Communicating junctions are numerous in the myocardium because they are crucial for transporting ions and conducting excitation between neighboring cardiac muscle cells. The ultrastructure of annular gap junctions is typical of gap (communicating) junctions. The TEM image depicts membranes of neighboring cells approaching one another closely so that only a narrow (2-3 nm) split #1, #2 remains between them. Gap junctions between cardiac muscle cells make up a part of junctional complexes or intercalated discs. They are found in the terminal portions of muscle cells. The gap junctions are really common in some tissues. One may find them in the nervous system (electrical synapses), muscles, epithelium, and endothelium.