Structure, classification and functional properties of synapses. Morphological and functional features of electrical and chemical synapses

2 The term synapse was proposed by Ch.
Sherrington in 1897
Translated from Greek means - to close.
Synapse is
structure,
through which
ensured
transmission of information
between nervous
cells, nerves and
muscular
cells.

3 CLASSIFICATION OF SYNAPSE

1. By location:
a.) central (brain and spinal cord)
- axosomatic, axoaxonal, axodendretic;
- dendrosomatic, dendrodendretic.
b.) peripheral (neuromuscular, neurosecretory).
2. By the nature of the action:
a.) exciting
b.) brake
3.) According to the signal transmission method:
a.) electrical;
b.) chemical;
c.) mixed.
4.) By development in ontogenesis:
a.) stable (synapses of the arcs of the unconditioned reflex);
b.) dynamic (appear in the process of development of the individual).

4 Localization of different types of synapses

6 Synapses

chemical
electric

6 7 The structure of the chemical synapse:

1. presynaptic
membrane;
2. postsynaptic
membrane;
3. synaptic cleft.
Dale principle:
one neuron emits
one mediator.
Currently
revised.

8 Structure of a chemical synapse

Presynaptic
membrane
formed by axonal
ending, which loses the myelin sheath in this place.
It contains synaptic vesicles with a diameter of 30-50 nm and
numerous mitochondria. Synaptic vesicles contain
mediator and ATP (constituting the quantum of the mediator), have
negative charge and
repelled by presynaptic
membranes, vesicles are concentrated in "active zones".
Each vesicle contains thousands of mediator molecules (for example,
acetylcholine) and ATP molecules.
Synaptic vesicles are in several fractions -
reserve and recirculating pool.
Is allocated in portions -
quanta.
The width of the synaptic cleft is 20-50 nm. She is
filled with intercellular fluid and contains structural
elements: basement membrane, consisting of fibrous fibers,
that connect pre- and postsynaptic
membranes. There are also enzymes that break down molecules.
mediator.

9

The postsynaptic membrane (or end plate) has
numerous
folds,
increasing
square
her
interaction with the mediator. There are no voltage dependent voltages on the membrane
ion channels, but the density of receptor-gated channels is high (their ion selectivity is low).
Number of receptors on the surface of the postsynaptic membrane
may vary. So, with a long allocation of large
quantities of the mediator - desensitization of receptors occurs. AT
in particular, the number of receptors on
postsynaptic membrane (elimination of receptors).
Except
This reduces their sensitivity to the mediator.
On the contrary, during denervation, when the release of the mediator sharply
decreases, the number of receptors can increase sharply.
Thus, the synapse is a highly dynamic structure,
which determines its plasticity.

10. 10 SYNAPSE PLASTICITY

Change occurs at all levels: it is change
the number of neurotransmitter receptors in the postsynapse,
changes
in
them
functional
able
and
post-translational modifications.
The most well-studied of these is phosphorylation.
This is a process of rapid change in the conformation of the receptor,
in which enzymes called kinases
attach a phosphoric acid residue to one of the
amino acids in the receptor polypeptide chain. It leads
to very strong changes in receptor conformation and
can seriously affect its performance.
Except
Togo,
phosphorylation
exposed
many other molecular targets found in
postsynapse. There is a change in the cytoskeleton, synthesis
additional proteins both in general in the cell and inside
spine.

11. 11 Elements of the neuromuscular synapse

12.

12
ultrast
ructura
nervously-
muscular
th
synapse

13. The release of the mediator in the synapse occurs in portions (quanta). The transmitter quantum is located in the synaptic vesicle and is released from

13 Quantum-vesicular theory.
The release of the mediator in the synapse occurs in portions
(quanta).
The transmitter quantum is located in the synaptic vesicle and
released from the nerve ending by exocytosis.
In 1954 Del Castillo and Katz
described PEP and MEPP in detail
at the neuromuscular junction.
They suggested that the mediator
freed up
certain
portions - quanta.
In 1955 Pali,
pallas,
De
Robertis and Bennett discovered
synaptic
vesicles
with
using
electronic
microscope.

14. 14 End plate potential

Excitatory postsynaptic potential (EPSP) exists
only locally on the postsynaptic membrane. Its magnitude
determined by the number of emitted mediator quanta. In connection with
this:
1) EPSP, unlike PD, is not subject to the "All or Nothing" law, but
obeys the summation rule:
The more mediator is released, the greater the value of EPSP.
2) The second difference between EPSP and PD is the electrotonic
distribution, i.e. potential decay with distance from the terminal
records.
Out of excitation - on the end plate are recorded
miniature
potentials
terminal
records
(MPKP),
which are small waves of depolarization, 0.5
mV. Their origin is associated with the spontaneous release of quanta
mediator
from
presynaptic
membranes,
due to
spontaneous adhesion of synaptic vesicles to the membrane (~1
quantum per second).
For the occurrence of EPSP, the simultaneous release of
several hundred mediator quanta.

15. 15

16. 16

Potentials and
terminal currents
records on
different
distances from
her

17. 17

If the synapse is excitatory, then it increases
permeability of the postsynaptic membrane
sodium and potassium. EPSP occurs. He exists
locally only on the postsynaptic membrane. But
if the magnitude of postsynaptic depolarization
membrane reaches a critical level, then EPSP
transforms into an action potential
efferent cell.
If the synapse is inhibitory, then the released neurotransmitter
increases the permeability of the postsynaptic
membranes for potassium and chlorine. Developing
hyperpolarization (TPSP) extends to
efferent cell membrane, increases the threshold
excitement and reduces excitability.

18. 18 Post-synaptic potentials

19. 19 Mechanism of transformation of vPKP/EPSP into cell PD

19
MECHANISM OF TRANSFORMATION
VPKP/EPSP IN PD CELLS
After the onset of VPKD, between the depolarized
end plate membrane and at rest
part of the electrically excitable membrane of a muscle fiber
adjacent to the end plate - there is a local
current. This current is due to the redistribution of Na+ ions,
entered
through
chemosensitive
channels
- between
end plate and sarcolemma.
If the magnitude of the local current allows depolarization
muscle fiber membrane
before
Ekr then open up
voltage-dependent Ca 2+ channels of the sarcolemma, input
calcium ions completes depolarization - PD occurs,
which then spreads along the muscle fiber.
So
the way
VPKP
outgrows
(or
is transformed) into the PD of the muscle fiber.

20. 20 Neuromuscular synapse

21. 21 Location of receptor-operated and voltage-gated channels on the muscle cell membrane.

Potential-dependent Ca
channels
PP= -80 mV
postsynaptic
membrane
-80 mV
Receptor-driven
channels
Potential-dependent Ca
channels
PP= -80mV

22.

22
The transmission of excitation to the nervous
- muscle synapse
neuromuscular junction
presynaptic ending
postsynaptic membrane
Electrosecretory conjugation
Release of acetylcholine
Acetylcholinesterase
H - ACh receptor
EPSP
PD of the sarcolemma
Reduction
muscles

23. 23 Metabolism of mediators: ACh

24. 24 Metabolism of mediators: ON

25. 25 According to the effect exerted by the mediator on the postsynaptic membrane, chemical synapses are divided into:

1. Ionotropic
2. Metabotropic

26. 26 Transmission of excitation in a chemical synapse

1. Neurotransmitter molecules
enter the membrane
synaptic vesicles,
located in
presynaptic terminal
and concentrating on
active zones
presynaptic membrane.
2. AP coming along the axon
depolarizes
presynaptic membrane.
3. Due to depolarization
open
voltage-dependent
Ca2+ channels, and Ca2+
enters the terminal.
4. Increase in intracellular
[Ca2+] triggers the fusion
synaptic vesicles with
presynaptic membrane
and neurotransmitter release
synaptic cleft
(exocytosis).

27. 27 Transmission of excitation in a chemical synapse

5. Neurotransmitter quanta,
entered the synaptic
gap, diffuse in it.
Part of neurotransmitter molecules
associated with specific
receptors for them
postsynaptic membrane.
6. Neurotransmitter bound
receptors are activated
leads to a change
polarization
postsynaptic membrane
or directly (the supply of ions
through ionotropic receptors)
or indirectly
ion channel activation
through the G-protein system
(metabotropic receptors).
7. Inactivation of neurotransmitters
occurs either through
enzymatic degradation, or
neurotransmitter molecules
taken up by cells.

28. 28 Ionotropic synapse

28
Ionotropic
th synapse

29. 29 Metabotropic synapse

30. 30 Postsynaptic receptors

Ionotropic
1. Fast
2. A single complex with
ion channel
3. Work for
channel opening
4. Nicotine
cholinergic receptors,
GABA receptors,
glycine
Metabotropic
1. Slow
2. Activation
enzyme cascades
3. Subsequently may
open or
close
(indirectly) channels
4. Muscarinic
cholinergic receptors,
receptors
majority
neuropeptides,
majority
receptors
catecholamines and
serotonin

31. 31

32. 32

Physiological features
chemical synapses:
- one-way conduction
- synaptic delay
- the quantum nature of the release of mediators
- depletion of the neurotransmitter with prolonged stimulation
(synapse fatigue)
- synapse lability is less than that of a nerve
- transformation of the rhythm of excitation
- high sensitivity to lack of O2 and poisons

33. 33 Classification of neuromuscular blockers

33 Classification of neuromuscular blockers
1.) Local anesthetics, block the conduction of excitation to
presynaptic membrane (novocaine, lidocaine, etc.).
2.) Blockers that prevent mediator release
from presynaptic endings (botulinum toxin, Mn,
prostaglandins).
3.)
blockers,
violating
back
capture
presynaptic
membrane
products
hydrolysis
mediator (choline),
thereby preventing its resynthesis
(hemocholine).
4.)
Blockers
ACh receptors
on the
postsynaptic
membrane:
a.) competitive action - tubocurarine.
b.) non-competitive action - prestonal, α-bungarotoxin.
5.) Blockers of anticholinergic action - depress
cholinosterase, which causes profound depolarization and
receptor inactivation. These include organophosphorus
compounds: dichlorvos, karbofos.

34. 34 Electric synapse.

Characteristic of the CNS, but also found in
periphery (heart, smooth muscle
the cloth).
Represent close contact
membranes of two cells.
The width of the synaptic cleft is an order of magnitude
less than in a chemical synapse.
The membranes of both cells share a common
integral proteins that form
intercellular ion channels (nexuses).
Their existence drastically reduces
intercellular resistance, which makes
possible distribution of bilateral
depolarization between cells.

35.

35
electrical synapse
1
3
1 - presynaptic
membrane
2 - postsynaptic
membrane
3 - nexus
2
3

36. 36 Ultrastructure of the nexus (gap contact)

37. 37 The structure and operation of the electrical synapse

- synaptic width
gaps 5 nm
- pore diameter 1 nm
- current drop in 2-4
times
- holding delay
0.1 ms

38.

39
Differences between an electrical synapse and
chemical:
- absence
-
-
synaptic delay
bilateral holding
excitement
refers to exciting
synapses
less sensitive to changes
temperature
much less fatigue

44. 44 Hierarchy of structural contractile components of skeletal muscle

45 Physiological properties of muscles
Excitability
Conductivity
Lability
Accommodation
Contractility

45. 45 Physiological properties of muscles

46
Physical properties of muscles
1.Extensibility - increase in size
under the influence of an external load.
2. Elasticity - return to original
condition after unloading.
3. Plasticity - maintaining a given
external load, length.
4.Viscosity - tensile strength.

46. 46 Physical properties of muscles

47
Skeletal Muscle Functions
(make up to 40% of body weight)
1. Moving the body in space
2. Moving body parts each
relative to a friend
3. Posture maintenance (static function)
4. Movement of blood and lymph
5. Thermoregulatory
6. Participation in breathing
7. Protection of internal organs
8. Depot of water, glycogen, proteins and salts
9. Receptor (proprio-, baro-, value-,
thermoreceptors).

47. 47 Functions of skeletal muscles (make up to 40% of body weight)

48
Types of skeletal fibers
Phase
fast fibers
with glycolytic type
oxidation (white)
They have
strong cuts,
fast fibers
oxidizing type
Implement fast
strong cuts and
but get tired quickly
weakly tired
slow fibers
oxidizing type
Perform a maintenance function
posture of a person. neuromotor units
these muscles contain the most mice. fibers
tonic
slow,
effectively
work in isometric
mode.
Muscular
fibers
not
generate PD
and not
obey the law "All or
nothing".
The axon of the motor neuron has
many synaptic
contacts
with
membrane
muscle fibers

48. 48 Types of skeletal fibers

49
Modes of muscle contractions
1. single
2. summation (full and incomplete)
dentate and smooth tetanus
3. optimum and pessimum frequency
cuts
4. contact

49. 49 Modes of muscle contractions

50.

51
Theories of summation of muscle contractions
1. Helmholtz - the principle of superpositions:
addition of amplitudes of single contractions.
2. Vvedensky - summation value
depends on the functional state
fabrics, i.e. from which phase (calculation
or refractoriness) is applied next
irritation.
3. Babsky - associated the value of summation with
accumulation of ATP and Ca 2+ left over from
previous cut.
4. Modern theory - with an increase
formation of actomyosin bridges.

Synapse - specialized structures that provide the transfer of excitation from one excitable cell to another. The concept of SINAPSE was introduced into physiology by C. Sherrington (connection, contact). The synapse provides functional communication between individual cells. They are divided into neuronerve, neuromuscular and synapses of nerve cells with secretory cells (neuro-glandular). There are three functional divisions in a neuron: soma, dendrite, and axon. Therefore, there are all possible combinations of contacts between neurons. For example, axo-axonal, axo-somatic and axo-dendritic.

Classification.

1) by location and belonging to 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) to a way of transmission of signals - chemical, electrical, mixed.

4) chemical are classified according to the mediator, with the help of which the transfer is carried out - cholinergic, adrenergic, serotonergic, glycinergic. etc.

Synapse structure.

The synapse consists of the following main elements:

Presynaptic membrane (in the neuromuscular synapse - 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.

The system of synthesis and release of the mediator.

its inactivation system.

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 vesicles;

3 - subsynaptic membrane of the muscle fiber;

4 - synaptic cleft;

5-postsynaptic membrane of the muscle fiber;

6 - myofibrils;

7 - sarcoplasm;

8 - nerve fiber action potential;

9 - end plate potential (EPSP):

10 - the action potential of the muscle fiber.

The part of the postsynaptic membrane that is opposite the presynaptic is called the subsynaptic membrane. A feature of the subsynaptic membrane is the presence in it of special receptors that are sensitive to a certain mediator and the presence of chemodependent channels. In the postsynaptic membrane, outside the subsynaptic, there are voltage-gated channels.

The mechanism of excitation transmission in chemical excitatory synapses. In 1936, Dale proved that when a motor nerve is stimulated, acetylcholine is released in the skeletal muscle at its endings. In synapses with chemical transmission, excitation is transmitted with the help of mediators (intermediaries). Mediators are chemical substances that ensure the transmission of excitation in synapses. The mediator in the neuromuscular synapse is acetylcholine, in excitatory and inhibitory neuronerve synapses - acetylcholine, catecholamines - adrenaline, norepinephrine, dopamine; serotonin; neutral amino acids - glutamine, aspartic; acidic amino acids - glycine, gamma-aminobutyric acid; polypeptides: substance P, enkephalin, somatostatin; other substances: ATP, histamine, prostaglandins.

Mediators, depending on their nature, 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 mediator in the presynaptic formation occurs due to its transport from the perinuclear region of the neuron with the help of a fast axstock; synthesis of a mediator occurring in synaptic terminals from its cleavage products; reuptake of the neurotransmitter from the synaptic cleft.

The presynaptic nerve ending contains structures for neurotransmitter synthesis. After synthesis, the neurotransmitter is packaged into vesicles. When stimulated, 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 there to a specific receptor. 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 mediator is synthesized in the presynaptic terminal from the material supplied here by axonal transport. The mediator is "inactivated", i.e. is either cleaved or removed from the synaptic cleft by a reverse transport mechanism to the presynaptic terminal.

The value of calcium ions in the secretion of the mediator.

The secretion of the mediator is impossible without the participation of calcium ions in this process. Upon depolarization of the presynaptic membrane, calcium enters the presynaptic terminal through specific voltage-gated calcium channels in this membrane. The concentration of calcium in the axoplasm is 110 -7 M, with the entry of calcium and increasing its concentration to 110 - 4 M mediator secretion occurs. The concentration of calcium in the axoplasm after the end of excitation is reduced by the work of systems: active transport from the terminal, absorption by mitochondria, binding by intracellular buffer systems. At 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. Quantum of acetylcholine includes approximately 10,000 molecules.

A synapse is a place of contact of a nerve cell with another neuron or executive organ. All synapses are divided into the following groups:

1.By transmission mechanism:

a. Electrical. In them, excitation is transmitted through an electric field. Therefore, it can be transmitted in both directions. There are few of them in the CNS.

b. Chemical. Excitation through them is transmitted with the help of FAV - a neurotransmitter. Most of them are in the CNS.

in. Mixed.

2. By localization:

a. Central, located in Ts.N.S.

b. Peripheral, outside of it. These are neuromuscular synapses and synapses of the peripheral parts of the autonomic nervous system.

3. According to the physiological:

a. Exciting

b. Brake

4. Depending on the neurotransmitter used for transmission:

a. Cholinergic - mediator acetylcholine (ACh).

b. Adrenergic - norepinephrine (NA).

in. Serotonergic - serotonin (ST).

d. Glycinergic - the amino acid glycine (GLI).

e. GABAergic - gamma-aminobutyric acid (GABA).

e. Dopaminergic - dopamine (DA).

well. Peptidergic mediators are neuropeptides. In particular, the role of neurotransmitters is performed by substance P, the opioid peptide β-endorphin, etc.

It is assumed that there are synapses where the functions of the mediator are performed by histamine, ATP, glutamate, aspartate.

5. By the location of the synapse:

a. Axo-dendritic (between the axon of one and the dendrite of the second neuron).

b. Axo-axonal

in. Axo-somatic

Dendro-somatic

e. Dendro-dendritic

The first three types are the most common.

The structure of all chemical synapses has a fundamental similarity. For example, an axo-dendritic synapse consists of the following elements:

1. Presynaptic ending or terminal (axon end).

2. Synaptic plaque, thickening of the ending.

3. Presynaptic membrane covering the presynaptic ending.

4. Synaptic vesicles in the plaque that contain the neurotransmitter.

5. Postsynaptic membrane covering the area of the dendrite adjacent to the plaque.

6. Synaptic cleft separating the pre- and postsynaptic membranes, 10-50 nM wide.

7. Chemoreceptors, proteins built into the postsynaptic membrane and specific for the neurotransmitter. For example, in cholinergic synapses, these are cholinergic receptors, adrenergic synapses are adrenoreceptors, etc. Rice.

Simple neurotransmitters are synthesized in presynaptic endings, peptide neurotransmitters are synthesized in the soma of neurons, and then transported along the axons to the endings.

J Mechanism of excitation transmission in chemical synapses

The mediator contained in the synaptic vesicles is formed either in the body of the neuron (and enters the synaptic ending, having passed through the entire axon), or in the synaptic plaque itself. For the synthesis of the mediator, enzymes are needed that are formed in the cell body on ribosomes. In the synaptic plaque, the mediator molecules accumulate and are “packed” into vesicles, in which they are stored until released. It was found (A. Fett and B. Katz, 1952) that one vesicle contains from 3 to 10 thousand acetylcholine molecules. This quantity is called the quantum of the mediator. When the nerve is stimulated in the presynaptic part of the synapse, from 250 to 500 vesicles are destroyed. The arrival of a nerve impulse (PD) in the synaptic plaque causes depolarization of the presynaptic membrane and an increase in its permeability for Ca2+ ions. The Ca2+ ions entering the synaptic plaque cause the fusion of synaptic vesicles with the presynaptic membrane and the release of their contents (exocytosis) into the synaptic cleft. After release of the mediator, the vesicle material is used to form new vesicles. Transmitter molecules diffuse through the synaptic cleft and bind to receptors located on the postsynaptic membrane, capable of recognizing the molecular structure of the mediator. Diffusion of the mediator through the synaptic cleft takes about 0.5 ms. When the receptor molecule binds to the mediator, its configuration changes, which leads to the opening of ion channels and the entry of ions into the postsynaptic cell, causing depolarization or hyperpolarization of its membrane, depending on the nature of the released mediator and the structure of the molecule receptor. The mediator molecules, after acting on the receptors, are immediately removed from the synaptic cleft by either reabsorption by the presynatic membrane, or by diffusion, or by enzymatic hydrolysis. Acetylcholine is hydrolyzed by the enzyme acetylcholinesterase located on the postsynaptic membrane. Then the cleavage products are absorbed back into the plaque and again converted there into acetylcholine. Nor-adrenaline is hydrolyzed by the enzyme monoamine oxidase. Excitatory and inhibitory postsynaptic potentials. In excitatory synapses, specific sodium and potassium channels open under the action of acetylcholine. And Na + ions enter the cell, and K + ions leave it in accordance with their concentration gradients. As a result, depolarization of the postsynaptic membrane occurs. It is called the excitatory postsynaptic potential (EPSP). Its amplitude is small, but the duration is longer than that of the action potential. In inhibitory synapses, mediator release increases the permeability of the postsynaptic membrane by opening specific channels for K+ and SG ions. Moving along concentration gradients, these ions cause membrane hyperpolarization, called inhibitory postsynaptic potential (IPSP).

electrical synapses

Electrical synapses have a special structure. The width of the synaptic cleft is 2–3 nm, and the total resistance to current from the side of the membranes and the fluid filling the cleft is very small. Ions that carry electrical currents cannot pass through lipid membranes, so they are transmitted through channel proteins. Such intercellular connections are called nexuses, or "gap junctions" (Fig. 42). In each of the two adjacent cell membranes are regularly distributed at small intervals<<коннексоны>> penetrating the entire thickness of the membrane. They are located in such a way that at the point of contact of the cells they are opposite each other, and their gaps are on the same line. The channels formed in this way have large diameters, which means high conductivity for ions; even relatively large molecules can pass through them. Gap junctions are common in the CNS and tend to connect groups of synchronously functioning cells.

Impulses pass through synapses without delay, can be conducted in both directions, and their transmission is not affected by drugs or other chemicals

22nd Neuromuscular synapses

The neuromuscular junction is a specialized type of synapse between the endings of a motor neuron (motoneuron) and the endomysium of muscle fibers. Each muscle fiber has a specialized area - the motor end plate, where the axon of the motor neuron branches, forming unmyelinated branches that run in shallow grooves along the surface of the muscle membrane. The membrane of the muscle cell - the sarcolemma - forms many deep folds called postsynaptic folds. The cytoplasm of the motor neuron endings is similar to the contents of the synaptic plaque. The excitation transfer mechanism is the same. As a result of excitation of the motor neuron, depolarization of the surface of the sarcolemma occurs, called the end plate potential (EPP). The magnitude of this potential is sufficient to generate an action potential that propagates along the sarcolemma deep into the fiber and causes muscle contraction.

The 23rd Neuron is the main structural and functional unit of the nervous system. Neurons are highly specialized cells adapted for receiving, encoding, processing, integrating, storing and transmitting information. The neuron consists of a body and processes of two types: short branching dendrites and a long process - an axon (Fig. 42). The cell body has a diameter of 5 to 150 microns. It is the biosynthetic center of the neuron, where complex metabolic processes take place. The body contains a nucleus and cytoplasm, which contains many organelles involved in the synthesis of cellular proteins (proteins). Axon. A long filamentous process of axon departs from the cell body, which performs the function of transmitting information. The axon is covered with a special myelin sheath that creates optimal conditions for signal transmission. The end of the axon strongly branches, its terminal branches form contacts with many other cells (nerve, muscle, etc.). Clusters of axons form a nerve fiber.
Dendrites are highly branching processes that extend in large numbers from the cell body. Up to 1000 dendrites can depart from one neuron. The body and dendrites are covered with a single membrane and form the receptive (receptive) surface of the cell. It contains most of the contacts from other nerve cells - synapses. The cell wall - the membrane - is a good electrical insulator. On both sides of the membrane there is an electrical potential difference - the membrane potential, the level of which changes when synaptic contacts are activated. The synapse has a complex structure (see Fig. 42). It is formed by two membranes: presynaptic and postsynaptic. The presynaptic membrane is located at the end of the axon that transmits the signal; postsynaptic - on the body or dendrites to which the signal is transmitted. In synapses, when a signal arrives, two types of chemicals are released from the synaptic vesicles - excitatory (acetylcholine, adrenaline, norepinephrine) and inhibitory (serotonin, gamma-aminobutyric acid). These substances - mediators, acting on the postsynaptic membrane, change its properties in the area of contacts. With the release of excitatory mediators, an excitatory postsynaptic potential (EPSP) arises in the contact area, with the action of inhibitory mediators, an inhibitory postsynaptic potential (IPSP), respectively, arises. Their summation leads to a change in the intracellular potential towards depolarization or hyperpolarization. When depolarized, the cell generates impulses that are transmitted along the axon to other cells or a working organ. During hyperpolarization, the neuron enters an inhibitory state and does not generate impulse activity (Fig. 43). The multiplicity and diversity of synapses provides the possibility of wide interneuronal connections and the participation of the same neuron in different functional associations.

Classification

Structural classification

Based on the number and arrangement of dendrites and axons, neurons are divided into non-axonal, unipolar neurons, pseudo-unipolar neurons, bipolar neurons, and multipolar (many dendritic trunks, usually efferent) neurons.

Axonless neurons- small cells, grouped near the spinal cord in the intervertebral ganglia, which do not have anatomical signs of separation of processes into dendrites and axons. All processes in a cell are very similar. The functional purpose of axonless neurons is poorly understood.

Unipolar neurons- neurons with one process, are present, for example, in the sensory nucleus of the trigeminal nerve in the midbrain.

bipolar neurons- neurons with one axon and one dendrite, located in specialized sensory organs - the retina, olfactory epithelium and bulb, auditory and vestibular ganglia.

Multipolar neurons- Neurons with one axon and several dendrites. This type of nerve cells predominates in the central nervous system.

Pseudo-unipolar neurons- are unique in their kind. One process departs from the body, which immediately divides in a T-shape. This entire single tract is covered with a myelin sheath and structurally represents an axon, although along one of the branches, excitation goes not from, but to the body of the neuron. Structurally, dendrites are ramifications at the end of this (peripheral) process. The trigger zone is the beginning of this branching (that is, it is located outside the cell body). Such neurons are found in the spinal ganglia.

Despite the commonality of the main features of the organization, chemical synapses differ in the mediators used, the nature of the action and the location. For this reason, there are many ways to classify chemical synapses.

By mediator type synapses are divided into cholinergic (mediator - ACh), glutamatergic (mediator - glutamate), adrenergic (mediator - norepinephrine), dopaminergic (mediator - dopamine), etc.

By effect synapses are divided into excitatory and inhibitory.

By location in the nervous system synapses are divided into central (located in the central nervous system) and peripheral (located in the peripheral nervous system).

Peripheral synapses are the contacts of axons with muscles of all types, as well as with gland cells. Peripheral synapses are larger than central ones and reach sizes of 50-100 microns (Fig. 3.26). So, on each mature skeletal muscle fiber there is only one neuromuscular synapse formed by the nerve terminal of the axon of the motor neuron.

Rice. 3.26.

Synaptic transmission in the end plate occurs with the participation of the ACh mediator and leads to the generation of a high-amplitude PCR (30-40 mV). Such a PPP is 2-3 times higher than the threshold for AP generation. Therefore, each single presynaptic AP, causing the generation of a high-amplitude PEP, in 100% of cases leads to the generation of muscle AP and subsequent contraction of the muscle fiber.

Synapses with internal organs (smooth muscle cells, cardiomyocytes, or gland cells) form the axons of postganglionic sympathetic and parasympathetic neurons. As a rule, in such axons, the grouping of vesicles and the release of the mediator do not occur from the final single bud, as in neuromuscular synapses, but along the course of the axon from its numerous varicose veins. There are up to 250-300 such extensions per 1 mm of axon length. The distance between the iresynaptic and postsynaptic membranes in such synapses is large - from 80 to 250 nm, and the released neurotransmitter directs its action to metabotropic iostsynatic receptors.

11a fig. 3.27 shows an example of a synapse formed by iostganglionic parasympathetic fibers in the smooth muscle tissue of the stomach. It can be seen that along the course of the postganglionic parasympathetic axon there are numerous varices containing synaptic vesicles with the ACh mediator. Ca 2+ channels are located here as part of the presynaptic membrane. Accordingly, under the influence of AP propagating along axons and caused by depolarization, the entry of calcium ions into varicose veins occurs in them, exocytosis of vesicles occurs, i.e. release of mediator quanta.

Rice. 3.27.

When ACh interacts with metabotropic mChRs of the postsynaptic membrane, after a long synaptic delay (1.5–2 ms compared to 0.3–0.5 ms in fast synapses), an EPSP lasting 20–50 ms occurs. For the occurrence of AP in a smooth muscle cell, it is necessary to achieve a threshold amplitude of EPSP of 8-25 mV. As a rule, a single presynaptic signal (single AP) is insufficient to cause calcium ions to enter the varicose veins and trigger vesicle exocytosis. Therefore, the release of the mediator from varicose veins of postganglionic axons is carried out only under the action of a certain amount (volley) of successive presynaptic APs. Transmission actuation in such contacts causes a change in the tone of muscle fibers in the walls of internal organs or causes secretion in glandular cells.

central synapses have a very large structural diversity. The most numerous are axodendritic and axosomatic synapses - contacts between the nerve terminal of the axon of one cell and the dendrite or body of another cell (Fig. 3.28).

Rice. 3.28.

There are, however, all other options: dendro-dendritic, somatodendritic, axo-axonal and other types of synapses. The ultrastructure of nerve terminals in the CYS demonstrates the characteristic features of a chemical synapse: the presence of synaptic vesicles, active zones in presynaptic buds, and postsynaptic receptors on the membrane of the target cell. The difference is the small size of the central synapses. Therefore, in the CNS, in chemical synapses in presynaptic buds, the number of active zones does not exceed 10, and in the majority it is reduced to 1-2. This is due to the small size of presynaptic buds (1–2 μm).

Along with simple synapses, consisting of one pre- and one postsynaptic endings, complex synapses also exist in the central nervous system. They are divided into several groups. In one group of complex synapses, the presynaptic ending of the axon forms several branches - membrane outgrowths ending in small buds. With their help, the axon contacts the dendrites of several neurons at once. In another group of complex synapses, the presynaptic endings of different axons converge on a small mushroom-like outgrowth of the dendrite (dendritic spine). These endings closely cover the postsynaptic zone - the head of the spine. Synaptic glomeruli, compact clusters of processes of different neurons that form a large number of mutual synapses, have an even more complex structure. Usually such glomeruli are surrounded by a sheath of glial cells (see Fig. 3.28).

The synapse can be considered as a functional unit of the nervous tissue, which ensures the transmission of information in the nervous system. However, the interaction of adjacent working synapses is an equally important condition for information processing in the central nervous system. It is the presence of complex synapses (especially synaptic glomeruli) that makes this process particularly efficient. Hence it is clear why the largest number of complex synapses is located precisely in those areas of the brain where the most complex signal processing takes place - in the cerebral cortex of the forebrain, the cerebellar cortex, and the thalamus.

The number of synapses on the membrane of one central neuron ranges on average from 2-5 thousand to 15 thousand or more. The location of the contacts is very variable. Synapses are present on the body of the neuron, its dendrites, and to a lesser extent on the axon. Of greatest importance for the activity of nerve cells are contacts with their soma, the bases of the dendrites, as well as the points of the first branching of the dendrites. The presynaptic function is most often performed by the terminal ramifications of axons (presynantic buds) or varicose extensions along the axon. Less often, thin dendritic branches can act as non-resynaptic structures.

As we have already noted, postsynaptic potentials in chemical synapses can be either depolarizing and excitatory (VISI) or hyperpolarizing and inhibitory (TPSP).

Introduction
Synapse classifications
The porocytosis hypothesis
Conclusion
Bibliography

Introduction

To date, a number of technologies for the implantation of various artificial organs have been created, which for a long time are not rejected by the body. One of the problems that hinders the development of this industry is the integration of the nervous system and cybernetic device. Simply put, in creating a connection between the nerve and the processor of the prosthesis.

The way out of this problem - graceful, and not requiring a rough introduction of electrodes into the nervous tissue - is to create a synaptic connection. Synapse - a product of nature itself - is an ideal form of integration of the work of both various nerve endings and effector organs (muscles, secretory tissue).

In order to do this, it is necessary to study the structure and physiology of various synapses.

synapse nerve impulse physiology

General provisions and history of discovery

A synapse is a point of contact between two neurons or between a neuron and a receiving effector cell. It serves to transmit a nerve impulse between two cells, and during synaptic transmission, the amplitude and frequency of the signal can be regulated. The transmission of impulses is carried out chemically with the help of mediators or electrically through the passage of ions from one cell to another. As a rule, a synapse is understood as a chemical synapse in which signals are transmitted using neurotransmitters. Typical synapses are formations formed by the axon terminals of one neuron and the dendrites of another (axo-dendritic synapses). But there are other types: axosomatic, axo-axonal and dendro-dendritic. The synapse between a motor neuron axon and a skeletal muscle fiber is called a motor end plate, or neuromuscular junction. There are two types of synapses in the nervous system: excitatory and inhibitory synapses. In excitatory synapses, one cell causes the activation of another. In this case, the excitatory mediator causes depolarization - the flow of Na + ions rushes into the cell. In inhibitory synapses, one cell inhibits the activation of another. This is due to the fact that the inhibitory mediator causes a flow of negatively charged ions into the cells, so depolarization does not occur.

The nerve impulse enters the synapse through the presynaptic ending, which is limited by the presynaptic membrane (presynaptic part) and is perceived by the postsynaptic membrane (postsynaptic part). The synaptic cleft is located between the membranes. The presynaptic ending contains many mitochondria and presynaptic vesicles containing the neurotransmitter. The nerve impulse entering the presynaptic ending causes the mediator to be released into the synaptic cleft. Molecules of mediators react with specific receptor proteins of the cell membrane, changing its permeability for certain - ions, which leads to the emergence of an action potential. Along with chemical synapses, there are electrotonic synapses, in which the transmission of impulses occurs directly in a bioelectrical way, between contacting cells.

Depending on the nature of the signals passing through synapses, synapses are divided into electrical synapses and chemical synapses. Chemical synapses are synapses in which transmission is carried out with the help of biologically active substances, and the substances that carry out the transmission are neurotransmitters.

· In 1897, Sherrington formulated the concept of synapses.

· For studies of the nervous system, including synaptic transmission, in 1906 the Nobel Prize was awarded to Golgi and Ramon y Cajal.

· In 1921, the Austrian scientist O. Loewi (O. Loewi) established the chemical nature of the transmission of excitation through synapses and the role of acetylcholine in it. Received the Nobel Prize in 1936 together with G. Dale (N. Dale).

· In 1933, the Soviet scientist A.V. Kibyakov established the role of adrenaline in synaptic transmission.

· 1970 - B. Katz (V. Katz, UK), U. von Euler (U. v. Euler, Sweden) and J. Axelrod (J. Axelrod, USA) received the Nobel Prize for discovering the role of norepinephrine in synaptic transmission.

Synapse classifications

According to the mechanism of transmission of a nerve impulse:

chemical - this is a place of close contact between two nerve cells, for the transmission of a nerve impulse through which the source cell releases a special substance, a neurotransmitter, into the intercellular space, the presence of which in the synaptic cleft excites or inhibits the receiver cell.

electrical (ephaps) - a place of closer fit of a pair of cells, where their membranes are connected using special protein formations - connexons (each connexon consists of six protein subunits). The distance between cell membranes in an electrical synapse is 3.5 nm (usual intercellular is 20 nm). Since the resistance of the extracellular fluid is small (in this case), impulses pass through the synapse without delay. Electrical synapses are usually excitatory.

mixed synapses - the presynaptic action potential creates a current that depolarizes the postsynaptic membrane of a typical chemical synapse, where the pre- and postsynaptic membranes do not fit snugly together. Thus, in these synapses, chemical transmission serves as a necessary reinforcing mechanism.

The most common chemical synapses. For the nervous system of mammals, electrical synapses are less characteristic than chemical ones.

By location and accessories structures :

peripheral

neuromuscular

neurosecretory (axo-vasal)

receptor-neuronal

central

axo-dendritic - with dendrites, including

axo-spiky - with dendritic spines, outgrowths on dendrites;

axo-somatic - with the bodies of neurons;

axo-axonal - between axons;

dendro-dendritic - between dendrites;

By neurotransmitter :

· aminergic, containing biogenic amines (for example, serotonin, dopamine);

Including adrenergic, containing adrenaline or norepinephrine;

cholinergic, containing acetylcholine;

Purinergic, containing purines;

peptidergic containing peptides.

At the same time, only one mediator is not always produced in the synapse. Usually the main mediator is ejected along with another, which plays the role of a modulator.

According to the sign of action

Exciting

brake.

If the former contribute to the emergence of excitation in the postsynaptic cell (as a result of the receipt of an impulse, the membrane depolarizes in them, which can cause an action potential under certain conditions.), Then the latter, on the contrary, stop or prevent its occurrence, prevent further propagation of the impulse. Usually inhibitory are glycinergic (mediator - glycine) and GABAergic synapses (mediator - gamma-aminobutyric acid).

There are two types of inhibitory synapses:

1) a synapse, in the presynaptic endings of which a mediator is released, hyperpolarizing the postsynaptic membrane and causing the appearance of an inhibitory postsynaptic potential;

2) axo-axonal synapse, providing presynaptic inhibition. Cholinergic synapse (s. cholinergica) - a synapse in which acetylcholine is a mediator.

In some synapses, postsynaptic compaction is present - an electron-dense zone consisting of proteins. According to its presence or absence, asymmetric and symmetrical synapses are distinguished. It is known that all glutamatergic synapses are asymmetric, while GABAergic synapses are symmetrical.

In cases where several synaptic extensions come into contact with the postsynaptic membrane, multiple synapses are formed.

Special forms of synapses include spiny apparatuses, in which short single or multiple protrusions of the postsynaptic membrane of the dendrite are in contact with the synaptic extension. Spiny apparatus significantly increase the number of synaptic contacts on the neuron and, consequently, the amount of information processed. "Non-spine" synapses are called "sessile". For example, all GABAergic synapses are sessile.

Structure of a chemical synapse

The vast majority of synapses in the nervous system of the animal kingdom are chemical synapses. They are characterized by the presence of several common features, although, nevertheless, the size and shape of the pre- and postsynaptic components vary very widely. Synapses in the mammalian cerebral cortex have preterminal axons about 100 nanometers thick and presynaptic buds with an average diameter of about 1 micrometer.

The chemical synapse consists of two parts: presynaptic, formed by a club-shaped extension of the end of the axon of the transmitting cell, and postsynaptic, represented by the contact area of the plasma membrane of the receiving cell. Between both parts there is a synaptic gap - a gap 10-50 nm wide between the postsynaptic and presynaptic membranes, the edges of which are reinforced with intercellular contacts.

The part of the axolemma of the club-shaped extension adjacent to the synaptic cleft is called the presynaptic membrane. The section of the cytolemma of the perceiving cell, which limits the synaptic cleft on the opposite side, is called the postsynaptic membrane; in chemical synapses it is relief and contains numerous receptors.

In the synaptic expansion, there are small vesicles, the so-called presynaptic or synaptic vesicles, containing either a mediator (a mediator in the transmission of excitation) or an enzyme that destroys this mediator. On the postsynaptic, and often on the presynaptic membranes, there are receptors for one or another mediator.

The same size of presynaptic vesicles in all synapses studied (40-50 nanometers) was first considered evidence that each vesicle is the minimum cluster whose release is required to produce a synaptic signal. Vesicles are located opposite the presynaptic membrane, which is due to their functional purpose for the release of the mediator into the synaptic cleft. Also near the presynaptic vesicle there are a large number of mitochondria (producing adenosine triphosphate) and ordered structures of protein fibers.

The synaptic cleft is a 20 to 30 nanometer wide space between the presynaptic vesicle and the postsynaptic membrane, which contains pre- and postsynapse binding structures built from proteoglycan. The width of the synaptic cleft in each individual case is due to the fact that the mediator extracted from the presynapse must pass to the postsynapse in a time that is significantly less than the frequency of nerve signals characteristic of neurons forming a synapse (the time it takes for the mediator to pass from the pre-to the postsynaptic membrane is of the order of several microseconds) .

The postsynaptic membrane belongs to the cell that receives nerve impulses. The mechanism of translation of the chemical signal of the mediator into an electrical action potential on this cell is receptors - protein macromolecules embedded in the postsynaptic membrane. With the help of special ultramicroscopic techniques, a fairly large amount of information on the detailed structure of synapses has been obtained in recent years.

Thus, an ordered structure of crater-like depressions 10 nanometers in diameter, pressed inwards, was discovered on the presynaptic membrane. At first they were called synaptopores, but now these structures are called vesicle attachment sites (VSPs). The receptacles are arranged in ordered groups of six separate recesses around the so-called compacted protrusions. Thus, densified protrusions form regular triangular structures on the inside of the presynaptic membrane, while SSV are hexagonal, and are the sites where vesicles open and eject the neurotransmitter into the synaptic cleft.

The structure of the electrical synapse

Unlike a chemical synapse, the synaptic cleft in an electrical synapse is extremely narrow (about 3.5 nanometers). Through the synaptic cleft of this type of synapses, spatially ordered protein channels with a hydrophilic pore, each about 5 nanometers in diameter, pass through, which perforate the pre- and postsynaptic membrane and are called connexons. In protostomes (nematodes, mollusks, arthropods), connexons are formed by proteins pannexins or innexins); in deuterostomes (ascidians, vertebrates), connexons are built from proteins of a different type - connexins, which are encoded by a different group of genes. Neither pannexins nor connexins have yet been found in echinoderms; they may have another family of proteins that form gap junctions and electrical synapses.

Vertebrates have both pannexins and connexins. But so far, not a single electrical synapse has been identified in vertebrates, where intercellular channels would be formed by pannexins.

Ions and small molecules, including fluorescent dyes artificially introduced into the cell, pass through connexins (or pannexins) that connect pre- and postsynaptic neurons. The passage of these dyes through the electrical synapse can be recorded even with a light microscope.

Electrical synapses allow for electrical conduction in both directions (as opposed to chemical ones); however, rectifying electrical synapses, that is, those that allow the passage of a nerve signal in only one direction, have recently been discovered in some crustaceans.

Mechanism of nerve impulse transmission

The arrival of an electrical impulse to the presynaptic membrane triggers the process of synaptic transmission, the first stage of which is the entry of Ca 2+ ions into the presynapse through the membrane through specialized calcium channels located near the synaptic cleft. The Ca 2+ ions, by a completely unknown mechanism, activate the vesicles crowded at their sites of attachment, and they release the neurotransmitter into the synaptic cleft. The Ca 2+ ions that entered the neuron, after activating the vesicles with the mediator, are deactivated in a time of the order of several microseconds due to deposition in mitochondria and presynapse vesicles.

The mediator molecules released from the presynapse bind to receptors on the postsynaptic membrane, as a result of which ion channels open in the receptor macromolecules (in the case of channel receptors, which is the most common type; when other types of receptors work, the signal transmission mechanism is different). Ions that begin to enter the postsynaptic cell through open channels change the charge of its membrane, which is a partial polarization (in the case of an inhibitory synapse) or depolarization (in the case of an excitatory synapse) of this membrane and, as a result, leads to inhibition or provocation of generation by the postsynaptic cell action potential.

Quantum-vesicular hypothesis

Widespread until recently as an explanation for the mechanism of neurotransmitter release from the presynapse, the hypothesis of quantum-vesicular exocytosis (QVE) implies that the “package”, or quantum, of the mediator is contained in one vesicle and is released during exocytosis (in this case, the membrane of the vesicle fuses with the cellular presynaptic membrane ). This theory has been the prevailing hypothesis for a long time - despite the fact that there is no correlation between the level of neurotransmitter release (or postsynaptic potentials) and the number of vesicles in the presynapse. In addition, the CBE hypothesis has other significant shortcomings.

The physiological basis of precisely the quantized release of the mediator should be the same amount of this mediator in each vesicle. The TBE hypothesis in its classical form is not suitable for describing the effects of quanta of different sizes (or different amounts of a mediator) that can be released during a single act of exocytosis. In this case, one must take into account that vesicles of different sizes can be observed in the same presynaptic bud; in addition, no correlation was found between the size of the vesicle and the amount of the mediator in it (that is, its concentration in the vesicles can also be different). Moreover, in the denervated neuromuscular synapse, Schwann cells generate a greater number of miniature postsynaptic potentials than is observed in the synapse before denervation, despite the complete absence of presynaptic vesicles localized in the region of the presynaptic button in these cells.

The porocytosis hypothesis

There is significant experimental evidence that the neurotransmitter is secreted into the synaptic cleft due to the synchronous activation of the hexagonal groups of the MPV (see above) and the vesicles attached to them, which became the basis for formulating the porocytosis hypothesis. This hypothesis is based on the observation that the vesicles attached to the MPV, upon receiving an action potential, synchronously contract and secrete the same amount of the mediator into the synaptic cleft each time, releasing only a part of the contents of each of the six vesicles. The term "porocytosis" itself comes from the Greek words poro (meaning pores) and cytosis (describing the transport of chemical substances across the plasma membrane of a cell).

Most of the experimental data on the functioning of monosynaptic intercellular junctions have been obtained from studies of isolated neuromuscular junctions. As in interneuronal synapses, in the neuromuscular synapses of the SSV, ordered hexagonal structures are formed. Each of these hexagonal structures can be defined as a "synaptomer" - that is, a structure that is the basic unit in the process of mediator secretion. The synaptomer contains, in addition to the actual pore recesses, protein filamentous structures containing linearly ordered vesicles; the existence of similar structures has also been proven for synapses in the central nervous system (CNS).

As mentioned above, the porocytic mechanism generates a neurotransmitter quantum, but without the membrane of an individual vesicle completely merging with the presynaptic membrane. A small coefficient of variation (less than 3%) for the values of postsynaptic potentials is an indicator that in a single synapse there are no more than 200 synaptomers, each of which secretes one transmitter quantum in response to one action potential. The 200 release sites (i.e., synaptomers that release the neurotransmitter) found on a small muscle fiber allow the calculation of a maximum quantum limit of one release site per micrometer of synaptic junction length, this observation rules out the possibility of neurotransmitter quanta occurring in the volume one vesicle.

Comparison of the porocytosis and quantum-vesicular hypotheses

Comparison of the recently accepted TBE hypothesis with the hypothesis of porocytosis can be carried out by comparing the theoretical coefficient of variation with the experimental one calculated for the amplitudes of postsynaptic electrical potentials generated in response to each individual neurotransmitter release from the presynapse. Assuming that the process of exocytosis takes place in a small synapse containing about 5,000 vesicles (50 for each micron of synapse length), postsynaptic potentials should be generated by 50 randomly selected vesicles, which gives a theoretical coefficient of variation of 14%. This value is approximately 5 times greater than the coefficient of variation of postsynaptic potentials obtained in experiments, thus, it can be argued that the process of exocytosis in the synapse is not random (does not coincide with the Poisson distribution) - which is impossible if explained in terms of the TBE hypothesis , but is consistent with the porocytosis hypothesis. The fact is that the porocytosis hypothesis assumes that all vesicles associated with the presynaptic membrane eject the mediator at the same time; at the same time, the constant amount of mediator ejected into the synaptic cleft in response to each action potential (the stability is evidenced by the low coefficient of variation of postsynaptic responses) can be quite explained by the release of a small volume of the mediator by a large number of vesicles - moreover, the more vesicles involved in the process, the the correlation coefficient becomes smaller, although this looks somewhat paradoxical from the point of view of mathematical statistics.

The so-called "Dale principle" (one neuron - one mediator) is recognized as erroneous. Or, as it is sometimes believed, it is refined: not one, but several mediators can be released from one end of a cell, and their set is constant for a given cell.

Conclusion

Thus, the question of the structure and principle of operation of the chemical synapse was considered. And although there are still questions that require clarification, nevertheless, the knowledge of synaptic connections between nervous tissue is a huge step in the field of neuroscience. It is he who allows the almost impossible - operations to restore nervous activity, the finest integration of a machine and living tissue, and in the future - a true symbiosis of living and artificial nature created by man.

Bibliography

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2. Saveliev BUT.AT. Methodology of synaptic self-organization and the problem of distal synapses of neurons // Magazine problems evolution open systems. - Kazakhstan, Almaty, 2006. - V.8. - No. 2. - S.96-104.

3. Eccles D.TO. Physiology of synapses. - M.: Mir, 1966. - 397 p.