Synaptic buttons: what they are and how they work

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

In these bulbs are stored the neurotransmitters, that is to say 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 estimated that the human brain contains 86 billion neurons, an astronomical number inconceivable for anyone. Therefore, it is not surprising that this cellular tissue is the cause of our thinking, our relationship with the environment, our emotions and any characteristics that define us as “autonomous beings”.

It is for these reasons that the knowledge of the nervous processes of our body becomes essential. Synaptic buttons are vital structures for the exchange of information between neuronsAnd that is why, in this space, you will find all the information you need about them.

    What are synaptic buttons?

    We cannot set out to study pathways as complex as synaptic bulbs without first defining where they are, what they produce, and how they relate to surrounding cells. Let’s do this.

    About the neuron

    The neuron is a type of cell like any other, Since it has its own nucleus, is demarcated from the rest of the middle and is able to feed, grow and differentiate (among many qualities).

    What makes this structure a distinctive unit is its specialization, because 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 that contains the nucleus, cytoplasm and organelles.
    • Dendrites: Numerous branching extensions of the cell body that are in contact with other neurons.
    • Axon: extension of the cell body in the form of an “elongated pearl necklace”.

    Synaptic buttons are located at the distal end of the neuronIn other words, at the end of the axons. The next step in understanding these complex structures is to find out that they store neurotransmitters, but what exactly are these molecules?

    About neurotransmitters

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

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

    Neurotransmitters, however foreign they may appear to the general population, they are nothing more than organic compounds like all those that make up living structures. For example, acetylcholine, one of the best known, is made up of carbon, oxygen, hydrogen and nitrogen.

    It is worth noting that these biological compounds are very similar to hormones, but one essential characteristic differentiates them: hormones generate responses in target cells regardless of their distance, as they circulate in the bloodstream. In contrast, neurotransmitters communicate with the immediate neuron only through the synapse.

    There is a wide variety of neurotransmitters, including acetylcholine, dopamine, norepinephrine, serotonin, glycine, and glutamate. Each has a special composition and function. For example, serotonin (which is 90% stored in the gastrointestinal tract and blood platelets) is an essential neuromodulator of mood, anger, memory, sexuality, and attention. Who would have thought that a small biomolecule would encode our daily behavior in this way?

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

    About the synapse

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

    In electrical synapses, information is transmitted by ion exchange between tightly adhered cells. Neurotransmitters do not play an essential role here, because nerve impulses are transmitted directly from one cell to another by the exchange of these molecules of an ionic nature. This is a “more basic” communication, present mainly in vertebrates less complex than mammals.

    On another side, chemical synapses are those used by previously named neurotransmitters to transmit information from a neuron to the target cell (Whether it’s a neuron or some other type of cell body). To simplify things, we will limit ourselves to saying that the arrival of the nerve impulse through the whole cell body at the level of the synaptic buttons promotes the release of the neurotransmitters stored there.

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

    Thus, neurotransmitters are released into the synaptic space, that is, the physical distance between the two neurons that transmit information, and then adhere to the membrane of the postsynaptic neuron, that is to say to the receptor of information which will be responsible for transmitting the new impulse to another cell target, and so on.

    While it may seem like a purely microscopic and metabolic world, all of these tiny biomolecules and electrical impulses are responsible for biological calculations that translate, in a behavioral realm, into essential processes such as environmental perception and human thought. Fascinating, isn’t it?

      Essential neuron endings

      So, as we have dissected in each of the previous sections, synaptic buttons are neural axon endings that store neurotransmitters and they release the means for the synapse to take place, that is, communication between neurons or from one neuron to another target cell.

      Several studies attempt to understand the effectiveness and nature of these synaptic bulbs. For example, in rodents it has been observed that there is a small number of thalamus-cortical buds, but these have a very efficient synapse due to their structural composition.

      We must keep in mind that cell bodies exhibit variations depending on their area of ​​action and function. For example, these surveys point out that pimples can have morphological diversity in terms of size, number, presence of mitochondria and number of vesicles (What we remember neurotransmitters store) refers to. All this probably conditions the efficiency and speed of transmission of the nerve signal.

      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 buds of these neurons have vesicles containing about 10,000 acetylcholine molecules which, when released and received by cells in muscle tissue, elicit a response in the individual’s muscles.

      conclusions

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

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

      Bibliographical references:

      • Arce, I. (1995). Neural networks for process control. Publication of the Mexican Institute of Chemical Engineers.
      • Camp, PP (2007). Physiological basis of visual training. Notes Physical education and sports, (88), 62-74.
      • Papazian, O., Alfonso, I., and Aragüez, N. (2009). Juvenile severe myasthenia gravis. Medicine (Buenos Aires), 69 (1).
      • Rodríguez Moreno, J. (2017). Synaptic structure of thalamus-cortical circuits: 3D quantitative analysis of synaptic buttons of posteromedial and posterior ventral nuclei of adult mice.
      • Synapse between neurons, University of Alcalá de Henares (UAH). Collected August 29 at http://www3.uah.es/bioquimica/Tejedor/bioquimica_ambiental/tema12/tema%2012-sinapsis.htm

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