mechanical body parts

first problem, nerves tend to go to many muscles, so you need to pick up the signal at or close to the muscle.

second problem, how do you monitor the signal being sent down the nerve....

There will be interface problems.

let's assume you can get a good proportional signal, It's a force demand signal from a control system.. ( the brain ). What you need is a position demand signal, the force the muscle is being asked to produce is irrelevant.

example, you are trying to lift a rail truck, full force is required from your muscle, but your arm is not moving at all.....

There are currently mechanical replacement arms, the problem that they have when it comes to making it move and function like a normal body part is all in the nerves. First, when somebody loses an arm, they also lose the nerves. Right now the nerve electrical impulses are sensed using an EKG type sensor, then translated into a motor action. The other problem that they have relating to the nerves is feedback. You can't have normal motion without having some sort of feedback. For example, current mechanical replacement arms take a lot of training to be used because the arm can crush a can, but because of no feedback, it will crush a glass. Again you have the problem of if the limb is lost, then you also lose the nerves.

Yet another problem with the nerves is the signal itself. If you ran an EKG on your arm one day, it would be different on another day doing the same activity. The signal also changes based on fatigue of the muscles.

Also, if you are trying to make a hand, good luck. Right now the Utah/MIT robotic arm is nearly equal to a human hand, in terms of motion, but its control is very complicated. Have you even given any consideration to how you would manage a system that is controlled by at least 18 different tendons, which translates into 18 motors? If a person loses their forearm, they would lose the nerves that control most of thoses tendons, how would you overcome that?

I would suggest that you focus research into being able to translate nerve impulses, and then figure out how to relay information back into the nervous system. If you can do that, you will find the "Holy Grail" of artificial limb replacement.

I don't get it. But then again I'm a total layman in these issues, so maybe you can elaborate.

Wherever the limb is severed, there must still be nerves left in the stump that remains. What's so hard about connecting those "loose wires" to the motor controls of the prosthetic ? Same thing with the feedback nerves: something must still be accessible in the remaining stump. I don't think the patient will make a big fuss about some needles intruding into the stump for maybe an inch, just to make a connection with the feedback nerves linking up to the brain.

Perhaps I'm overlooking important problems of a whole different kind. Are you implying that when a nerve, either for motoric steering (output) or for feedback information (input), is cut somewhere along the way, then the entire path dies right up to the brain ?

Since they use an EKG sensor to identify nerve activity, it usually is attached over a muscle. So, technically you are correct in that the main wire is there. What you lose is the separate wires that are read using the EKG. While attaching wires directly into the nervous system to control a prostetic would be appealing to an engineer, you would have to get some very small wires that would make the whole system very delicate. Remember, the nerve cells are very small, and I don't think that we have any way of doing microsurgury to properly connect to individual cells. Whenever we try to connect any type of electrical signal back into the body (pacemakers and cochlear implants), they target areas where the imput is needed.

As for feedback through the nerves, you run into a problem with sending the proper signals back. It isn't like a computer system. As I mentioned before nerve function varies from day to day, and can change depending on fatigue. What this means is that one day a signal to use maximum force would be different than the same signal the next day.

Right now the technology and understanding of the human body do not exist. I say this because if we were able to fully interface with nerves, blindness, paralysis, and loss of limbs, would not be a problem. Medical research would be put into producing better products for these things, rather than understanding them.

the nerves are not wires, and you have a bunch to different muscles.... some nerves will be returning signals to the brain. unlike wires the individual strands going to muscles are not necessarily in nice bunches in a nerve so there is no single connection area for a given muscle in the nerve cross section.

You can't just strip off the insulation and clamp on a terminal with a screw. The body is an incredibly hostile environment. and there are problems with the risk of infection if you have to bring a wire through the skin.

And if your CRUDE probe cross conects a bunch of output nerves to a set of pain nerves??

No, but just because it's there does not mean you can tap into it.

Take an old mobile phone, try to connect two wires to it's circuit board... It's a trivial problem compared to connecting to a living nerve.

everyone here all is saying things that are true. but by placing a little reciever to the nerve and placing another one into the arm it would allow the user to have complete comtrol and not depending on the nerves and wires of the arm it would act just like the arm