Students will then poke the second paper clip into Point B of the straw structure as shown in the figures below. These paper clips represent the tendons that attach the muscles to the bones.
Once the paper clips have been properly attached, the students will hook the rubber band onto each of the paper clips as show in the diagram below. This represents the bicep muscle.
Once the students have created their model, they should be able to pull the rubber band to simulate bicep muscle contraction.
Explain: Tell students that the muscles that are attached to and move the bones are called skeletal muscles. These muscles are attached to bones by a tough cord called a tendon. Skeletal muscles pull bones to move them. Muscles do not push bones. The names of the muscles in the upper arm are the biceps and triceps. Have students flex their arm. Feel the top of the arm. This is called the bicep. Have students discuss how this is similar to what they saw happen with their arm model. Now straighten your arm. The muscle on the other side of the upper arm, the tricep contracts, and your arm straightens.
Elaborate: Students can draw conclusions about how other skeletal muscles work to move other bones. Have students formulate a plan in order to construct a model of either a hand or leg, using similar materials from the arm model. This could be done on a separate day.