Endplate contributions to the safety factor for neuromuscular transmission.

The neuromuscular junction (NMJ), for most extremity and axial skeletal muscle fibers, with the exception of extraocular, middle ear, and some facial and pharyngeal muscles, is a 'slave' synapse that is designed to activate the muscle fiber every time the nerve terminal is activated. The fidelity of the NMJ hinges upon the electrical depolarization produced by activation of acetylcholine receptors (AChRs), called the endplate potential (EPP), being larger than is needed to trigger an action potential (AP) in the skeletal muscle fiber. The safety factor (SF) is a measure of how much larger the EPP is than the depolarization needed to trigger an AP (EAP). The SF depends on the amount of transmitter released, AChR density, EAP, and the effectiveness of the EPP in stimulating the Na(+) channels that trigger the AP. This study focuses on the postsynaptic factors that influence the SF and how the SF is altered in myasthenia gravis.