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Learning how muscles work with bones to help our bodies move.
Did you know that even when you are standing perfectly still, hundreds of tiny 'engines' inside you are working hard to keep you upright and breathing?
Your body has over 600 muscles that act like engines to move your parts. These are divided into two main groups. Voluntary muscles are the ones you control with your thoughts. When you decide to kick a ball or wave to a friend, your brain sends a signal to these muscles to move. Involuntary muscles, on the other hand, work automatically. You don't have to remind your stomach to digest lunch or your lungs to breathe; these muscles work hours a day, even when you are fast asleep!
Quick Check
If you are blinking your eyes to clear some dust, but you didn't 'think' about doing it, is that muscle action mostly voluntary or involuntary?
Answer
Involuntary (though blinking can be both, the automatic part is involuntary).
Muscles have one very important rule: they pull, they never push. To move a bone, a muscle must get shorter and thicker. This is called contraction. Muscles are attached to your bones by tough, cable-like strings called tendons. Because muscles can only pull, they usually work in pairs. While one muscle pulls to bend a joint, a different muscle on the other side pulls to straighten it back out. They are the ultimate teamwork experts!
1. Hold your arm out straight. 2. To bend your elbow, your bicep muscle (on top) contracts. 3. The bicep pulls on the tendon, which pulls the bone in your lower arm up. 4. To straighten it, the bicep relaxes and the tricep (on the bottom) pulls.
Quick Check
Can a single muscle push a bone away to straighten your arm?
Answer
No, muscles can only pull. A different muscle must pull from the other side to straighten the arm.
The most important muscle in your body is your heart. It is made of a special type of tissue called cardiac muscle. Unlike your leg muscles, which might get tired after a long race, the heart is built to never get tired. It is an involuntary muscle that pumps blood to every corner of your body. If your heart beats about times every minute, it will beat over times in just one day!
If a student's heart beats times per minute while resting, how many times does it beat during a minute rest period?
1. Identify the rate: beats / minute. 2. Multiply by the time: . 3. Result: beats.
When you jump, your body uses 'antagonistic pairs.' 1. To crouch down, your hamstrings (back of thigh) contract to bend the knee. 2. To explode upward, your quadriceps (front of thigh) must contract to pull the leg straight. 3. This requires perfect timing between the two muscles so they don't pull against each other at the same time!
Which of these is an example of a voluntary muscle action?
What is the name of the tissue that connects muscle to bone?
Muscles can push bones to make them move in the opposite direction.
Review Tomorrow
Tomorrow morning, try to identify one muscle you used 'voluntarily' and one that worked 'involuntarily' while you got ready for school.
Practice Activity
Place your hand on your bicep and slowly lift a heavy water bottle. Feel the muscle get shorter and harder? That is contraction in action!