The ability of two neurons to talk to each other starts with the resting membrane potential (RMP), which in turn allows neurons to propagate action potentials. To explain the RMP we start with two fluid-filled compartments separated by a semi-permeable membrane. These two fluid-filled compartments represent the inside and outside of the cell. On one side of the membrane is the intracellular space, and the other side is the extracellular space. The membrane wall itself is impermeable to sodium and potassium but within the membrane, sodium and potassium leak channels allow these two ions to move down their gradients.