Structure of smooth muscle tissues

Individual smooth muscle cells are usually densely packed within a tissue.The amount of extracellular space ranges from as little as 15% in some visceral smooth muscles to as much as 50 to 60% in some large arteries, such as the rat aortic media (Gabella 1990). Adjacent smooth muscle cells within a tissue exhibit junctions along the plasma membrane that enable them to be functionally coupled. Gap junctions, which are much more common in some muscle types than in others, provide hydrophilic channels that connect the cytoplasm of adjoining muscle cells, and allow for the exchange of ions and small molecules. Intermediate junctions, also called attachment plaques, are junctions of the plasmalemma of adjacent cells at the sites of attachment of the myofilaments. These junctions provide mechanical coupling between adjacent smooth muscle cells (see Section 2.3). 

The overall structural configuration of groups of smooth muscle cells varies widely among different organs. In some tissues, such as the taenia coli, smooth muscle cells are grouped into cords or bands that run approximately parallel to the long axis of the tissue. The walls of many hollow 

There is no apparent lateral register between myofilaments in smooth muscle cells. No striations or regular repeats are visible by electron or light microscopy comparable to those observed in striated muscle tissues. In vertebrate visceral smooth muscles, bundles of parallel actin filaments are 

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