A motor unit consists of one alpha motor neuron together with all the muscle fibers it stimulates. Since the human body contains, on average, 250,000,000 muscle cells and approximately 420,000 motor neurons, a motor unit will generally consist of a single motor neuron paired with many muscle fibers. In strength training, the early strength gains seen by novices are often not gains in size or number of muscle fibers, but activation of motor units that had been previously dormant.
The motor neuron is a specialized type of nervous cell that runs between the central nervous system and the muscles. Neurons typically consist of a cell body — the axon — and the dendrites. If a neuron were to be seen as a tree, the axon would be analogous to the trunk and the dendrites to the branches. Neurons found within the brain normally have relatively short axons, but neurons that are part of a motor unit — because they must connect to the muscles of the body — have elongated axons that run through the spinal cord, and out to the associated muscle fibers. Each muscle fiber is connected to a particular dendrite, and it is through the dendrites that messages are relayed between the central nervous system and the muscle fiber.
Is an autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatigability? It is an autoimmune disorder, in which weakness is caused by circulating antibodies that block acetylcholine