|
Robert Krampf's Experiment of the Week |
|
|
|
This Week's Experiment - #188 Don't Push |
|
|
|
It has been a while since I did a biology related experiment, so this week we |
|
are going to take a look at how your muscles work. In particular, we are |
|
going to examine the muscles that move your arm. For this experiment, you |
|
will need: |
|
|
|
your arm |
|
|
|
First, lets examine a muscle that most people are familiar with. Hold your |
|
arm out in front of you and make your hand into a fist. Bend your elbow and |
|
bring your hand near your shoulder. This should cause the muscles of your |
|
upper arm to tighten and bulge. Place your other hand around your upper arm. |
|
Straighten your arm and bend it again several times, noticing how the muscle |
|
changes as you do. |
|
|
|
Muscles are wonderful things, but most people really do not know how they |
|
work. Your muscles move you by pulling or relaxing. That is all. Muscles |
|
cannot push. |
|
|
|
Wait a minute. I can hear you saying that muscles must be able to push. How |
|
can pulling muscles open a door that says PUSH? (I frequently find myself |
|
pulling on push doors.) Lets think about the muscles. When a muscle is |
|
relaxed, it is longer and thinner. When you tense the muscle, it contracts, |
|
to get shorter and thicker. If the muscle was not attached to anything, this |
|
would not do much. When you tensed your muscles, you would just get lumpier. |
|
Luckily, our muscles are attached to our bones. When you tighten the |
|
muscles in your upper arm, they get shorter. They are attached to your |
|
shoulder at one end and to the bones of your lower arm at the other end. The |
|
muscle pulls your lower arm bones towards your shoulder, bending your arm. |
|
|
|
What happens when you straighten your arm? Your muscles can only pull, so |
|
your upper arm muscles cannot simply push your lower arm away. Instead, you |
|
need a different set of muscles to pull your arm in the other direction. Try |
|
flexing your arm a few times and see if you can find the muscle that |
|
straightens your arm. (Hint: Try tensing your arm to hold it very straight. |
|
Then notice which muscles tighten.) |
|
|
|
Did you find them? If not, try putting your other hand on your shoulder, |
|
against your neck. Your fingers should reach over your shoulder, onto your |
|
back. Now, straighten your arm and tense the muscles. You should feel the |
|
muscles on the back of your shoulder tighten. |
|
|
|
How can muscles tightening in your shoulder make your arm straighten? These |
|
muscles are attached to a long, stringy tissue called a tendon. This tendon |
|
reaches down your arm and attaches to the other side of your lower arm bones. |
|
When the muscles of your upper arm tighten, they bend your arm. To |
|
straighten your arm, you relax the muscles of your arm and tighten the |
|
muscles in your shoulder. These muscles pull on the tendon, which pulls on |
|
the bones of your lower arm to extend them. |
|
|
|
Your body works much like a puppet. You pull one string to bend your arm and |
|
pull the opposite string to extend it. Try to find the muscles that move |
|
your fingers. (Another hint: Most of them are not in your hand.) If you |
|
look closely at the front and back of your wrist as you move your fingers, |
|
you can probably see the tendons that attach your fingers to the muscles that |
|
move them. Put your fingers lightly around your wrist and I am certain you |
|
will be able to feel the tendons moving. When you have that figured out, |
|
then think about how muscles that can only pull let you stick out your |
|
tongue. That should keep you busy until next week. |
|
|
|
**************************************** |
|
Get volume 1 of the Experiment of the Week postings in book form! To order, |
|
send $9.95, plus $3.00 postage and handling to: |
|
|
|
Robert Krampf |
|
PO Box 60982 |
|
Jacksonville, FL 32236-0982 |
|
|
|
Include your e-mail address and I will notify you when I get your order. |
|
|
|
*************************** |
|
|
|
If you would like to be on the list, just send me an e-mail at [email protected], asking to be added to the Experiment of the Week List. |
|
|
|
Check out our web site at: |
|
http://www.krampf.com |
|
|
|
From Robert Krampf's Science Education Company |
|
4850 A1A South |
|
St. Augustine, FL 32084 |
|
(904) 471-4578 |
|
|
|
|