Quantal Nature of the End-plate Potential

Abstract

THE liberation of acetylcholine from the motor nerve endings in skeletal muscle is believed to take place in a quantal manner. The arrival of the action potential at the nerve terminals elicits the release of a number of packets of acetylcholine molecules of fairly uniform size, each of them producing a unit of depolarization in the post-synaptic membrane. This view is derived from the statistical analysis of the random step-wise fluctuations in the amplitude of successive end-plate potentials recorded from single neuromuscular junctions blocked by excess magnesium ions or lack of calcium ions¹. The average magnitude of the steps was found to be identical with the mean size of the miniature end-plate potentials recorded from the same junction and due to the spontaneous extrusion of single acetylcholine quanta from the resting nerve endings.