Dave checks out how nerves and muscles move prosthetic limbs.
Segment Length: 6:45
Try to use a clothespin to substitute for fine motor hand functions like picking up coins or counting and moving sheets of paper. Could you unzip a zipper or tie a shoelace? Try using chopsticks. Both tools can be viewed as kinds of prostheses - not too different from the look of a prosthetic claw hand.
If you were born without your hands or lost them in an accident, how would you pick up things? If you lost a foot in an accident, how would you walk? What characteristics would the ideal artificial hand have - what would you need to be able to do with it to live normally? What about a foot?
What would your ideal prosthesis look like? How would it work? What kinds of prostheses do you think exist right now? Is it possible that you've seen someone with a prosthetic limb and haven't even noticed it? Why?
What would it be like to lose a hand, a foot, or even an entire arm or leg? Scary, that's for sure. How can amputees pick up things or walk or play soccer or write a letter? Although nothing is as good as the original flesh and bone, doctors can provide artificial replacements, called prostheses, for some damaged body parts. In addition to replacing lost functions, prostheses can result in cosmetic improvements for the patient and build self-confidence.
Simple prostheses like peg legs have been around for centuries. If they do not use sophisticated electronics, these artificial limbs are called static prostheses. One kind of artificial arm, for example, ends in a pair of hooks rather than a hand. The other end is attached to the remaining portion of the patient's arm, and then to a harness that straps over the shoulders. By moving the shoulder, the patient can pull on the harness, which in turn pulls on flexible cables to open and close the hooks, allowing the person to grasp objects. There is no sense of touch in this type of prosthesis, so the user has to watch closely what he or she is doing.
Dynamic prostheses, on the other hand, use sophisticated electronics. They can do this because the nerve and muscle systems in the human body are electrical. For example, an amputee with a myoelectric arm tenses his or her remaining arm muscle. Sensors detect this muscle electricity (myoelectricity) and transmit the signal to the artificial hand, powered by batteries, which then opens or closes.
Signals also can go from the environment to the patient, allowing an approximation of the sense of touch. For example, some prosthetic hands have sensors that can detect heat or cold and transmit that information to electrodes on the patient's skin.
Researchers are still improving prostheses. New materials allow artificial feet to press and spring on the ground very much like a real foot. One type of artificial foot transmits electronic information about pressure to amputees, allowing them to balance because they can tell whether their weight is on the toes, heels, or sides of the feet.
Artificial limbs: They look and work more like the real thing. (1995, Nov) Mayo Clinic Health Letter, p. 6.
Builder of hopes. (1995, Apr 17) Sports Illustrated, p. 5.
Field, R. (1993, Oct 15) Two big steps forward: With new prostheses, the paralyzed walk and amputees walk with feeling. Medical World News, p. 32.
Kelly, A. (1991, Feb-Mar) Advancement in prosthetics: New materials, high technology, and personal service benefit prosthetic patients. Independent Living, p. 42.
McClellan, D. (1993, July) Soft wear for artificial limbs. Technology Review, p. 22.
Ridley, K. (1994, Oct) Artificial sensations. Technology Review, p. 11.
Orthotics and Prosthetics online:
Work as a group to imitate the cooperative movements of your muscles.
Think of all the movements your hands make. These movements require sets of muscles that put opposing stress on the jointed bones in your fingers and palms. If one muscle in the set pulls harder, the hand opens. If another pulls harder, the hand closes. The muscles must work together to give you control over your movements. You can make a simple model of this process in your classroom.
Ask a prosthetist to come by and show several different types of prostheses-lower extremity, upper extremity, etc.
A thermometer is a sensor. Your eyes and skin are highly sophisticated sensors. How many other sensors can you list, both natural and invented?
Marionettes are related to prostheses, since you work their hands and feet from a distance. Construct a simple marionette out of paper, string, and paper fasteners. How easy is it to make working arms and legs?
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