The Nernst equation determines the resting potential of cell membranes based on ion concentration. Excitable cells generate an electrical impulse that changes membrane permeability, making the Nernst equation inaccurate. The Goldman equation is preferred for a more accurate assessment of membrane potential.
The Nernst equation determines the resting potential of cell membranes in the body as a factor of the concentration of ions inside and outside the cell. Cells are the basic unit of the body and the environment inside the cell is separated from the outside by a cell membrane. The intracellular environment contains a different concentration of ions from that of the extracellular environment, therefore an electric charge develops, which is defined as the resting potential. The most influential ions in determining the resting potential are those to which the cell membrane is most permeable: sodium and potassium. There is a higher concentration of potassium inside the cell than outside the cell, and the reverse is true for the sodium ion.
For many of the body’s cells, the resting potential remains constant throughout the cell’s lifespan. For excitable cells such as nerve and muscle cells, however, the resting potential simply refers to the membrane potential when the cell is not excited. An excitable cell is one that generates an electrical impulse that causes the cell to contract, in the case of a muscle cell, or emit a signal, in the case of a nerve cell.
The excitation causes the membrane permeability to change to ions, mainly potassium and sodium. This allows for the flow of ions from the area of higher concentration to the area of lower concentration and this flow causes an electric current which will change the charge across the membrane. Therefore, the Nernst equation is not applicable in this case, because the Nernst equation only takes into account the ion concentration when there is no permeability across the cell membrane.
The Nernst equation takes into account constants such as Faraday’s constant, the universal gas constant, the absolute temperature of the body and the valence of the ions considered. Potassium is the most commonly considered ion in the equation. It is the most permeable ion, so it flows more through the membrane.
The Nernst equation has been criticized because it assumes that there is no net flux of ions across the cell membrane. Realistically, there is never a net flow of ions, because ions either leak out or are actively pumped out of the cell across the membrane. In many cases, the more universal Goldman equation is preferred when predicting membrane potential. Goldman’s equation takes into account membrane permeability to ions for a more accurate assessment of membrane potential and can be used for excitable and non-excitable cells.
Protect your devices with Threat Protection by NordVPN
