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 nervous system- 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 clavate 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 various 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, before 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 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.
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The connection between two adjacent neurons (nerve cells) is called a synapse. Synapses are connections that connect one neuron (presynaptic) to another (postsynaptic). Essentially, synapses are small constrictions. There is no physical connection between cells. Small densities, called synaptic knobs, at the end of each presynaptic axon approach the dendrites, axons, or postsynaptic cell bodies. It is through synaptic cones that neurotransmitters come out.
Neurotransmitters
Neurotransmitters are molecules that perform the role chemical signals, transmitting an electrical impulse from one cell to another. They are located at the synapses between the synaptic pathways of one neuron and the dendrites of another. Chemicals, which allow the smooth transmission of impulses through neurons, are called excitatory neurotransmitters. Inhibitory neurotransmitters block electrical impulses.Connection between two neurons
Anatomy of a synapse
At the end of the axon there is a synaptic cone. It does not touch the neighboring neuron, but leaves a small gap, or synapse, between the pre- and postsynaptic membranes. Mitochondria in the axon produce the energy needed to release neurotransmitters. They reside in small vesicles (cavities) before exiting through the presynaptic lattice, crossing the cleft, and moving to the postsynaptic membrane.
How do synapses work?
1 The nerve impulse enters the synaptic cone of the neuron.2 Neurotransmitters are released at the synapse.
3
Neurotransmitters quickly pass through the gap, and the molecules land on receptors on the membrane of the postsynaptic neuron.
4
This causes changes in the permeability of the postsynaptic membrane to sodium ions, and its positive ions pass into the postsynaptic neuron, causing depolarization. As a result, the nerve impulse is transmitted to the next neuron.
I.A. Borisova
Synapse(Greek σύναψις, from συνάπτειν - hug, clasp, shake hands) - the place of contact between two neurons or between and the effector cell receiving the signal. Serves for transmission between two cells, and during synaptic transmission the amplitude and frequency of the signal can be adjusted.
The term was introduced in 1897 by the English physiologist Charles Sherrington.
Synapse structure
A typical synapse is axo-dendritic chemical. Such a synapse consists of two parts: presynaptic, formed by a club-shaped extension of the ending of the axon of the transmitting cell and postsynaptic, represented by the contacting area of the cytolemma of the receiving cell (in this case, the area of the dendrite). A synapse is a space separating the membranes of contacting cells to which nerve endings approach. 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.
Between both parts there is a synaptic cleft - a gap 10-50 nm wide between the postsynaptic and presynaptic membranes, the edges of which are strengthened by intercellular contacts.
The part of the axolemma of the clavate extension adjacent to the synaptic cleft is called presynaptic membrane. A section of the cytolemma of the receptive cell, limiting the synaptic cleft with opposite side, called postsynaptic membrane, in chemical synapses it is prominent and contains numerous.
In the synaptic extension there are small vesicles, the so-called synaptic vesicles, containing either a mediator (a substance that mediates transmission) or an enzyme that destroys this mediator. On the postsynaptic, and often on the presynaptic membranes, there are receptors for one or another mediator.
Classification of synapses
Depending on the mechanism of nerve impulse transmission, there are
- chemical;
- electrical - cells are connected by highly permeable contacts using special connexons (each connexon consists of six protein subunits). The distance between cell membranes in the electrical synapse is 3.5 nm (usual intercellular distance is 20 nm)
Since the resistance of the extracellular fluid is low (in this case), impulses pass through the synapse without delay. Electrical synapses are usually excitatory.
Two release mechanisms have been discovered: with complete fusion of the vesicle with the plasmalemma and the so-called “kissed and ran away” (eng. kiss-and-run), when the vesicle connects to the membrane, and small molecules exit it into the synaptic cleft, while large molecules remain in the vesicle. The second mechanism is presumably faster than the first, with the help of it synaptic transmission occurs when the content of calcium ions in the synaptic plaque is high.
The consequence of this structure of the synapse is the unilateral conduction of the nerve impulse. There is a so-called synaptic delay- the time required for the transmission of a nerve impulse. Its duration is about - 0.5 ms.
The so-called “Dale principle” (one - one mediator) has been recognized as erroneous. Or, as is sometimes believed, it is more precise: not one, but several mediators can be released from one end of a cell, and their set is constant for a given cell.
History of discovery
- In 1897, Sherrington formulated the idea of synapses.
- For his studies of the nervous system, including synaptic transmission, in 1906 Nobel Prize received Golgi and Ramon y Cajal.
- In 1921, the Austrian scientist O. Loewi established chemical nature transmission of excitation through synapses and the role of acetylcholine in it. Received the Nobel Prize in 1936 together with H. Dale.
- In 1933, the Soviet scientist A.V. Kibyakov established the role of adrenaline in synaptic transmission.
- 1970 - B. Katz (Great Britain), U. v. Euler (Sweden) and J. Axelrod (USA) received the Nobel Prize for the discovery of rolinorepinephrine in synaptic transmission.
A synapse is a structural and functional formation that ensures transmission
I sense excitations from a neuron to the cell it innervates (nervous, glandular, muscle)
noyu). Synapses can be divided into the following types:
1) according to the method of excitation transmission – electrical, chemical;
2) by localization – central, peripheral;
3) according to functional characteristics – excitatory, inhibitory;
4) according to the structural and functional characteristics of the postsynaptic receptors
membranes – cholinergic, adrenergic, serotonergic, etc..
2. Structure of the myoneural synapse
The myoneural synapse consists of:
a) presynaptic membrane;
b) postsynaptic membrane;
c) synaptic cleft.
The presynaptic membrane is the electrogenic membrane of the presynaptic
ski terminals (nerve fiber endings). In presynaptic terminals
mediators (transmitters) are formed and accumulate in vesicles (vesicles)
acetylcholine, norepinephrine, histamine, serotonin, gamma-aminobutyric acid
and others.
The postsynaptic membrane is part of the membrane of the innervated cell
ki, in which chemosensitive ion channels are located. In addition, on
the postsynaptic membrane contains receptors for one or another mediator
ru and enzymes that destroy them, for example, cholinergic receptors and cholinesterase.
Synaptic cleft - filled with intercellular fluid, located
located between the pre- and postsynaptic membranes.
3. The mechanism of excitation through the myoneural synapse
The myoneural synapse is formed by the axon of the motor neuron on the striated
muscle fiber. Excitation through the myoneural synapse is transmitted using
acetylcholine. Under the influence of nerve impulses, the presynaptic membrane depolarizes
zuzyatsya. Acetylcholine is released from the vesicles and enters the synaptic cleft.
The release of the mediator occurs in portions - quanta. Acetylcholine diffuses
through the synaptic cleft to the postsynaptic membrane. On the postsynaptic mem-
brane mediator interacts with the cholinergic receptor. As a result, its
permeability to sodium and potassium ions and end plate potential occurs
(EPSP) or excitatory postsynaptic potential (EPSP). According to the mechanism of circular
currents under its influence, an action potential arises in areas of the muscle membrane
of the fiber adjacent to the postsynaptic membrane.
The connection between acetylcholine and the cholinergic receptor is fragile. The mediator is destroyed by holy
Nesterase. The electrical state of the postsynaptic membrane is restored
pours.
4. Physiological properties of synapses
Synapses have the following physiological properties:
a) unilateral conduction of excitation (valve property) – due to
structural features of the synapse;
b) synaptic delay - due to the fact that it takes a certain time to
conduction of excitation through the synapse;
c) potentiation (facilitation) of subsequent nerve impulses –
occurs because for each subsequent impulse more energy is allocated
d) low lability – due to the peculiarities of metabolic and physical
e) relatively easy occurrence of inhibition and rapid development tired
niya - due to low lability.
f) desensitization – decreased sensitivity of the cholinergic receptor to acetylcholine
Spinal cord, features of its structure. Types of neurons. Functional differences between the anterior and posterior roots of the spinal cord. Bell-Magendie law. Physiological significance of the spinal cord. “Laws” of reflex activity of the spinal cord.
The spinal cord contains: 1. motor neurons(effector, motor nerve
cells, from 3%), 2. interneurons(interneurons, intermediate, 97% of them).
Motor neurons are divided into three types:
1) α – motor neurons, innervate skeletal muscles;
2) γ – motor neurons, innervate muscle proprioceptors;
3) neurons of the autonomic nervous system, the axons of which innervate the nerve
ny cells located in the autonomic ganglia, and through them internal
organs, vessels and glands.
2. Functional significance of the anterior and posterior roots of the spinal cord
(Bell-Magendie law)
Bell-Magendie's Law: “All afferent nerve impulses enter the spinal
the brain through the dorsal roots (sensitive), and all efferent nerve impulses
leave (exit) the spinal cord through the anterior (motor) roots.”
3. Functions of the spinal cord
The spinal cord performs two functions: 1) reflex, 2) conductor.
Due to the reflex activity of the spinal cord, a number of simple and
complex unconditioned reflexes. Simple reflexes have two-neuron reflexes -
nal arcs, complex - three or more neural reflex arcs.
The reflex activity of the spinal cord can be studied on “spinal abdomen”
nykh" - animals in which the brain is removed and the spinal cord is preserved.
4. Nerve centers of the spinal cord.
In the lumbosacral region of the spinal cord there are: 1. urinary center
nia, 2. defecation center, 3. reflex centers of sexual activity.
In the lateral horns of the thoracic and lumbar spinal cord are located:
1) spinal vasomotor centers, 2) spinal sweat centers.
In the anterior horns of the spinal cord they are located at different levels centers of motion
gating reflexes(centers of extero- and proprioceptive reflexes).
5. Spinal cord pathways
The following pathways of the spinal cord are distinguished: 1) ascending(affe-
rental) and 2) descending(efferent).
Ascending pathways connect the body’s receptors (proprio-, tactile, pain-
higher) with different parts of the brain.
Descending tracts of the spinal cord: 1) pyramidal, 2) extrapyramidal. Pira-
midpath - from neurons of the anterior central gyrus of the cerebral cortex to
spinal cord is not interrupted. Extrapyramidal pathway - also starts from the neuro-
new to the anterior central gyrus and ends in the spinal cord. This path is a lot
neural, it is interrupted in: 1) subcortical nuclei; 2) diencephalon;
3) midbrain; 4) medulla oblongata.
Regulation of vascular tone. Local regulation (autoregulation). Nervous regulation of vascular tone (vasoconstrictor and vasodilator nerves). Humoral regulation of vascular tone. Blood pressure indicators in children.
There are two types of vascular tone:
Basal (myogenic);
Neurogenic.
Basal tone.
If the vessel is denervated and the sources of humoral influences are eliminated, the basal vascular tone can be revealed.
There are:
A) electrogenic component- caused by spontaneous electrical activity of myocytes of the vascular wall. The greatest automaticity is in the precapillary sphincters and arterioles;
b) non-electrogenic component (plastic)- caused by stretching of the muscle wall due to blood pressure on it.
It is shown that the automaticity of smooth muscle cells increases under the influence of their stretching. Their mechanical (contractile) activity also increases (i.e., a positive feedback is observed: between the value of blood pressure and vascular tone).
Local humoral regulation.
1. Vasodilators:
A) nonspecific metabolites - are continuously formed in tissues, and at the site of formation they always prevent the narrowing of blood vessels, and also cause their dilation (metabolic regulation).
These include - CO2, carbonic acid, H+, lactic acid, acidification (accumulation of acidic products), decreased O2 tension, increased osmotic pressure due to the accumulation of low molecular weight products, nitric oxide (N0) (a product of vascular endothelial incretion).
b) BAS (when acting at the site of release) - are formed by specialized cells that are part of the vascular environment.
1. Vasodilating biologically active substances (at the site of release) -
acetylcholine, histamine, bradykinin, some prostaglandins, prostacyclin, secreted by the endothelium, can mediate its effect through nitric oxide.
2. Vasoconstrictor biologically active substances (when acting at the site of release) - are formed by specialized cells that are part of the vascular environment - catecholamines, serotonin, some prostaglandins, endothelial 1-peptide, 21-amino acid, vascular endothelial incretion product, as well as thromboxane A2, released by platelets during aggregation.
The role of biologically active substances in the distant regulation of vascular tone.
Along with nervous influences, various biologically active substances that have a distant, vasomotor effect play an important role in the regulation of vascular tone:
Hormones (vasopressin, adrenaline); parahormones (serotonin, bradykinin, angiotensin, histamine, opiate peptides), endorphins and enkephalins.
Basically, these biologically active substances have a direct effect, since most smooth muscle vessels have specific receptors for these biologically active substances.
Some biologically active substances cause an increase in vascular tone, while others reduce it.
Functions of the endothelium of small blood vessels and their role in the regulation of hemodynamic processes, hemostasis, immunity:
1. Self-sufficiency of the structure (self-regulation of cell growth and restoration).
2. Formation of vasoactive substances, as well as activation and inactivation of biologically active substances circulating in the blood.
3. Local regulation of smooth muscle tone: synthesis and secretion of prostaglandins, prostacyclin, endothelins and NO.
4. Transmission of vasomotor signals from capillaries and arterioles to larger vessels (creator connections).
5. Maintaining anticoagulant properties of the surface (release of substances that prevent various types hemostasis, ensuring the mirror surface, its non-wetting).
6. Implementation of protective (phagocytosis) and immune (binding of immune complexes) reactions.
7. Formation of vasoactive substances, as well as activation and inactivation of biologically active substances circulating in the blood.
8. Local regulation of smooth muscle tone: synthesis and secretion of prostaglandins, prostacyclin, endothelins and NO.
9. Transmission of vasomotor signals from capillaries and arterioles to larger vessels (creator connections).
10. Maintaining the anticoagulant properties of the surface (releasing substances that prevent various types of hemostasis, ensuring the surface is mirror-like and non-wettable).
11. Implementation of protective (phagocytosis) and immune (binding of immune complexes) reactions.
Neurogenic tone is caused by activity vasomotor center(SDC) in the medulla oblongata, at the bottom of the IV ventricle (V.F. Ovsyannikov, 1871, discovered by cutting the brain stem at various levels), represented by two departments(pressor and depressor).
