Resting Membrane Potential
Resting Membrane Potential Introduction
Membrane potentials refer to the voltage difference between the inside and the outside of a cell membrane. And when the cell is in a resting state, the corresponding membrane potential is called resting membrane potential. It is the result of the movement of different ion species through various ion channels and transporters in the plasma membrane, such as uniporters, cotransporters, and pumps. By inserting a microelectrode into a cell and comparing the charge to a reference electrode in the extracellular fluid, the resting membrane potential can be measured. In general, the resting membrane potential typically is around -70 millivolts (mV). The membrane potential changes are essential for neural signaling so that the resting membrane potential is really important for the nervous system.
Resting Membrane Potential Generation
There are two major factors for resting membrane potential generation, which include the difference in ion concentration inside and outside the cell, as well as the selective permeability of the cell membrane.
Without the help of ion channel proteins that span the membrane, most ions and molecules cannot cross the lipid bilayer as the cell membranes are selectively permeable. It has been found that potassium (K⁺), sodium (Na⁺), chloride (Cl⁻), and calcium (Ca²⁺) are the most common intra- and extracellular ions in the nervous tissue. When the neuron is at a resting state, the potassium (K⁺) channels would be the main type of ion channel to allow K⁺ to migrate across the membrane. In this case, the movement of K⁺ would determine the resting membrane potential.
The differences in ion concentration inside the cell compared to outside are determined by the sodium-potassium (Na⁺/K⁺) pump activity. As a transmembrane protein, it pumps two K⁺ ions in, and then three Na⁺ ions pumps out of the cell. The established concentration gradients result in higher K⁺ concentration inside and higher Na⁺ concentration outside of neurons. Then K⁺ can diffuse to a lower concentration area via its concentration gradient. And finally, the negative charge is generated and the net effect is the observed negative resting potential.
Fig.1 Schematic diagram for the generation of the membrane potential.
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