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

A summary of the law of all or nothing and how it describes the functioning of neurons.

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

One of the most famous in relation to the electrical activity of our body is known as the law of all or nothing.. Let's explore the peculiarities of this rule and its implications.

• Related article, "How do neurons work?"

What is the law of all or nothing and how it describes neuronal activation.

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

Therefore, the electric current will run through the entire neuron, from the dendrites that receive it, to the end of its axon, which in some cases can reach the end of its axon.which in some cases can be as long as meters. The other option, according to the law of all or nothing, is that this electric current is not transmitted at all, since the action potential has not been intense enough to pass from the previous neuron to this one. There is no middle ground for neuronal electrical distribution.

This is where the so-called excitability threshold comes into play, since in order to transmit the nerve impulse a certain amount of current is needed 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 electrical impulse would not be transmitted to the adjoining cell, thus terminating at that moment the path of the electrons.

Another characteristic of the all-or-nothing law is that, if the threshold of excitability is reached and therefore the action potential is transmitted, it will travel through the whole neuron with a constant intensity, without fluctuations.without fluctuations. Hence, either it occurs as a whole, maintaining its full strength, or it does not occur, with no other possibilities.

Associated pathologies: epilepsy

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

It would be the case, for example, of epilepsy, a neurological disease that can generate different symptoms both at psychological and physical level, from seizures that are triggered by these electrical imbalances that we mentioned in different areas of the brain.

When this pathology exists and the electrical movement between neurons is governed by the law of all or nothing, action potentials of higher than normal intensity are generated in certain brain areas.The action potentials, which excite the cell membrane of the next neuron and therefore transmit the current, contracting muscle fibers and causing spasms, when in other circumstances these 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 proven to be effective.One of the most common is 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 be in conflict with the electrical activity of the brain.

But the ones that interest us, in terms of the relationship with the law of all or nothing, 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 pharmacological route used to tackle this problem is to try to block other sites of electrical transmission, such as calcium channels.such as T, N or L-type calcium channels. We also find others whose mission is to modulate the activity of the h current, 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.

Criticism of the concept from the scientific field

Although when we speak of 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 (it is a law for a reason!), there are some studies that, although they do not criticize that the concept is wrong, because it is not possible to affirm such a thing, they do try to give a more complete vision, with certain brushstrokes that modify the concept.with certain touches that would modify the original definition.

This is the case of the 2014 study by Barco et al. conducted 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 generated in the sodium channels that are activated by action potentials.

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

What they want to get at is that in the use of the verbal formula, the law of all or nothing, they are attributing (always according to the authors) a kind of decision capacity by which, according to the conditions of that particular cell, it can become excited or not with the action potential, and instead this is a question that obeys superior rules, specifically those of the electrical mechanisms underlying this whole process.

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

Although part of the discussion is focused on lexical issues, what the authors give more importance to is their concern for the apparent lack of importance that, according to them, is given to the mechanisms of both the molecules and the transmission of electricitywithin 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 this point, since it is a studied and globally accepted issue that, with these few exceptions, is considered not to give rise to any type 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 and therefore not significant criticisms.

In conclusion

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

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

Bibliographical references:

• Barco, J., Duque, J.E., Barco, J.A. (2014). All-or-nothing principle: a misinterpreted concept or a wrong 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.