Federal Agency for Education
State educational institution
higher professional education
"Ryazan State University named after S.A. Yesenin"
Institute of Psychology, Pedagogy and Social Work
Test work in the discipline “Neurophysiology and fundamentals of VND”
on the topic: “The concept of a synapse, the structure of a synapse.
Transmission of excitation in the synapse"
Completed by a student of group 13L
1st year OZO (3) A.I. Sharova
Checked:
professor of medical sciences
O.A. Belova
Ryazan 2010
1. Introduction……………………………………………………………..3
2. Structure and functions of the synapse……………………………………...6
3. Transmission of excitation at the synapse………………………………….8
4. Chemical synapse……………………………………………………………9
5. Isolation of the mediator……………………………………………...10
6. Chemical mediators and their types……………………………..12
7. Conclusion……………………………………………………………15
8. List of references……………………………………………………………....17
Introduction.
Our body is one big clockwork mechanism. It consists of a huge number of tiny particles that are located in in strict order and each of them performs certain functions and has its own unique properties. This mechanism - the body, consists of cells, connecting their tissues and systems: all this as a whole represents a single chain, a supersystem of the body. The greatest variety of cellular elements could not work as a single whole if the body did not have a sophisticated regulatory mechanism. The nervous system plays a special role in regulation. All the hard work nervous system- regulation of the work of internal organs, control of movements, whether simple and unconscious movements (for example, breathing) or complex movements of a person’s hands - all this, in essence, is based on the interaction of cells with each other. All this is essentially based on the transmission of a signal from one cell to another. Moreover, each cell does its own job, and sometimes has several functions. The variety of functions is provided by two factors: the way cells are connected to each other, and the way these connections are arranged. The transition (transfer) of excitation from a nerve fiber to the cell it innervates (nerve, muscle, secretory) occurs through a specialized formation called a synapse.
Structure and functions of the synapse.
Every multicellular organism, every tissue consisting of cells needs mechanisms that ensure intercellular interactions. Let's look at how they are carried out interneuronalinteractions. Information travels along a nerve cell in the form action potentials. The transfer of excitation from axon terminals to an innervated organ or other nerve cell occurs through intercellular structural formations - synapses (from the Greek “Synapsis” - connection, connection). The concept of synapse was introduced by the English physiologist C. Sherrington in 1897, to denote the functional contact between neurons. It should be noted that back in the 60s of the last century THEM. Sechenov emphasized that without intercellular communication it is impossible to explain the methods of origin of even the most elementary nervous process. The more complex the nervous system is, and the greater the number of constituent neural brain elements, the more important the importance of synaptic contacts becomes.
Different synaptic contacts differ from each other. However, with all the diversity of synapses, there are certain common properties of their structure and function. Therefore, we first describe the general principles of their functioning.
Synapse - is a complex structural formation consisting of
presynaptic membrane - electrogenic membrane at the axon terminal, forms a synapse on the muscle cell (most often this is the terminal branch of the axon)
postsynaptic membrane - the electrogenic membrane of the innervated cell on which a synapse is formed (most often this is a section of the body membrane or dendrite of another neuron)
synaptic cleft - the space between the presynaptic and postsynaptic membrane, filled with fluid, which in composition resembles blood plasma
Synapses can be between two neurons (interneuronal), between neuron and muscle fiber (neuromuscular), between receptor formations and processes of sensory neurons (receptor-neuronal), between neuron processes and other cells ( glandular).
There are several classifications of synapses.
1. By localization:
1) central synapses;
2) peripheral synapses.
Central synapses lie within the central nervous system and are also found in the ganglia of the autonomic nervous system.
Central synapses- these are contacts between two nerve cells, and these contacts are heterogeneous and, depending on the structure on which the first neuron forms a synapse with the second neuron, they are distinguished:
a) axosomatic, formed by the axon of one neuron and the body of another neuron;
b) axodendritic, formed by the axon of one neuron and the dendrite of another;
c) axoaxonal (the axon of the first neuron forms a synapse on the axon of the second neuron);
d) dendrodentrite (the dendrite of the first neuron forms a synapse on the dendrite of the second neuron).
There are several types peripheral synapses:
a) myoneural (neuromuscular), formed by the axon of a motor neuron and a muscle cell;
b) neuroepithelial, formed by the axon of a neuron and a secretory cell.
2. Functional classification of synapses:
1) excitatory synapses;
2) inhibitory synapses.
excitatory synapse- synapse in which the postsynaptic membrane is excited; an excitatory postsynaptic potential arises in it and the excitation that comes to the synapse spreads further.
Inhibitory synapse- A. Synapse, on the postsynaptic membrane of which an inhibitory postsynaptic potential arises, and the excitation that comes to the synapse does not spread further; B. excitatory axo-axonal synapse, causing presynaptic inhibition.
3. According to the mechanisms of excitation transmission in synapses:
1) chemical;
2) electric;
3) mixed
Peculiarity chemical synapses lies in the fact that the transfer of excitation is carried out using a special group chemicals – mediators. It is more specialized than an electrical synapse.
There are several types chemical synapses, depending on the nature of the mediator:
a) cholinergic.
b) adrenergic.
c) dopaminergic. They transmit excitement using dopamine;
d) histaminergic. They transmit excitation with the help of histamine;
e) GABAergic. In them, excitation is transferred with the help of gamma-aminobutyric acid, i.e., the process of inhibition develops.
Adrenergic synapse - synapse, the mediator of which is norepinephrine. It transmits excitation with the help of three catecholamines; There are a1-, b1-, and b2 - adrenergic synapses. They form neuroorgan synapses of the sympathetic nervous system and synapses of the central nervous system. Excitation of a-adrenoreactive synapses causes vasoconstriction, contraction of the uterus; b1- adrenoreactive synapses - increased heart function; b2 - adrenoreactive - dilation of the bronchi.
Cholinergic synapse - the mediator in it is acetylcholine. They are divided into n-cholinergic and m-cholinergic synapses.
In m-cholinergic At the synapse, the postsynaptic membrane is sensitive to muscarine. These synapses form neuroorgan synapses of the parasympathetic system and synapses of the central nervous system.
In n-cholinergic At the synapse, the postsynaptic membrane is sensitive to nicotine. This type of synapse is formed by neuromuscular synapses of the somatic nervous system, ganglion synapses, synapses of the sympathetic and parasympathetic nervous system, and synapses of the central nervous system.
Electrical synapse- in it, excitation from the pre- to the postsynaptic membrane is transmitted electrically, i.e. ephaptic transmission of excitation occurs - the action potential reaches the presynaptic terminal and then spreads through intercellular channels, causing depolarization of the postsynaptic membrane. In an electrical synapse, the transmitter is not produced, the synaptic cleft is small (2 - 4 nm) and there are protein bridges-channels, 1 - 2 nm wide, along which ions and small molecules move. This contributes to low postsynaptic membrane resistance. This type of synapse is much less common than chemical synapses and differs from them in a higher speed of excitation transmission, high reliability, and the possibility of two-way conduction of excitation.
Synapses have a number of physiological properties :
1) valve property of synapses, i.e., the ability to transmit excitation in only one direction from the presynaptic membrane to the postsynaptic;
2) synaptic delay property, due to the fact that the rate of excitation transmission decreases;
3) potentiation property(each subsequent impulse will be conducted with a shorter postsynaptic delay). This is due to the fact that the transmitter from the previous impulse remains on the presynaptic and postsynaptic membrane;
4) low synapse lability(100–150 pulses per second).
Transmission of excitation at the synapse.
The mechanism of transmission across synapses remained unclear for a long time, although it was obvious that signal transmission in the synaptic region differs sharply from the process of conducting an action potential along the axon. However, at the beginning of the 20th century, a hypothesis was formulated that synaptic transmission occurs either electric or chemically. The electrical theory of synaptic transmission in the central nervous system was recognized until the early 50s, but it lost ground significantly after the chemical synapse was demonstrated in a number of cases. peripheral synapses. So, for example, A.V. Kibyakov, Having conducted an experiment on the nerve ganglion, as well as the use of microelectrode technology for intracellular recording of the synaptic potential of CNS neurons, it was possible to draw a conclusion about the chemical nature of transmission in interneuronal synapses of the spinal cord.
Microelectrode studies recent years showed that at certain interneuron synapses there is an electrical transmission mechanism. It has now become obvious that there are synapses with both a chemical transmission mechanism and an electrical one. Moreover, in some synaptic structures both electrical and chemical transmission mechanisms function together - these are the so-called mixed synapses.
If electrical synapses are characteristic of the nervous system of more primitive animals (nervous diffusion system of coelenterates, some synapses of crayfish and annelids, synapses of the nervous system of fish), although they are found in the brain of mammals. In all the above cases, impulses are transmitted via depolarizing the action of an electric current that is generated in the presynaptic element. I would also like to note that in the case of electrical synapses, impulse transmission is possible in both one and two directions. Also in lower animals contact between presynaptic And postsynaptic element is carried out through just one synapse - monosynaptic form of communication, however, in the process of phylogenesis there is a transition to polysynaptic form of communication, that is, when the above contact is made through a larger number of synapses.
However, in this work, I would like to dwell in more detail on synapses with a chemical transmission mechanism, which make up the majority of the synaptic apparatus of the central nervous system of higher animals and humans. Thus, chemical synapses, in my opinion, are particularly interesting, since they provide very complex cell interactions, and are also associated with a number of pathological processes and change their properties under the influence of certain medications.
The area of contact between two neurons is called synapse.
Internal structure axodendritic synapse.A) Electrical synapses. Electrical synapses are rare in the mammalian nervous system. They are formed by gap junctions (nexuses) between the dendrites or somata of adjacent neurons, which are connected by cytoplasmic channels with a diameter of 1.5 nm. The signal transmission process occurs without synaptic delay and without the participation of mediators.
Through electrical synapses, electrotonic potentials can spread from one neuron to another. Due to the close synaptic contact, modulation of signal transmission is impossible. The task of these synapses is to simultaneously excite neurons that perform the same function. An example is the neurons of the respiratory center of the medulla oblongata, which synchronously generate impulses during inhalation. In addition, an example is the neural circuits that control saccades, in which the point of fixation of the gaze moves from one object of attention to another.
b) Chemical synapses. Most synapses in the nervous system are chemical. The functioning of such synapses depends on the release of transmitters. The classic chemical synapse is represented by a presynaptic membrane, a synaptic cleft, and a postsynaptic membrane. The presynaptic membrane is the part of the club-shaped extension of the nerve ending of the cell that transmits the signal, and the postsynaptic membrane is the part of the cell that receives the signal.
The transmitter is released from the club-shaped extension by exocytosis, passes through the synaptic cleft and binds to receptors on the postsynaptic membrane. Under the postsynaptic membrane there is a subsynaptic active zone, in which, after activation of the receptors of the postsynaptic membrane, various biochemical processes occur.
The club-shaped extension contains synaptic vesicles containing mediators, as well as a large number of mitochondria and cisterns of the smooth endoplasmic reticulum. The use of traditional fixation techniques in the study of cells makes it possible to distinguish presynaptic seals on the presynaptic membrane, limiting the active zones of the synapse, to which synaptic vesicles are directed with the help of microtubules.
Axodendritic synapse. Section of the spinal cord specimen: synapse between the terminal portion of the dendrite and, presumably, a motor neuron.
The presence of round synaptic vesicles and postsynaptic compaction is characteristic of excitatory synapses.
The dendrite was cut in the transverse direction, as evidenced by the presence of many microtubules.
In addition, some neurofilaments are visible. The synapse site is surrounded by a protoplasmic astrocyte.
Processes occurring in two types of nerve endings. (A) Synaptic transmission of small molecules (eg, glutamate).
(1) Transport vesicles containing membrane proteins of synaptic vesicles are directed along microtubules to the plasma membrane of the club-shaped thickening.
At the same time, enzyme and glutamate molecules are transferred by slow transport.
(2) Vesicle membrane proteins exit plasma membrane and form synaptic vesicles.
(3) Glutamate is loaded into synaptic vesicles; mediator accumulation occurs.
(4) Vesicles containing glutamate approach the presynaptic membrane.
(5) As a result of depolarization, exocytosis of the mediator occurs from partially destroyed vesicles.
(6) The released transmitter spreads diffusely in the region of the synaptic cleft and activates specific receptors on the postsynaptic membrane.
(7) Synaptic vesicle membranes are transported back into the cell by endocytosis.
(8) Partial reuptake of glutamate into the cell occurs for reuse.
(B) Transmission of neuropeptides (eg, substance P) occurring simultaneously with synaptic transmission (eg, glutamate).
The joint transmission of these substances occurs in the central nerve endings of unipolar neurons, which provide pain sensitivity.
(1) Vesicles and peptide precursors (propeptides) synthesized in the Golgi complex (in the perikaryon region) are transported to the club-shaped extension by rapid transport.
(2) When they enter the area of the club-shaped thickening, the process of formation of the peptide molecule is completed, and the vesicles are transported to the plasma membrane.
(3) Depolarization of the membrane and transfer of vesicle contents into the intercellular space by exocytosis.
(4) At the same time, glutamate is released.
1. Receptor activation. Transmitter molecules pass through the synaptic cleft and activate receptor proteins located in pairs on the postsynaptic membrane. Activation of receptors triggers ionic processes that lead to depolarization of the postsynaptic membrane (excitatory postsynaptic action) or hyperpolarization of the postsynaptic membrane (inhibitory postsynaptic action). The change in electrotonicity is transmitted to the soma in the form of an electrotonic potential that decays as it spreads, due to which the resting potential in the initial segment of the axon changes.
Ionic processes are described in detail in a separate article on the website. When excitatory postsynaptic potentials predominate, the initial segment of the axon is depolarized to a threshold level and generates an action potential.
The most common excitatory neurotransmitter of the central nervous system is glutamate, and the inhibitory one is gamma-aminobutyric acid (GABA). In the peripheral nervous system, acetylcholine serves as a transmitter for motor neurons of striated muscles, and glutamate for sensory neurons.
The sequence of processes occurring at glutamatergic synapses is shown in the figure below. When glutamate is transferred together with other peptides, the release of peptides occurs via extrasynaptic pathways.
Most sensory neurons, in addition to glutamate, also secrete other peptides (one or more), released in different parts of the neuron; however, the main function of these peptides is to modulate (increase or decrease) the efficiency of synaptic glutamate transmission.
In addition, neurotransmission can occur through diffuse extrasynaptic signal transmission, characteristic of monoaminergic neurons (neurons that use biogenic amines to mediate neurotransmission). There are two types of monoaminergic neurons. In some neurons, catecholamines (norepinephrine or dopamine) are synthesized from the amino acid tyrosine, and in others, serotonin is synthesized from the amino acid tryptophan. For example, dopamine is released both in the synaptic region and from axonal varicosities, in which the synthesis of this neurotransmitter also occurs.
Dopamine penetrates into the intercellular fluid of the central nervous system and, until degradation, is able to activate specific receptors at a distance of up to 100 microns. Monoaminergic neurons are present in many structures of the central nervous system; disruption of impulse transmission by these neurons leads to various diseases, including Parkinson's disease, schizophrenia and major depression.
Nitric oxide (a gaseous molecule) is also involved in diffuse neurotransmission in the glutamatergic neuronal system. Excessive influence of nitric oxide has a cytotoxic effect, especially in those areas where the blood supply is impaired due to arterial thrombosis. Glutamate is also a potentially cytotoxic neurotransmitter.
In contrast to diffuse neurotransmission, traditional synaptic signal transmission is called “conductor” due to its relative stability.
V) Resume. Multipolar neurons of the CNS consist of soma, dendrites and axon; the axon forms collateral and terminal branches. The soma contains smooth and rough endoplasmic reticulum, Golgi complexes, neurofilaments and microtubules. Microtubules penetrate the entire neuron and take part in the process anterograde transport synaptic vesicles, mitochondria and membrane-building substances, and also provide retrograde transport of “marker” molecules and destroyed organelles.
There are three types of chemical interneuronal interactions: synaptic (eg, glutamatergic), extrasynaptic (peptidergic), and diffuse (eg, monoaminergic, serotonergic).
Chemical synapses are classified according to their anatomical structure into axodendritic, axosomatic, axoaxonal and dendro-dendritic. The synapse is represented by pre- and postsynaptic membranes, a synaptic cleft and a subsynaptic active zone.
Electrical synapses ensure the simultaneous activation of entire groups, forming electrical connections between them due to gap-like contacts (nexuses).
Diffuse neurotransmission in the brain. Axons of glutamatergic (1) and dopaminergic (2) neurons form tight synaptic contacts with the process of the stellate neuron (3) of the striatum.
Dopamine is released not only from the presynaptic region, but also from the varicose thickening of the axon, from where it diffuses into the intercellular space and activates dopamine receptors of the dendritic trunk and capillary pericyte walls.
Disinhibition. (A) Excitatory neuron 1 activates inhibitory neuron 2, which in turn inhibits neuron 3.
(B) The appearance of the second inhibitory neuron (2b) has the opposite effect on neuron 3, since neuron 2b is inhibited.
Spontaneously active neuron 3 generates signals in the absence of inhibitory influences.
2. Medicines - “keys” and “locks”. The receptor can be compared to a lock, and the mediator can be compared to a key that matches it. If the process of mediator release is disrupted with age or as a result of any disease, medicine can play the role of a “spare key”, performing a function similar to a mediator. This drug is called an agonist. At the same time, in case of excessive production, the mediator can be “intercepted” by a receptor blocker - a “fake key”, which will contact the “lock” receptor, but will not cause its activation.
3. Braking and disinhibition. The functioning of spontaneously active neurons is inhibited by the influence of inhibitory neurons (usually GABAergic). The activity of inhibitory neurons, in turn, can be inhibited by other inhibitory neurons acting on them, resulting in disinhibition of the target cell. The process of disinhibition is an important feature of neuronal activity in the basal ganglia.
4. Rare types of chemical synapses. There are two types of axoaxonal synapses. In both cases, the club-shaped thickening forms an inhibitory neuron. Synapses of the first type are formed in the region of the initial segment of the axon and transmit a powerful inhibitory effect of the inhibitory neuron. Synapses of the second type are formed between the club-shaped thickening of the inhibitory neuron and the club-shaped thickening of excitatory neurons, which leads to inhibition of the release of transmitters. This process is called presynaptic inhibition. In this regard, the traditional synapse provides postsynaptic inhibition.
Dendro-dendritic (D-D) synapses are formed between the dendritic spines of the dendrites of adjacent spiny neurons. Their task is not to generate a nerve impulse, but to change the electrotonus of the target cell. In successive D-D synapses, synaptic vesicles are located in only one dendritic spine, and in reciprocal D-D synapses, in both. Excitatory D-D synapses are shown in the figure below. Inhibitory D-D synapses are widely represented in the switching nuclei of the thalamus.
In addition, there are a few somato-dendritic and somato-somatic synapses.
Axoaxonal synapses of the cerebral cortex. The arrows indicate the direction of the impulses.
(1) Presynaptic and (2) postsynaptic inhibition of the spinal neuron traveling to the brain. The arrows indicate the direction of impulse conduction (inhibition of the switching neuron under the influence of inhibitory influences is possible).
Excitatory dendro-dendritic synapses. The dendrites of three neurons are depicted. Reciprocal synapse (right). The arrows indicate the direction of propagation of electrotonic waves.
Educational video - structure of a synapse
Synapses are specialized structures that ensure the transfer of excitation from one excitable cell to another. The concept of SYNAPS was introduced into physiology by Charles Sherrington (connection, contact). The synapse provides functional communication between individual cells. They are divided into neuromuscular, neuromuscular and synapses of nerve cells with secretory cells (neuroglandular). A neuron has three functional sections: soma, dendrite, and axon. Therefore, all possible combinations of contacts exist between neurons. For example, axo-axonal, axo-somatic and axo-dendritic.
Classification.
1) by location and affiliation with the relevant structures:
- peripheral(neuromuscular, neurosecretory, receptor-neuronal);
- central(axo-somatic, axo-dendritic, axo-axonal, somato-dendritic. somato-somatic);
2) mechanism of action - excitatory and inhibitory;
3) the method of signal transmission - chemical, electrical, mixed.
4) chemicals are classified according to the mediator through which transmission is carried out - cholinergic, adrenergic, serotonergic, glycinergic. etc.
Synapse structure.
A synapse consists of the following main elements:
Presynaptic membrane (in the neuromuscular junction - this is the end plate):
Postsynaptic membrane;
Synaptic cleft. The synaptic cleft is filled with oligosaccharide-containing connective tissue, which plays the role of a supporting structure for both contacting cells.
System of synthesis and release of the mediator.
A system for its inactivation.
In the neuromuscular synapse, the presynaptic membrane is part of the membrane of the nerve ending in the area of its contact with the muscle fiber, the postsynaptic membrane is part of the membrane of the muscle fiber.
The structure of the neuromuscular synapse.
1 - myelinated nerve fiber;
2 - nerve ending with mediator bubbles;
3 - subsynaptic membrane of muscle fiber;
4 - synaptic cleft;
5-postsynaptic membrane of muscle fiber;
6 - myofibrils;
7 - sarcoplasm;
8 - nerve fiber action potential;
9 -end plate potential (EPSP):
10 is the action potential of the muscle fiber.
The part of the postsynaptic membrane that is located opposite the presynaptic membrane is called the subsynaptic membrane. A feature of the subsynaptic membrane is the presence in it of special receptors that are sensitive to a specific transmitter and the presence of chemo-dependent channels. In the postsynaptic membrane, outside the subsynaptic membrane, there are voltage-gated channels.
The mechanism of excitation transmission in chemical excitatory synapses. In 1936, Dale proved that when a motor nerve is irritated at its endings, acetylcholine is released into the skeletal muscle. In synapses with chemical transmission, excitation is transmitted using mediators (intermediaries). Mediators are chemical substances that ensure the transmission of excitation in synapses. The mediator at the neuromuscular synapse is acetylcholine, at the excitatory and inhibitory neuromuscular synapses - acetylcholine, catecholamines - adrenaline, norepinephrine, dopamine; serotonin; neutral amino acids - glutamic, aspartic; acidic amino acids - glycine, gamma-aminobutyric acid; polypeptides: substance P, enkephalin, somatostatin; other substances: ATP, histamine, prostaglandins.
Depending on their nature, mediators are divided into several groups:
Monoamines (acetylcholine, dopamine, norepinephrine, serotonin.);
Amino acids (gamma-aminobutyric acid - GABA, glutamic acid, glycine, etc.);
Neuropeptides (substance P, endorphins, neurotensin, ACTH, angiotensin, vasopressin, somatostatin, etc.).
The accumulation of the transmitter in the presynaptic formation occurs due to its transport from the perinuclear region of the neuron using fast acstock; synthesis of a mediator that occurs in synaptic terminals from the products of its cleavage; reuptake of transmitter from the synaptic cleft.
The presynaptic nerve ending contains structures for neurotransmitter synthesis. After synthesis, the neurotransmitter is packaged into vesicles. When excited, these synaptic vesicles fuse with the presynaptic membrane and the neurotransmitter is released into the synaptic cleft. It diffuses to the postsynaptic membrane and binds to a specific receptor there. As a result of the formation of the neurotransmitter-receptor complex, the postsynaptic membrane becomes permeable to cations and depolarizes. This results in an excitatory postsynaptic potential and then an action potential. The transmitter is synthesized in the presynaptic terminal from material arriving here by axonal transport. The mediator is “inactivated”, i.e. either cleaved or removed from the synaptic cleft by a mechanism of reverse transport to the presynaptic terminal.
The importance of calcium ions in mediator secretion.
Secretion of the mediator is impossible without the participation of calcium ions in this process. When the presynaptic membrane is depolarized, calcium enters the presynaptic terminal through specific voltage-gated calcium channels in that membrane. The calcium concentration in the axoplasm is 110 -7 M, when calcium enters and its concentration increases to 110 - 4 M secretion of the mediator occurs. The concentration of calcium in the axoplasm after the end of excitation is reduced by the operation of the systems: active transport from the terminal, absorption by mitochondria, binding by intracellular buffer systems. In a state of rest, irregular emptying of the vesicles occurs, with the release of not only single molecules of the mediator, but also the release of portions, quanta of the mediator. A quantum of acetylcholine includes approximately 10,000 molecules.
Last updated: 09/29/2013
Synapse - definition, structure, role of synapse in the structure of the nervous system
A synapse in the structure of the nervous system is a small area at the end of a neurite that is responsible for transmitting information between nerve cells. Two cells participate in its formation - transmitting and receiving.
Definition of the concept
A synapse is a small section at the end of a neuron. With its help, information is transferred from one neuron to another. Synapses are located in those areas of nerve cells where they contact each other. In addition, synapses are present in places where nerve cells come into contact with various muscles or glands of the body.
Synapse structure
The structure of the synapse consists of three parts, each of which has its own functions in the process of information transmission. Both cells, transmitting and receiving, are involved in its structure.
At the end of the axon of the transmitting cell there is the initial part of the synapse - the presynaptic ending. It is capable of triggering in the cell (the term has several names - “neurotransmitters”, “intermediaries”, “transmitters”) - special chemical substances, thanks to which the transmission of an electrical signal is realized between two neurons.
The middle part of the synapse is the synaptic cleft - the space between two interacting nerve cells. It is through this gap that the electrical impulse from the transmitting cell goes.
The final part of the synapse is part of the receiving cell and is called the postsynaptic ending - a fragment of the cell in contact with many sensitive receptors in its structure.
The mechanism of the synapse
From the presynaptic terminal down the axon of the neuron passes electric charge from the transmitting cell to the receiving cell. It triggers the release of neurotransmitters into the synaptic cleft. These mediators move through the synaptic cleft to the postsynaptic ending of the next cell, where they interact with its numerous receptors. This process causes a chain of biochemical reactions and, as a result, provokes the launch of an electrical impulse with a brief change in its potential in a cell area. This phenomenon is known as an action potential (or a wave of excitation during the passage of a nerve signal).
