What causes the flow of K+ and Na+ during action potentials?

In its resting state, the cell prefers to bind K+. When activated, conformational changes within the gelatinous protein-water matrix of the cell gain a higher affinity for Na+. Bound K+ is replaced with Na+, and the two cations diffuse through the (H3O2-)n plasma membrane in quantities of roughly 3x10^-12 moles/cm3 (Ling, 1992). As the activated state ends, this process is reversed.