Structure and Function of Smooth Muscle with Special Reference to Mast Cells

The structure of the smooth muscle tissue is quite different from that of other muscle tissue subtypes. The primary smooth muscle structural and functional unit – the smooth muscle myocyte (Myocytus nonstriatus) has unique structure, arrangement and innervation. The spindle shape of the mononucleated smooth muscle cell permits a close contact among cells in the splanchnic and vascular walls. Regardless of its location in the body, the communication between tightly packed adjacent spindle-shaped mononucleated smooth muscle cells occurs via a specific junction, referred to as Macula communicans (nexus, gap junction). The space between the different macular connexons is about 2 nm, which allows low-molecular compounds to pass from one cell to another. This type of junction is analogous to the plasmodesma (pl. plasmodesmata), encountered in cells of plants. The basement membrane covering each smooth muscle cell, is absent at gap junction sites.