English: Illustration of motor neuron stimulation. (a) The cell nucleus is responsible for synthesizing input from dendrites and deciding whether or not to generate signals. Following a stroke or spinal cord injury, muscles are impaired because motor neurons no longer receive sufficient input from the central nervous system. (b) A functional electrical stimulation system injects electrical current into the cell. (c) The intact but dormant axon receives the stimulus and propagates an action potential to (d) the neuromuscular junction. (e) The corresponding muscle fibers contract and generate (f) muscle force. (g) A train of negative pulses is produced. (h) Depolarization occurs where negative current enters the axon at the “active” electrode indicated.