Did everyone bring their muscles today? Let me see them! Good job! Did you know that you have over 640 muscles in your bodies? They help you run, jump, and play, but they also do things like pump blood throughout your body and help you digest your food. You control some of your muscles, while others - like your heart - do their jobs all by themselves. Try telling your stomach to digest your food. Can you do that? No, it just does it on its own, right? Muscles are made up of cells called muscle fibers. These cells form a type of elastic tissue- sort of like a rubber band. Thousands of small fibers make up each muscle and, when you exercise, these muscle fibers grow. So even though everyone has the same amount of muscles, some people will have bigger muscles. Although exercise helps your muscles to become bigger and stronger, too much exercize can cause your muscles to get tired and start to slow down. Sometimes overworked muscles can suddenly tighten up and become painful. This is called a cramp. When your muscles get tired, they need time to rest so they can get more oxygen and food,and can get rid of wastes.
Let's Experiment! Hold your right arm straight out in front of you. Count how many times you can open and close your fist in thirty seconds. Now rest for fifteen seconds. Try it again. Open and close your fist as many times as you can in thirty seconds. How many times were you able to do it each time? The second number should be smaller because your muscles were tired out.
Now, hold your arms straight up over your head. I want you to keep them there while I continue the lesson. Keep them there as long as you can, and we'll see who can keep them up the longest.
Maybe you've heard a story from the Bible where Moses was told to do what you are doing right now. The Israelites were fighting an important battle and God told Moses to stand on a hill above the battle and hold his hands up like this. As long as his hands stayed up, the Israelites would be winning. But if his hands came down, the enemy would start to win. Eventually Moses' muscles got tired and a couple of his friends had to use their muscles to help him. If you haven't ever heard that story, ask your mom or dad to read it to you tonight.
Three Types of Muscles
You have three different types of muscles in your body. Can anyone name them for me? Raise you hand if you know . . . Just kidding! There are three types of muscles in our body: smooth muscles, cardiac muscles, and skeletal muscles.
Smooth Muscles Smooth muscles usually form smooth layers, with one layer of muscle behind the other. Smooth muscles are sometimes called involuntary muscles because you can't control them. Your brain and body tell these muscles what to do without you even thinking about it. Smooth muscles are at work all over your body. In your stomach and intestines, they contract and relax to digest food and move it through the body. In your bladder, they allow you to hold in urine until you can get to the bathroom and they help you to push it out. Smooth muscles are also at work in your eyes, keeping them focused and causing you to blink.
Cardiac Muscle The kind of muscle that makes up your heart is called cardiac muscle. The thick muscles of the heart contract to pump blood out and then relax to let blood back in after it has circulated through the body. Just like smooth muscle, cardiac muscle works all by itself. You don't have to tell your heart to beat. It works even when you aren't thinking about it.
Skeletal Muscle Skeletal Muscles are the kind of muscle you think of when we say "muscle" - the ones that you all showed me when I asked you earlier. Skeletal muscles are voluntary muscles, which means you can control what they do. The skeletal muscles work with your bones to allow you to move. Most skeletal muscles are attached to one end of a bone. They stretch all the way across a joint (the place where two bones meet) and then attach again to another bone. Skeletal muscles are held to the bones by tendons. Tendons are cords made of tough tissue that connect bones and muscles. Did you know that the muscles that move our fingers are not in our fingers? Our fingers are very strong and yet are able to move around quickly and easily because of tendons which connect parts of our fingers to big muscles in our forearms. Watch the bottom of your wrist as you open and close your hand. Can you see the tendons and muscles moving in your arm? Muscles work by relaxing and contracting. When they contract, muscles pull on bones or tendons where they are attached. It is the pulling motion that allows you to move and do the function that you want. When they relax, muscles let you rest. Muscles ALWAYS pull. They NEVER push. Muscles often work in pairs so that they can pull in opposite directions.
Smooth Muscles Smooth muscles usually form smooth layers, with one layer of muscle behind the other. Smooth muscles are sometimes called involuntary muscles because you can't control them. Your brain and body tell these muscles what to do without you even thinking about it. Smooth muscles are at work all over your body. In your stomach and intestines, they contract and relax to digest food and move it through the body. In your bladder, they allow you to hold in urine until you can get to the bathroom and they help you to push it out. Smooth muscles are also at work in your eyes, keeping them focused and causing you to blink.
Let's Experiment! OK, you're going to have to put your hands down now. Hold them in front of your face and hold the tips of your pointer fingers out so they are close but not touching. Try to keep your fingers perfectly still without moving them at all. Now, stare at your fingers and try not to blink. What happens? Does it look like your fingers are bouncing around? That is because the involuntary muscles in your eyes are trying to blink. Eye muscles are the busiest muscles in the body. Scientists estimate they may move more than 100,000 times a day!
Cardiac Muscle The kind of muscle that makes up your heart is called cardiac muscle. The thick muscles of the heart contract to pump blood out and then relax to let blood back in after it has circulated through the body. Just like smooth muscle, cardiac muscle works all by itself. You don't have to tell your heart to beat. It works even when you aren't thinking about it.
Skeletal Muscle Skeletal Muscles are the kind of muscle you think of when we say "muscle" - the ones that you all showed me when I asked you earlier. Skeletal muscles are voluntary muscles, which means you can control what they do. The skeletal muscles work with your bones to allow you to move. Most skeletal muscles are attached to one end of a bone. They stretch all the way across a joint (the place where two bones meet) and then attach again to another bone. Skeletal muscles are held to the bones by tendons. Tendons are cords made of tough tissue that connect bones and muscles. Did you know that the muscles that move our fingers are not in our fingers? Our fingers are very strong and yet are able to move around quickly and easily because of tendons which connect parts of our fingers to big muscles in our forearms. Watch the bottom of your wrist as you open and close your hand. Can you see the tendons and muscles moving in your arm? Muscles work by relaxing and contracting. When they contract, muscles pull on bones or tendons where they are attached. It is the pulling motion that allows you to move and do the function that you want. When they relax, muscles let you rest. Muscles ALWAYS pull. They NEVER push. Muscles often work in pairs so that they can pull in opposite directions.
Let's Experiment! Look at this MODEL OF A FINGER that I built. It shows how the tendons going to our fingers allow them to open and close. See how it curls like a real finger when I pull on this string? Doctors call this "flexion". Notice that when I release the string, the finger straightens part way because of gravity, but not all the way. To get it to straighten all the way, which is called "extension", I need to pull on another string. This works like a real hand. Tendons, connected to pairs of muscles which are pulling in opposite directions, work together to allow you to bend and straighten your fingers.
Place your left hand on the top muscle of your right upper arm. You are touching a muscle called the biceps. Make a tight fist and bring the fist toward your shoulder. Your biceps will shorten and become harder as your arm is raised. Un-clench your fist, and stretch your arm out in front of you. Notice the change in size, shape, and hardness of your biceps?
Now place your left hand under your upper arm. You are touching a muscle called the triceps. The triceps and biceps are paired muscles that pull in opposite directions. Biceps bend the arm while triceps straighten the arm. Make a tight fist, and move your arm toward and away from your shoulder. You can feel your triceps changing in size, shape, and hardness. Most of the movements of your body use at least two muscles working against each other. There are actually six muscles that work together to allow you to roll your eyes up, down, and sideways.
COLORING PAGE SHOWING BICEPS AND TRICEPS IN ARM
More Muscle Facts
* About 1/2 of a man's body weight is muscle, and about 1/3 of a woman's.
* The largest muscle in the body is the gluteus maximus in your buttocks.
* There are about 200 muscles that work together when you walk.
* The smallest muscle in the body is the stapedius, which is located in the middle ear.
* Your tongue is actually made of a group of muscles that work together to allow you to talk and help you chew food.
* The strongest muscle in your body is the one that allows you to close your jaw.
Activity Pages For This Lesson
Muscle System Word Find
Find the hidden words related to the muscular system.
Muscle Worksheet
Label the muscles
Projects To Do At Home
Brown Paper School book: Blood and Guts
This book includes several additional experiments which parents can do with their children at home to provide additional learning about the muscular system. The are directions for building a model arm, for dissecting a (beef) muscle, and for doing a muscle-tendon-joint dissection on a chicken wing, as well as some additional athletic activities the children can do to observe their muscles in action. While this book does contain some evolutionary references, the experiments are very good and it has wonderful drawings and step by step directions for dissections.
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