Pathogenesis of MG: current state of the artStructure and function of the NMJ. The terminal arborization of α-motor neuron axons from the ventral horns of the spinal cord and brainstem provides the nerve terminals that form the NMJ (Figure 1). These myelinated axons reach the muscles through peripheral nerves; then each axon divides into branches that innervate many individual muscle fibers. As it approaches its target fiber, each branch loses the myelin sheath and further subdivides into many presynaptic boutons, which contain ACh-loaded synaptic vesicles and face the surface of the muscle fiber at the NMJ ( Figure 1). The synaptic bouton and the muscle surface are separated by the synaptic cleft, a 20 nm-thick space that contains acetylcholinesterase (AChE) and other proteins and proteoglycans involved in

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