At the neuromuscular junction, intracellular recording from the end plate reveals spontaneous miniature end plate potentials of about 0.4 mV occurring randomly at rest. Each of these events represents:

• A Opening of a single postsynaptic nicotinic receptor channel
• B A propagated action potential in the terminal Schwann cell
• C Leakage of acetylcholine through the presynaptic membrane without vesicle fusion
• D Spontaneous exocytosis of one synaptic vesicle containing acetylcholine ✓

Explanation

Acetylcholine is stored in quantal packages of roughly 10,000 molecules per vesicle. Random spontaneous fusion of a single vesicle releases one quantum, producing a miniature end plate potential of about 0.4 mV, far too small to reach threshold. A nerve-evoked end plate potential is the summed response to hundreds of quanta released simultaneously by calcium entry. A single channel opening produces only a tiny current transient, not a measurable 0.4 mV potential, eliminating option A.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.