The transfer of information between nerve cells is carried out by neurotransmitters, whose message is recognized by the receiving cell and translated into biological responses in a specialized structure called “synapse”. All nervous activities, from the simplest reflex activities to higher functions, such as learning and memory, depend on the transfer of information between nerve cells and, therefore, on the number of synapses and the effectiveness of each synapse in the release of the neurotransmitter. Synaptic transmission plays a key role in understanding the functioning of the nervous system, and in this Psychology-Online article we will take a closer look What is a neuronal synapse, the different types and how it works.
What is the neuronal synapse
The definition of neuronal synapses says synapses are connections between neurons that allow the nerve signal to spread. Nerve cells are part of a kind of “network.” The function of synapses is that they allow neurons to dialogue, thus transmitting the impulses that give the brain the possibility of governing the human body.
Neurons are made up of a larger central part, the cell body, and subtle “tentacles” (axons) that extend towards other neurons. Along the axons, the nervous impulse travels that will be transformed into instructions for the body. These “tentacles”, in their terminal part, are made up of junctions responsible for transmitting (through impulses and particular substances) information, rubbing against nearby cells. They are the synapses and there are thousands for each neuron (between 5,000 and 100,000). He named them “synapses” after the Nobel Prize in medicine. Charles Scott Sherringtonin 1897. And only in the middle of the 20th century were they “photographed” for the first time, thus giving the first visual proof of their existence.
There are different structures and functions.
Structure of the neuronal synapse
Each nerve cell (neuron) is made up of a wider part, the cell body, and filaments, called axons, along which the nervous impulse propagates thanks to small and brief changes in the electrical potential of the cell membrane. The filaments end in an enlarged area, called synaptic button, which usually rests on or is very close to the cell body of another neuron. The signal transfer Electrical activity between excitable cells takes place in these specialized regions, and more precisely the cell that sends the signal is called a presynaptic cell, while the one that receives it is called a postsynaptic cell. The space that physically separates the two communicating cells is the intersystemic space or synaptic fissure.
Types of neuronal synapses and how they work
According to communication strategies, synapses are divided into two types:
electrical synapses
Electrical synapses are found in the , in smooth muscle and cardiac tissue, and in neuroendocrine tissues. At electrical synapses, cells are separated by a synaptic cleft 2-4 nm, therefore so narrow that it can be considered a virtual space. Indeed, it can also be stated that between pre- and postsynaptic cells there is a true electrical continuity guaranteed by the presence of gap junctions.
electrical synapses can pass current in both directions and it is a type of very fast transmission, because it results from a direct passage of current from the presynaptic element to the postsynaptic element (the delay with which the postsynaptic cell responds by producing an action potential is a few tenths of a millisecond). Therefore, electrical synapses are located in areas of the central nervous system and in tissues in which cells must generate synchronous action potentials to carry out their task.
How does the electrical neuronal synapse work? electrical synapses They directly communicate the interior of the presynaptic cell with the interior of the postsynaptic cell. The cells, in this case, are united by ion channels of very low resistance, which allow the passage of ion currents induced by the action potential. Nerve transmission through electrical synapses is very fast, almost immediate. Its function includes the coordination of cardiac action potentials, the synchronization of neuronal electrical activity, the exchange of metabolites, and the passage of signal molecules from one cell to another.
chemical synapses
At chemical synapses, the arrival of an action potential at the presynaptic cell causes the release of a neurotransmitter which determines the electrical response in the postsynaptic element. In the case of chemical synapses there is a relatively wide synaptic cleft (20-40 nm), as well as structural specializations that allow the presynaptic element to be distinguished from the postsynaptic element.
- The presynaptic cell It is characterized by an esocytotic system and synaptic vesicles.
- The postsynaptic neuron It is characterized by the presence of receptor molecules for the neurotransmitter located in the region of the plasma membrane located in front of the presynaptic cell. This specialization of the pre- and postsynaptic element makes transmission through chemical synapses is unidirectional.
How does the chemical neuronal synapse work? At chemical synapses, the two cells are not in contact with each other, but they are seperated through a small gap (0.03 μm), called the synaptic cleft. The presence of this interruption makes the direct passage of ionic currents impossible, therefore, in order to continue its journey, the impulse must “change identity.” Thus, the electrical signal is converted into a chemical signal and crosses the synaptic cleft in this form, to then be converted back into an electrical impulse.
How to improve neuronal synapse
Today it has been shown that specific experiences can increase the number of synapses per neuron, as an effect of axonal stimulation and a dendrite growth process. In favor of this hypothesis, it is interesting to note that, for example, Cognitive therapy and stimulating experiences increase the number of synapses and how, in view of the role of synaptic potentiation phenomena in learning processes, it is possible to affirm that neuronal remodeling, activated by cognitive therapy, constitutes a true process of “synaptic reabsorption”. In these articles you will find more information about and .
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