Resting Potential

Resting potential definition is that, it is the imbalance of electrical charge that persists between the interior of electrically excitable neurons a.k.a nerve cells, and their surroundings. The resting membrane potential value or a typical value of resting membrane potential is from − 60 to − 95 millivolts, where 1 millivolt = 0.001 volts, and the inside of the cell remains negatively charged. 

In this article, we will discuss the resting potential of a neuron,  resting potential and action potential, and the typical value of resting membrane potential.

Resting Membrane Potential

For our nervous system to function well, neurons must be able to send and receive electrical signals. These signals are possible because each neuron has a charged cellular membrane, i.e., a voltage or the potential difference between the inside and the outside, and the charge of this membrane can generate variations in response to neurotransmitter molecules released from other neurons and environmental or surrounding stimuli. To understand how neurons communicate or function, we must first understand the baseline of “resting” membrane charge.

Resting Membrane Potential of A Neuron

A neuron remains negatively charged at the rest state. The inside of a cell is approximately 70 millivolts or - 70 mV (This typical value of resting membrane potential is called the resting membrane potential) more negative than the outside (Please note that at resting stage nerve cell has the number varies by neuron type and by species). Resting membrane potential definition says that the resting membrane potential occurs because of the differences between the concentrations of ions inside and outside the cell. 

Let’s suppose that the membrane was equally permeable to all ions, if each type of ion would have flown across the membrane, then the system would reach the equilibrium stage. Since ions cannot cross the membrane at their will because there are different concentrations of various ions inside and outside the cell. Generally, the difference in the number of positively charged potassium ions, i.e., K+ ions inside and outside the cell controls the resting membrane potential.

How is Resting Membrane Potential Maintained?

At resting stage nerve cell has accumulated K+ ions that reside inside the cell because of the net movement with the concentration gradient. The negative resting membrane potential is maintained by raising the concentration level of cations outside the cell, i.e., in the extracellular fluid relative to inside the cell, i.e.,  the cytoplasm.

Resting Potential And Action Potential

A cell membrane creates a negative charge within the cell. The cell membrane is more permeable to potassium ion movement than the movement of sodium ions. In neurons, K+ ions are maintained at higher concentrations within the cell; however, outside the cell, Na+ ions are present at higher-level concentrations. The cell possesses potassium and sodium leakage channels that allow the two cations to release their concentration gradient.

Typically, the neurons have more potassium leakage channels than sodium ones. Therefore, potassium diffuses out of the cell at a pace than the sodium leaks in. Because more cations leave the cell than entering into it; this, in turn, results in the interior of the cell being negatively charged relative to the outside of the cell. 

The process of resting and action potential discussed above explains the action of the sodium-potassium pump that helps to maintain the resting potential, once established. 

Action Potential

In the field of physiology, an action potential or AP occurs when the membrane potential of a specific cell at a particular location rises and falls with turbulence; this depolarization then causes adjacent cells to depolarize in the same manner. Action potentials take place in animal cells, or simply, excitable cells that include neurons, endocrine cells, muscle cells, and plant cells as well.

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Point to Note:

The relatively static or resting membrane potential is the ground value for trans-membrane voltage. The relatively static a.k.a resting potential or simply the resting voltage of quiescent cells is called the resting membrane potential. A resting membrane potential opposes the specific dynamic electrochemical phenomena in neurons. It is known as the action potential and graded membrane potential.

If the inside of a cell becomes electronegative (i.e., if the potential difference or the voltage reaches a level higher than that of the resting potential), then the membrane or the cell becomes hyperpolarized. 

However, when the inside of the cell becomes less negative (i.e., the potential reaches below the resting potential value), the process is depolarization.