Today we explored the structure and function of the human hand. First I asked the girls to trace their hands on paper. Then we identified the different components of the hand and added them to the drawing. We identified the fingernails and knuckles on the back side of the hand, and located the joints and the palm on the front side of the hand. The girls remembered how to lift their fingerprints from our crime scene activity, and added them to the fingertips.
We tested the importance of opposable thumbs by trying to lift a plastic cup without using the thumb. It was not an easy task. It is interesting to know that there are hardly any muscles in the fingers, instead tendons connect the fingers to the palm. Fingers movement is controlled by the muscles in the palm or forearm. When the muscles contract the tendons pull on fingers, which make them move. To understand this concept, we built a simple robotic hand.
For the robotic hand, we used a foam sheet to create the skin, straws to create the bones, and strings to create the tendons. The straws have small holes in lieu of joints (which I prepared in advance). To create the holes the straw was folded and a small corner was cut off. Each girl received 2 straws with 2 "joints" to use for the pinky and thumb, and 3 straws with 3 "joints" for the index, middle, and ring fingers.
After cutting the foam sheet in the shape of a hand, the girls taped the straws to the fingers and palm. This part was a bit tricky, since the straws had be positioned with "joints" openings facing up. The final step was to thread the string through the straws to create the tendons.
The robotic hand is ready. Pulling the strings causes the fingers to move, similar to the way tendons move the fingers in the hand.