parts of our bodies that help too!

Plus, as we get older, our tonsils don’t do as much work because the rest of our bodies get stronger at fighting germs. In fact, if you’re a kid, your tonsils are probably bigger than an adult’s! By the time we reach about age nine, our tonsils start to shrink.

And as our tonsils get smaller, so do our chances of a sore throat from tonsillitis. But my doctor still checks on them to see how they’re doing!

Okay, now last thing I'm going to check out is your x-ray.  That's just a special type of picture that shows the parts inside your body to help make sure everything is in the right place.  Maybe you've gotten an x-ray before.  If you have, you might have seen one of the most important parts of your body: the thing that holds you all together, your skeleton.

You may have seen skeletons, like the ones they have of dinosaurs in a museum or maybe plastic models of human skeletons, like this, maybe you've even seen dancing skeletons around Halloween, but do you know how important, cool, and powerful your skeleton really is?

Let's get to know your bones, from how they help you move to the different kinds you have and the super special job they have to do. Let's get started.

One of your skeleton's important jobs is of course to hold your body up. Your muscles are strong, but they need a frame, something to hold on to. Without a skeleton, you'd be all loosey goosey, and you wouldn't be shaped like you. And it goes both ways, without your muscles, your skeleton would just be a pile of bones, it's only by squeezing and relaxing your muscles that you're able to move your bones. So that silly dancing Halloween skeleton is just pretend, because it doesn't have muscles.

So your bones are hard enough to hold the weight of the rest of your body, but they're also hard enough to act like a protective shield around your soft, squishy organs. Your ribs, for example, are bones that protect your lungs and heart, so that even if you get a big strong bear hug, your insides don't get squeezed, too.

And speaking of strong, the strongest bone in your body is also the biggest, longest and heaviest bone you have. It's the bone that goes from your hip to your knee, called the femur, and that bone has to be big and strong because when you run, jump, walk, or even just stand still, a lot of the weight of your body falls on your femurs.

Now where do you think your smallest bone might be? The very smallest bone you have is actually in your ear. This little bone called the stapes looks kind of like a stirrup. Even in adults, it's only about the size of a grain of rice. But this tiny bone has a big job. When sounds enter your ear, they make this little bone move back and forth, these vibrations are what your ear picks up as sound. So without this teeny tiny bone, you wouldn't be able to hear.

Now I have a question: how many bones do you think we have? Well, it kinda depends. It sounds crazy, but you have fewer bones now than when you were born. Newborn babies have about 300 bones, but by the time you've finished growing, you'll only have 206. So where did all those extra bones go? Nowhere! As babies grow, some of their bones grow together, or fuse into one bigger bone, for example, your skull.

Your hard noggin is actually 21 bones fused together, plus one that's always separate, your jaw. Your skull starts out as a bunch of separate bones because that leaves lots of room for your brain to get bigger. And once you're fully grown, the fused parts make an incredibly strong shield to protect your precious brain.

One final fun fact about your skeleton: your bones are alive. Even though we often thing of skeletons as not living, like the ones we see in museums or models, your bones are full of living cells. Some of these cells are what make your bones grow and repair them if they get hurt, and other cells, which are tucked away in the thick spongy layer deep inside your bones, have a very special job. They make your blood. That's right, most of the stuff that's in your blood is actually made inside your bones. It's because your bones are alive that they're able to grow, like they're doing in you right now, and they won't be done until you're about 25 years old. But even then your bones will still be busy holding you up, helping you hear, and making your blood.

So bones in museums are cool, and Halloween skeletons are fun don't get me wrong, but nothing's more scary powerful than your own living skeleton and all the great stuff it does for you.

Squeaks, everything is looking great.  You are in excellent health.  What do you think of Squeaks' upgrades?  Do you have any questions for him or how about questions about going to the doctor?  If you do, we have a website where you can send them.  Grab a grown-up and go to Patreon.com/SciShowKids to check it out.  Thanks, and we'll see you next time here at the Fort.  

(Endscreen)