What is a synapse, what types and how they occur

The synapse is the region responsible for carrying out communication between two or more neurons, or from a neuron to an effector organ, that is, a muscle or a gland.

It has the function send signals through synaptic transmission, to take place some specific action in the body.

Millions of synapses happen daily in the human body. They are what cause your muscle to retract quickly when touching something very hot, for example, and they also send important neurotransmitters throughout the cells, such as dopamine, serotonin, among others.

Where does the synapse occur?

The synapse can occur in three different places, depending solely on the type of communication to be made and the message that needs to be sent. Are they:

Axodendritic: happens between the axon of the first neuron and the dendrite of the second neuron;
axo-axon: occurs between the axon of the first neuron and the axon of the second neuron;
axosomatic: happens between the axon of the first neuron and the body of the second neuron;

To better understand where these synapses happen, you need to know the structure of a neuron and its functions.

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As illustrated in the image below, the neuron is a nerve cell with a different structure from conventional cells and aims to generate electrical impulses. This is because the central and peripheral nervous systems work specifically with electricity.

neuron structure Structure of a neuron

O cell body this is where the electrical stimulus that will travel through the entire neuron begins;
You dendrites they are the branches responsible for joining other neurons, initiating a communication between them;
O axon it is the channel responsible for transmitting the electrical impulse from the nucleus to the end of the neuron;
THE myelin sheath it is the coating present on the axon and its function is to insulate the electricity that passes through the axon;
You ranvier's nodules, present between the myelin sheaths, are responsible for increasing the speed of the electrical impulse that passes through the axon;
O axon terminal or synaptic terminal has the function of connecting to other neurons.

Every part of the neuron is important in the entire process of any type of synapse. This is because they occur in different places in the cell and transmit different messages to the body.

Synapse types and how they occur

There are two types of nerve synapses, the electrical and chemical. Both happen in the nervous system, but in different ways, depending on different actions for communication between neurons to take place.

electrical synapse

For electrical synapse communication to take place, two or more neurons must send information to each other. The neuron above the synaptic cleft, the small space between them, we call the neuron presynaptic, since what is after the slit we call a neuron postsynaptic.

At the electrical synapse, the neurons are extremely close, because in this case the synaptic cleft is smaller. They also have an important binding protein called connexin.

The connexins create a path, like a kind of tubing, allowing the ions present in the presynaptic neuron to pass to the postsynaptic one, and vice versa, as shown in the image below.

electrical synapse Electrical synapse representation

THE represents in presynaptic neuron;
B represents the postsynaptic neuron;
O number 1 represents the mitochondria, responsible for releasing the ions with the information that will be sent from one neuron to another;
O number 2 it is the communicating junction (or GAP), the channel created by the connexin protein, so that ions can reach from one neuron to another;
O number 3 represents the communication made in the cytoplasm of the other neuron.

As we can see, the electrical synapse is bidirectional, that is, it allows the exchange of information from one neuron to another. It happens in fewer numbers, at a very high speed, and can only be found in specific and restricted places in the brain.

This type of synapse is responsible for acting on communications and stimuli for the heart muscle, bladder and uterus.

chemical synapse

Unlike the electrical synapse, the chemical synapse is one-way, going from the presynaptic to the postsynaptic neuron. In it, the neurons approach each other, but do not touch, because in this case the synaptic cleft is larger.

The chemical synapse starts with the neurotransmitters, which are chemical substances produced within the presynaptic neuron and carry the information that needs to be taken to the postsynaptic neuron. These substances have information that will generate some kind of action in the body.

However, as there is no great approximation of the neurons, the process is longer and depends on other important factors.

As the image below illustrates, neurotransmitters are within synaptic vesicles, which are like bags that hold these substances, waiting for some stimulus to break and release them.

While the bags are approaching the terminal buttons (open spaces at the end of the presynaptic neuron membrane, responsible for releasing neurotransmitters) an action potential occurs that stimulates the release of calcium.

Calcium is the protein responsible for creating a channel in the neuron membrane and “pushing” the synaptic vesicles to the end of the membrane. After this stimulus they break down and release neurotransmitters.

When released, they make their way to the synaptic cleft and bind to postsynaptic neuron receptors, which are prepared to receive the message and send it throughout the postsynaptic neuron and consequently to the specific region of the body.

The action that takes place after release depends solely on the neurotransmitter that will be released. Dopamine, for example, is the neurotransmitter responsible for controlling feelings and for the reward mechanism of the nervous system.

Differences between electrical synapse and chemical synapse

The chemical synapse happens at a reduced speed, as it needs many steps throughout its process. The electric one happens at high speed;
The electrical synapse takes place in specific regions of the brain, while the chemistry takes place throughout the nervous system and in greater quantity;
At the electrical synapse, neurons are very close and are able to exchange information directly, while at the chemical synapse, the help of neurotransmitters, which act as messengers of the information;
In the electrical synapse, communication is bidirectional, that is, information is exchanged from the presynaptic neuron to the postsynaptic and vice versa, while chemistry is unidirectional, with the flow of information only going from the presynaptic neuron to the synaptic post.