The document summarizes key concepts about cell membrane physiology: The plasma membrane is a fluid lipid bilayer embedded with proteins. It uses different transport mechanisms like diffusion, facilitated diffusion, and active transport to control what moves in and out. Active transport uses ATP and transports substances against their concentration gradient, like the sodium-potassium pump maintaining sodium and potassium gradients. The membrane potential and action potentials allow cells to communicate via opening and closing of ion channels.