Sympathetic and parasympathetic nervous system, their structure and functions. Sympathetic nervous system. autonomic nervous system. Anatomy What functions does the parasympathetic department regulate

In structure, it is similar to the sympathetic one - it also consists of central and peripheral formations. The central part (segmental centers) is represented by the nuclei of the middle, medulla oblongata and sacral spinal cord, and the peripheral part is represented by nerve nodes, fibers, plexuses, as well as synaptic and receptor endings. The transmission of excitation to the executive organs, as in the sympathetic system, is carried out along a two-neuron path: the first neuron (preganglionic) is located in the nuclei of the brain and spinal cord, the second is far on the periphery, in the nerve nodes. The preganglionic parasympathetic fibers are similar in diameter to the sympathetic ones, are equally myelinated, and the mediator of both types of fibers is acetylcholine.

Despite the noted similarities, the parasympathetic nervous system differs from the sympathetic in a number of ways.

1. Its central formations are located in three different parts of the brain.

2. The nodes of the parasympathetic system in the bulk are small, located diffusely on the surface or in the thickness of the innervated organs.

3. A characteristic feature of the parasympathetic system is the presence of numerous nerve nodes and individual nerve cells in the nerves (intranstal ganglia and neurons).

4. The processes of parasympathetic preganglionic neurons are much longer than those of sympathetic ones, while those of postganglionic neurons, on the contrary, are very short.

5. The zone of distribution of parasympathetic fibers is much smaller; they innervate not all, but only certain organs, which are also supplied with sympathetic innervation.

6. Postganglionic fibers of the parasympathetic system transmit impulses through acetylcholine, and sympathetic fibers, as a rule, with the participation of norepinephrine.

The segmental centers of the parasympathetic system in the midbrain are represented by the nuclei of the oculomotor nerve (Westphal-Edinger-Jakubovich), located in the tegmentum of the brain legs under the Sylvian aqueduct at the level of the superior tubercles of the quadrigemina. In the medulla oblongata, the segmental parasympathetic centers are:

1) superior salivary nuclei of the facial nerve (VII pair);

2) lower salivary nuclei of the glossopharyngeal nerve (IX pair), located in the middle part of the rhomboid fossa on the border of the bridge and the medulla oblongata;

3) the dorsal nucleus of the vagus nerve (X pair), which forms an elevation visible to the naked eye at the bottom of the rhomboid fossa, called the triangle of the vagus nerve. In addition, close to the dorsal is the nucleus of the solitary tract, which is the sensory nucleus of the vagus nerve. (Fig. 6)

All of these nuclei are entirely composed of neurons of the reticular type with long, slightly branched dendrites, and only due to the compact arrangement of cells stand out from the neighboring reticular formation.

Preganglionic fibers from the midbrain nuclei exit as part of the oculomotor nerve, (Fig. 7.8) penetrate through the palpebral fissure into the orbit and end in synapses on the efferent cells of the ciliary node located in the depths of the orbit. The neurons of this node are characterized by a rounded shape, medium size, and a diffuse arrangement of elements of the tigroid substance. The postganglionic fibers of this node form two short ciliary nerves - lateral and medial. They enter the eyeball and branch out in the accommodative smooth muscles of the ciliary body and in the muscle that constricts the pupil. The reflex of changing the size of the pupil and the installation of the lens are under the control of the centers of the posterior thalamus, anterior colliculus and the cerebral cortex. During anesthesia, sleep, and disturbance of the cortex, the pupil is maximally narrowed, which indicates a functional or structural break in the pathways between the accessory nucleus and the cerebral cortex.

From the superior salivary nucleus, the preganglionic fibers first go as part of the facial nerve, then, separating from it, form a large stony nerve, which then connects to the deep stony nerve, forming the nerve of the pterygoid canal, which reaches the node of the same name. (Fig. 7.8) The postganglionic fibers of the pterygoid (or pterygopalatine) node innervate the mucous glands of the nasal cavity, the ethmoid and sphenoid sinuses, the hard and soft palate, and the lacrimal glands.

Part of the preganglionic fibers of the superior salivary nucleus, emerging as part of the facial nerve, pass through the tympanic string into the lingual nerve, in its composition they reach the submandibular and sublingual nodes located on the surface of the salivary glands of the same name. The postganglionic fibers of the nodes enter the parenchyma of these glands.

The fibers emerging from the lower salivary nucleus enter the glossopharyngeal nerve and then, as part of the tympanic nerve, reach the ear node. (Fig. 7.8) Postganglionic fibers in the auricular-temporal nerve enter the parotid salivary gland.

Pterygopalatine, auricular, submandibular and sublingual nodes consist of multipolar neurons of irregular polygonal shape, morphologically similar to each other. On their bodies there are numerous depressions in which satellite cells are located. A characteristic feature of their cytoplasm is the lattice distribution of elements of the tigroid substance. Their short dendrites do not extend beyond the node. They, twisting near the bodies of neurons, form closed spaces.

The vagus nerve (X pair of cranial nerves) is the largest nerve that provides parasympathetic innervation to many organs of the neck, thoracic and abdominal cavities. It exits the cranial cavity through the jugular foramen and in the very initial part of the nerve along its course there are successively two nodes: jugular (upper) and nodal (lower). The jugular ganglion contains mostly sensitive pseudo-unipolar neurons, similar to the nerve cells of the spinal ganglions.

Rice. 6. Segmental parasympathetic centers of the brain.

1 - nuclei of the oculomotor nerve: A - median nucleus, B - additional nuclei; 2 - upper salivary nuclei; 3 - lower salivary nuclei; 4 - dorsal nuclei of the vagus nerve.

Rice. 7. Scheme of efferent parasympathetic innervation.

1 - accessory nucleus of the oculomotor nerve; 2 - upper salivary nucleus; 3 - lower salivary nucleus; 4 - the posterior nucleus of the vagus nerve; 5 - lateral intermediate nucleus of the sacral spinal cord; 6 - oculomotor nerve; 7 - facial (intermediate) nerve; 8 - glossopharyngeal nerve; 9 - vagus nerve; 10 - pelvic internal nerves; 11 - ciliary knot; 12 - pterygopalatine node; 13 - ear node; 14 - submandibular node; 15 - sublingual node; 16 - nodes of the pulmonary plexus; 17 - nodes of the cardiac plexus; 18 - celiac nodes; 19 - nodes of the gastric and intestinal plexuses; 20 - nodes of the pelvic plexus.

Rice. 8. Scheme of the cranial part of the parasympathetic nervous system.

1 - oculomotor nerve; 2 - facial (intermediate) nerve; 3 - glossopharyngeal nerve; 4 - accessory nucleus of the oculomotor nerve; 5 - upper salivary nucleus; 6 - lower salivary nucleus; 7 - ciliary knot; 8 - pterygopalatine node 9 - submandibular node; 10 - ear node. Branches of the trigeminal nerve: 11 - I branch; 12 - II branch; 13 - III branch; 14 - node of the trigeminal nerve; 15 - vagus nerve; 16 - posterior nucleus of the vagus nerve; 17 - lacrimal gland; 18 - mucous gland of the nasal cavity; 19 - parotid salivary gland; 20 - small salivary and mucous glands of the oral cavity; 21 - sublingual salivary gland; 22 - submandibular salivary gland.

The central process of the neurons of the jugular ganglion goes to the nuclei of the vagus nerve (the dorsal nucleus of the medulla oblongata and the sensitive nucleus of the solitary tract), the peripheral process goes to the innervated organs and forms interoceptors in them. A branch departs from the jugular node to the membranes of the brain and the ear branch. Nodal (bottom) node ( gangi. nodosum) consists mainly of effector neurons, but also contains sensory cells, the same as in the jugular node. It is adjacent to the cranial cervical sympathetic ganglion and forms connections with it by a network of fibers. Branches depart from the nodular node to the hypoglossal, accessory, glossopharyngeal nerves and to the carotid sinus region, and the upper laryngeal and depressor nerves depart from its lower pole. The depressor nerve innervates the heart, aortic arch, and pulmonary artery.

The vagus nerve has a very complex structure. According to the composition of efferent fibers, it is predominantly parasympathetic. Among these efferents, fibers formed by the axons of the cells of the dorsal nuclei of the medulla oblongata predominate. These preganglionic fibers, as part of the main trunks of the vagus nerves and their branches, go to the internal organs, where, along with sympathetic fibers, they participate in the formation of nerve plexuses. The bulk of the preganglionic fibers ends on the neurons of the autonomic nodes that are part of the plexuses of the organs of the digestive, respiratory systems and heart. But part of the preganglionic fibers does not reach the organ nodes. The fact is that in the thickness of the vagus nerve throughout, as well as in the composition of its branches, there are numerous parasympathetic neurons in the form of nodules and individual cells (Fig. 9). In humans, the vagus nerve of each side contains up to 1700 neurons. Among them there are sensitive pseudo-unipolar cells, but most of them are multipolar effector neurons. It is on these cells that part of the preganglionic fibers ends, breaking up into terminals that form synapses.

The axons of these intrastem neurons form postganglionic fibers, which, following in the composition of the vagus nerves, innervate the smooth muscles of organs, the heart muscle and glands. The vagus nerves also contain pre- and postganglionic sympathetic fibers, which entered into them as a result of connections with the cervical nodes of the sympathetic trunk. The vagus nerves also include afferent fibers formed by the peripheral processes of the neurons of the spinal ganglions, following to the abdominal organs, as well as ascending fibers formed by the axons of sensitive Type II Dogel cells located in the intramural nodes of the internal organs. In addition to those named, in each vagus nerve there are somatic motor fibers emerging from the double nucleus of the medulla oblongata. They innervate the striated muscles of the pharynx, soft palate, larynx, and esophagus.

Branches depart from the cervical part of the vagus nerve, providing parasympathetic innervation of the pharynx, larynx, thyroid and parathyroid glands, thymus, trachea, esophagus and heart. The branches of the thoracic part of the nerve are also involved in the formation of the plexuses of the esophagus and trachea; bronchial branches also come out of it, entering the pulmonary plexus. In the abdomen, the vagus nerve

Rice. 9. Vegetative unilateral frog neuron under the epineurium of the branch of the vagus nerve. Live microscopy. phase contrast. SW. 400.

1 - epineurium;

2 - the nucleus of the neuron;

3 - branch of the vagus nerve.

separates the branches that form a dense gastric plexus, from which stems extend to the duodenum and liver. The celiac branches originate primarily from the right vagus nerve and enter the celiac and superior mesenteric plexuses. Further, the preganglionic fibers of the vagus trunk, together with sympathetic fibers, form the inferior mesenteric, abdominal aortic and other plexuses of the abdominal cavity, the branches of which reach the extra- and intraorgan nodes of the liver, spleen, pancreas, small and upper parts of the large intestine, kidneys, adrenal glands, etc.

The nuclei of the sacral part of the parasympathetic nervous system are located in the intermediate zone of the gray matter of the spinal cord at the level of II-IV sacral segments. The preganglionic fibers from these nuclei through the anterior roots first enter the sacral spinal nerves, then, separating from them as part of the pelvic internal nerves, enter the lower hypogastric (pelvic) plexus. Parasympathetic preganglionic cells end in the periorgan nodes of the pelvic plexus, or in the nodes located inside the pelvic organs. Part of the sacral preganglionic fibers goes up and enters the hypogastric nerves, superior hypogastric and inferior mesenteric plexus. Postganglionic fibers terminate on the smooth muscles of organs, some vessels, and glands. In addition to parasympathetic and sympathetic efferents, the pelvic splanchnic nerves also contain afferent fibers (mainly large myelinated). Pelvic splanchnic nerves carry out parasympathetic innervation of some organs of the abdominal cavity and all organs of the small pelvis: descending colon, sigmoid and rectum, bladder, seminal vesicles, prostate and vagina.

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In this article, we will consider what the sympathetic and parasympathetic nervous systems are, how they work, and what are their differences. We have previously covered the topic as well. The autonomic nervous system, as you know, consists of nerve cells and processes, thanks to which there is a regulation and control of internal organs. The autonomic system is divided into peripheral and central. If the central is responsible for the work of the internal organs, without any division into opposite parts, then the peripheral is just divided into sympathetic and parasympathetic.

The structures of these departments are present in every internal human organ and, despite opposite functions, work simultaneously. However, at different times, one or another department is more important. Thanks to them, we can adapt to different climatic conditions and other changes in the external environment. The autonomic system plays a very important role, it regulates mental and physical activity, and also maintains homeostasis (the constancy of the internal environment). If you rest, the autonomic system activates the parasympathetic and the number of heartbeats decreases. If you start running and experiencing great physical exertion, the sympathetic department turns on, thereby accelerating the work of the heart and blood circulation in the body.

And this is only a small section of the activity that the visceral nervous system performs. It also regulates hair growth, constriction and expansion of the pupils, the work of one or another organ, is responsible for the psychological balance of the individual, and much more. All this happens without our conscious participation, which at first glance seems difficult to treat.

Sympathetic division of the nervous system

Among people who are unfamiliar with the work of the nervous system, there is an opinion that it is one and indivisible. However, in reality, things are different. So, the sympathetic department, which in turn belongs to the peripheral, and the peripheral refers to the vegetative part of the nervous system, supplies the body with the necessary nutrients. Thanks to its work, oxidative processes proceed quite quickly, if necessary, the work of the heart accelerates, the body receives the proper level of oxygen, and breathing improves.

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Interestingly, the sympathetic department is also divided into peripheral and central. If the central part is an integral part of the work of the spinal cord, then the peripheral part of the sympathetic has many branches and ganglions that connect. The spinal center is located in the lateral horns of the lumbar and thoracic segments. The fibers, in turn, depart from the spinal cord (1 and 2 thoracic vertebrae) and 2,3,4 lumbar. This is a very brief description of where the divisions of the sympathetic system are located. Most often, the SNS is activated when a person finds himself in a stressful situation.

Peripheral department

Representing the peripheral department is not so difficult. It consists of two identical trunks, which are located on both sides along the entire spine. They start from the base of the skull and end at the coccyx, where they converge into a single knot. Thanks to internodal branches, two trunks are connected. As a result, the peripheral part of the sympathetic system passes through the cervical, thoracic and lumbar regions, which we will consider in more detail.

• Neck department. As you know, it starts from the base of the skull and ends at the transition to the thoracic (cervical 1 rib). There are three sympathetic nodes, which are divided into lower, middle and upper. All of them pass behind the human carotid artery. The upper node is located at the level of the second and third vertebrae of the cervical region, has a length of 20 mm, a width of 4 - 6 millimeters. The middle one is much more difficult to find, as it is located at the intersections of the carotid artery and the thyroid gland. The lower node has the largest value, sometimes even merges with the second thoracic node.
• Thoracic department. It consists of up to 12 nodes and it has many connecting branches. They stretch to the aorta, intercostal nerves, heart, lungs, thoracic duct, esophagus and other organs. Thanks to the thoracic region, a person can sometimes feel the organs.
• The lumbar region most often consists of three nodes, and in some cases it has 4. It also has many connecting branches. The pelvic region connects the two trunks and other branches together.

Parasympathetic department

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This part of the nervous system begins to work when a person tries to relax or is at rest. Thanks to the parasympathetic system, blood pressure decreases, the vessels relax, the pupils constrict, the heart rate slows down, and the sphincters relax. The center of this department is located in the spinal cord and brain. Thanks to the efferent fibers, the hair muscles relax, the release of sweat is delayed, and the vessels expand. It is worth noting that the structure of the parasympathetic includes the intramural nervous system, which has several plexuses and is located in the digestive tract.

The parasympathetic department helps to recover from heavy loads and performs the following processes:

• Reduces blood pressure;
• Restores breath;
• Expands the vessels of the brain and genital organs;
• Constricts pupils;
• Restores optimal glucose levels;
• Activates the glands of digestive secretion;
• It tones the smooth muscles of the internal organs;
• Thanks to this department, purification occurs: vomiting, coughing, sneezing and other processes.

In order for the body to feel comfortable and adapt to different climatic conditions, the sympathetic and parasympathetic divisions of the autonomic nervous system are activated at different times. In principle, they work constantly, however, as mentioned above, one of the departments always prevails over the other. Once in the heat, the body tries to cool down and actively releases sweat, when you need to warm up urgently, sweating is blocked accordingly. If the vegetative system works correctly, a person does not experience certain difficulties and does not even know about their existence, except for professional necessity or curiosity.

Since the topic of the site is devoted to vegetovascular dystonia, you should be aware that due to psychological disorders, the autonomic system is experiencing failures. For example, when a person has a psychological trauma and experiences a panic attack in a closed room, his sympathetic or parasympathetic department is activated. This is a normal reaction of the body to an external threat. As a result, a person feels nausea, dizziness and other symptoms, depending on. The main thing that should be understood by the patient is that this is only a psychological disorder, and not physiological abnormalities, which are only a consequence. That is why drug treatment is not an effective remedy, they only help to remove the symptoms. For a full recovery, you need the help of a psychotherapist.

If at a certain point in time the sympathetic department is activated, there is an increase in blood pressure, the pupils dilate, constipation begins, and anxiety increases. Under the action of the parasympathetic, constriction of the pupils occurs, fainting may occur, blood pressure decreases, excess mass accumulates, and indecision appears. The most difficult thing for a patient suffering from a disorder of the autonomic nervous system is when he is observed, since at this moment violations of the parasympathetic and sympathetic parts of the nervous system are observed simultaneously.

As a result, if you suffer from a disorder of the autonomic nervous system, the first thing to do is to pass numerous tests to rule out physiological pathologies. If nothing is revealed, it is safe to say that you need the help of a psychologist who will relieve the disease in a short time.

The internal organs of our body (like the heart, stomach, intestines) are controlled by a part known as the autonomic nervous system (ANS). In most situations, we are not aware of how the ANS functions, it happens in an involuntary way. For example, we cannot see the work of blood vessels in the same way as we can influence the heart rate. Although most autonomous functions are reflexive, some of them can be controlled consciously, but to a certain extent. These are swallowing, breathing and sexual arousal.

Providing homeostasis, autonomous (or is very important in choosing a way of behavior, actions controlled by the brain. This happens in emergency situations that provoke stress and require us to concentrate internal forces in the fight against the current situation, as well as under relaxing circumstances that contribute to recovery and rest.

ANS consists of three departments:

Sympathetic nervous system (SNS);

Parasympathetic nervous system (PNS);

It mediates reactions associated with stressful situations by increasing and increasing blood pressure. It ensures that the body is ready to act immediately in stressful situations or dangers. This is in line with the classic "fight or flight" response mediated by the two main chemical messengers, epinephrine (adrenaline) and norepinephrine. For this reason, the SNS is called the "working nerve".

The parasympathetic nervous system, in contrast, is the "calm" part of the ANS. It is also known as the "Nerve of Calm". While the sympathetic nervous system prepares the body for stressful situations, the PNS serves as a “refueling” of energy and recovery. It stimulates the actions that occur when the body is at rest, especially during meals, naps, sexual arousal.

But the sympathetic and parasympathetic divisions of the ANS, although they function against each other, are not opposites. Rather, it is an interconnected complex that creates balance within our body. Between these departments there are dynamic interactions that are regulated by second messengers (cyclic adenosine monophosphate and cyclic guanosine monophosphate). For example, when the heart receives neural stimulation from the PNS, the heart rate slows down, and vice versa, when the heart receives neural stimulation from the SNS neurons, the heart rate increases.

Sympathetic activation can inhibit parasympathetic activation presynaptically. Similarly, the parasympathetic nervous system is involved in presynaptic inhibition of the movement of sympathetic nerves.

The functions of a balanced autonomic nervous system are vital. If the interaction between the “working nerve” and the “nerve of calmness” is disrupted, some restrictions arise, thereby endangering the quality of life.

Thus, overstimulation of the SNS can lead to problems such as anxiety, hypertension, and digestive disorders. Overstimulation of the PNS can result in low blood pressure and a feeling of fatigue.

The parasympathetic nervous system, like the sympathetic one, is not concentrated in one area, but is distributed over a large area. The autonomic centers of the PNS are located in the region of the brain stem and the region of the sacral spinal cord. In the medulla oblongata, the cranial nerves VII, IX, and X form the preganglionic parasympathetic fibers. From or the spinal cord, a preganglionic fiber (long) is carried towards the ganglia, which are located very close to the target organ, and makes a synapse. The synapse uses a neurotransmitter called acetylcholine. In this area, from the ganglion, a postganglionic fiber (short) is projected directly onto the target organ, also using acetylcholine.

Acetylcholine acts on two types of cholinergic receptors: muscarinic and nicotinic (or acetylcholine) receptors. Although the parasympathetic nervous system uses acetylcholine (as a neurotransmitter), peptides (cholecystokinin) can also perform this function.

The peripheral part of the parasympathetic nervous system provides bilateral connections between the parasympathetic centers and the innervated substrate. It is represented by nerve nodes, trunks and plexuses. In the peripheral part of the parasympathetic nervous system, the cranial and sacral parts are distinguished.

Preganglionic fibers from the cranial centers go along the III, VII, IX and X pairs of cranial nerves, from the sacral - along S 2, S 3, S 4 spinal nerves. From the latter, parasympathetic fibers enter the pelvic splanchnic nerves. Preganglionic fibers go to near- or intraorgan nodes, on the neurons of which they end in synapses.

cranial part. Anatomy, function. Nerve conductors originating from the cranial parasympathetic centers provide innervation to the organs of the head, neck, chest and abdominal cavities and are associated with the parasympathetic nuclei of the midbrain (Fig. 36, Parasympathetic division of the autonomic nervous system).

eyelash knot, on the neurocytes of which preganglionic fibers of the accessory nucleus of the oculomotor nerve end, gives postganglionic fibers as part of short ciliary nerves to the eyeball and innervates the muscle that narrows the pupil and the ciliary muscle.

Pterygopalatine node. In this node, the preganglionic parasympathetic fibers of the intermediate nerve end (begins in the superior salivary nucleus). Processes of cells of the pterygopalatine ganglion (postganglionic fibers) as part of the palatine nerves ( nn. palatini), posterior nasal branches of the great palatine nerve (rr. nasalesposteri-oresn. palatinimajores), n. sphenopalatinus The ophthalmic branches are innervated by the mucous glands of the nasal cavity, the ethmoid bone and the sphenoid sinus, the hard and soft palate, and the lacrimal glands.

Another part of the preganglionic parasympathetic fibers of the intermediate nerve in the string tympani ( chordatympani) reaches the lingual nerve ( n. lingualis from the III branch of the trigeminal nerve), along which it goes to the submandibular (gangl. submandibu-lare) and sublingual ( gangl. sublinguale) nodes located on the surface of the salivary glands of the same name. In these nodes, the preganglionic conductors end. Postganglionic fibers enter the parenchyma of the salivary glands of the same name.

Generally the function of parasympathetic innervation is increased secretion and vasodilation. Hypersalivation can be observed with bulbar and pseudobulbar syndrome, helminthic invasion, etc. In general the function of sympathetic innervation is the inhibition of the secretion of the glands of the mucous membrane, the narrowing of the lumen of the vessels. Hyposalivation and inhibition of the function of the salivary glands may accompany Sjögren's syndrome, diabetes mellitus, chronic gastritis, stress and depressive states, etc. In addition, xerostomia (dry mouth) is described with acute transient total dysautonomia(damage to vegetative fibers of an infectious-allergic nature) and with focal lesions of the brain(poor prognostic sign).

Parasympathetic fibers of the glossopharyngeal ( n. glossopharyngeus) and wandering ( n. vagus) nerves are involved in the formation of the tympanic plexus (through the tympanic nerve), which lies in the cavity of the same name. From the tympanic plexus, parasympathetic preganglionic fibers in the lesser petrosal nerve ( n. petrosusminor) are directed through the exit of the same name and along the groove on the anterior surface of the pyramid of the temporal bone reach the torn opening.

After passing through the opening, the small stony nerve reaches the ear node ( ganglionoticum). Postganglionic conductors (processes of the nerve cells of the ear node) follow the ear-temporal nerve ( n. auriculotemporalis- from the III branch of the trigeminal nerve) and in its composition enter the parotid salivary gland, providing it with secretory innervation.

The preganglionic fibers of the vagus nerve reach the parasympathetic near- or intraorgan nodes, where numerous nodes and plexuses form and postganglionic fibers begin.

Vegetative plexuses, in the formation of which is involved n. vagus. The branches of the vagus nerve are represented in the following nerve plexuses.

Neck: pharyngeal plexus (innervates the muscles and mucous membrane of the pharynx, thyroid and parathyroid glands), thyroid plexus (provides parasympathetic innervation of the thyroid gland), laryngeal plexus, upper and lower cervical cardiac branches.

Chest: tracheal, bronchial, esophageal branches.

Abdominal part: gastric, hepatic, celiac branches.

The vagus nerve is involved in the parasympathetic innervation of the liver, spleen, pancreas, kidneys and adrenal glands. Its branches innervate the duodenum, jejunum, and ileum (small intestine), as well as the caecum, ascending, and transverse colon (large intestine). The influence of the vagus nerve affects the slowing of the heart rate, narrowing of the bronchial lumen, increased peristalsis of the stomach and intestines, increased secretion of gastric juice, etc.

Cross part. Anatomy, function. The nuclei of the sacral part of the parasympathetic nervous system are located in the intermediate-lateral nucleus ( nucl. intermediolateralis) the lateral horn of the gray matter of the spinal cord at the level of S 2 -S 4 segments. The processes of the cells of this nucleus (preganglionic fibers) enter the spinal nerves along the anterior roots. As part of six to eight pelvic splanchnic nerves ( nn. splanchnicipelvini) they separate from the anterior branches most often of the third and fourth sacral spinal nerves and enter the lower hypogastric plexus.

Parasympathetic preganglionic fibers end on the cells of the periorgan nodes of the lower hypogastric plexus or on the neurocytes of the intraorgan nodes of the pelvic organs. Part of the preganglionic fibers has an ascending direction and enters the hypogastric nerves, superior hypogastric and inferior mesenteric plexus. Postganglionic fibers reach the innervated substrate, ending on the cells of the unstriated muscles of organs, vessels, and glands.

In addition to parasympathetic and sympathetic, the pelvic splanchnic nerves contain afferent nerve fibers (mainly large myelinated).

Function. Due to the pelvic splanchnic nerves, parasympathetic innervation of some organs of the abdominal cavity and all organs of the small pelvis is carried out: the descending colon, sigmoid and rectum, the bladder, seminal vesicles, the prostate gland in men and the vagina in women.

Damage symptoms of the peripheral part of the autonomic nervous system are directly related to the loss or irritation of the corresponding element of the system.

Metasympathetic division of the autonomic nervous system (enteric system). A complex of microganglionic formations, which are located in the walls of internal organs with motor activity (heart, intestines, ureter, etc.), and ensure their autonomy. The function of the nerve nodes is, on the one hand, in the transfer of central (sympathetic, parasympathetic) influences to the tissues, and on the other hand, in the integration of information coming through local reflex arcs. They are independent entities capable of functioning with full decentralization. Several (5–7) nearby nodes are combined into a single functional module, the main units of which are oscillator cells that ensure the autonomy of the system, interneurons, motor neurons, and sensory cells. Separate functional modules constitute a plexus, due to which, for example, a peristaltic wave is organized in the intestine.

The work of the metasympathetic division of the autonomic nervous system does not depend on the activity of the sympathetic and parasympathetic systems, but can be modified under their influence. So, for example, activation of parasympathetic influence enhances intestinal motility, and sympathetic influence weakens it.

The balance of influences of the sympathetic and parasympathetic divisions of the autonomic nervous system. Normally, the sympathetic and parasympathetic systems are constantly active; their basal activity level is known as tone. The sympathetic and parasympathetic nervous systems have an antagonistic effect on organs and tissues. However, at the level of the organism, their antagonism is relative, since under physiological conditions the activation of one system (with the necessary participation of the suprasegmental apparatus) leads to the activation of the other, which maintains homeostasis and at the same time provides mechanisms for adapting to changing environmental conditions. Sympathetic influences are predominantly excitatory in nature, parasympathetic influences are predominantly inhibitory, normally returning the physiological system to the basic balance (Table 7).

Table 7

Influence of sympathetic and parasympathetic
stimulation on organs and tissues

The main effects of the sympathetic nervous system are associated with enhanced activation of the body, stimulation of catabolism. This allows you to develop more powerful muscle activity, which is especially important for the adaptation of the body under stress.

The tone of the sympathetic system predominates during vigorous activity, emotional states, and the term fight or flight reaction is applicable to its effects. Parasympathetic activity, on the contrary, prevails during sleep, rest, at night (“sleep is the realm of the vagus”), stimulates the processes of anabolism.

10.3. Features of autonomic innervation and symptoms of its violation on the example of some internal organs

Autonomic innervation of the eye. Anatomy, function, symptoms of the lesion. The eye receives both sympathetic and parasympathetic innervation. In response to visual stimuli coming from the retina, the visual apparatus is accommodated and the magnitude of the light flux (pupillary reflex) is regulated (Fig. 37, Autonomic innervation of the eye and reflex arc of the pupil's reaction to light (according to: S. W. Ransen and S. L. Clark)).

Afferent part reflex arcs is represented by neurons of the visual pathway. The axons of the third neuron pass as part of the optic nerve, the optic tract and end at the subcortical reflex visual centers in the superior colliculus. From here, impulses are transmitted to the paired parasympathetic autonomous Yakubovich-Edinger-Westphal nuclei of their own and opposite sides and to the neurons of the ciliospinal center through the reticular formation along the reticulospinal tract.

efferent part of the parasympathetic The reflex arc is represented by preganglionic fibers running from the autonomous nuclei as part of the oculomotor nerve to the orbit to the ciliary ganglion. After switching in the ciliary ganglion, the postganglionic fibers in the short ciliary nerves reach the ciliary muscle and the pupillary sphincter. Provides constriction of the pupil and accommodation of the eye to far and near vision . The efferent part of the sympathetic the reflex arc is represented by preganglionic fibers coming from the nuclei of the ciliospinal center through the anterior roots, spinal nerves, white connecting branches into the sympathetic trunk; then, along the internodal connections, they reach the upper sympathetic node and here they end on the cells of the efferent neuron. Postganglionic fibers as part of the internal carotid nerve go into the cranial cavity, forming sympathetic plexuses around the carotid artery, cavernous sinus, ophthalmic artery, and reach the ciliary ganglion . Sympathetic efferent fibers are not interrupted in this node, but in transit go to the eyeball to the muscle that dilates the pupil. They dilate the pupil and constrict the vessels of the eye. .

When the sympathetic part of the reflex arc is turned off at any level from the spinal cord to the eyeball, a triad of symptoms occurs: pupil constriction (miosis), narrowing of the palpebral fissure (ptosis) and retraction of the eyeball (enophthalmos). This triad of symptoms is referred to as Claude Bernard-Horner syndrome . Occasionally, other signs of the complete Bernard-Horner symptom complex are recorded in clinical practice: homolateral anhidrosis of the face; hyperemia of the conjunctiva and half of the face; heterochromia of the iris (depigmentation). Allocate Bernard-Horner syndrome of peripheral and central origin. The first occurs when the center of Bunge or the paths to the muscle that dilates the pupil is affected. Most often this occurs due to a tumor, hemorrhage, syringomyelia in the zone of the ciliospinal center; diseases of the pleura and lungs, additional cervical ribs, injuries and operations in the neck can also serve as a cause. The processes taking place in the region of the trigeminal nerve and the trigeminal node may also be accompanied by Bernard-Horner syndrome and pain in the region of the I branch of the V nerve ( Reeder's syndrome). May also be observed congenital Bernard-Horner syndrome. It is usually associated with birth trauma (damage to the brachial plexus).

When the sympathetic fibers leading to the eyeball are stimulated, the pupil and palpebral fissure expand. Possible exophthalmos - reverse Horner's syndrome, or Pourfure du Petit syndrome.

A change in the size of the pupil and pupillary reactions is observed in many physiological (emotional reactions, sleep, breathing, physical effort) and pathological (poisoning, thyrotoxicosis, diabetes, encephalitis, Adie's syndrome, Argyle Robertson's syndrome, etc.) conditions. Very narrow (pinpoint) pupils may be the result of an organic lesion of the brain stem (trauma, ischemia, etc.). Possible reasons miosis in coma - poisoning with drugs, cholinomimetic agents, cholinesterase inhibitors, in particular organophosphorus compounds, mushrooms, nicotine, as well as caffeine, chloral hydrate. Cause mydriasis there may be damage to the midbrain or oculomotor nerve trunk, severe hypoxia, poisoning with anticholinergics (atropine, etc.), antihistamines, barbiturates, carbon monoxide (the skin turns pink), cocaine, cyanides, ethyl alcohol, adrenomimetic drugs, phenothiazide derivatives ( antipsychotics), tricyclic antidepressants, and brain death. Spontaneous periodic paroxysmal rhythmic constriction and dilation of both pupils may also be observed, lasting for several seconds ( hippus with meningitis, multiple sclerosis, neurosyphilis, etc.), which may be associated with a change in the function of the roof of the midbrain; alternately arising expansion of one or the other pupil ( jumping pupils with neurosyphilis, epilepsy, neurosis, etc.); Pupils dilate on deep inspiration and contract on exhalation Somagi symptom with pronounced vegetative lability).

Bladder innervation. The act of urination is carried out by the coordinated activity of the muscles that receive both somatic innervation (external urethral sphincter) and autonomic. In addition to these muscles, the muscles of the anterior abdominal wall, pelvic floor, and diaphragm also take part in the act of voluntary urination. The mechanism of regulation of urination includes a segmental apparatus of the spinal cord, which is under the control of the cortical centers: together they implement an arbitrary component of regulation (Fig. 38, Innervation of the bladder (according to P. Duus)).

Afferent parasympathetic part represented by cells of the intervertebral nodes S 1 -S 2. The dendrites of pseudounipolar cells end in the mechanoreceptors of the bladder wall, and the axons as part of the posterior roots go to the lateral horns of the sacral segments of the spinal cord S 2 -S 4 .

Efferent parasympathetic part begins in the lateral horns of the sacral segments, from where the preganglionic fibers (through the anterior roots, spinal nerves, sacral plexus and pelvic splanchnic nerves) approach the parasympathetic nodes near the bladder or in its wall. Postganglionic fibers innervate the muscle that ejects urine (detrusor) and the internal sphincter of the bladder. Parasympathetic stimulation causes contraction of the detrusor and relaxation of the internal sphincter. Paralysis of parasympathetic fibers causes bladder atony.

afferent sympathetic part It is represented by pseudounipolar cells of the intervertebral nodes L 1 -L 2, the dendrites of which end with receptors lying in the wall of the bladder, and the axons go as part of the posterior roots and end in the lateral horns of the Th 12 -L 2 segments of the spinal cord.

efferent sympathetic part begins in the lateral horns of Th 12–L 2 segments. Preganglionic fibers (as part of the anterior roots, spinal nerves, white connecting branches) enter the paravertebral sympathetic trunk and without interruption pass to the prevertebral inferior mesenteric node. The postganglionic branches of the latter, as part of the hypogastric nerves, approach the internal sphincter of the urethra. They provide contraction of the internal sphincter and relaxation of the muscle that expels urine. Damage to sympathetic fibers does not have a pronounced effect on bladder function. The role of sympathetic innervation is mainly limited to the regulation of the lumen of the vessels of the bladder and the innervation of the muscle of the cystic triangle, which prevents seminal fluid from entering the bladder at the time of ejaculation.

The external sphincter (unlike the internal one) is a striated muscle and is under voluntary control. Afferent impulses from the bladder come not only to the lateral horns. Part of the fibers ascends as part of the posterior and lateral cords to the center of the trusor, located in the reticular formation of the bridge near the blue spot ( locus ceruleus). There, the fibers switch to the second neuron, which in the ventrolateral nuclei of the thalamus ends on the third neuron, the axon of which reaches the sensory region of urination ( gyrusfornicatus). Associative fibers connect this area with the motor area of ​​urination - the paracentral lobule. Efferent fibers go as part of the pyramidal pathway and end on the motor nuclei of the anterior horns of the S 2 -S 4 segments of the spinal cord. Peripheral neuron as part of the sacral plexus, branches of the pudendal nerve approaches the external sphincter of the urethra.

If the sensitive part of the sacral reflex arc is damaged, the urge to urinate is not felt, the reflex to empty the bladder is lost. Overdistension of the bladder develops, or paradoxical urinary incontinence. This condition occurs when the roots are damaged (with diabetes mellitus or sciatica) or the posterior columns (for example, with spinal tabes). urinary disorder by type true urinary incontinence occurs when the lateral columns (S 2 -S 4), afferent and efferent fibers are damaged (myelitis, tumor, vascular pathology, etc. can cause such a disorder). With a bilateral violation of the connections of the cortical center of the bladder with the spinal centers, a disorder of the function of urination of the central type develops: urinary retention, subsequently changing occasional incontinence or, in milder cases, imperative urges urination (detrusor hyperreflexia).

Autonomic innervation of the rectum. The regulation of the act of defecation is carried out in the same way as the act of urination: the internal sphincter of the rectum receives a double vegetative innervation, the external - somatic. All nerve centers and impulse transmission pathways are similar to those used to regulate urination. The difference in emptying the rectum is the absence of a special displacer muscle, the role of which is performed by the abdominal press. Parasympathetic stimulation causes rectal peristalsis and relaxation of the internal sphincter muscle. Sympathetic stimulation inhibits peristalsis (Fig. 39, Innervation of the rectum (according to P. Duus)).

Transverse lesion of the spinal cord above the level of the lumbosacral center causes stool retention. A break in the afferent pathways disrupts the flow of information about the degree of filling of the rectum; interruption of outgoing motor impulses paralyzes the abdominal press. The contraction of the sphincter in this case is often insufficient due to the reflex arising spastic paresis. A lesion that involves the sacral spinal cord (S2–S4) results in loss of the anal reflex, which is accompanied by fecal incontinence and, if the fecal matter is thin or soft, stool leakage.

Vegetative innervation of the genital organs. Efferent parasympathetic fibers start from the lateral horns of the S 2 -S 4 segments of the spinal cord (erection center), repeat the ways of regulating urination (the second neuron is located in the prostatic plexus). pelvic splanchnic nerves ( nn. splanchnicipelvini) cause vasodilatation of the cavernous bodies of the penis, pudendal nerves ( nn. pudendi) innervate the sphincter muscle of the urethra, as well as ischiocavernosus ( mm. ishiocavernosi) and bulbospongius muscles ( mm. bulbospongiosi) (Fig. 40, Innervation of the male genital organs (according to P. Duus)).

Efferent sympathetic fibers begin in the lateral horns L 1 -L 2 (ejaculation center) of the segments of the spinal cord and through the anterior roots, the nodes of the sympathetic trunk, interrupted in the hypogastric plexus, reach the seminal ducts, seminal vesicles and the prostate gland along the paravascular branches of the hypogastric plexus.

The reproductive centers are partly under neurogenic influence, realized through the reticulospinal fibers, partly under the humoral influence from the higher hypothalamic centers.

According to Krucke (1948), dorsal longitudinal bundle ( ), or the Schutz bundle, has a continuation in the form of an unmyelinated parapendymal bundle ( fasciculus parependimalis), descending on both sides of the central canal to the sacral spinal cord. It is believed that this path connects the diencephalic genital centers located in the region of the gray tubercle with the sexual center of the lumbosacral localization.

Bilateral damage to the sacral parasympathetic center leads to impotence. Bilateral damage to the lumbar sympathetic center is manifested by a violation of ejaculation (retrograde ejaculation), testicular atrophy is observed. With a transverse injury of the spinal cord at the level of the thoracic region, impotence occurs, which can be combined with reflex priapism and involuntary ejaculation. Focal lesions of the hypothalamus lead to a decrease in sexual desire, weakening of erection, delayed ejaculation. The pathology of the hippocampus and limbic lobe is manifested by a weakening of all phases of the sexual cycle or complete impotence. During right hemispheric processes, sexual stimuli fade, unconditioned reflex reactions weaken, the emotional sexual attitude is lost, and libido is weakened. With the left hemispheric processes, the conditioned reflex component of libido and the erectile phase are weakened.

Violations of sexual function and its components can be induced by a wide range of diseases, but in most cases (up to 90%) this is due to psychological causes.

Combined suprasegmental and segmental disorders. Each higher vegetative link is included in the regulation in the event that the adaptive capabilities of a lower level have been exhausted. Therefore, some syndromes of autonomic disorders have a similar clinical picture in segmental and suprasegmental disorders, and it is impossible to determine the level of damage without using special examination methods.

Questions to control

1. What are the similarities and differences in the structure of the autonomic and somatic nervous systems?

2. What structures belong to the centers of the sympathetic division of the autonomic nervous system?

3. What is the peripheral part of the sympathetic division of the autonomic nervous system?

4. What formations are represented by the centers of the parasympathetic division of the autonomic nervous system?

5. What cranial nerves belong to the parasympathetic division of the autonomic nervous system?

6. What structures of the eye are innervated by the parasympathetic division of the autonomic nervous system, and which structures are sympathetic?

Chapter 11

MEMBERS OF THE BRAIN AND SPINAL
LIQUID

Includes sympathetic and parasympathetic.

The sympathetic system has one focus in the spinal cord. Its beginning is the lateral horns of the spinal cord from the 1st-2nd thoracic to the 3rd-4th lumbar segments. The neurites of these neurons exit the spinal cord along the anterior roots and reach the sympathetic nodes, being prenodular fibers that make up the white connecting branches that connect the spinal cord with the nodes. The neurites of the neuron located in them emerge from the nodes. These neurites are post-nodular fibers that make up the gray connecting branches that connect the nodes with all efferent nerves.

The parasympathetic system includes: 1) focus in, from which the parasympathetic fibers of the oculomotor nerve emanate; 2) the focus in, from which the parasympathetic fibers of the facial (drum string), glossopharyngeal, vagus and hypoglossal nerves emanate, and 3) the focus in the sacral spinal cord.

The sense organs, the nervous system, the striated muscles, the smooth muscles that dilate the pupil, the sweat glands, most of the blood vessels, the ureters, and the spleen are innervated only by sympathetic fibers. The ciliary muscles of the eye and the muscles that narrow the pupil are innervated only by parasympathetic fibers. Parasympathetic nerves innervate only certain organs. The second feature of parasympathetic innervation is the location of parasympathetic nodes on organs or inside organs, such as in the heart. The third feature is the selective attitude towards hormones and poisons and the difference in excitatory mediators.

Autonomic neurons, fibers and endings in which norepinephrine is formed and acts are called adrenergic, and those in which acetylcholine is formed and acts - cholinergic.

The main synthesis of norepinephrine occurs in the body of the adrenergic neuron, from which its vesicles pass into the axon endings. In vertebrates, norepinephrine is also synthesized at the axon endings, where norepinephrine, which is formed in the chromaffin, also accumulates.

The functions of the sympathetic nervous system are more similar to the action of norepinephrine than adrenaline.

The main site for the synthesis of acetylcholine is the body of the cholinergic neuron, from where it spreads to the nerve endings. This synthesis occurs with the participation of the enzyme choline acetylase.

More norepinephrine accumulates in the endings of adrenergic neurons than in the endings of cholinergic neurons, since acetylcholine is destroyed by a very active cholinesterase faster than norepinephrine by monoamine oxidase, o-methyltransferase, etc.

There are two types of cholinesterase: 1) true, or acetylcholinesterase (AXE), which catalyzes the hydrolysis of acetylcholine, and 2) false cholinesterase (ChE), which breaks down, in addition to acetylcholine, other choline esters. AChE is located in the synapses of the nervous system and myoneural apparatus and regulates the conduction of nerve impulses in them, destroying excess acetylcholine. ChE is present in the same place as AChE, as well as in the intestinal mucosa and other tissues and protects against the destruction of AChE. An excess of acetylcholine inhibits the activity of AChE without affecting the activity of ChE.

When the sympathetic nerves are stimulated, the organ is characterized by a slow reaction after the onset of their irritation, i.e., a long latent period and a long aftereffect, which depends on the relative stability of norepinephrine. The action of the parasympathetic nerves begins immediately after irritation, after a short latent period, and may stop even during irritation, for example, when the vagus nerves of the heart are stimulated. This short duration and low persistence of the effect of irritation of the parasympathetic nerves is explained by the fact that the acetylcholine released in their endings is rapidly destroyed.

There is an interaction between the sympathetic and parasympathetic nerves, which is expressed in the fact that separate stimulation of these nerves causes opposite effects on the part of some organs, and the simultaneous excitation of both nerves often leads to the fact that the sympathetic nerves enhance the function of the parasympathetic ones.