Biochemistry - The Chemical Reactions of Living Cells, Volume 1 - D. Metzler 1980

Setting
Eukaryotic cells
Plasma membrane

A thin (~8 nm) outer Cell membrane, the Plasmalemma (Fig. 1–4), regulates the influx and efflux of substances, conducts impulses in nerve and Muscle fibers, and participates in chemical interactions with other Cells. Folds of the outer membrane often project deep into the Cytoplasm; for example, in striated muscle cells, they form the T-system tubules, which are involved in conducting the excitation that triggers contraction (Chap. 4). Folds of The Plasma Membrane can also connect with the nuclear envelope, creating direct channels (one or more) between the extracellular environment and the perinuclear space [12].

Vesicles formed by the plasma membrane sometimes pinch off into the cytoplasm and fuse with Lysosomes. In this way, The Cell can engulf solid particles (phagocytosis) or liquid droplets (pinocytosis) from the surrounding environment. The surface of cells specialized for the secretion or absorption of specific substances from the extracellular fluid (such as cells lining the renal tubules or secretory Cells of the Pancreas) typically features ultra-fine projections known as microvilli, which significantly increase the cell surface area. In some cases, the processes of adjacent cells come into contact with one another, thereby ensuring closer intercellular adhesion.