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 systems. This system works by sending electrochemical impulses with different information and orders to the different structures that are part of our organism.

It was formerly believed that the nervous system was a continuous network without separation between elements, until Ramon y Cajal, by means of tinctures such as Golgi’s, made it possible to identify that it is actually formed by a set of cells separated from each other: the neurons. These are separated by small spaces, but do not stop communicating with each other. The connection between them is known as synapse .

What is a synapse?

The concept of synapse, first described 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 channel for the transmission of information .

The main function of this connection is to allow the transmission of information between different neurons. It is therefore a fundamental element in the functioning of the organism, making it possible to carry out and coordinate all the processes that allow the different vital functions to be performed, as well as both basic and superior physical and mental capacities.

This connection is also very useful not only for transmitting information but also for regulating it: the presence of the synaptic space makes the presynaptic neuron able to recapture neurotransmitters if too much has been released . It is also very useful in the sense that it allows the waste generated by the neuronal functioning to be eliminated by each cell, preventing it from being worn out by the concentration of such waste.

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 interrelationship: presynaptic neuron, synaptic space and postsynaptic neuron.

1. Presynaptic neuron

This part refers to the neuron that sends the information to another. This action usually takes place through the emission of neurotransmitters by the synaptic vesicles from 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 , usually between twenty to forty nanometers. This is the space in which the transmission of information between neurons occurs.

3. Post-synaptic neuron

This is the receptor part in the relationship between neurons. More than the neuron itself, reference would be made to the part of the neuron that receives the information from the presynaptic neuron. Generally these are the dendrites , although depending on the type of connection they may 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. Thus, we can find among others the following types.

Types according to what is transmitted

Depending on the type of element that is transmitted between neurons, we can find the following. Despite the distinction, it should be taken into account that it is common for the same neuron to 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 bioelectric (that is, although chemical elements are transmitted between neurons, they generate electrical alterations).

Chemical synapse

This is the majority type of synapse in our body . In these synapses the information is transmitted chemically, through the sending by the presynaptic neuron of different neurotransmitters that the postsynaptic neuron captures through different receptors, whose action generates an alteration in the form of a postsynaptic excitatory or inhibitory potential that may or may not end 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, the information is transmitted directly at the electrical level by the direct flow of ions between the pre- and post-synaptic component. They are not versatile, since their action does not allow one neuron to inhibit the action of another . In this type of synapse there is actually contact between pre- and postsynaptic neurons, through the gap bonds 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 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 an excitatory effect, facilitating the post-synaptic neuron to perform an action potential and continue the transmission of the message by generating the 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 hyper-polarizing the post-synaptic cell. It becomes more difficult for information to be transmitted through the post-synaptic neuron to others connected to it.

Depending on the place of connection

Depending on where they are connected, the following types of synapses can be found.

Axodendriatic 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 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 . It usually has inhibitory effects on the latter.

Axo-axonal 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 post-synaptic neuron, altering the possibility of the latter releasing certain amounts of neurotransmitters to a third one with which it is connected by another route.

Bibliographic references

  • Kandel, E.R.; Schwartz, J.H. & Jessell, T.M. (2001). Principles of neuroscience. Fourth edition. McGraw-Hill Interamerican. Madrid.