Synapses: what they are, types and functions

Perhaps, the most important part of the nervous system: the place where neurons communicate.

The nervous system is one of the most important elements for our existence and survival, as it allows the management, organization and and survival, since it allows the management, organization and functioning of the rest of the body systems. This system works by sending electrochemical impulses with different information and orders to the different structures that are part of our organism.

Formerly it was believed that the nervous system was a continuous network without separation between elements, until Ramón y Cajal, by means of stains such as Golgi's, made it possible to identify that in reality it is formed by a group of cells separated from each other: the 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 are neuronal synapses and what are their different types according to various ways of classification.

What is a synapse?

The concept of synapse, first described by Ramón y Cajal and baptized by Sherrington, refers to the existence of a connection between two neurons, characterized by the presence of a small space that serves as a pathway for the transmission of information.. In other words: the existence of synapses shows us that neurons do not form a compact cellular tissue, but that they interconnect with each other in complex ways and maintain 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, making possible the realization and coordination of all the processes that allow the different vital functions to be carried out, as well as the physical and mental capacities, both basic and superior.

This connection is also of great utility not only for transmitting information, but also for regulating it: the presence of the synaptic space makes the presynaptic neuron to reuptake neurotransmitters if an excessive amount of neurotransmitters has been released.. It is also very useful in the sense that it allows the waste generated by neuronal functioning to be eliminated by each cell, preventing its wear and tear due to the concentration of such waste.

In addition, it must be taken into account that throughout the life cycle of a neuron it changes the number and the way in which it establishes these connections with other nerve cells; our ability to learn and adapt to the situations we are exposed to on a daily basis depends on this.

Main components

The synapse between two neurons, the connection and link 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 information to another neuron. This action is usually carried out through the emission of neurotransmitters by the synaptic vesicles of the terminal boutons at the end of the axon, which in turn are received by the postsynaptic neuron membrane. of the terminal boutons 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 existing between two neuronsIt is generally between twenty to forty nanometers. It is the space in which the transmission of information between neurons actually takes place.

3. Postsynaptic neuron

This is the receiving part in the relationship between neurons. More than the neuron itself, it would refer to the part of the neuron that receives the information coming from the presynaptic neuron. Generally these are the dendritesalthough 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 challenges of survival 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 according to what is transmitted

According to the type of element transmitted between neurons, we can find the following. In spite of their distinction, it should be noted that it is frequent that the same neuron can have a chemical and electrical connection at the same time, as well as the fact that the information that travels through the system is generally bioelectrical.It is also the fact that the information that travels through the system is generally bioelectrical (i.e., although chemical elements are transmitted between neurons, what they generate are electrical alterations).

Chemical synapses

This is the type of synapse in our organism.. In these synapses the information is transmitted chemically, through the sending by the presynaptic neuron of different neurotransmitters that the postsynaptic neuron captures by means of different receptors, whose action generates an alteration in the form of excitatory or inhibitory postsynaptic potential that can end 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 the two neurons.

Electrical synapses

In this type of synapse, information is transmitted directly at the electrical level as ions flow directly between the pre- and postsynaptic component. They have no versatility, since their action does not allow one neuron to inhibit the action of another neuron.. 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 characteristic of the optic nerve and its connection with cones and rods in the eye.. Also of 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

A type of synapse in which the transmission of information has excitatory effects, facilitating the postsynaptic neuron to make an action potential. and the transmission of the message is continued by generating depolarization of its membrane.

Inhibitory synapse

In this case, the action or activation of this type of synapse hinders the appearance of an action potential by hyperpolarizing the postsynaptic cell. It becomes more difficult for information to be transmitted through the postsynaptic neuron to other neurons connected to it.

Depending on the place of connection

Depending on where they are connected to each other, we can find the following types of synapses.

Axodendritic synapses

The most frequent and prototypical type of connection. The synaptic connection is between the axon of the presynaptic neuron and the dendrites of the postsynaptic neuron.. It usually has excitatory effects.

Axosomatic synapses

In this type of synapse, the axon of the presynaptic neuron connects to the soma or nucleus of the postsynaptic neuron. connects with the soma or nucleus of the postsynaptic neuron.. Generally has inhibitory effects on the second.

Axo-axonic synapses

This type of connection usually occurs in such a way as to exert modulatory effects on the release of certain amounts of neurotransmitter from one neuron to another. A connection is produced between the axon of the presynaptic neuron and the postsynaptic neuron, altering the possibility of the latter releasing certain amounts of neurotransmitter to a third neuron with which it is connected by another pathway.