The autonomic nervous system (ANS) mainly provides innervation to internal organs.

Divided by:

Sympathetic department
Parasympathetic department
Metasympathetic (Enteral)

Differences between the autonomic nervous system and the somatic NS:

Not under mind control
The possibility of autonomous functioning (even with a complete breakdown of communication with the central nervous system)
The generalized nature of the spread of excitation in the peripheral part of the ANS (especially in the sympathetic part).
The presence of a vegetative ganglion in the efferent section of the reflex arc. Thus, the efferent part of the ANS is represented by two neurons: a preganglionic neuron within the CNS (brain stem, spinal cord), and a postganglionic neuron in the autonomic ganglion. Those. the bodies of the last neurons of the vegetative arches are taken out of the CNS.
Low conduction velocity (type B preganglionic fibers, type C postganglionic fibers)
Target tissues for ANS: smooth muscle cells, striated cardiac muscle, glandular tissue (for somatic - striated skeletal MT). Sympathetic fibers are able to influence glycogenolysis in the liver and lipolysis in fat cells (metabolic effect)

Usually, the internal organs have a double innervation: sympathetic and parasympathetic, however, the bladder and ciliary muscle receive mainly parasympathetic, vessels, sweat glands, filamentous muscles of the skin, spleen, uterus, brain, sensory organs, adrenal glands - only sympathetic.

Higher vegetative centers

structures of the limbic system, basal ganglia, CGM, hypothalamus (anterior nuclei - the zone of parasympathetic nuclei, posterior nuclei - the zone of sympathetic nuclei), the central gray matter of the midbrain, the reticular formation (its neurons form the vital centers of the medulla oblongata SSC, DC).

Nerve centers (central section) of the sympathetic nervous system- intermediate-lateral nuclei of the lateral horns of the spinal cord C VIII— LII — III

Nerve centers (central section) of the parasympathetic nervous system- vegetative nuclei of the III pair (oculomotor nerve - Yakubovich's nucleus), VII (facial nerve - superior salivary), IX (glossopharyngeal nerve - inferior salivary), X (vagus nerve - posterior nucleus), intermediate-lateral nuclei of the spinal cord S II -S IV

At the level of the working sections, efferent cells are laid, the axons of which do not go immediately to the working organ, unlike the somatic ones, but are interrupted in the peripheral autonomic ganglion. Here they switch to the last neurons. The fibers of the neurons of the spinal cord are called preganglionic. Preganglionic fibers switch in the autonomic ganglion to the next neuron, the axon of which is called postganglionic.

Sympathetic autonomic ganglion

The ganglion is covered with a capsule on top. Here are the following cells:

Sensory neurons
Efferent neurons
Chromaffin cells that secrete catecholamines (regulate the level of excitability of node cells.

Functions of the ganglion: conductor, circuit and receptor.

The neurons of the autonomic ganglion have the same properties as the neurons of the central nervous system.

Parasympathetic autonomic ganglion

The ganglion is covered with a capsule on top. It contains the following cells:

Sensitive - Type 2 Dogel cells, their receptors can be mechano-, thermo-, chemosensitive.
The effector neurons are Type 1 Dogel cells with many short dendrites and one axon extending beyond the ganglion.
Intercalated - Dogel cells of the 3rd type.
The ganglion also contains chromaffin cells that secrete catecholamines, possibly serotonin, ATP, neuropeptides (regulatory function).

Physiology of the autonomic ganglion

(switching from preganglionic to postganglionic fibers)

Low lability of autonomic ganglia neurons (10-15 pulses per second), in somatic ganglia 200 pulses/sec.
Long synaptic delay, more than 5 times.
The long duration of the EPSP (20-50 ms), the duration of the action potential is 1.5-3 ms due to the prolonged trace hyperpolarization of ganglion neurons.
Spatial and sequential summation plays an important role.

Mediator: in the autonomic ganglia - preganglionic neurons secrete ACh.

At the level of the ganglion, convergence and divergence (multiplication) are well developed.

Sympathetic division of the autonomic nervous system

Sympathetic autonomic ganglia are located in the sympathetic trunk, prevertebral nodes, plexus nodes (abdominal aortic, superior and inferior hypogastric).

The preganglionic fibers are short and highly branched. Postganglionic fibers are long, thin, branching many times, forming plexuses. Well developed animation.

The mediator of postganglionic adrenergic sympathetic fibers is HA (90%), adrenaline (7%), dopamine (3%). The mediator is stable and shows its activity for a long time. NA binds to α and β-adrenergic receptors of effector organs. The classification is based on their sensitivity to pharmaceutical preparations: α-adrenergic receptors are blocked by phentolamine, β - by propranolol. Adrenoreceptors are present not only on organs innervated by sympathetic fibers (heart, adipose tissue, blood vessels, pupil dilator muscle, uterus, vas deferens, intestines) (α 1 and β 1), but also outside synapses (on platelets, skeletal muscles, endocrine and exocrine glands) (α 2 and β 2), as well as on the presynaptic membrane.

The transfer of excitation is faster than through the sympathetic department. The effects are short term.

Influences:

Permanent (tonic)
Phase (starting) - a sharp change in function (pupillary reflex)
Adaptive-trophic

Adaptive-trophic influence of the sympathetic nervous system of Orbeli-Ginetsinsky

This is an adaptation of metabolic processes to the level of functional activity. The idea of trophic influence was formulated by I.P. Pavlov. In an experiment on a dog, he discovered a sympathetic branch going to the heart, the irritation of which caused an increase in heart contractions, without changing the frequency. Strengthening of contractions of a tired muscle is associated with the activation of metabolic (trophic) processes under the influence of NA. It activates specific receptors in the membrane of muscle fibers, triggers a cascade of chemical reactions in the cytoplasm that accelerate the synthesis of macroergs, and increases the excitability of peripheral receptors. The presence of trophogens in the nerve endings is assumed. Trophogens include nucleotides, some amino acids, prostaglandins, catecholamines, serotonin, ACh, complex lipids, gangliosides.

Parasympathetic division of the autonomic nervous system

Parasympathetic autonomic ganglia (far from the central nervous system) are located inside the organs (intramurally) or near the organs (ciliary, pterygopalatine, ear, sublingual, submandibular nodes), in the nodes of the plexuses.

The preganglionic fibers are long and weakly branched. Postganglionic fibers are short, branching little. Animation is underdeveloped.

Mediator of postganglionic parasympathetic fibers ACh.

Acetylcholine on effector cells is bound by M-cholinergic receptors. M-cholinergic receptors are excited by muscarine, blocked by curare poison.

Acetylcholine is an unstable neurotransmitter the main part is destroyed by acetylcholinesterase to choline and acetate, which are then captured by the presynaptic membrane and used for synthesis. A smaller part diffuses into the interstitium and blood.

Influences:

Permanent (tonic)
Phase (starting) - a sharp change in function (inhibition of the heart, activation of peristalsis, pupil constriction)

The tone of the vegetative centers

Many preganglionic and ganglionic neurons have a constant activity called tone. At rest, the frequency of electrical impulses in autonomic fibers is 0.1-5 imp/s. The tone of autonomic neurons is subject to diurnal fluctuations: sympathotonus is higher during the day, lower at night, during sleep the tone of parasympathetic fibers increases. Sympathotonus provides a constant vascular tone. The tonic influence of the vagus nerve (vagotonus) on the heart constantly restrains the heart rate. The higher the motor activity in a person, the more pronounced the parasympathetic tone (decrease in heart rate in athletes). Causes of vegetative tone:

spontaneous activity. A high level of spontaneous activity is characteristic of RF neurons.
The flow of afferent impulses from various reflexogenic zones.
The action of biologically active substances and metabolites

Vegetative reflexes. Classification:

Closing level:

central (somatovegetative reflex - has a common afferent part with a somatic reflex)
peripheral, autonomous (the arc of the reflex can be closed outside the central nervous system in the autonomic ganglion intraorganically or extraorganically, the existence of an axon reflex is possible)

According to the location of the receptors:

Interoceptive (mechano-, chemo-, thermo-, noce-, polymodal receptors)

a) Viscero-visceral (carotid sinus, solar plexus, peristalsis)

b) Viscero-cutaneous (corresponding to the Zakharyin-Ged zones)

c) Viscero-motor (stimulation of interoreceptors can cause motor reactions).

Autonomic ganglia can be divided, depending on their location, into three groups:
- vertebrates (vertebral),
- prevertebral (prevertebral),
- intra-organ.
Vertebral ganglia belong to the sympathetic nervous system. They are located on both sides of the spine, forming two border trunks (they are also called sympathetic chains). The vertebral ganglia are connected to the spinal cord by fibers that form white and gray connecting branches. Along the white connecting branches - rami comroimicantes albi - the preganglionic fibers of the sympathetic nervous system go to the nodes.

Fibers of post-ganglionic sympathetic neurons are sent from nodes to peripheral organs either along independent nerve pathways or as part of somatic nerves. In the latter case, they go from the nodes of the border trunks to the somatic nerves in the form of thin gray connecting branches - rami commiinicantes grisei (their gray color depends on the fact that the postganglionic sympathetic fibers do not have pulpy membranes). The course of these fibers can be seen in rice. 258.

In the ganglia of the border trunk, most of the sympathetic preganglionic nerve fibers are interrupted; a smaller part of them passes through the border trunk without interruption and is interrupted in the prekertebral ganglia.

prevertebral ganglia located at a greater distance from the spine than the ganglia of the border trunk, at the same time they are at some distance from the organs innervated by them. The prevertebral ganglia include the ciliary ganglion, the superior and middle cervical sympathetic ganglia, the solar plexus, and the superior and inferior 6 ganglia. In all of them, with the exception of the ciliary node, sympathetic preganglionic fibers are interrupted, which have passed without interruption the nodes of the border trunk. In the ciliary node, the parasympathetic preganglionic fibers that innervate the muscles of the eye are interrupted.

TO intraorgan ganglia include plexuses rich in nerve cells located in the internal organs. Such plexuses (intramural plexuses) are found in the muscular walls of many internal organs, such as the heart, bronchi, middle and lower thirds of the esophagus, stomach, intestines, gallbladder, bladder, as well as in the glands of external and internal secretion. On the cells of these nerve plexuses, as shown by histological studies of B. I. Lavrentiev and others, parasympathetic fibers are interrupted.

. Autonomic ganglia play a significant role in the distribution and propagation of nerve impulses passing through them. The number of nerve cells in the ganglia is several times (32 times in the superior cervical spmatic ganglion, 2 times in the ciliary ganglion) more than the number of preganglionic fibers coming to the ganglion. Each of these fibers forms synapses on many ganglion cells.

Autonomous (vegetative) nerve nodes (ganglia) can be located along the spine (paravertebral ganglia) or in front of it (prevertebral ganglia), as well as in the wall of organs: the heart, bronchi, digestive tract, bladder and others (intramural ganglia) or near their surface . Sometimes they look like small (from a few cells to several tens of cells) clusters of neurons located along some nerves or lying intramurally (microganglia). Preganglionic fibers (myelinated) are suitable for the vegetative nodes, containing processes of cells whose bodies lie in the central nervous system. These fibers strongly branch and form numerous synaptic endings on the cells of the vegetative nodes. Due to this, a large number of terminals of preganglionic fibers converge on each neuron of the ganglion. In connection with the presence of synaptic transmission, vegetative nodes are classified as nerve centers of the nuclear type.

Autonomic nerve ganglions according to their functional characteristics and localization are divided into:
Sympathetic ganglions(para- and prevertebral) receive preganglionic fibers from cells located in the autonomic nuclei of the thoracic and lumbar segments of the spinal cord. The neurotransmitter of preganglionic fibers is acetylcholine, and postganglionic fibers - norepinephrine (with the exception of sweat glands and some blood vessels that have cholinergic sympathetic innervation). In addition to these neurotransmitters, enkephalins, substance P, somatostatin, cholecystokinin are detected in the nodes.

Parasympathetic ganglions(intramural, lying near the organs or nodes of the head) receive preganglionic fibers from cells located in the autonomic nuclei of the medulla oblongata and midbrain, as well as the sacral spinal cord. These fibers leave the central nervous system as part of the 3rd, 7th, 9th, 10th pairs of cranial nerves and the anterior roots of the sacral segments of the spinal cord. The neurotransmitter of pre- and postganglionic fibers is acetylcholine. In addition to it, the role of mediators in these ganglia is played by serotonin, ATP, and possibly some peptides.

Most of the internal organs have a dual autonomic innervation, that is, they receive postganglionic fibers from cells located in both sympathetic and parasympathetic nodes. The reactions mediated by the cells of the sympathetic and parasympathetic nodes often have the opposite direction, for example: sympathetic stimulation enhances, and parasympathetic stimulation inhibits cardiac activity.

The general plan of the structure of the sympathetic and parasympathetic ganglions is similar. The vegetative node is covered with a connective tissue capsule and contains diffusely or groups located bodies of multipolar neurons, their processes in the form of non-myelinated or, less commonly, myelinated fibers and endoneurium. The bodies of neurons have an irregular shape, contain an eccentrically located nucleus, and are surrounded (usually not completely) by shells of glial satellite cells (mantle gliocytes). Often there are multinucleated and polyploid neurons.

Due to their high autonomy, the complexity of organization, and the peculiarities of mediator exchange, some authors distinguish intramural nodes and associated pathways as an independent metasympathetic division of the autonomic nervous system. In particular, the total number of neurons in the intramural nodes of the intestine is higher than in the spinal cord, and in terms of the complexity of their interaction in the regulation of peristalsis and secretion, they are compared with a minicomputer.

Three types of neurons are described in the intramural nodes:
In the autonomic nervous system distinguish between central and peripheral regions. The central sections of the sympathetic nervous system are represented by the nuclei of the lateral horns of the thoracolumbar section of the spinal cord. In the parasympathetic nervous system, the central divisions include the nuclei of the middle and medulla oblongata, as well as the nuclei of the lateral horns of the sacral spinal cord. Parasympathetic fibers of the craniobulbar region exit as part of the III, VII, IX and X pairs of cranial nerves.
Peripheral divisions of the autonomic nervous system formed by nerve trunks, ganglia and plexuses.

Autonomic reflex arcs begin with a sensitive neuron, the body of which lies in the spinal node (ganglion), as well as in the somatic reflex arc. Association neurons are found in the lateral horns of the spinal cord. Here, nerve impulses switch to intermediate preganglionic neurons, the processes of which leave the central nuclei and reach the autonomic ganglia, where they transmit impulses to the motor neuron. In this regard, nerve fibers are distinguished preganglionic and postganglionic. The first of them leave the central nervous system as part of the ventral roots of the spinal nerves and cranial nerves. In both the sympathetic and parasympathetic systems, preganglionic nerve fibers belong to cholinergic neurons. The axons of neurons located in the autonomic ganglia are called postganglionic. They do not form direct contacts with effector cells. Their terminal sections along their course form extensions - varicose veins, which include mediator vesicles. There is no glial membrane in the area of varicose veins, and the neurotransmitter, released into the environment, affects effector cells (for example, gland cells, smooth myocytes, etc.).

in the peripheral ganglia sympathetic nervous system, as a rule, there are adrenergic efferent neurons (with the exception of neurons that have synaptic connections with sweat glands, where sympathetic neurons are cholinergic). In the parasympathetic ganglia, efferent neurons are always cholinergic.

ganglia are clusters of multipolar neurons (from a few cells to tens of thousands). Extraorganic (sympathetic) ganglia have a well-defined connective tissue capsule, as a continuation of the perineurium. The parasympathetic ganglia are usually located in the intramural nerve plexuses. The ganglia of the intramural plexuses, like other autonomic nodes, contain autonomic neurons of local reflex arcs. Multipolar neurons with a diameter of 20-35 μm are located diffusely, each neuron is surrounded by ganglion gliocytes. In addition, neuroendocrine, chemoreceptor, bipolar, and, in some vertebrates, unipolar neurons have also been described. In the sympathetic ganglia there are small intensely fluorescent cells (MYF cells) with short processes and a large number of granular vesicles in the cytoplasm. They secrete catecholamines and have an inhibitory effect on the transmission of impulses from the preganglionic nerve fibers to the efferent sympathetic neuron. These cells are called interneurons.

Among large multipolar neurons vegetative ganglia are distinguished: motor (type I-type Dogel cells), sensitive (type II-type Dogel cells) and associative (type III-type Dogel cells). Motor neurons have short dendrites with lamellar extensions ("receptive pads"). The axon of these cells is very long, goes beyond the ganglion as part of postganglionic thin non-myelinated nerve fibers and ends on smooth myocytes of the internal organs. Type I cells are called long-axon neurons. Neurons of the II-nd type - equidistant nerve cells. 2-4 processes depart from their body, among which it is difficult to distinguish an axon. Without branching, the processes go far from the body of the neuron. Their dendrites have sensitive nerve endings, and the axon terminates on the bodies of motor neurons in neighboring ganglia. Type II cells are sensitive neurons of local autonomic reflex arcs. Type III Dogel cells are similar in body shape to type II autonomic neurons, but their dendrites do not extend beyond the ganglion, and the neurite goes to other ganglia. Many researchers consider these cells to be varieties of sensitive neurons.

Thus, in peripheral autonomic ganglia there are local reflex arcs consisting of sensory, motor, and possibly associative autonomic neurons.

Intramural autonomic ganglia in the wall of the digestive tract differ in that in their composition, in addition to motor cholinergic neurons, there are inhibitory neurons. They are represented by adrenergic and purinergic nerve cells. In the latter, the mediator is a purine nucleotide. In the intramural autonomic ganglia, there are also peptidergic neurons that secrete vasointestinal peptide, somatostatin, and a number of other peptides, with the help of which neuroendocrine regulation and modulation of the activity of tissues and organs of the digestive system are carried out.

Educational video of the anatomy of the autonomic nervous system (ANS)

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The autonomic ganglia are an accumulation of numerous multipolar nerve cells.
The size of the autonomic ganglia varies significantly. In this regard, there are large, medium-sized, small and very small (microganglia) ganglia.
It should be noted that in addition to the anatomically isolated ganglia, along the autonomic branches of the peripheral nerves, there are a large number of nerve cells similar to the nerve cells of the autonomic ganglion. These neurons, migrating here during embryogenesis, are localized along the nerves singly or form small groups - microganglia.
The vegetative ganglion is covered from the surface with a fibrous connective tissue capsule, from which numerous layers of connective tissue extend inside, forming the stroma of the node. Through these layers, blood vessels pass into the node, feeding it and forming a capillary network in it. In the capsule and stroma of the node, receptors are often found near the blood vessels - diffuse, bushy or encapsulated.
Multipolar nerve cells of the autonomic ganglion were first described by A.S. Dogel. At the same time, Dogel singled out 3 types of nervous autonomic ganglion cells, which are called Dogel cellsI, II, III type. The morphological and functional characteristics of Dogel cells differ significantly.
Dogel cellsItype according to their functional significance, they are effector (motor) neurons. These are more or less large nerve cells, with somewhat short dendrites that do not extend beyond this ganglion. The longer axon of these cells extends beyond the ganglion and goes to the working apparatus - smooth muscle cells, glandular cells, forming motor (or, respectively, secretory) nerve endings on them. The axons and dendrites of Type I Dogel cells are non-pulmonic. Dendrites often form lamellar extensions, on which (as well as on the cell body) synaptic endings are located, which are formed by branches of the preganglionic nerve fiber.
The bodies of neurons in the autonomic ganglion, in contrast to the spinal ganglion, are arranged randomly throughout the node and more loosely (i.e., more rarely). On preparations stained with hematoxylin or other general histological dyes, the processes of nerve cells remain unidentified, and the cells have the same rounded, processless shape as in the spinal nodes. The body of each nerve cell (as in the spinal ganglion) is surrounded by a layer of flattened elements of oligodendroglia - a layer of satellites.
To the outside of the layer of satellites there is still a thin connective tissue capsule. Type I Dogel cells are the main cellular form of autonomic ganglia.
Dogel cellsIItype are also multipolar nerve cells, with several long dendrites and a neurite extending beyond a given ganglion into neighboring ganglia. The surface of the axon is covered with myelin. The dendrites of these cells begin as receptor apparatuses in smooth muscles. From a functional point of view, type II Dogel cells are sensitive. In contrast to the sensitive pseudo-unipolar nerve cells of the spinal ganglion, type II Dogel cells apparently form the receptor (afferent) link of local reflex arcs, which are closed without the nerve impulse entering the central nervous system.
Dogel cellsIIItype are local associative (inserted) elements that connect several cells of type II and II with their processes. Their dendrites are short, but longer than those of type I cells; they do not go beyond the limits of this ganglion, but form basket-shaped branches that wrap around the bodies of other cells of this ganglion. The neurite of a type III Dogel cell goes to another ganglion and there enters into a synaptic connection with type I cells. Consequently, type III cells are included as an associative link in local reflex arcs.
It should be noted that there is such a point of view that Type III Dogel cells have a receptor or effector nature.
The ratio of the number of cells of I and II types of Dogel in various vegetative ganglia is not the same. Parasympathetic ganglia, in contrast to the sympathetic ganglia, are characterized by the predominance of cells with short intracapsular dendrites, the absence or small amount of pigment in the cells. In addition, in the parasympathetic ganglia, as a rule, the bodies lie much more compactly than in the sympathetic ganglia. In addition, the sympathetic ganglia contain MYTH cells(small cells with intense fluorescence).
Through the vegetative ganglion there are three types of pathways: centripetal, centrifugal and peripheral (local) reflex.
Centripetal pathways are formed by sensory processes of pseudounipolar cells of the spinal ganglion, beginning with receptors in the innervated tissues, as well as inside the ganglion. These fibers transit through the autonomic ganglia.
Centrifugal pathways are represented by preganglionic fibers that branch many times in the vegetative node and form synapses on many cell bodies of effector neurons. For example, in the upper cervical ganglion, the ratio of the number of preganglionic fibers entering it to postganglionic fibers is 1:32. This phenomenon leads, upon excitation of preganglionic fibers, to a sharp expansion of the area of excitation (effector hyperalization). Due to this, a relatively small number of central autonomic neurons provide nerve impulses to all organs and tissues. So, for example, when an animal is irritated by preganglionic sympathetic fibers passing through the anterior roots of the IY thoracic segment, vasoconstriction of the skin of the head and neck, dilation of the coronary vessels, narrowing of the vessels of the skin of the forelimb, the vessels of the kidney and spleen can be observed.
The continuation of these pathways are postganglionic fibers reaching the innervated tissues.
Peripheral (local) reflex pathways begin in the tissues with branchings of the processes of their own sensitive neurons of the autonomic ganglia (i.e., Type II Dogel cells). The neurites of these cells end on Type I Dogel cells, whose postganglionic fibers are part of the centrifugal pathways.
The morphological substrate of the reflex activity of the autonomic nervous system is the reflex arc. For the reflex arc of the autonomic nervous system, all three links are characteristic - receptor (afferent), autonomic (associative) and effector (motor), but their localization is different than in the somatic.
It is interesting to note that many morphologists and physiologists point to the absence of its own afferent (receptor) link in its composition as a distinctive feature of the autonomic nervous system, i.e. they believe that the sensitive innervation of the internal organs, blood vessels, etc. carried out by the dendrites of the pseudounipolar cells of the spinal ganglion, i.e. somatic nervous system.
It is more correct to consider that the spinal nodes contain neurons that innervate the skeletal muscles, skin (ie neurons of the somatic nervous system), and neurons innervating all internal organs, blood vessels (ie autonomic neurons).
In a word, the affective link, as in the somatic (animal) nervous system, in the autonomic nervous system is represented by a cell lying in the spinal ganglion.
The body of the neuron of the associative link is located, unlike the somatic reflex neural arch, not in the region of the posterior horn, but in the lateral horns of the gray matter, and the axon of these cells extends beyond the brain and ends in one of the autonomic ganglia.
Finally, the greatest differences between the animal and autonomic reflex arcs are observed in the efferent link. Thus, the body of an efferent neuron in the somatic nervous system is located in the gray matter of the spinal or cerebral ganglion, and only its axon goes to the periphery as part of one or another cranial or spinal nerve. In the autonomic system, the bodies of effector neurons are located on the periphery: they are either scattered along the course of some nerves or form clusters - autonomic ganglia.
Thus, due to such localization of effector neurons, the autonomic nervous system is characterized by the presence of at least one break in the efferent pathway that passes in the autonomic ganglion, i.e. here the neurites of the intercalary neurons contact with the effector neurons, forming synapses on their bodies and dendrites. Therefore, the autonomic ganglia are peripheral nerve centers. In this they are fundamentally different from the spinal ganglia, which are not nerve centers, because. they do not have synapses and there is no switching of nerve impulses.
Thus, the spinal nodes are mixed formations, animal-vegetative.
A feature of the reflex arc of the sympathetic nervous system is the presence of short preganglionic fibers and very long postganglionic fibers.
A feature of the reflex arc of the parasympathetic nervous system is, on the contrary, the presence of very long preganglionic and very short postganglionic fibers.
The main functional differences between the sympathetic and parasympathetic systems are as follows. mediator, i.e. Sympathin (a substance identical to the hormone of the adrenal medulla - noadrenaline) is a substance that is formed in the region of synapses and carries out chemical impulse transmission in sympathetic nerve endings.
The mediator in the parasympathetic nerve endings is the “vagus substance” (a substance identical to acetylcholine). However, this difference concerns only postganglionic fibers. Synapses formed by preganglionic fibers in both the sympathetic and parasympathetic systems are cholinergic, i.e. as a mediator, they form a choline-like substance.
These chemical substances - mediators and by themselves, even without irritation of the autonomic nerve fibers, cause effects in the working organs similar to the action of the corresponding autonomic nerve fibers. So, noadrenaline, when injected into the blood, accelerates the heartbeat, but slows down the peristalsis of the intestinal tract, and acetylcholine, on the contrary. Noadrenaline causes narrowing, and acetylcholine - the expansion of the lumen of the vessels.
Cholinergic and synapses formed by the fibers of the somatic nervous system.
The activity of the autonomic nervous system is under the control of the cerebral cortex, as well as the subcortical autonomic centers of the striatum and, finally, the autonomic centers of the diencephalon (the nucleus of the hypothalamus).
In conclusion, it should be noted that the doctrine of the autonomic nervous system was also greatly contributed by Soviet scientists B.I. Lavrentiev, A.A. Zavarzin, D.I. Golub, awarded state prizes.
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