What is the safety margin for neuromuscular transmission?
In the normal subject, the amount of ACh released from the presynaptic nerve terminal decreases with each repeated nerve depolarization at a slow rate.
This means fewer receptors are activated at the muscle endplate, generating fewer MEPPs and a lower EPP.
However, the number of receptors is still high enough that this slight decline in ACh output does not drive the EPP below the depolarization threshold for the muscle fiber, and full contraction still occurs.
This functional redundancy is known as the safety margin for neuromuscular transmission.
