The synapse is ... The structure of the synapse. Nervous, muscular and chemical synapses

Synapse is a specific area of contact of the processes of nerve cells and other unexcitable and excitable cells, which provide the transmission of an information signal. The synapse is morphologically formed by the contacting membranes of 2 cells. The membrane, which refers to the process of nerve cells, is called the presynaptic membrane of the cell into which the signal comes in, the second name is post-synaptic. Together with the accessory of the postsynaptic membrane, the synapse can be interneuronal, neuromuscular and neurosecretory. The word synapse was introduced in 1897 by Charles Sherrington (English physiologist).

What is a synapse?

A synapse is a special structure that provides the transfer from the nerve fiber of the nerve impulse to another nerve fiber or nerve cell, and that the nerve fiber from the receptor cell (areas of contact of one another with nerve cells and other nerve fibers) affects two nerve cells .

The synapse is a small department in the end of the neuron. With his help, information is transferred from the first neuron to the second. The synapse is located in three sections of the nerve cells. Also, the synapses are in the place where the nerve cell comes into contact with different glands or muscles of the body.

What does the synapse consist of?

The structure of the synapse has a simple circuit. It is formed from 3 parts, each of which performs certain functions during the transfer of information. Thus, such a structure of the synapse can be called suitable for the transmission of a nerve impulse. Directly on the process of information transfer, two main cells act: the receptor and the transmitting. At the end of the axon of the transmitting cell, there is a presynaptic ending (the initial part of the synapse). It can affect the cell to trigger neurotransmitters (this word has several meanings: mediators, mediators or neurotransmitters) - certain chemicals through which an electrical signal is transmitted between the two neurons.

The synaptic cleft is the middle part of the synapse - this is the gap between the two interacting nerve cells. Through this gap, an electrical impulse comes from the transmitting cell. The final part of the synapse is the perceiving part of the cell, which is the postsynaptic end (the contacting fragment of the cell with different sensitive receptors in its structure).

Mediators of the synapse

Mediator (from Latin Media - transmitter, middleman or middle). Such neurotransmitter mediators are very important in the process of nerve impulse transmission.

The morphological difference between the inhibitory and excitatory synapse is that they do not have a release mechanism for the mediator. The mediator in the inhibitory synapse, motoneuron, and other inhibitory synapse is considered an amino acid glycine. But the inhibitory or exciting character of the synapse is determined not by their mediators, but by the property of the postsynaptic membrane. For example, acetylcholine gives an exciting effect in the neuromuscular synapse of terminals (vagus nerves in the myocardium).

Acetylcholine serves as an excitatory mediator in the cholinergic synapses (the presynaptic membrane in it is played by the ending of the motor neuron spinal cord), at the synapse on Ranshaw cells, in the presynaptic terminal of the sweat glands, the medulla of the adrenocortis, in the intestinal synapse and in the ganglia of the sympathetic nervous system. Acetylcholia-nestereza and acetylcholine were also found in fractions of different parts of the brain, sometimes in large numbers, but in addition to the cholinergic synapse on Ranshaw cells, the remaining cholinergic synapses could not yet be identified. According to scientists, the mediator excitatory function of acetylcholine in the central nervous system is very likely.

Cathelhomins (dopamine, norepinephrine and adrenaline) are considered adrenergic mediators. Adrenaline and norepinephrine are synthesized at the end of the sympathetic nerve, in the cell of the cephalic substance of the adrenal gland, the spinal cord and the brain. Amino acids (tyrosine and L-phenylalanine) are considered the starting material, and adrenaline is the final product of synthesis. Intermediate substance, which includes norepinephrine and dopamine, also perform the function of mediators in the synapse, created in the endings of the sympathetic nerves. This function can be either inhibitory (secretory glands of the intestine, several sphincters and smooth muscle of the bronchi and intestines), or excitatory (smooth muscles of certain sphincters and blood vessels, in the synapse of the myocardium - noradrenaline, in the undercover brain nucleus - dopamine).

When the neurotransmitter mediators complete their function, catecholamine is absorbed by the presynaptic nerve ending, while transmembrane transport is involved. During the absorption of mediators, synapses are protected against premature depletion of the reserve during a long and rhythmic work.

Synapse: the main types and functions

Langley in 1892, it was suggested that the synaptic transmission in the vegetative ganglion of mammals is not electrical, but chemical. After 10 years, Eliott found out that the adrenaline from the adrenal is obtained from the same effect as the stimulation of the sympathetic nerves.

After this, it was suggested that adrenaline is capable of being secreted by neurons and, when excited, is excreted by a nerve ending. But in 1921 Levi made an experiment in which he established the chemical nature of transmission in the vegetative synapse among the heart and vagus nerves. He filled the frog's heart vessels with saline solution and stimulated the vagus nerve, creating a slowing of the heartbeat. When the fluid was transferred from the inhibited stimulation of the heart to the unstimulated heart, it beat more slowly. It is clear that the stimulation of the vagus nerve caused the release of a retarding substance into the solution. Acetylcholine completely reproduced the effect of this substance. In 1930, Feldberg and his collaborator finally established the role in the synaptic transmission of acetylcholine in the ganglion to the autonomic nervous system .

Synapse chemical

The chemical synapse is fundamentally different in the transmission of irritation with a mediator from presynaps to postsynaps. Therefore, differences are formed in the morphology of the chemical synapse. The chemical synapse is more common in the vertebral CNS. Now it is known that a neuron is able to isolate and synthesize a pair of mediators (coexisting mediators). Neurons also have neurotransmitter plasticity - the ability to alter the main mediator during development.

Neuromuscular synapse

This synapse carries out the transmission of excitation, however, this relationship can be destroyed by various factors. Transmission ends during the blockade of ejection into the synaptic cleft of acetylcholine, also during its excess in the zone of postsynaptic membranes. A lot of poisons and drugs affect the capture, the output that is associated with the holinoreceptors of the postsynaptic membrane, then the muscle synapse blocks the transmission of excitation. The body dies during choking and stopping the contraction of the respiratory muscles.

Botulinus is a microbial toxin in the synapse, it blocks the transmission of excitation, destroying the syntaxin at the presynaptic terminal of the protein, controlled by the release into the synaptic cleft of acetylcholine. Several poisonous warfare agents, pharmacological drugs (neostigmine and proserin), as well as insecticides block the excitation in the neuromuscular synapse by inactivating acetylcholinesterase, an enzyme that destroys acetylcholine. Therefore, there is accumulation in the zone of the postsynaptic membrane of acetylcholine, the sensitivity to the mediator decreases, the output from the postsynaptic membranes and the immersion in the cytosol of the receptor block. Acetylcholine will be ineffective, and the synapse will be blocked.

Synapse nervous: features and components

Synapse is the connection of the place of contact among two cells. Each of them is enclosed in its electrogenic membrane. The nervous synapse consists of three main components: the postsynaptic membrane, the synaptic cleft and the presynaptic membrane. Post-synaptic membrane - this is the nerve end, which passes to the muscle and descends inside the muscle tissue. In the presynaptic region, there are vesicles - these are closed cavities that have a mediator. They are always in motion.

Approaching the membrane of the nerve endings, the vesicles merge with it, and the mediator enters the synaptic cleft. In one vesicle contains a quantum of the mediator and mitochondria (they are needed for the synthesis of the mediator - the main energy source), then acetylcholine is synthesized from choline and, under the action of the enzyme acetylcholinesterase, is processed into acetyl CoA).

Synaptic cleft among post- and presynaptic membranes

In different synapses the size of the gap is different. This space is filled with intercellular fluid, in which there is a mediator. Post-synaptic membrane covers the place of contact of the nerve end with the innervated cell in the myoneural synapse. In certain synapses the postsynaptic membrane creates a crease, the contact area increases.

Additional substances that are part of the postsynaptic membrane

In the zone of the postsynaptic membrane, the following substances are present:

- Receptor (holinoretseptor in the myoneural synapse).

- Lipoprotein (has a great similarity with acetylcholine). This protein has an electrophilic end and an ionic head. The head enters the synaptic cleft, interaction with the cationic head of acetylcholine occurs. Because of this interaction, there is a change in the postsynaptic membrane, then depolarization occurs, and potentially dependent Na channels are revealed. Depolarization of the membrane is not considered a self-reinforcing process;

- Gradual, its potential on the postsynaptic membrane depends on the number of mediators, that is, the potential is characterized by the property of local excitations.

- Cholinesterase - is considered a protein, which has an enzymatic function. In structure, it is similar to a cholinergic receptor and has similar properties with acetylcholine. Cholinesterase destroyed acetylcholine, at first the one that is associated with cholinergic receptor. Under the influence of cholinesterase holinoretseptor removes acetylcholine, repolarization of the postsynaptic membrane is formed. Acetylcholine is cleaved to acetic acid and choline, which is necessary for trophism of muscle tissue.

Using active transport, choline is excreted onto the presynaptic membrane, it is used to synthesize a new mediator. Under the influence of the mediator the permeability in the postsynaptic membrane changes, and under cholinesterase sensitivity and permeability return to the initial value. Chemoreceptors are able to interact with new mediators.