Resting membrane potential: what is it and how does it affect neurons?

An overview of this phenomenon that occurs in neurons and allows them to communicate.

Neurons are the basic unit of our nervous system and, thanks to their work, it is possible to transmit the nerve impulse to reach brain structures that allow us to think, remember, feel and much more.

But these neurons are not transmitting impulses all the time. There are times when they rest. It is during these moments that the resting membrane potential the resting membrane potentiala phenomenon which we explain in more detail below.

What is the membrane potential?

Before further understanding how the resting membrane potential is produced and also how it is altered, it is necessary to understand the concept of membrane potential.

For two nerve cells to exchange information it is necessary for them to modify the voltage of their membranes, resulting in an action potential.which will result in an action potential. That is, an action potential is understood as a series of changes in the membrane of the neuronal axon, which is the elongated structure of neurons that serves as a cable.

Changes in membrane voltage also involve changes in the physicochemical properties of this structure. This allows changes in the permeability of the neuron, making it easier and more difficult for certain ions to enter and exit.

The membrane potential is defined as the electrical charge on the nerve cell membrane. It is the difference between the potential between the inside and the outside of the neuron..

What is the resting membrane potential?

The resting membrane potential is a phenomenon that occurs when the nerve cell membrane is not altered by either excitatory or inhibitory action potentials. The neuron does not signal, that is, it is not sending any type of signal to other nerve cells to which it is connected and, therefore, it is in a resting state.

The resting potential is determined by the concentration gradients of ions, both inside and outside the neuron.The resting potential is determined by the concentration gradients of ions, both inside and outside the neuron, and by the permeability of the membrane in letting or not letting these same chemical elements through.

When the neuron membrane is in a resting state, the inside of the cell has a more negative charge relative to the outside. Normally, in this state, the membrane has a voltage close to -70 microvolts (mV). That is, the inside of the neuron has 70 mV less than the outside, although it is worth mentioning that this voltage can vary, between -30 mV and -90 mV. In addition, at this time there are more sodium ions (Na) outside the neuron and more potassium ions (K) inside it..

How is it produced in neurons?

The nerve impulse is nothing more than the exchange of messages between neurons electrochemically. That is, when different chemical substances enter and leave the neurons, altering the gradient of these ions in the internal and external environment of the nerve cells, electrical signals are produced. Since ions are charged elements, changes in their concentration in these media also imply changes in the voltage of the neuronal membrane.

In the nervous system the main ions that can be found are Na and K, although calcium (Ca) and chlorine (Cl) also stand out. Na, K and Ca ions are positive, while Cl is negative. The nerve membrane is semipermeable, selectively letting some ions in and out.

Both outside and inside the neuron, the concentrations of ions try to balance each other.However, as mentioned above, the membrane makes this difficult, since it does not allow all ions to exit or enter in the same way.

In the resting state, K ions pass through the neuronal membrane with relative ease, whereas Na and Cl ions have more trouble passing through. During this time, the neuronal membrane prevents the exit of negatively charged proteins to the neuronal exterior. The resting membrane potential is determined by the non-equivalent distribution of ions between the inside and outside of the cell.

An element of fundamental importance during this state is the sodium-potassium pump. This structure of the neuronal membrane serves as a regulatory mechanism for the concentration of ions inside the nerve cell. It functions in such a way that for every three Na ions that leave the neuron, two K. This causes the concentration of Na ions to be higher on the outside and the concentration of K ions to be higher on the inside.

Membrane changes at rest

Although the main topic of this article is the concept of resting membrane potential, it is necessary to explain, very briefly, how changes in membrane potential occur while the neuron is at rest. For the nerve impulse to be given, the resting potential must be altered. Two phenomena occur so that the electrical signal can be transmitted: depolarization and hyperpolarization.

Depolarization

In the resting state, the interior of the neuron is electrically charged with respect to the exterior.

However, if electrical stimulation is applied to this nerve cell, i.e. by receiving the nerve impulse, a positive charge is applied to the neuron. Upon receiving a positive charge, the cell becomes less negative with respect to the outside of the neuron, almost with zero charge.The cell becomes less negative with respect to the outside of the neuron, almost with zero charge, and, therefore, the membrane potential decreases.

2. Hyperpolarization

If in the resting state the cell is more negative than the outside and, when depolarized, does not have a significant charge difference, in the case of hyperpolarization it happens that the cell is more positively charged than its outside.

When the neuron receives several stimuli that depolarize it, each one of them causes the membrane potential to change progressively..

After several of them, the point is reached where the membrane potential changes greatly, making the electrical charge inside the cell very positive, while the outside becomes negative. The resting membrane potential is exceeded, causing the membrane to become more polarized than normal or hyperpolarized.

This phenomenon occurs for about two milliseconds.. After that very brief period of time, the membrane returns to its normal values. The rapid inversion in the membrane potential is, in itself, what is called action potential and is what causes the transmission of the nerve impulse in the direction of the axon to the terminal button of the dendrites.

Bibliographical references:

• Cardinali, D.P. (2007). Applied neuroscience. Its fundamentals. Editorial Médica Panamericana. Buenos Aires.
• Carlson, N. R. (2006). Physiology of behavior 8th Ed. Madrid: Pearson.
• Guyton, C.A. & Hall, J.E. (2012) Treatise on Medical Physiology. 12th ed. McGraw Hill.
• Kandel, E.R.; Schwartz, J.H. & Jessell, T.M. (2001). Principles of neuroscience. Fourth edition. McGraw-Hill Interamericana. Madrid.