How does a prosthetic arm and hand work?
Watching the horrific injuries to the soldiers in Iraq and the rehab they have to go through, I wonder how those prosthetic arms and hands turn and move an grasp. Thanks for your help.
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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.