Resting membrane potential

The resting membrane potential of a neurone is the electrical potential, or voltage, across the plasma membrane of an unstimulated nerve cell^[1]. It occurs when the net flow of ions across the plasma membrane equals zero. In humans this is said to be around -70 mV^[2]. This means that the inside of the cell is negatively charged in comparison to the outside.

Resting membrane potentials are maintained by two different types of ion channels: the sodium-potassium pump and the sodium and potassium leak channels. Firstly, there is a higher concentration of thepotassium ions inside the cell in comparison to the outside of the cell. This creates an unequal distribution of potassium ions, or more accurately, a potassium ion gradient is created. Therefore, following the concentration gradient, the potassium ions will diffuse from the inside of the cell to outside of the cell via its leaky channels. As the potassium ions leave the cell, it increases the number of anions trapped inside the cell, hence accumulating the negative charges and the positive charges are accumulated outside of the cell. Therefore more positively charged ions are being removed from the cell than are entering it making the inside environment of the cell comparatively negative to the outside^[3].

The sodium-potassium pump moves three sodium ions out of the cell for every two potassium ions it moves into the cell continuously. It, therefore, maintains the large potassium ion gradient across the membrane, which in turn provided the basis for resting membrane potential. The negatively charged macromolecules or ions, usually chloride ions, cannot pass through the plasma membrane as they are too large to be moved in or out of the cell via the chloride channels. This is due to the channels being too large and bulky, hence anions remain trapped inside the cell^[4].

The resting membrane potential can be measured by placing one microelectrode inside the cell and another outside the cell. The values are generated in millivolts (mV). The ratios of the negative charges and positive charges between inside and outside of the cells are compared^[5].

References

1. ↑ Jeff Hardin, Gregory Bertoni, Lewis J. Kleinsmith. Becker's World of the Cell, Eighth edition. p G-20.
2. ↑ Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P. (2008) Molecular Biology of the Cell, 5th edition, New York: Garland Science (page 669)
3. ↑ Jeff Hardin, Gregory Bertoni, Lewis J. Kleinsmith. Becker's World of the Cell. p.368-369
4. ↑ Khan Academy. The Neurone and Nervous System. The Membrane Potential. How ions cross the membrane. [Online]. Available at: https://www.khanacademy.org/science/biology/human-biology/neuron-nervous-system/a/the-membrane-potential
5. ↑ Jeff Hardin, Gregory Bertoni, Lewis J. Kleinsmith. Becker's World of the Cell. p367