Mechanism of Action of Calcium Calcium is essential for maintaining the functional integrity of nervous, muscular, and skeletal system. It controls excitability of nerves and muscles and regulates permeability of cell membrane. It also regulates cell adhesion and maintains integrity of cell membrane. Calcium acts as intracellular messenger for hormones, autacoids, and transmitters. It is required for excitation-contraction coupling in all types of muscle and excitation-secretion coupling in exocrine and endocrine glands. It is essential for release of transmitters from nerve endings and other release reactions. It is also essential for impulse generation in heart and determines level of automaticity and A-V conduction. Calcium is also required for blood-coagulation.