When there is damage only to the central nervous system, the muscle and its nerve supply remain healthy. The reason they don’t work is that they are cut off from the command signals coming from the brain.

FES applied near the muscle or nerve can then substitute artificial electrical signals for the missing normal motor signals. The carefully controlled electrical impulses make the muscle contract.

Things are different when there is also denervation. When that happens, the nerve-muscle connection is broken.  Stimulating the nerve with FES pulses will not make the muscle contract. Electrical pulses applied to the nerve or muscle will face the same barrier faced by the normal signals from the brain.

This happens in peripheral nerve disorders or injuries, in diseases of the nerve-muscle junction, and in muscle diseases.

Recently, researchers have started to design special stimulation equipment to activate denervated muscle directly and bypass the damaged peripheral nerve.

The biggest problem is that the muscle fatigues and gets weak very quickly.

Multiple sclerosis (MS) also produces problems in transmission of nerve signals. While SCI is caused by a physical insult, MS is caused by degrading of the natural insulation on nerves. Depending on where this happens, the symptoms can vary from weakness and numbness to eye problems and dizziness.

The ideal solution to neurological problems such as these is regeneration. It involves causing the central nervous system to grow new neurons to replace the ones that are injured or sick. Scientists who are working on this problem are doing basic research about how cells and nerves grow.

They are studying cells and animals to learn more about nerve cell growth in humans. Some experiments are looking at the possible benefits of electrical stimulation applied very shortly after injury to the spinal cord.

We all hope that someday FES won’t be needed anymore because regeneration will have solved the problem of paralysis. But, that day is many years in the future.