The nervous system is one of the most important elements for our existence and survival, since it allows the management, organization and functioning of the rest of the body’s systems. This system works by sending electrochemical impulses with different information and orders for the different structures that are part of our body.
In the past, it was believed that the nervous system was a continuous network without separation between elements, until Ramón y Cajal, through dyes such as Golgi, made it possible to identify that it is actually made up of a set of cells separated from each other: neurons. . These are separated by small spaces, but they do not stop communicating with each other. The connection between them is what is known as a synapse
Throughout this article you will find a summary of what neuronal synapses are and what their different types are according to various classification methods.
The concept of synapse, described for the first time by Ramón y Cajal and named by Sherrington, refers to the existence of a connection between two neurons, characterized by the presence of a small space that serves as a route for the transmission of information That is to say: the existence of synapses shows us that neurons do not form a compact cellular tissue, but rather interconnect with each other in complex ways and maintaining a certain independence from each other.
The main function of this connection is to allow the transmission of information between the different neurons. It is therefore a fundamental element in the functioning of the organism, enabling the realization and coordination of all the processes that allow the different vital functions to be carried out, as well as both basic and higher physical and mental capacities.
This connection is also very useful not only to transmit information, but also to regulate it: the presence of the synaptic space makes the presynaptic neuron can reuptake neurotransmitters if an excessive amount has been released Likewise, it is very useful in the sense that it allows the waste generated by neuronal functioning to be eliminated by each cell, preventing its wear due to the concentration of said waste.
Furthermore, it must be taken into account that throughout the life cycle of a neuron the number and the way in which it establishes these connections with other nerve cells changes; Our ability to learn and adapt to the situations to which we are exposed on a daily basis depends on it.
Main components
The synapse between two neurons, the connection and linkage between them that allows information to be transmitted, is not an isolated element, but is composed of three main components among which we find part of both neurons in interrelation: presynaptic neuron, synaptic space and postsynaptic neuron.
1. Presynaptic neuron
This part refers to the neuron that sends the information to another. This action is usually carried out through the release of neurotransmitters by synaptic vesicles of the terminal buttons at the end of the axon, which in turn will be received by the membrane of the postsynaptic neuron.
2. Synaptic space
The synaptic space or synaptic cleft is the space between two neurons, generally between twenty to forty nanometers. This is the space in which the transmission of information between neurons occurs.
3. Postsynaptic neuron
This is the receiving part in the relationship between neurons. Rather than the neuron itself, reference would be made to the part of it that receives the information from the presynaptic neuron. These are generally the dendrites although depending on the type of connection they can also be the soma or the axon.
Types of synapses
There is not only one type of synapse, but different classifications and typologies can be found depending on different parameters, such as the place where they generate the connection with another neuron or the type of elements that circulate between them.
This is to be expected, taking into account that the nervous system has been evolving to adjust in the best possible way to the survival challenges to which it is necessary to adapt; Taking into account that having only one way to create connections between neurons would not be efficient (because different parts of the body are associated with different functions), there are several ways to establish these links between nerve cells. Thus, we can find, among others, the following types of synapses.
Types depending on what is transmitted
Depending on the type of element that is transmitted between neurons, we can find the following. Despite its distinction, it must be taken into account that It is common that the same neuron can have a chemical and electrical connection at the same time as well as the fact that the information that runs through the system is generally bioelectric (that is, although chemical elements are transmitted between neurons, what they generate are electrical alterations).
chemical synapses
Its about major type of synapse in our body In these synapses, information is transmitted chemically, through the presynaptic neuron sending different neurotransmitters that the postsynaptic neuron captures through different receptors, whose action generates an alteration in the form of an excitatory or inhibitory postsynaptic potential that can terminate or not with the generation of an action potential by the postsynaptic neuron. They are versatile synapses, since some neurons can inhibit the action of others depending on what is activated. There is no physical contact between both neurons.
electrical synapses
In this type of synapse, information is transmitted directly at an electrical level by directly flowing ions between the pre- and postsynaptic component. They do not have versatility, since its action does not allow one neuron to inhibit the action of another In this type of synapse there is actually a contact between pre- and postsynaptic neuron, through gap junctions or channels formed by proteins.
They are typical of the optic nerve and its connection with cones and rods in the eye Also invertebrate animals.
Types according to the effect
The interaction between neurons can have mainly two effects, which correspond to the following types of synapses.
excitatory synapse
Type of synapse in which the transmission of information has excitatory effects, facilitating the postsynaptic neuron to perform an action potential and the transmission of the message continues by generating the depolarization of its membrane.
inhibitory synapse
In this case, the action or activation of this type of synapse makes it difficult for an action potential to appear by hyperpolarizing the postsynaptic cell. It becomes more difficult for information to be transmitted through the postsynaptic neuron to others connected to it.
Depending on connection location
Depending on where they connect to each other, we can find the following types of synapses.
axodendritic synapses
The most frequent and prototypical type of connection. The synaptic connection occurs between the axon of the presynaptic neuron and the dendrites of the postsynaptic neuron It generally has excitatory effects.
axosomatic synapses
In this type of synapse, the axon of the presynaptic neuron connects with the soma or nucleus of the postsynaptic It generally has inhibitory effects on the second.
Axo-axonic synapses
This type of connection usually occurs in such a way that modulating effects are exerted when one neuron releases certain amounts of neurotransmitter to another. A connection is produced between the axon of the presynaptic and postsynaptic neuron, altering the possibility of it releasing certain amounts of neurotransmitters to a third with which it connects through another route.
