T he nervous system is made up of an extensive network of nerve connections whose basic component is the neuron . These connections allow the control and management of the different mental processes and behaviours of which human beings are capable, allowing us to stay alive, run, speak, relate, imagine or love.

Nerve connections occur between various neurons or between neurons and internal organs, generating electrochemical impulses that are transmitted between neurons until they reach their target. However, these nerve cells are not attached to each other.
Among the different neurons that form part of the nervous system we can find a small space through which communication with the next neuron or neurons takes place. These spaces are called synaptic spaces .

Synapse and synaptic space

The synaptic space or synaptic cleft is the small space that exists between the end of one neuron and the beginning of another . It is an extracellular space of between 20 and 40 nanometres and filled with synaptic fluid that forms part of the neuronal synapse, together with the pre- and postsynaptic neurons. Thus, it is in this space or synaptic cleft where the transmission of information from one neuron to another takes place , the neuron that releases the information being called presynaptic while the one receiving it is called postsynaptic neuron.

There are different types of synapses : it is possible that the synaptic space connects the axons of two neurons to each other, or directly the axon of one and the soma of another. However, the type of synapse in which the axon of one neuron and the dendrites of another communicate, called axodendritic synapse, is the most common. Likewise, it is possible to find electrical and chemical synapses, the latter being much more frequent and of which I will speak in this article.

The transmission of information

The involvement of the synaptic space, although passive, is essential in the transmission of information. When an action potential arrives (caused by the
depolarization, repolarization and hyperpolarization in the axon cone) at the end of the presynaptic axon the terminal buttons of the neuron are activated , which expel a series of proteins and neurotransmitters to the outside, substances that exert a chemical communication between neurons that the next neuron will pick up through the dendrites (although in the electrical synapses this does not occur).

It is in the synaptic space where neurotransmitters are released and radiated, and from there they will be captured by the post-synaptic neuron.
The neuron that has emitted the neurotransmitters will recapture the excess neurotransmitter that remains in the synaptic space and that the postsynaptic neuron does not let pass, taking advantage of them in the future and maintaining the balance of the system (it is in this process of recapturing that many psychotropic drugs, such as SSRIs, interfere).

Enhancing or inhibiting electrical signals

Once the neurotransmitters are captured,
the post-synaptic neuron would react in this case the continuation of the nerve signal by generating excitatory or inhibitory potentials, which will allow or not the propagation of the action potential (the electrical impulse) generated in the axon of the presynaptic neuron by altering the electrochemical balance.

And that’s because
the synaptic connection between neurons does not always involve the passage of the nerve impulse from one neuron to another , but can also cause it not to replicate and become extinct, depending on the type of connection that is stimulated.

To better understand this, we must think that the nerve connections are not just two neurons, but that we have a great multitude of interrelated circuits that can cause a signal that a circuit has emitted to be inhibited. For example, in the case of an injury, the brain sends pain signals to the affected area, but through another circuit the sensation of pain is temporarily inhibited to allow the escape of the harmful stimulus.

What is the synapse for?

Given the process that follows the transmission of information, we can say that the synaptic space has the main function of allowing communication between neurons,
by regulating the passage of electrochemical impulses that govern the functioning of the organism .

In addition, thanks to it, neurotransmitters can remain for a time in the circuit without the need for the presynaptic neuron to be activated, so that although initially they are not captured by the postsynaptic neuron, they could be used later.

In the opposite sense, it also allows surplus neurotransmitter to be recaptured by the presynaptic neuron,
or degraded by different enzymes that can be emitted by the membrane of the neurons, such as MAO.

Finally, the synaptic space facilitates the possibility of removing from the system the waste generated by nerve activity, which could lead to the poisoning of neurons and their death.

Synapses throughout life

The human being as an organism is continuously active throughout the entire life cycle, whether it is executing an action, feeling, perceiving, thinking, learning…
All these actions mean that our nervous system is permanently activated , emitting nerve impulses and transmitting orders and information from one neuron to another through the synapses.

When a connection is formed, the neurons come together thanks to neurotrophic factors that make it easier for them to attract or repel each other, although they never touch. When they connect, they leave a small intermediate gap, the synaptic space, thanks to the modulating action of the same neurotrophic factors. The creation of synapses is called synaptogenesis, being especially important in the fetal stage and in early childhood . However, synapses are formed throughout the entire life cycle, through the continuous creation and pruning of neuronal connections.

The activity of life and the different actions we carry out have an effect on synaptic activity: if a circuit is largely repeated, it is strengthened, while if it is not exercised for a long time, the connection between neuronal circuits is weakened.

Bibliographic references:

  • Bear, M.F.; Connors, B.W. & Paradiso, M.A. (2002). Neuroscience: exploring the brain. Barcelona: Masson.
  • Kandel, E.R.; Schwartz, J.H. & Jessell, T.M. (2001). Principles of neuroscience. Fourth edition. McGraw-Hill Interamerican. Madrid.