A cell is the smallest living thing in the human organism, and all living structures in the human body are made of cells. There are hundreds of different types of cells in the human body, which vary in shape (e.g. round, flat, long and thin, short and thick) and size (e.g. small granule cells of the cerebellum in the brain (4 mm), up to the huge oocytes (eggs) produced in the female reproductive organs (100 mm) and function. However, all cells have three main parts, the plasma membrane, the cytoplasm and the nucleus. The plasma membrane (often called the cell membrane) is a thin flexible barrier that separates the inside of the cell from the environment outside the cell and regulates what can pass in and out of the cell. Internally, the cell is divided into the cytoplasm and the nucleus. The cytoplasm is where most functions of the cell are carried out. It looks a bit-like mixed fruit jelly, where the watery jelly is called the cytosol; and the different fruits in it are called organelles. The cytosol also contains many molecules and ions involved in cell functions. Different organelles also perform different cell functions and many are also separated from the cytosol by membranes. The largest organelle, the nucleus is separated from the cytoplasm by a nuclear membrane. It contains the DNA (genes) that code for proteins necessary for the cell to function. The inside environment of a cell is called the intracellular fluid (ICF), (intra- within; referred to all fluid contained in cytosol, organelles and nucleus) while the environment outside a cell is called the extracellular fluid (ECF) (extra- outside of; referred to all fluid outside cells). Plasma, the fluid part of blood, is the only ECF compartment that links all cells in the body. The plasma (cell) membrane separates the inner environment of a cell from the extracellular fluid. It is composed of a fluid phospholipid bilayer (two layers of phospholipids) and other molecules. Not many substances can cross the phospholipid bilayer, so it serves to separate the inside of the cell from the extracellular fluid. Other molecules found in the membrane include cholesterol, proteins, glycolipids and glycoproteins. Cholesterol, a type of lipid, makes the membrane a little stronger. Different proteins found either crossing the bilayer (integral proteins) or on its surface (peripheral proteins) have many important functions. Channel and transporter (carrier) proteins regulate the movement of specific molecules and ions in and out of cells. Receptor proteins in the membrane initiate changes in cell activity by binding and responding to chemical signals, such as hormones (like a lock and key). Other proteins include those that act as structural anchors to bind neighbouring cells and enzymes. Glycoproteins and glycolipids in the membrane act as identification markers or labels on the extracellular surface of the membrane. Thus, the plasma membrane has many functions and works as both a gateway and a selective barrier. Submit Your Manuscript at https://www.imedpub.com/submissions/anatomical-science-research.html or mail us to anatomicalsci@scholarlymed.com Regards Jacqueline Managing Editor Journal of Anatomical Science and Research