Kin 305 tutorial #1 questions: why does a membrane potential exists in the cardiac myocytes. Action potentials require the membrane potential in order to exist. The membrane potential allows sodium ions to flow down the electrochemical gradient, commencing the ap. The membrane potential also exists due to different membrane permeability for potassium, sodium, and calcium ions. The high permeability for potassium ions allows more potassium efflux down a concentration gradient. The ventricle walls are 8-9 mm thick for the left ventricle; 3-4 mm for the right ventricle. The left ventricle needs to be thicker because it needs to pump blood out to various parts of the entire body, whereas the right ventricle is only pumping blood to the lungs. The permeability for k is highest because we need a very negative resting membrane potential. The nernst equation calculates the equilibrium potential for given amounts of intracellular, and extracellular ion concentrations for one particular type of ion.