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Body Electricity by Rylee and Kristin

I'm Rylee. My friend Kristin and I went to The Bakken Museum in Minneapolis. This place focuses on electricity and the human body. It's of special interest to me, because I use a myoelectric prosthetic arm. My arm works with electrodes, which sense electrical signals in my muscles. I want to know: how do the electrical signals in my body help my arm work?

What did we do?
The Bakken has over two-thousand electricity gadgets, but the one we're interested in is BioPac. The BioPac is an electromyograph or EMG. It shows electrical signals in muscles. We connected the electrodes from the BioPac to the muscle in our arm, and flexed our muscle. Our muscle made a signal that the BioPac could detect and display on a computer screen. This let us compare the size of the signal in different cases.

What did we find out?
We collected muscle signals for when we closed our hand quickly, and closed it slowly. We did the same for squeezing tightly, and squeezing gently. We found that the electrical signal was a little different in each case. Squeezing hard made a large signal, but squeezing gently made a small one. Closing our hand quickly made a short signal, but squeezing slowly made a longer signal. My prosthetic arm must detect these differences, too, so that's how it knows to open quickly or slowly, or squeeze tightly or not.

What can you do?
  • Do a muscle reflex test. Have a friend hold a ruler above your hand, right you're your thumb and index finger are. Without telling you when, have your friend release the ruler. You try to pinch it between your thumb and finger as soon as you notice it falling. How far does the ruler fall before you grab it? Do a comparison with the other members of your family. Who has the quickest reflexes?
  • Use your sense of touch to determine which muscles are activated when you do a simple motion, such as bending your arm at the elbow. Have your friend bend his or her arm, then straighten, then bend, over and over. Place your hand on your friend's shoulder, upper arm, and lower arm, and feel which muscles tense up during the motion. Are different muscles at work during straightening, compared to bending? Make a sketch that shows which muscles you think are involved in this process.
  • Use this human body investigation as a science fair project idea for your elementary or middle school science fair! Then tell us about it!
more resources
Muscle Contractions

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