The cell membrane of the contractile unit

The cell membrane was initially considered only as a barrier delimiting the cytoplasm from the extracellular environment but further research revealed that the cell membrane has a number of functions that are essential to the cell [1]. Structurally, the cell membrane is formed by a lipid bilayer (Fig. 3.1), with each of the two layers composed of molecules called phospholipids. The lipid component is, by definition, water-repellent, while the phosphate component is hydrophilic. The membrane is formed as the phosphate moves toward the outer surface of the cell, attracted by the aqueous environment, which the inwards-oriented lipids seek to escape. An additional and very important component of this double lipid structure consists of the membrane proteins.