Homeschool Printables and Resources

Try this demonstration:

Stand in an open doorway. Press the back of your hands against the door frame as if you are trying to raise your arms. Stay in this position for about one minute, pressing against the door frame the whole time!

from: 39 Easy Animal Biology Experiments by Robert Wood

Your arms will rise by themselves.

The brain sent signals to the muscles to raise the arms. This signal was sent for a long enough period to put tension on the muscles. When you stepped out of the doorway, some of the tension was still there, and the arms began to rise.

More details:

The brain is the master control center of the body. The brain constantly receives information from the senses about conditions both inside the body and outside it. The brain rapidly analyzes this information and then sends out messages that control body functions and actions. The brain also stores information from past experience, which makes learning and remembering possible.
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from World Book