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Pneumatics can be applied to model muscles in the human system. Some basic information about how muscles work is necessary to fully appreciate the pneumatic replacement system that can represent the contraction of muscle fibers.
Materials
• Syringes (4): two 10 cc, two 20 cc
• Plastic tubing
• Tag board or foam meat trays
• Brass Brads or screws and nuts
• Tape
• Hole punch
• Side cutters or utility knife
Starting
Ask students to flex their biceps. Recall the names of the arm muscles and how the levers in the arm operate. Challenge students to observe their own flexed muscles. Ask them to describe the shape of the muscle when it is flexed versus when it is at rest. Ask them to describe the length of the muscle when it is flexed versus relaxed. Review basic information about how muscles are paired.
How do muscles work? Listen to students prior knowledge and ideas about how muscles work. Provide basic information:
Muscles
Muscles are composed of thousands of microscopic elongated cells.
The muscle cells are bundled together into packages surrounded by a thin membrane, or fascia, to form a “muscle.”
You can actually feel individual muscles because they are separated by these membranes. At each end of the muscle is an attachment called a tendon. The tendons attach directly to the bone.
Nerves stimulate the cells to contract. Inside the cells are protein fibers that can change their shape depending on what chemical signal they receive. Contracting and relaxing is a complex chemical process. Muscles always work in pairs. One contracts, pulling the bone toward the origin. The other relaxes and allows it to stretch.
When the muscle contracts it shortens the connection between the origin and insertion on the bone. A shortened muscle pulls the bone as shown.
Engineering an Arm: Procedures
1) Cut two pieces of foam to represent the humerus and the ulna.
2) Using a hole punch, follow the pattern to make holes at the pivot of the humerus and ulna and at muscle origins and insertions.
3) Attach the humerus to the ulna with a brad using washers on all three surfaces.
4) Verify that the model arm will articulate freely by attaching two strings to represent the triceps and biceps. Articulate the muscle and look for problems of binding or buckling. You may need to add a radius (in red below) to strengthen the ulna.
5) Prepare pneumatic activators by taking two 5 ml syringes and taping on each end a piece of foam. Holes are punched in the ends of the foam pieces so they can be attached to the arm.
It may help to clip-off part of the plunger side so that the foam will sit more securely. See below:
5) Connect the syringes as shown below and then add tubing and paired syringes.
6) Experiment with actuators to simulate the muscle movement. What must a syringe (biceps muscle) do to pull the arm up? What has to happen to the triceps at the same time?
Manipulate the arms to perfect the rhythm of how the muscles have to work in pairs and coordinate movement. If one student “is the biceps” and another “is the triceps,” they must coordinate their activity to make the arm move smoothly. If the muscles do not coordinate correctly the arm “spasms” and works poorly. If proper electrical signals don’t reach the muscles, limbs act the same way. People who suffer from some kinds of diseases experience an inability to move because muscles are not signaled or coordinated correctly.
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