<P> The structure has been variously referred to by different writers as the ectoplast (de Vries, 1885), Plasmahaut (plasma skin, Pfeffer, 1877, 1891), Hautschicht (skin layer, Pfeffer, 1886; used with a different meaning by Hofmeister, 1867), plasmatic membrane (Pfeffer, 1900), plasma membrane, cytoplasmic membrane, cell envelope and cell membrane . </P> <P> Some authors that did not believe that there was a functional permeable boundary at the surface of the cell preferred to use the term plasmalemma (coined by Mast, 1924) for the external region of the cell . </P> <P> Cell membranes contain a variety of biological molecules, notably lipids and proteins . Material is incorporated into the membrane, or deleted from it, by a variety of mechanisms: </P> <Ul> <Li> Fusion of intracellular vesicles with the membrane (exocytosis) not only excretes the contents of the vesicle but also incorporates the vesicle membrane's components into the cell membrane . The membrane may form blebs around extracellular material that pinch off to become vesicles (endocytosis). </Li> <Li> If a membrane is continuous with a tubular structure made of membrane material, then material from the tube can be drawn into the membrane continuously . </Li> <Li> Although the concentration of membrane components in the aqueous phase is low (stable membrane components have low solubility in water), there is an exchange of molecules between the lipid and aqueous phases . </Li> </Ul>

The cell membrane is also called the plasma membrane and is made of a phospholipid bilayer