All or nothing law: what it is and why it is important in neurology

Within physiology there are different rules that are always followed and that help us to more easily understand the functioning of the organism.

One of the most famous in relation to the electrical activity of our body is what is known as the law of all or nothing.. We are going to explore the peculiarities of this norm and its implications.

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What is the all or nothing law and how does it describe neural activation?

When we talk about electrical transmission between neurons, and from neurons to muscle fibers, we always refer to the action potentials like that little current that transmits information from cell to cell. In this electrical transmission of the action potential, two things can happen: that it occurs completely in the entire cell, or that it does not occur, but it will never occur in part. This is what is known as the principle or the law of all or nothing.

Therefore, the electrical current will travel through the entire neuron, from the dendrites that receive it, to the end of its axon

, which in some cases can even measure meters. The other option, according to the law of all or nothing, is that said electric current is not transmitted at all, since that the action potential was not intense enough to pass from the previous neuron to this. There is no middle ground for neuronal electrical distribution.

Here the so-called excitability threshold would come into play, and it is that to transmit the nerve impulse a amount of current determined in each case (it will depend on the specific conditions of each case, since it is not always a fixed number). If this excitability threshold is not reached, the law of all or nothing would be fulfilled and the impulse electrical would not be transmitted to the attached cell, thus ending at that moment the journey of the electrons.

Another feature of the all-or-nothing law is that, if the excitability threshold is reached and therefore the action potential is transmitted, it will do so by going through the entire neuron with a constant intensitywithout any fluctuations. Hence, either it occurs as a whole, maintaining all its force, or it does not occur, without other possibilities.

Associated pathologies: epilepsy

We have seen that the law of all or nothing explains one of the fundamentals of the electrical activity of our brain. The problem is when for various reasons, be it an organic disease, a trauma, a tumor or the effect of a external effect, among other reasons, generate an imbalance in the functioning of electrical circuits neural.

This would be the case, for example, of the epilepsy, a neurological disease that can generate different symptoms both psychologically and physically, from seizures that are triggered by those electrical imbalances that we mentioned in different areas of the brain.

As this pathology exists and the electrical movement between neurons is governed by the law of all or nothing, action potentials of higher intensity than normal are generated in certain brain areas, which excite the cell membrane of the next neuron and therefore transmit the current, reaching the contraction of muscle fibers and causing the spasms, when in other circumstances those action potentials would not have been so high and therefore would not have caused all this symptomatology.

To correct this pathology there are different methods that have been shown to be effective., being one of the most common the use of pharmacology, with the so-called antiepileptic drugs. There are 8 different types, many of them focused on controlling the transmission of various neurotransmitters that would conflict with the electrical activity of the brain.

But the ones that interest us, in relation to the all-or-nothing law, would be those that are designed to control neuronal electrical impulses. In this sense we find, for example, those compounds whose effect is to block sodium channels (responsible for electrical transmission) of repetitive action. Some of the best known drugs of this type are oxcarbazepine, carbamazepine or phenytoin, among others.

Another of the pharmacological pathways that are used to tackle this problem is to try to block other places of electrical transmission., such as T, N or L type calcium channels. We also find others whose mission is to manage to modulate the activity of current h, that which is activated by hyperpolarization. All of them work along the lines of correcting electrical activity, governed by the law of all or nothing.

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Criticism of the concept from the scientific field

Although when we talk about the law of all or nothing, we do so with the certainty that it is a mechanism that works in all cases without leaving any option to chance (for a reason it is a law!), there are some studies that, although they do not criticize that the concept is wrong, because such a thing cannot be affirmed, they do try to give a more complete vision, with certain brushstrokes that would modify the original definition.

This is the case of the study by Barco et al., from 2014, carried out at the University of Manizales in Colombia. For these authors, the concept of the all-or-nothing law is explained in a partly contradictory way, or at least not in the most adequate way. And to make such a statement, they base their study on the electrostatic process that is generated in sodium channels that are activated by action potentials.

The authors of this study thoroughly explain the entire procedure involved in the action potential and how an electrical imbalance occurs in the membrane when reaching a certain intensity, which draws certain ions into the cytoplasm and triggers the transmission of electricity throughout the cell. So far it is an observable process in which there is little room for discussion.

Where they want to arrive is that in the use of the verbal formula, law of all or nothing, they are attributing (always according to the authors) a kind of decision-making capacity by which, depending on the conditions of that specific cell, it can become excited or not with the action potential, and On the other hand, this is a question that obeys higher rules, specifically those of the electrical mechanisms underlying all this. process.

They also criticize the fact that it is called the all-or-nothing law, in that the "nothing" part is an irrelevant concept that is not providing any information, since that it is not a phenomenon that occurs to its maximum or minimum extent (nothing, in this case), but rather a matter that either occurs or does not occurs.

Although part of the discussion is centered on lexical issues, what the authors give most importance to is their concern for the apparent lack of importance that, according to them, is given to the mechanisms of both molecules and the transmission of electricity, within the concept of the law of all or nothing.

It must be said that, although there is such a study on this issue, the truth is that the all-or-nothing law formula has not been a source of conflict beyond from this point, since it is a matter that has been studied and globally accepted and, with few exceptions, it is considered that it does not give rise to any kind of confusion and that synthesizes in very few words the very clear concept that it intends to express, so we would be talking about very isolated criticisms and therefore not significant.

In conclusion

We have studied in depth what are the keys to understanding the processes that are unleashed during the transmission of electricity between one neuron and the next (and among others types of cells, such as muscle cells) and the importance of understanding the law of all or nothing to know how channels open (sodium and potassium, the most common) to this movement of ions of different charge that triggers the electrical passage between cell and cell, as long as the necessary voltage for it has been reached.

It is essential to know this rule and all similar ones to be clear about one of the most basic mechanisms of the functioning of the nervous system, and The all-or-nothing law is undoubtedly one of the most elementary, so if we want to understand what happens in our brain, we have to keep it very close. clear.

Bibliographic references:

• Barco, J., Duque, J.E., Barco, J.A. (2014). All or nothing principle: a misunderstood concept or a mistaken dogma? Archives of Medicine (Col).
• Solís, H., López-Hernández, E., Cortés-Gasca D. (2008). Neuronal excitability and potassium channels. Archives of Neurosciences.
• Suarez R.E. (1994). Thresholds: contribution to the study of excitation and propagation of electrical activity in biological tissues stimulated by external electrodes. Montevideo. University of the Republic.