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Under what conditions is the parasympathetic nervous system activated? What is special about the sympathetic system of the heart?

The sympathetic department is part of the autonomic nervous tissue, which, together with the parasympathetic, ensures the functioning of internal organs and chemical reactions responsible for the life of cells. But you should know that there is a metasympathetic nervous system, part of the autonomic structure, located on the walls of organs and capable of contracting, contacting directly with the sympathetic and parasympathetic, making adjustments to their activity.

The human internal environment is directly influenced by the sympathetic and parasympathetic nervous system.

The sympathetic division is localized in the central nervous system. Spinal nerve tissue operates under the control of nerve cells located in the brain.

All elements of the sympathetic trunk, located on two sides of the spine, are directly connected to the corresponding organs through nerve plexuses, and each has its own plexus. At the bottom of the spine, both trunks in a person are united together.

The sympathetic trunk is usually divided into sections: lumbar, sacral, cervical, thoracic.

The sympathetic nervous system is concentrated near the carotid arteries of the cervical region, in the thoracic - the cardiac and pulmonary plexus, in the abdominal cavity the solar, mesenteric, aortic, hypogastric.

These plexuses are divided into smaller ones, and from them impulses move to the internal organs.

The transition of excitation from the sympathetic nerve to the corresponding organ occurs under the influence of chemical elements - sympathins, secreted by nerve cells.

They supply the same tissues with nerves, ensuring their relationship with the central system, often having the opposite effect on these organs.

The influence that the sympathetic and parasympathetic nervous systems have can be seen from the table below:

Together they are responsible for cardiovascular organisms, digestive organs, respiratory structures, secretions, the work of smooth muscle of hollow organs, and control metabolic processes, growth, and reproduction.

If one begins to predominate over the other, symptoms of increased excitability appear: sympathicotonia (the sympathetic part predominates), vagotonia (the parasympathetic part predominates).

Sympathicotonia manifests itself in the following symptoms: fever, tachycardia, numbness and tingling in the extremities, increased appetite without the appearance of weight loss, indifference to life, restless dreams, fear of death for no reason, irritability, absent-mindedness, decreased salivation, as well as sweating, migraine appears.

In a person, when the increased work of the parasympathetic department of the autonomic structure is activated, increased sweating appears, the skin feels cold and damp to the touch, a decrease in heart rate occurs, it becomes less than the prescribed 60 beats in 1 minute, fainting, salivation and respiratory activity increase. People become indecisive, slow, prone to depression, and intolerant.

The parasympathetic nervous system reduces the activity of the heart and tends to dilate blood vessels.

Functions

The sympathetic nervous system is a unique design of an element of the autonomic system, which, in the event of a sudden need, is capable of increasing the body’s ability to perform work functions by collecting possible resources.

As a result, the design carries out the work of organs such as the heart, reduces blood vessels, increases muscle capacity, frequency, strength of the heart rhythm, performance, and inhibits the secretory and absorption capacity of the gastrointestinal tract.

The SNS supports functions such as the normal functioning of the internal environment in an active position, coming into action during physical effort, stressful situations, illnesses, blood loss and regulates metabolism, for example, an increase in sugar, blood clotting, and others.

It is most fully activated during psychological shocks, through the production of adrenaline (enhancing the action of nerve cells) in the adrenal glands, which allows a person to react faster and more effectively to suddenly arising factors from the outside world.

Adrenaline can also be produced when the load increases, which also helps a person cope with it better.

After coping with the situation, a person feels tired, he needs to rest, this is due to the sympathetic system, which has most fully used up the body’s capabilities, due to the increase in body functions in a sudden situation.

The parasympathetic nervous system performs the functions of self-regulation, protection of the body, and is responsible for human bowel movements.

Self-regulation of the body has a restorative effect, working in a calm state.

The parasympathetic part of the activity of the autonomic nervous system is manifested by a decrease in the strength and frequency of the heart rhythm, stimulation of the gastrointestinal tract with a decrease in glucose in the blood, etc.

By carrying out protective reflexes, it rids the human body of foreign elements (sneezing, vomiting, etc.).

The table below shows how the sympathetic and parasympathetic nervous systems act on the same elements of the body.

Treatment

If you notice signs of increased sensitivity, you should consult a doctor, as this can cause ulcerative, hypertensive diseases, or neurasthenia.

Only a doctor can prescribe correct and effective therapy! There is no need to experiment with the body, since the consequences if the nerves are in a state of excitability are quite a dangerous manifestation not only for you, but also for people close to you.

When prescribing treatment, it is recommended, if possible, to eliminate factors that excite the sympathetic nervous system, be it physical or emotional stress. Without this, no treatment will most likely help; after taking a course of medication, you will get sick again.

You need a cozy home environment, sympathy and help from loved ones, fresh air, good emotions.

First of all, you need to make sure that nothing raises your nerves.

The medications used in treatment primarily belong to the group of potent drugs, so they should be used carefully only as directed or after consultation with a doctor.

Prescribed medications usually include: tranquilizers (Phenazepam, Relanium and others), antipsychotics (Frenolone, Sonapax), sleeping pills, antidepressants, nootropic drugs and, if necessary, cardiac drugs (Korglikon, Digitoxin) ), vascular, sedative, vegetative drugs, a course of vitamins.

It is good to use physiotherapy, including physical therapy and massage, you can do breathing exercises and swimming. They are good at helping to relax the body.

In any case, ignoring the treatment of this disease is categorically not recommended; it is necessary to consult a doctor in a timely manner and carry out the prescribed course of therapy.

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In this article we will look at 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 is known, consists of nerve cells and processes, thanks to which the regulation and control of internal organs occurs. The autonomic system is divided into peripheral and central. If the central one is responsible for the work of internal organs, without any division into opposite parts, then the peripheral one is divided into sympathetic and parasympathetic.

The structures of these departments are present in every internal organ of a person and, despite their opposing functions, they work simultaneously. However, at different times, one or another department turns out to be 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 (constancy of the internal environment). If you rest, the autonomic system engages the parasympathetic system and the number of heartbeats decreases. If you start running and experience heavy physical activity, the sympathetic department turns on, thereby speeding up the heart and blood circulation in the body.

And this is only a small slice of the activity that the visceral nervous system carries out. It also regulates hair growth, contraction and dilation of pupils, the functioning 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 is why at first glance it seems difficult to treat.

Sympathetic 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 everything is different. Thus, the sympathetic department, which in turn belongs to the peripheral, and the peripheral belongs to the autonomic 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 division is also divided into peripheral and central. If the central one is an integral part of the work of the spinal cord, then the peripheral part of the sympathetic has many branches and nerve nodes that connect. The spinal center is located in the lateral horns of the lumbar and thoracic segment. The fibers, in turn, extend from the spinal cord (1st and 2nd thoracic vertebrae) and 2,3,4 lumbar vertebrae. This is a very brief description of where the sympathetic system is located. Most often, the SNS is activated when a person finds himself in a stressful situation.

Peripheral department

It is not so difficult to imagine the peripheral part. 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 tailbone, where they converge into a single unit. Thanks to the internodal branches, the two trunks are connected. As a result, the peripheral section of the sympathetic system passes through the cervical, thoracic and lumbar regions, which we will consider in more detail.

  • Cervical region. As you know, it starts from the base of the skull and ends at the transition to the thoracic (cervical 1st ribs). There are three sympathetic nodes here, 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 cervical vertebrae, 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 size, sometimes even merging with the second thoracic node.
  • Thoracic department. It consists of up to 12 nodes and has many connecting branches. They reach out 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 has 4. It also has many connecting branches. The pelvic region connects the two trunks and other branches together.

Parasympathetic Division

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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, blood vessels relax, pupils constrict, heart rate slows down, and sphincters relax. The center of this department is located in the spinal cord and brain. Thanks to efferent fibers, the hair muscles relax, sweat secretion is delayed, and blood vessels dilate. 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 breathing;
  • Dilates blood vessels in the brain and genital organs;
  • Constricts the pupils;
  • Restores optimal glucose levels;
  • Activates the digestive secretion glands;
  • Tones the smooth muscles of internal organs;
  • Thanks to this department, cleansing 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 parts 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 itself and actively secretes sweat; when it urgently needs to warm up, sweating is accordingly blocked. If the autonomic 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 dedicated to vegetative-vascular dystonia, you should know that due to psychological disorders, the autonomic system experiences disruptions. For example, when a person has suffered 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 is that the patient should understand that this is only a psychological disorder, and not physiological deviations, which are only a consequence. This is why medication treatment is not an effective remedy; they only help relieve symptoms. For a full recovery, you need the help of a psychotherapist.

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

As a result, if you suffer from a disorder of the autonomic nervous system, the first thing you should do is undergo 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 quickly relieve you of your illness.

The parasympathetic nervous system constricts the bronchi, slowing and weakening heart contractions; constriction of heart vessels; replenishment of energy resources (synthesis of glycogen in the liver and strengthening of digestion processes); strengthening the processes of urine formation in the kidneys and ensuring the act of urination (contraction of the muscles of the bladder and relaxation of its sphincter), etc. The parasympathetic nervous system mainly has triggering effects: constriction of the pupil, bronchi, activation of the digestive glands, etc.

The activity of the parasympathetic department of the autonomic nervous system is aimed at the ongoing regulation of the functional state, at maintaining the constancy of the internal environment - homeostasis. The parasympathetic department ensures the restoration of various physiological indicators, sharply changed after intense muscular work, and the replenishment of expended energy resources. The mediator of the parasympathetic system, acetylcholine, reduces the sensitivity of adrenergic receptors to the action of adrenaline and noradrenaline, and has a certain anti-stress effect.

Rice. 6. Autonomic reflexes

Effect of body position on heart rate

(bpm). (Po. Mogendovich M.R., 1972)

3.6.4. Autonomic reflexes

Through the autonomic sympathetic and parasympathetic pathways, the central nervous system carries out some autonomic reflexes, starting from various receptors of the external and internal environment: viscero-visceral (from internal organs to internal organs - for example, the respiratory-cardiac reflex); dermo-visceral (from the skin - changes in the activity of internal organs when irritating active points of the skin, for example, acupuncture, acupressure); from the receptors of the eyeball - Aschner's ocular-heart reflex (decrease in heartbeat when pressing on the eyeballs - parasympathetic effect); motor-visceral - for example, orthostatic test (increased heart rate when moving from a lying position to a standing position - sympathetic effect), etc. (Fig. 6). They are used to assess the functional state of the body and especially the state of the autonomic nervous system (assessing the influence of its sympathetic or parasympathetic department).

11. CONCEPT OF THE NERVOMUSCULAR (MOTOR) SYSTEM. MOTOR UNITS (MU) AND THEIR CLASSIFICATION. FUNCTIONAL FEATURES OF DIFFERENT TYPES OF DE AND THEIR CLASSIFICATION. FUNCTIONAL FEATURES OF DIFFERENT TYPES OF MU (ACTIVATION THRESHOLD, SPEED AND FORCE OF CONTRACTION, FATIGUE, ETC.) The meaning of the type of MU for various types of muscle activity.

12. Muscle composition. Functional capabilities of different types of muscle fibers (slow and fast). Their role is in the manifestation of muscle strength, speed and endurance. One of the most important characteristics of skeletal muscles that influence the force of contraction is the composition (composition) of muscle fibers. There are 3 types of muscle fibers - slow non-fatiguing (type I), fast non-fatiguing or intermediate (type 11-a) and fast fatigable (type 11-b).

Slow fibers (type 1), also referred to as SO - Slow Oxydative (English - slow oxidative) - these are hardy (fatigue-free) and easily excitable fibers, with a rich blood supply, a large number of mitochondria, myoglobin reserves and

using oxidative energy generation processes (aerobic). On average, a person has 50% of them. They easily get into work at the slightest muscle tension, are very durable, but do not have sufficient strength. Most often they are used when maintaining non-load static work, for example, when maintaining a pose.

Fast fatigue fibers (type 11-b) or FG - Fast Glycolytic (fast glycolytic) use anaerobic energy production processes (glycolysis). They are less excitable, turn on under heavy loads and provide fast and powerful muscle contractions. But these fibers quickly tire. There are approximately 30% of them. Intermediate type fibers (I-a) are fast, tireless, oxidative, about 20% of them. On average, different muscles are characterized by different ratios of slow non-fatiguing and fast fatigable fibers. Thus, in the triceps muscle of the shoulder, fast fibers predominate (67%) over slow fibers (33%), which provides the speed-strength capabilities of this muscle (Fig. 14), and the slower and more durable soleus muscle is characterized by the presence of 84% slow and only 16 % fast fibers (Saltan B., 1979).

However, the composition of muscle fibers in the same muscle has enormous individual differences, depending on the innate typological characteristics of a person. By the time a person is born, his muscles contain only slow fibers, but under the influence of nervous regulation, a genetically specified individual ratio of muscle fibers of different types is established during ontogenesis. As a person moves from adulthood to old age, the number of fast fibers in a person noticeably decreases and, accordingly, muscle strength decreases. For example, the largest number of fast fibers in the outer head of the 4th head of the thigh muscle of a man (about 59-63%) is observed at the age of 20-40 years, and at the age of 60-65 years their number is almost 1/3 less (45%) .

Rice. 14. Composition of muscle fibers in different muscles

Slow ones - in black; fast - gray

The number of certain muscle fibers does not change during training. Only an increase in the thickness (hypertrophy) of individual fibers is possible, as well as some change in the properties of the intermediate fibers. When the training process is aimed at developing strength, the volume of fast fibers increases, which ensures an increase in the strength of the trained muscles.

The nature of nerve impulses changes the force of muscle contraction in three ways:

The mechanical conditions of the muscle - the point of application of its force and the point of application of resistance (lifted load) - are essential. For example, when bending at the elbow, the weight of the load being lifted can be about 40 kg or more, while the strength of the flexor muscles reaches 250 kg, and the traction of the tendons reaches 500 kg.

There is a certain relationship between the force and speed of muscle contraction, which has the form of a hyperbola (strength - speed relationship, according to A. Hill). The higher the force developed by the muscle, the lower the speed of its contraction, and vice versa, as the speed of contraction increases, the magnitude of the force decreases. The muscle working without load develops the greatest speed. The speed of muscle contraction depends on the speed of movement of the transverse bridges, i.e., on the frequency of rowing movements per unit time. In fast MUs, this frequency is higher than in slow MUs, and, accordingly, more ATP energy is consumed. During contraction of muscle fibers, approximately 5 to 50 cycles of attachment and detachment of cross bridges occur in 1 s. In this case, no fluctuations in force are felt in the whole muscle, since the motor units work asynchronously. Only with fatigue does synchronous operation of the motor unit occur, and tremors appear in the muscles (fatigue tremor).

13. SINGLE AND TETANIC CONTRACTION OF MUSCLE FIBER. ELECTROMYOGRAM. With a single suprathreshold stimulation of the motor nerve or the muscle itself, excitation of the muscle fiber is accompanied by

single contraction. This form of mechanical response consists of 3 phases: a latent or latent period, a contraction phase and a relaxation phase. The shortest phase is the latent period, when electromechanical transmission occurs in the muscle. The relaxation phase is usually 1.5-2 times longer than the contraction phase, and when tired, it drags on for a considerable time.

If the intervals between nerve impulses are shorter than the duration of a single contraction, then the phenomenon of superposition occurs - the superposition of the mechanical effects of muscle fibers on each other and a complex form of contraction is observed - tetanus. There are 2 forms of tetanus - jagged tetanus, which occurs with less frequent stimulation, when each subsequent nerve impulse enters the relaxation phase of individual single contractions, and continuous or smooth tetanus, which occurs with more frequent stimulation, when each subsequent impulse enters the contraction phase ( Fig. 11). Thus, (within certain limits) there is a certain relationship between the frequency of excitation impulses and the amplitude of contraction of MU fibers: at a low frequency (for example, 5-8 impulses per 1 s)

Rice. P. Single reduction, serrated and complete tetanus soleus muscle person (according to: Zimkin N.V. et al., 1984). The upper curve is muscle contraction, the lower curve is the mark muscle irritation, frequency is indicated on the right irritationI

single contractions occur, with an increase in frequency (15-20 impulses per 1 s) - jagged tetanus, with a further increase in frequency (25-60 impulses per 1 s) - smooth tetanus. A single contraction is weaker and less tiring than a tetanic contraction. But tetanus provides several times more powerful, although short-term, contraction of muscle fiber.

The contraction of a whole muscle depends on the form of contraction of individual motor units and their coordination in time. When providing long-term, but not very intense work, individual motor units contract alternately (Fig. 12), maintaining the overall muscle tension at a given level (for example, when running long and ultra-long distances). In this case, individual motor units can develop both single and tetanic contractions, which depends on the frequency of nerve impulses. Fatigue in this case develops slowly, since, working in turns, the motor units have time to recover in the intervals between activations. However, for a powerful short-term effort (for example, lifting a barbell), synchronization of the activity of individual motor units is required, i.e., simultaneous excitation of almost all motor units. This, in turn, requires simultaneous activation

Rice. 12. Different modes of operation of motor units(DE)

corresponding nerve centers and is achieved as a result of long-term training. In this case, a powerful and very tiresome tetanic contraction is carried out.

The amplitude of contraction of a single fiber does not depend on the strength of suprathreshold stimulation (the “All or Nothing” law). In contrast, as the strength of suprathreshold stimulation increases, the contraction of the whole muscle gradually increases to maximum amplitude.

The work of a muscle with a small load is accompanied by a rare frequency of nerve impulses and the involvement of a small number of motor units. Under these conditions, by placing discharge electrodes on the skin above the muscle and using amplification equipment, it is possible to register single action potentials of individual units on the screen of an oscilloscope or using ink on paper. In the case of significant voltages, the action potentials of many units are algebraically summed up and a complex integrated system arises. a curve recording the electrical activity of a whole muscle - an electromyogram (EMG).

The shape of the EMG reflects the nature of the muscle work: with static efforts it has a continuous appearance, and with dynamic work it has the appearance of individual bursts of impulses, confined mainly to the initial moment of muscle contraction and separated by periods of “electrical silence”. The rhythmicity of the appearance of such bursts is especially well observed in athletes during cyclic work (Fig. 13). In young children and people unadapted to such work, clear periods of rest are not observed, which reflects insufficient relaxation of the muscle fibers of the working muscle.

The greater the external load and the force of muscle contraction, the higher the amplitude of its EMG. This is due to an increase in the frequency of nerve impulses, the involvement of a larger number of motor units in the muscle and synchronization

Rice. 13. Electromyogram of antagonist muscles during cyclic work

their activities. Modern multichannel equipment allows simultaneous recording of EMG of many muscles on different channels. When an athlete performs complex movements, it is possible to see on the obtained EMG curves not only the nature of the activity of individual muscles, but also to evaluate the moments and order of their inclusion or switching off in various phases of motor acts. EMG recordings obtained in natural conditions of motor activity can be transmitted to recording equipment by telephone or radio telemetry. Analysis of the frequency, amplitude and shape of EMG (for example, using special computer programs) allows one to obtain important information about the characteristics of the technique of the sports exercise being performed and the degree of its mastery by the examined athlete.

As fatigue develops with the same amount of muscle effort, the EMG amplitude increases. This is due to the fact that the decrease in the contractility of tired motor units is compensated by the nerve centers by involving additional motor units in the work, i.e., by increasing the number of active muscle fibers. In addition, the synchronization of motor unit activity increases, which also increases the amplitude of the total EMG.

14. The mechanism of contraction and relaxation of muscle fiber. Sliding theory. The role of the sarcoplasmic reticulum and calcium ions in contraction. With an arbitrary internal command, human muscle contraction begins in approximately 0.05 s (50 ms). During this time, the motor command is transmitted from the cerebral cortex to the motor neurons of the spinal cord and along the motor fibers to the muscle. Having approached the muscle, the excitation process must overcome the neuromuscular synapse with the help of a mediator, which takes approximately 0.5 ms. The mediator here is acetylcholine, which is contained in synaptic vesicles in the presynaptic part of the synapse. The nerve impulse causes the movement of synaptic vesicles to the presynaptic membrane, their emptying and release of the transmitter into the synaptic cleft. The effect of acetylcholine on the postsynaptic membrane is extremely short-lived, after which it is destroyed by acetylcholinesterase into acetic acid and choline. As acetylcholine reserves are consumed, they are constantly replenished by its synthesis in the presynaptic membrane. However, with very frequent and prolonged impulses of the motor neuron, the consumption of acetylcholine exceeds its replenishment, and the sensitivity of the postsynaptic membrane to its action decreases, as a result of which the conduction of excitation through the neuromuscular synapse is disrupted. These processes underlie the peripheral mechanisms of fatigue during prolonged and heavy muscular work.

The transmitter released into the synaptic cleft attaches to the receptors of the postsynaptic membrane and causes depolarization phenomena in it. A small subthreshold stimulation causes only local excitation of small amplitude - the end plate potential (EPP).

When the frequency of nerve impulses is sufficient, the EPP reaches a threshold value and a muscle action potential develops on the muscle membrane. It (at a speed of 5) spreads along the surface of the muscle fiber and extends transversely

tubes inside the fiber. By increasing the permeability of cell membranes, the action potential causes the release of Ca ions from the cisterns and tubules of the sarcoplasmic reticulum, which penetrate the myofibrils to the binding centers of these ions on actin molecules.

Under the influence of Sadlin, tropomyosin molecules rotate along the axis and hide in the grooves between the spherical actin molecules, opening the sites of attachment of myosin heads to actin. Thus, so-called cross bridges are formed between actin and myosin. In this case, the myosin heads perform rowing movements, ensuring the sliding of actin filaments along the myosin filaments from both ends of the sarcomere to its center, i.e., a mechanical reaction of the muscle fiber (Fig. 10).

The energy of the rowing motion of one bridge produces movement of 1% of the length of the actin filament. For further sliding of contractile proteins relative to each other, bridges between actin and myosin must disintegrate and form again at the next Ca binding site. This process occurs as a result of the activation of myosin molecules at this moment. Myosin acquires the properties of the enzyme ATPase, which causes the breakdown of ATP. The energy released during the breakdown of ATP leads to destruction

Rice. 10. Scheme of electromechanical connection in muscle fiber

On A: resting state, on B - excitation and contraction

yes - action potential, mm - muscle fiber membrane,

p _ transverse tubes, t - longitudinal tubes and tanks with ions

Sa, a - thin filaments of actin, m - thick filaments of myosin

with thickenings (heads) at the ends. Z-membranes are limited

sarcomeres of myofibrils. Thick arrows - potential propagation

actions during fiber excitation and movement of ions in Caiz tanks

and longitudinal tubules into myofibrils, where they contribute to the formation

bridges between actin and myosin filaments and the sliding of these filaments

(fiber contraction) due to the rowing movements of the myosin heads.

existing bridges and the formation in the presence of San bridges at the next section of the actin filament. As a result of repeating such processes of repeated formation and disintegration of bridges, the length of individual sarcomeres and the entire muscle fiber as a whole is reduced. The maximum concentration of calcium in the myofibril is achieved within 3 ms after the onset of the action potential in the transverse tubules, and the maximum tension of the muscle fiber is achieved after 20 ms.

The entire process from the appearance of a muscle action potential to the contraction of a muscle fiber is called electromechanical coupling (or electromechanical coupling). As a result of muscle fiber contraction, actin and myosin are more evenly distributed within the sarcomere, and the cross-striations of the muscle visible under a microscope disappear.

Relaxation of the muscle fiber is associated with the work of a special mechanism - the “calcium pump”, which pumps Caiz ions of myofibrils back into the tubes of the sarcoplasmic reticulum. This also uses ATP energy.

15. The mechanism for regulating the force of muscle contraction (the number of active motor units, the frequency of motor neuron impulses, the synchronization of contraction of muscle fibers of different motor units over time). The nature of nerve impulses changes the force of muscle contraction in three ways:

1) an increase in the number of active MUs - this is a mechanism for the involvement or recruitment of MUs (first, slow and more excitable MUs are involved, then high-threshold fast MUs);

2) an increase in the frequency of nerve impulses, resulting in a transition from weak single contractions to strong tetanic contractions of muscle fibers;

3) an increase in the synchronization of motor units, while the force of contraction of the whole muscle increases due to the simultaneous traction of all active muscle fibers.

The complex structure of the human body provides for several sublevels of nervous regulation of each organ. Thus, the sympathetic nervous system is characterized by the mobilization of energy resources to perform a specific task. The autonomic department controls the work of structures in their functional rest, for example, at the time of sleep. Correct interaction and activity of the autonomic nervous system as a whole is the key to good health of people.

Nature has wisely distributed the functional responsibilities of the sympathetic and parasympathetic divisions of the autonomic nervous system - according to the location of their nuclei and fibers, as well as their purpose and responsibility. For example, the central neurons of the sympathetic segment are located exclusively in the lateral horns of the spinal cord. In the parasympathetic, they are localized in the trunk of the hemispheres.

Distant, effector neurons in the first case are always located on the periphery - present in the paravertebral ganglia. They form various plexuses, the most important of which is the solar one. It is responsible for the innervation of intra-abdominal organs. Whereas parasympathetic effector neurons are located directly in the organs they innervate. Therefore, responses to impulses sent to them from the brain occur faster.

Differences can also be observed in functional characteristics. Vigorous human activity requires activation of the heart, blood vessels, and lungs - the activity of sympathetic fibers increases. However, in this case, digestion processes are inhibited.

At rest, the parasympathetic system is responsible for the innervation of the intracavitary organs - digestion, homeostasis, and urination are restored. It’s not without reason that after a hearty lunch you want to lie down and sleep. The unity and indivisibility of the nervous system lies in the close cooperation of both departments.

Structural units

The main centers of the vegetative system are localized:

  • mesencephalic section - in the structures of the midbrain, from which they arise from the fiber of the oculomotor nerve;
  • bulbar segment - in the tissues of the medulla oblongata, which is further represented by both the facial and vagus nerves, the glossopharyngeal nerve;
  • thoracolumbar region - lumbar and thoracic ganglia in the spinal segments;
  • sacral segment - in the sacral region, the parasympathetic nervous system innervates the pelvic organs.

The sympathetic division removes nerve fibers from the brain to the border segment - the paravertebral ganglia in the spinal cord area. It is called the symptomatic trunk because it contains several nodes, each of which is interconnected with individual organs through nerve plexuses. The transmission of impulses from nerve fibers to innervated tissue occurs through synapses - with the help of special biochemical compounds, sympathins.

The parasympathetic department, in addition to the intracranial central nuclei, is represented by:

  • preganglionic neurons and fibers - lie as part of the cranial nerves;
  • postagglionic neurons and fibers - pass to innervated structures;
  • terminal nodes - located near intracavitary organs or directly in their tissues.

The peripheral nervous system, represented by two sections, is practically beyond conscious control and functions independently, maintaining the constancy of homeostasis.

The essence of interaction

In order for a person to adapt and adapt to any situation - external or internal threat, the sympathetic as well as the parasympathetic parts of the autonomic nervous system must interact closely. However, they have the exact opposite effect on the human body.

Parasympathetics are characterized by:

  • lower blood pressure;
  • reduce breathing rate;
  • expand the lumen of blood vessels;
  • constrict the pupils;
  • adjust the concentration of glucose in the bloodstream;
  • improve the digestive process;
  • tone smooth muscles.

Protective reflexes also include the introduction of parasympathetic activity - sneezing, coughing, retching. It is inherent for the sympathetic department of the autonomic nervous system to increase the parameters of the cardiovascular system - pulse rate and blood pressure numbers, and increase metabolism.

A person learns that the sympathetic department predominates by a feeling of heat, tachycardia, restless sleep and fear of death, and sweating. If more parasympathetic activity is present, the changes will be different - cold, clammy skin, bradycardia, fainting, excessive salivation and shortness of breath. With balanced functioning of both departments, the activity of the heart, lungs, kidneys, and intestines corresponds to the age norm and the person feels healthy.

Functions

Nature has determined that the sympathetic department takes an active part in many important processes in the human body - especially the motor state. It is primarily assigned the role of mobilizing internal resources to overcome various obstacles. For example, it activates the sphincter of the iris, the pupil dilates, and the flow of incoming information increases.

When the sympathetic nervous system is excited, the bronchi expand to increase the supply of oxygen to the tissues, more blood flows to the heart, while at the periphery the arteries and veins become narrow - a redistribution of nutrients. At the same time, the stored blood is released from the spleen, as well as the breakdown of glycogen - the mobilization of additional energy sources. The digestive and urinary structures will be subject to oppression - the absorption of nutrients in the intestines slows down, the bladder tissue relaxes. All efforts of the body are aimed at maintaining high muscle activity.

The parasympathetic effect on cardiac activity will be expressed in the restoration of rhythm and contractions, normalization of blood regulation - blood pressure corresponds to the parameters familiar to a person. The respiratory system will be subject to correction - the bronchi narrow, hyperventilation stops, and the concentration of glucose in the bloodstream decreases. At the same time, motility in the intestinal loops increases - products are absorbed faster, and hollow organs are freed from contents - defecation, urination. Additionally, parasympathetic activity increases saliva secretion but reduces sweating.

Disorders and pathologies

The structure of the autonomic system as a whole is a complex plexus of nerve fibers that act together to maintain stability within the body. Therefore, even minor damage to one of the centers will negatively affect the innervation of internal organs as a whole. For example, with a high tone of the sympathetic nervous system, a huge amount of adrenal hormones constantly enters the blood of people, which provokes surges in blood pressure, tachycardia, sweating, hyperexcitation, and rapid exhaustion of strength. While lethargy and drowsiness, increased appetite and hypotension will be signs of disruption in the autonomic department.

Clinical signs of diseases of the peripheral nervous system are directly related to the level at which the nerve fiber is damaged and the cause - inflammation, infection, or injury, tumor process. Characteristic symptoms of inflammation are tissue swelling, pain, increased temperature, and movement disorders in the part of the body that the segment innervates. The specialist must take into account the possibility of irradiation of signs - their distance from the primary focus of the disease. For example, changes in the oculomotor nerve can be expressed in drooping eyelids, increased tear production, and difficulty moving the eyeball.

If the sympathetic nervous system suffers in the pelvic area, which is typical for children, then enuresis and intestinal obstruction are formed. Or problems with the reproductive system in adults. In case of injuries, the clinical picture will be dominated by tissue damage, bleeding, and subsequently paresis and paralysis.

Principles of treatment

Suspicions of disorders of the sympathetic system or parasympathetic department must be confirmed by an examination by a neurologist, the results of laboratory and instrumental studies.

Only after assessing the general health of a person and identifying the causes of the disease, a specialist will select the optimal treatment regimen. If a tumor is diagnosed, it will be removed surgically or subjected to radiation or chemotherapy. To speed up rehabilitation after an injury, the doctor will prescribe physiotherapeutic procedures, drugs that can accelerate regeneration, as well as means to prevent secondary infection.

If the sympathetic nervous structure suffers from an excess of hormones, the endocrinologist will select medications to change their concentration in the bloodstream. Additionally, decoctions and infusions of medicinal herbs with a calming effect are prescribed - lemon balm, chamomile, as well as mint and valerian. According to individual indications, they resort to the help of antidepressants, anticonvulsants or antipsychotics. The names, doses and duration of treatment are the prerogative of the neurologist. Self-medication is absolutely unacceptable.

The sanatorium-resort treatment has proven itself to be excellent - mud therapy, hydrotherapy, hirudotherapy, radon baths. Complex effects from the inside - rest, proper nutrition, vitamins and from the outside - healing wraps with herbs, mud, baths with medicinal salt, bring all parts of the peripheral nervous system back to normal.

Prevention

The best treatment for any disease is, of course, prevention. To prevent functional failures in the innervation of a particular organ, experts recommend that people follow the basic principles of a healthy lifestyle:

  • give up bad habits - consumption of tobacco and alcohol products;
  • get a good night's sleep - at least 8–9 hours of sleep in a ventilated, darkened, quiet room;
  • adjust the diet - the predominance of vegetables, various fruits, herbs, cereals;
  • compliance with the water regime - taking at least 1.5–2 liters of purified water, juices, fruit drinks, compotes, so that toxins and waste are removed from the tissues;
  • daily activity - long walks, visiting the pool, gym, mastering yoga, Pilates.

A person who carefully monitors his health and visits a doctor for an annual medical examination will have calm nerves at any level. Therefore, they know about such problems as sweating, tachycardia, shortness of breath, high blood pressure only by hearsay, from their relatives.

Table of contents of the topic "Autonomic (autonomic) nervous system.":
1. Autonomic (autonomic) nervous system. Functions of the autonomic nervous system.
2. Autonomic nerves. Exit points of autonomic nerves.
3. Reflex arc of the autonomic nervous system.
4. Development of the autonomic nervous system.
5. Sympathetic nervous system. Central and peripheral divisions of the sympathetic nervous system.
6. Sympathetic trunk. Cervical and thoracic sections of the sympathetic trunk.
7. Lumbar and sacral (pelvic) sections of the sympathetic trunk.

9. Peripheral division of the parasympathetic nervous system.
10. Innervation of the eye. Innervation of the eyeball.
11. Innervation of the glands. Innervation of the lacrimal and salivary glands.
12. Innervation of the heart. Innervation of the heart muscle. Innervation of the myocardium.
13. Innervation of the lungs. Innervation of the bronchi.
14. Innervation of the gastrointestinal tract (intestine to the sigmoid colon). Innervation of the pancreas. Innervation of the liver.
15. Innervation of the sigmoid colon. Innervation of the rectum. Innervation of the bladder.
16. Innervation of blood vessels. Innervation of blood vessels.
17. Unity of the autonomic and central nervous systems. Zones Zakharyin - Geda.

Parasympathetic part historically develops as a suprasegmental department, and therefore its centers are located not only in the spinal cord, but also in the brain.

Parasympathetic centers

Central part of the parasympathetic division consists of the head, or cranial, section and the spinal, or sacral, section.

Some authors believe that parasympathetic centers are located in the spinal cord not only in the region of the sacral segments, but also in other parts of it, in particular in the lumbar-thoracic region between the anterior and posterior horn, in the so-called intermediary zone. The centers give rise to efferent fibers of the anterior roots, causing vasodilation, delayed sweating and inhibition of contraction of involuntary hair muscles in the area of ​​the trunk and limbs.

Cranial section in turn, consists of centers located in the midbrain (mesencephalic part), and in the rhomboid brain - in the pons and medulla oblongata (bulbar part).

1. Mesencephalic part presented nucleus accessorius n. oculomotorii and the median unpaired nucleus, due to which the muscles of the eye are innervated - m. sphincter pupillae and m. ciliaris.

2. Boulevard part represented by n ucleus saliva tonus superior n. facialis(more precisely, n. intermedius), nucleus salivatorius inferior n. glossopharyngei And nucleus dorsalis n. vagi(see corresponding nerves).