Membrane Potential

Abstract A thin lipid bilayer membrane with embedded proteins surrounds all cells. The potential difference across this membrane depends on the ion concentrations on either side of this membrane and the permeability of the membrane to those ions. The permeability of the membrane is controlled by ion channel proteins that span the plasma membrane. These proteins form water‐filled pores that permit ions to cross the hydrophobic membrane. The ion concentration gradient is formed by ion pumps that use energy from adenosine triphosphate (ATP) hydrolysis to move ions against their concentration gradients. The ionic gradient forms a chemical force, while selective permeability of the membrane via ion channel regulation generates an electrical force. Together these forces govern the movement of ions across the plasma membrane to generate the membrane potential. Key Concepts All cells generate and maintain a membrane potential. The membrane potential is essential for cell viability, since all cells use the energy of the membrane potential to transport essential molecules (e.g. amino acids) across the plasma membrane. The membrane potential is generated by the combination of chemical and electrical forces. Ion pumps use cellular energy to transport ions across the cell membrane to establish the ionic gradients that form the chemical force. Ion channels form selective ion pathways across the plasma membrane to help form the electrical force. Neurons and other excitable cells regulate ion channel activity to alter the membrane potential and produce electrical signals such as the action potential.