Related Experiment Video
Updated: Aug 15, 2026

The Neuromuscular Junction: Measuring Synapse Size, Fragmentation and Changes in Synaptic Protein Density Using Confocal Fluorescence Microscopy
Published on: December 26, 2014
Fine structural localization of calcium binding sites in the neuromuscular junction
Abstract:
By means of electron cytochemical analysis of rat neuromuscular junctions subjected to perfusion with a calcium-containing (5 mM) aldehyde fixative, two kinds of presynaptic calcium binding sites were demonstrated. "A" sites are located above openings of junctional folds; these triangular elements are identical with presynaptic protrusions of the active zone and probably comprise calcium channels of the presynaptic membrane, "B" sites, located within the terminal axoplasm, are associated to multivesicular bodies probably accumulating surplus intracellular calcium. This fine structural arrangement enables a highly parsimonious usage of extracellular calcium in inducing release of acetylcholine from synaptic vesicles. Junctional folds of the postsynaptic membrane may funnel calcium ions exactly to spatially restricted calcium channels. Having entered the terminal through the channels opened by the arrival of nerve action potential, calcium ions may exert their action upon synaptic vesicles accumulated in the closest vicinity by means of stripping off hydration barriers and by inducing membrane fusions, that finally result in quantal release of acetylcholine from the terminal.
More Related Videos
08:41Dissection of Single Skeletal Muscle Fibers for Immunofluorescent and Morphometric Analyses of Whole-Mount Neuromuscular Junctions
Published on: August 14, 2021
11:12Registration of Calcium Transients in Mouse Neuromuscular Junction with High Temporal Resolution using Confocal Microscopy
Published on: December 1, 2021
Related Concept Videos
Cross-bridge Cycle
Overview of Skeletal Muscle
Neuromuscular Junction And Blockade
The Neuromuscular Junction
Relaxation of Skeletal Muscles
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.
Smooth Muscle Contraction
The onset of contraction is triggered by an increase in calcium ions within the sarcoplasm, similar to the process in striated muscle. However, smooth muscles have a relatively smaller reservoir of the sarcoplasmic...