In order to understand the treatment of miasthenia gravis and miasthenic sindrome, the morphology, physiology and pharmacology of the motor unit were reviewed. Electromiographic, pharmacologic and electrophysiologic studies accomplished by several authors have special caractheristics which define miasthenia gravis and miasthenic sindrome. Certain venoms such as those from Elapidae can produce signals and symptoms resembling those produced by neuromuscular blocking drugs.