ELIF: How are amputees able to control and move prosthetic limbs right out of the box?
Not sure exactly in terms of how it moves but there’s a thing called phantom limb. Basically, because your body is so used to having all your limbs before the amputation, it still feels and acts like you still have whatever limbs were amputated. I’m guessing when prosthetics are attached, especially soon after the amputation, the feeling of phantom limb helps them control it like normal
Actions to move your hand originate in the brain and travel through the nervous system to muscles which contract making the movement.
When a limb is amputated the muscles making the movements may be gone but the nerves transporting the message are still present up to the point of the amputation.
Electrodes are placed at these points which detect the small electrical changes in the nerves. The prosthetic is then calibrated to complete certain movements based on electrical signals received.
So you think “rotate wrist”, signal travels from your brain, to your spine, down your arm, into the electrode, into the computer, which tells the wrist to rotate.
There are two kinds of prosthetics. They both have different goals in mind. For example, a cosmetic prosthetic limb, called a cosmesis, is designed with appearance in mind rather than controllability. Advanced plastics and pigments uniquely matched to the patient’s own skin tone allow a modern day cosmesis to take on an amazingly life-like appearance. Even details such as freckles, hair and fingerprints can be included, bringing the cosmesis to the point where it’s nearly indistinguishable from the original missing arm or leg.
Other prosthetics are designed to actually be somewhat of a replacement in functionallity for the amputee.
I think your question aimed at the prosthetics that aren’t body powered and appear to have a mind of their own.
These devices actually listen to muscles remaining in the residual limb that the patient can still contract. Because muscles generate small electrical signals when they contract, electrodes placed on the surface of the skin can measure muscle movements. Although no buttons are physically pressed by the muscles in this case, their contractions are detected by the electrodes and then used to control the prosthetic limb. Scientific term is myoelectric prosthetics;)
I hope my answer could help.
Have a good day!