What is the Difference Between Membrane Potential and Action Potential

The main difference between membrane potential and action potential is that membrane potential is the difference in charge between the inside and outside of the neuron whereas action potential is the electric potential on the neuron when the electrical signal passes through the neuron.

Membrane potential and action potential are two types of electrical potentials that can occur on the plasma membrane of the neuron.  

Key Areas Covered

1. What is Membrane Potential
– Definition, Characteristics, Importance
2. What is Action Potential
– Definition, Characteristics, Importance
3. Similarities Between Membrane Potential and Action Potential
– Outline of Common Features
4. Difference Between Membrane Potential and Action Potential
– Comparison of Key Differences

Key Terms

Action Potential, Membrane Potential

What is Membrane Potential

Membrane potential is the charge difference between the inside and the outside of the plasma membrane of a neuron at rest. Therefore, it is also called the resting membrane potential or resting voltage. The resting potential exists due to the differences in membrane permeabilities for potassium, sodium, calcium, and chloride ions. Generally, this occurs due to the variable functional activity of the ion channels, ion transporters, and exchangers. The resting membrane potential is a relatively stable value of the transmembrane potential of plant and animal cells.

Figure 1: Membrane Potential

The membrane permeability of the potassium ions is much higher than the other ions. The extracellular membrane carries a positive charge due to this strong gradient of potassium ions. Ion pumps are also responsible for the concentration gradient of potassium ions.

What is Action Potential

The action potential is the membrane potential of a specific location on the plasma membrane of the neuron where a rapid rise and fall occurs. It is a depolarization of the resting membrane potential. Then, the depolarization of a particular location of the plasma membrane causes the adjacent locations to depolarize. Usually, an action potential occurs in excitable cells such as neurons, muscle cells, and some plant cells.

Figure 2: Action Potential

Moreover, an action potential fires when the membrane potential could reach the threshold of -55 mV. After that, the cell membrane undergoes depolarization, increasing the membrane potential up to +40 mV. Generally, depolarization occurs through a rapid sodium influx. In response to the threshold, all the sodium channels open and allow the movement of sodium ions inside the cell membrane. However, at the peak, the sodium ions close up while opening the potassium ions. That, in turn, allows the movement of potassium ions outside the cell membrane. This process of depolarization is known as hyperpolarization.

Similarities Between Membrane Potential and Action Potential

• Membrane Potential and action potential are two types of electrical potentials that occur on the plasma membrane of the neuron.
• Both types of potentials occur due to the unequal distribution of ions.

Difference Between Membrane Potential and Action Potential

Definition

Membrane potential refers to the difference between the electric potential in the intracellular and extracellular matrices of the cell when it isn’t excited while action potential refers to the change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell.

Significance

Generally, the membrane potential is the charge difference between the inside and the outside of the plasma membrane of a neuron at rest while the action potential is the charge difference on the plasma membrane of the neuron when an electrical signal is passing through the neuron.

Occurrence

Membrane potential occurs when the neuron is at rest while action potential occurs when an electrical signal is passing through the membrane.

Value

Membrane potential is -70 mV while action potential is +40 mV.

Type of the Potential

Membrane potential is static while action potential is a rapid rise and fall of the potential on the membrane.

Action of the Voltage-Gated Ion Channels

Voltage-gated sodium channels are closed in the membrane potential while voltage-gated sodium channels open at the action potential.

Movement of Ions

Membrane potential occurs due to the differences in the membrane permeabilities of the potassium, sodium, calcium, and chloride ions while the action potential occurs due to the huge influx of sodium ions.

Importance

Membrane potential does not allow the transmission of nerve impulses while action potential transmits nerve impulses.

Followed by

Moreover, the membrane potential is followed by an action potential or a graded potential while an action potential is followed by the hyperpolarization of the plasma membrane.   

Conclusion

In brief, the membrane potential is the charge difference between the inside and the outside of the plasma membrane of the neuron. It occurs when the neuron is at rest. In contrast, the action potential is the charge difference between the inside and the outside of the plasma membrane when an electrical signal is passing through the neuron. Membrane potential is -70 mV and it occurs due to the permeability differences of the sodium, calcium, potassium, and chloride ions. However, an action potential occurs due to the rapid influx of sodium ions. It allows the transmission of a nerve impulse. Therefore, the main difference between membrane potential and action potential is the charge on the plasma membrane.

References:

1. “Membrane Potential.” Membrane Potential – an Overview | ScienceDirect Topics.
2. Grider MH, Jessu R, Kabir R. Physiology, Action Potential. [Updated 2022 May 15]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-.

Image Courtesy:

1. “Sodium-potassium pump and diffusion” By BruceBlaus – Own work (CC BY 3.0) via Commons Wikimedia
2. “Action potential” By Chandres – Own Work (CC BY-SA 3.0) via Commons Wikimedia