A Hearty Muscle
Ever thought about why your heart can pump blood day in and day out? It's because the heart is a - you guessed it - muscle. The muscle that makes up the heart is called the myocardium (say: my-oh-car-dee-um). It is sometimes also called cardiac muscle. The thick muscles of the heart contract (tighten up) to pump blood out and then relax (loosen up) to let blood back in after it's circulated through the body.

Just like smooth muscle, cardiac muscle works all by itself with no help from you. The brain and nervous system tell the heart muscle what to do and how fast to pump blood, and the heart muscle does the rest. This means pumping blood every minute of the day, every day of their lives.

Seeking Skeletal Muscle
So you know which muscles help you digest food, and which ones pump blood - but what about the ones that help you do everything else, from kicking a soccer ball to spooning dog food into your dog's dish?

The muscles that allow you to do these types of things are called your skeletal muscles. They are also sometimes called striated (say: stry-ay-ted) muscle (striated is a fancy word meaning striped), because the light and dark parts of the muscle fiber make them look striped.

Skeletal muscles are also known as voluntary muscles - these are the muscles that you can control. Your leg won't bend to kick the ball unless you want it to, and your dog's dinner won't find its way into the dish unless you tell your muscles to make it happen.

These muscles help to make up the musculoskeletal (say: muss-kew-low-skell-it-ull) system - the combination of your muscles and your skeleton. Together, the skeletal muscles work with your bones to give your body power and strength. In most cases, a skeletal muscle is attached to one end of a bone. It stretches all the way across a joint (the "hinged" place where two bones meet), and then attaches again to another bone.

Want to see a skeletal muscle in action? Try making a muscle with your arm. The muscle in the top half of your arm contracts, and it pulls the bones in the lower half of your arm along with it. After you make the muscle, let your arm relax. What happens to the lower part of your arm as you relax your upper arm?

Now try bending your leg, as if you were getting ready to kick a ball. The muscles in the back of your thigh contract, and they pull your leg bones up and back. Pretend to kick that imaginary ball now - and as you relax the muscles in back of your thigh and contract the muscles in the front, the bones in your lower leg will come down.

Skeletal muscles come in many different sizes and shapes to allow them to do many types of jobs. The biggest and most powerful muscles are in your back, near your spine. These muscles help keep you upright and standing tall. They also give your body the power it needs to lift and push things. So the next time you need to push that dog of yours into the car for his vet appointment, say thank you to your back muscles!

Muscles in your neck and the top part of your back aren't as large, but they are capable of some pretty amazing things: try rotating your head around, back and forth, and up and down to feel the power of the muscles in your neck. These muscles also hold your head high.

Experiment to see what you can do with other muscles in your body - how many directions can you move them in? Try doing an imaginary hula-hoop to see how the muscles around your abdomen and hips work. Sit cross-legged to check out how the biggest muscles in your legs pull on the bones to get them in the right position.

And most importantly, don't forget to find a mirror and check out the muscles in your face! The muscles in people's faces don't all attach directly to bone like they do in the rest of the body; instead, many of them attach under the skin. (The same goes for some other primates like gorillas, monkeys, and chimpanzees.) This allows you to contract your facial muscles just a tiny bit and make dozens of different kinds of faces. Even the smallest movement can turn a smile into a frown. You can raise your eyebrow to look surprised, or wiggle your nose. And while you're looking at your face, don't pass over your tongue - a muscle that's only attached at one end! Your tongue is actually made of a group of muscles that work together to allow you to talk and help you chew food. Stick out your tongue and wiggle it to see the power of those strong, flexible tongue muscles. Say aaah!

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