What is “synapse”?
The synapse refers to the interneuronal joint that is produced to allow the passage of the nerve impulse from one cell with the same characteristics as the impulse to another . In conclusion, it is the dialogue that occurs between neurons , about the functions they have to fulfill.
There are different ways to classify the types of synapses that occur. In principle, three criteria can be established to do so and these will be detailed below:
1. Types of synapses depending on the contact area:
Axodendritic: It is the type that is best known. In detail, what happens is that there is an electrochemical impulse that travels until it reaches the end of the membrane , called the presynaptic or terminal button, where there are vesicles that are loaded with neurotransmitters. When excited, these open releasing the aforementioned neurotransmitters, towards what is known as the synaptic cleft, they make that transfer, joining the postsynaptic receptors of a dendrite or dendritic spine resulting in the transmission of the nerve impulse to the membrane postsynaptic. This is how what is called synapse is produced.
Axosomatic : The passage of the impulse occurs in the same way as in the axodendritic synapse, with the difference that the transfer is caused from the axon in the presynaptic terminal or button to the soma of a presynaptic neuron . This occurs frequently, since an axon can exhibit several synaptic buttons, taking place simultaneously, which is designated by the name of axodendrosomatic synapses.
Axoaxonic : It is the result of the connection that occurs between the axon of a presynaptic neuron and the fraction of another axon , known as the axon terminal, of a postsynaptic neuron, at the beginning of the myelin sheath.
2. Types of synapses according to the postsynaptic effect:
Excitatory synapse: it is the product of the stimulation of a postsynaptic neuron through a message that leads to an action called depolarization , whose function is to open the sodium channels, in the event that a neurotransmitter adheres to the receptor. This operation results in what is known as PPE or excitatory postsynaptic potential. If this action reaches a high point of excitement, an action potential is created. That is to say. a transitory increase in the membrane, caused by the circulation of ions with positive characteristics towards the interior of the postsynaptic unit.
Inhibitory synapse: it is characterized by the emergence, in the membrane of a postsynaptic neuron, of a hyperpolarization . This originates if potassium channels (expelled to the extracellular zone) and chlorine (entering the innermost part of the neuron) are discovered. As long as the hyperpolarization persists, the neuron will be disabled, resulting in the difficulty of provoking an action potential, necessitating a higher increase in action. In short, this type of synapse occurs if the communication works by reducing or blocking the postsynaptic action .
3. Types of synapses according to the procedure of information transfer
Chemical synapses: generally, synapses are of this type and it is produced by means of a substance. The route is based on the fact that a neurotransmitter fulfills the function of link , linking the pair of neurons. It spreads through a reduced area, attaching itself to receptors, which are characterized by being on the postsynaptic membrane and by being specific protein molecules.
Electrical synapse: in this type of synapse, faster than the chemical synapse, the transfer that originates in the ions, from cell to cell, through which they are designated: “gap junctions” or communicating associations, conduits constituted by the articulation of protein supplements, made up of proteins called connexins.