Myasthenia gravis and myasthenic syndromes
The neuromuscular junction represents a synapse between the motor nerve terminal and the surface of the muscle fiber, but the synaptic and postsynaptic elements are somewhat different from those in a central synapse. The neuromuscular junction is vulnerable to a variety of disease largely because it has no blood-brain barrier and is accessible to circulating factors. Poisoning by environmental insecticides or self-administered insecticides are common, and there are varieties of plant extracts that interfere with neuromuscular transmission. One of the most common disorders is caused by autoantibodies, to molecules on the postsynaptic membrane that cause autoimmune myasthenia gravis (MG). This chapter concentrates on the mechanisms at the neuromuscular junctions, which lead to various autoimmune disorders like MG. There are now four well-defined disorders in which autoantibodies are thought to be pathogenic, namely MG, muscle-specific kinase antibody-Associated MG, Lambert-Eaton myasthenic syndrome, and acquired neuromyotonia. Their identification depends on a variety of approaches, often including an element of serendipity and deductive reasoning. © 2007 Elsevier Inc. All rights reserved.