Synaptic buttons: what they are and how they work

Synaptic boutons are one of the most important parts of neurons; let's see why.

Synaptic boutons, also called terminal axons or synaptic bulbs, are divisions of the extreme part of the axon that form synapses with the axon.are divisions of the extreme part of the axon that form synapses with other neurons or with muscle cells or glands.

These bulbs store neurotransmitters, i.e., the biomolecules responsible for transmitting information from one neuron to another cell type (either a target tissue of another biological nature or another neuron).

Recent studies have calculated that the human brain contains 86 billion neurons, an astronomical figure inconceivable to anyone. Therefore, it is not surprising that this cellular network is the cause of our thinking, relationship with the environment, emotions and any characteristic that defines us as "autonomous entities".

For these reasons, it is essential to know the nervous processes in our body. Synaptic buttons are vital structures for the exchange of information between neurons.For this reason, in this space we tell you everything you should know about them.

What are synaptic buttons?

We cannot embark on investigating such complex paths as the synaptic bulbs without first defining where they are located, what they produce and what is their relationship with the surrounding cells. Let's get down to it.

About the neuron

The neuron is a cell type like any other cell type.It has its own nucleus, is delimited from the rest of the environment and is capable of nourishment, growth and differentiation (among many other qualities).

What makes this structure a distinctive unit is its specialization, since its function is to receive, process and transmit information through chemical and electrical signals.. Quickly, we can distinguish three main parts in the morphology of the neuron:

• Soma: cell body containing the nucleus, cytoplasm and organelles.
• Dendrites: numerous and branched extensions of the cell body that are in contact with other neurons.
• Axon: prolongation of the cell body in the form of an "elongated bead necklace".

The synaptic boutons are located at the distal end of the neuron, i.e. at the end of the axon.that is, at the end of the axons. The next part of understanding these complex structures is to discover that they store neurotransmitters, but what exactly are these molecules?

About neurotransmitters

As we have said before, neurotransmitters are organic molecules that allow the transmission of information from one neuron to another cell body. Several bibliographic sources state that for a neurotransmitter to be considered a neurotransmitter it must meet certain characteristics. We list them for you:

• The substance must be present inside the neuron.
• The enzymes that allow the synthesis of the substance must be present in the area where the neurotransmitter is produced.
• The effect of the neurotransmitter must be promoted even if it is applied to the target cell exogenously.

Neurotransmitters, as foreign as they may seem to the general population, are nothing more than organic compounds like all other neurotransmitters, are nothing more than organic compounds like all those that make up living structures.. For example, acetylcholine, one of the most famous, is composed of carbon, oxygen, hydrogen and nitrogen.

It should be noted that these biological compounds are very similar to hormones, but they differ in one essential characteristic: hormones generate responses in target cells no matter how far away they are, since they circulate in the bloodstream. In contrast, neurotransmitters only communicate with the immediate neuron through the synapse.

There is a considerable variety of neurotransmitters, including acetylcholine, dopamine, noradrenaline, serotonin, glycine and glutamate.. Each has a special composition and function. For example, serotonin (90% of which is stored in the gastrointestinal tract and Blood platelets) is an essential neuromodulator of mood, anger, memory, sexuality and attention. Who knew that a small biomolecule would so encode our day-to-day behavior?

We have understood where the synaptic buttons are and what they store, but a new term has just come into play: the synapse. We have no choice but to address this process in the following lines.

About the synapse

Neurons communicate with each other by a process called synapse.. This can be electrical or chemical in nature, depending on the method of information transmission.

In electrical synapses, information is transmitted by an exchange of ions between closely adherent cells. Neurotransmitters do not play an essential role here, since the nerve impulse is transmitted directly from one cell to another by the exchange of these ionic molecules. This is a "more basic" communication, mostly present in less complex vertebrates than mammals.

On the other hand, chemical synapses are those that use the previously mentioned neurotransmitters to transmit information from a neuron to a target cell (be it a neuron or another type of cell body). (whether it is a neuron or another type of cell body). To simplify things, we will limit ourselves to say that the arrival of the nerve impulse through the whole cell body to the synaptic boutons promotes the release of the neurotransmitters stored there.

These biomolecules are stored in vesicles or "bubbles". When the excitatory signal reaches these bulbs, the vesicles fuse with the bulb membrane, allowing the release of the stored neurotransmitters by a process called "exocytosis".

Thus, the neurotransmitters are released into the synaptic space, i.e., the physical distance between the two neurons that are transmitting information, to later to adhere to the membrane of the post-synaptic neuron, i.e., the information receptor that will transmit the new impulse to another cellular target, and so on. to another cellular target, and so on.

Although it may seem a merely microscopic and metabolic world, all these small biomolecules and electrical impulses are responsible for the biological calculations that translate, at a behavioral level, into such essential processes as the perception of the environment and human thought. Fascinating, isn't it?

Essential neuron endings

So, as we have dissected in each of the previous sections, synaptic boutons are terminations of the axon of the neuron that store neurotransmitters and release them to the and release them into the environment so that synapses can be made, i.e. communication between neurons or between a neuron and another target cell.

Several studies try to understand the efficacy and nature of these synaptic bulbs. For example, in rodents it has been observed that there are a reduced number of thalamo-cortical boutons, but they show a very efficient synapse due to their structural composition.

We must take into account that cell bodies show variations according to their area of action and function. For example, this research shows that for example, these investigations underline that boutons can present morphological diversity in terms of size, number, presence of mitochondria and number of vesicles (which store neurotransmitters) present. All this, presumably, conditions the efficiency and speed of nerve signal transmission.

Other studies show us clear examples of the functionality of these buttons in specific processes and diseases, for example, in neuromuscular junctions. For example, the terminal boutons of these neurons present vesicles with about 10,000 molecules of acetylcholine, which when released and received by the muscle tissue cells elicit a response in the individual's musculature.

Conclusions

As we have seen, synaptic boutons are one more piece of the puzzle for understanding the relationship and communication between the components of our nervous system. They store neurotransmitters, the biomolecules responsible for transmitting information between the pre-synaptic cell and the post-synaptic cell..

Without this communication at the microscopic and cellular level, life as we understand it would not be possible. For example, for a finger to receive the signal to move in the presence of fire, this stimulus must be received by the brain, and without the communication between each of the components of our body, this signal would never arrive. For all these reasons, we could say that the synapse is the response mechanism that allows life as we know it today in animals.

Bibliographical references:

• Arce, E. (1995). Redes neuronales para el control de procesos. Publication of the Mexican Institute of Chemical Engineers.
• CamPo, P. P. (2007). Physiological bases of visual training. Apunts Educación Física y Deportes, (88), 62-74.
• Papazian, O., Alfonso, I., & Araguez, N. (2009). JUVENILE MYASTHENIA GRAVIS. Medicina (Buenos Aires), 69(1).
• Rodriguez Moreno, J. (2017). Synaptic structure of thalamo-cortical circuits: quantitative 3D analysis of synaptic boutons in the ventral posteromedial and posterior nuclei of the adult mouse.
• Synapses between neurons, Universidad de Alcalá de Henares (UAH). Retrieved August 29 at http://www3.uah.es/bioquimica/Tejedor/bioquimica_ambiental/tema12/tema%2012-sinapsis.htm.