What does not apply to the nervous system. What is the nervous system? Nervous system activity, condition and protection

The nervous system (sustema nervosum) is a complex of anatomical structures that ensure the individual adaptation of the body to the external environment and the regulation of the activity of individual organs and tissues.

Only one like this can exist biological system, which is able to act accordingly external conditions in close connection with the capabilities of the organism itself. It is this single goal - the establishment of behavior and state of the organism that is adequate to the environment - that the functions of individual systems and organs at each moment in time are subordinated to. In this regard, the biological system acts as a single whole.

The nervous system acts as integrative system, linking into one whole sensitivity, motor activity and the work of other regulatory systems (endocrine and immune). The nervous system, together with the endocrine glands, is the main integrating and coordinating apparatus, which, on the one hand, ensures the integrity of the body, and on the other, its behavior adequate to the external environment.

The nervous system includes the brain and spinal cord, as well as nerves, ganglia, plexuses, etc. All these formations are predominantly built from nervous tissue, which: - is capable of being excited under the influence of irritation from the environment internal or external to the body and - conducts excitation in the form of a nerve impulse to various nerve centers for analysis, and then - transmits the “order” generated in the center to the executive organs to perform the body's response in the form of movement (movement in space) or change in function internal organs. Excitement -- active physiological process, with which some types of cells respond to external influences. The ability of cells to generate excitation is called excitability. Excitable cells include nerve, muscle and glandular cells. All other cells have only irritability, i.e. the ability to change their metabolic processes when exposed to any factors (stimulants). In excitable tissues, especially nervous tissues, excitation can spread along the nerve fiber and is a carrier of information about the properties of the stimulus. In muscle and glandular cells, excitation is a factor that triggers their specific activity - contraction, secretion. Inhibition in the central nervous system is an active physiological process, the result of which is a delay in the excitation of the nerve cell. Together with excitation, inhibition forms the basis of the integrative activity of the nervous system and ensures the coordination of all functions of the body.

The human nervous system is classified:

according to the conditions of formation and type of management as:

• - Lower nervous activity
• - Higher nervous activity

by the method of transmitting information as:

• - Neuro humoral regulation
• - Reflex activity

by localization area as:

• - Central nervous system
• - Peripheral nervous system

by functional affiliation as:

• - Autonomic nervous system
• - Somatic nervous system
• - Sympathetic nervous system
• - Parasympathetic nervous system

General characteristics of the nervous system:

The nervous system consists of neurons, or nerve cells, and neuroglia, or neuroglial cells.

These are the main structural and functional elements both in the central and peripheral nervous systems. Neurons are excitable cells, meaning they are capable of generating and transmitting electrical impulses (action potentials). Neurons have different shape and size, they form processes of two types: axons and dendrites. A neuron usually has several short branched dendrites, along which impulses travel to the neuron body, and one long axon, along which impulses travel from the neuron body to other cells (neurons, muscle or glandular cells). The transfer of excitation from one neuron to other cells occurs through specialized contacts - synapses.

The processes of neurons are surrounded by membranes and combined into bundles, which form nerves. The membranes isolate the processes of different neurons from each other and contribute to the conduction of excitation. The sheathed processes of nerve cells are called nerve fibers. The number of nerve fibers in different nerves ranges from 102 to 105. Most nerves contain processes of both sensory and motor neurons. Interneurons are predominantly located in the spinal cord and brain, their processes form the pathways of the central nervous system. Most nerves human body mixed, that is, they contain both sensory and motor nerve fibers. That is why, when nerves are damaged, sensory disorders are almost always combined with motor disorders. Irritation is perceived by the nervous system through the sensory organs (eye, ear, organs of smell and taste) and special sensitive nerve endings - receptors located in the skin, internal organs, blood vessels, skeletal muscles and joints.

Neuroglia:

Neuroglial cells are more numerous than neurons and make up at least half the volume of the CNS, but unlike neurons they cannot generate action potentials. Neuroglial cells are different in structure and origin; they perform auxiliary functions in the nervous system, providing support, trophic, secretory, delimitation and protective functions.

Neurohumoral regulation (Greek neuron nerve + lat. humor fluid) - the regulating and coordinating influence of the nervous system and biologically contained in the blood, lymph and tissue fluid active substances on the vital processes of the human and animal body. Numerous specific and nonspecific metabolic products (metabolites) are involved in the neurohumoral regulation of functions. Neurohumoral regulation is important for maintaining the relative constancy of the composition and properties of the internal environment of the body, as well as for adapting the body to changing living conditions. Interacting with the somatic (animal) nervous system and endocrine system, the neurohumoral regulatory function ensures the maintenance of constancy of homeostasis and adaptation to changing environmental conditions. Long time Nervous regulation was actively opposed to humoral regulation. Modern physiology has completely rejected the opposition individual species regulation (for example, reflex - humoral-hormonal or other). At the early stages of the evolutionary development of animals, the nervous system was in its infancy. Communication between individual cells or organs in such organisms was carried out using various chemicals secreted by working cells or organs (i.e., it was humoral in nature). As the nervous system improved, humoral regulation gradually came under the controlling influence of a more advanced nervous system. At the same time, many transmitters of nervous excitation (acetylcholine, norepinephrine, gemma-aminobutyric acid, serotonin, etc.), having fulfilled their main role - the role of mediators and avoided enzymatic inactivation or recapture nerve endings, enter the blood, carrying out a distant (non-mediator) effect. In this case, biologically active substances penetrate through histohematic barriers into organs and tissues, direct and regulate their vital functions.

Reflex activity: Reflex (lat. reflexus turned back, reflected) is the body’s response to external or internal stimulation with the participation of the nervous system, ensuring the emergence, change or cessation of the functional activity of organs, tissues or the whole organism, carried out with the participation of the central nervous system in response to stimulation of body receptors. The reflex path in the body is a chain of sequentially interconnected neurons that transmit irritation from the receptor to the spinal cord or brain, and from there to the working organ (muscle, gland). This is called a reflex arc. Each neuron in the reflex arc performs its own function. Among neurons, three types can be distinguished: - perceiving irritation - sensitive (afferent) neuron, - transmitting irritation to the working organ - motor (efferent) neuron, - connecting sensory and motor neurons - intercalary (associative neuron). In this case, excitation is always carried out in one direction: from the sensitive to the motor neuron. A reflex is an elementary unit of nervous action. Under natural conditions, reflexes are not carried out in isolation, but are combined (integrated) into complex reflex acts that have a certain biological orientation. Biological significance reflex mechanisms consist in regulating the functioning of organs and coordinating their functional interaction in order to ensure the constancy of the internal environment of the body, maintaining its integrity and the ability to adapt to constantly changing environmental conditions.

According to the classification of I.I. Pavlov, all reflexes are divided into innate, or unconditioned (they are specific and relatively constant), and individually acquired, or conditioned reflexes (they are variable and temporary in nature and are developed in the process of interaction of the body with the environment). Unconditioned reflexes are divided into simple (food, defensive, sexual, visceral, tendon) and complex reflexes (instincts, emotions). Conditioned reflexes are reactions of the body (reflexes) produced under certain conditions during the life of a person or animal on the basis of innate without conditioned reflexes. Unlike unconditioned reflexes, conditioned reflexes have the ability to form quickly (when the body needs it in a given situation) and to fade away just as quickly (when the need for them disappears). The totality of unconditioned reflexes constitutes higher nervous activity. Higher nervous activity is the integrative activity of the higher parts of the central nervous system (cerebral cortex and subcortical centers), ensuring the most perfect adaptation of animals and humans to the environment.

The nervous system is usually divided into central and peripheral.

There is another classification of the nervous system, independent of the first. According to this classification, the nervous system is divided into somatic and autonomic.

The somatic nervous system (from the Latin word “soma” - body) refers to the part of the nervous system (both cell bodies and their processes) that controls the activity of skeletal muscles (body) and sensory organs. This part of the nervous system is largely controlled by our consciousness. That is, we are able to bend or straighten an arm, leg, and so on at will.

However, we are unable to consciously stop perceiving, for example, sound signals.

The autonomic nervous system (translated from Latin “vegetative” - plant) is part of the nervous system (both cell bodies and their processes), which controls the processes of metabolism, growth and reproduction of cells, that is, functions common to both animals and for plant organisms. The autonomic nervous system is responsible, for example, for the activity of internal organs and blood vessels.

The autonomic nervous system is practically not controlled by consciousness, that is, we are not able to relieve a spasm of the gallbladder at will, stop cell division, stop intestinal activity, or dilate or constrict blood vessels.

There are several systems in the human body, including digestive, cardiovascular and muscular. The nervous system deserves special attention - it forces the human body to move, react to irritating factors, see and think.

The human nervous system is a set of structures that performs regulation function of absolutely all parts of the body, responsible for movement and sensitivity.

In contact with

Types of the human nervous system

Before answering the question that people are interested in: “how the nervous system works,” it is necessary to understand what it actually consists of and what components it is usually divided into in medicine.

With the types of NS, not everything is so simple - it is classified according to several parameters:

• localization area;
• type of management;
• method of transmitting information;
• functional accessory.

Localization area

The human nervous system, according to its area of ​​localization, is central and peripheral. The first is represented by the brain and bone marrow, and the second consists of nerves and the autonomic network.

The central nervous system performs regulatory functions with all internal and external organs. She forces them to interact with each other. Peripheral is the one that, in connection with anatomical features located outside the spinal cord and brain.

How does the nervous system work? The PNS responds to irritating factors by sending signals to the spinal cord and then to the brain. Afterwards, the central nervous system organs process them and again send signals to the PNS, which causes, for example, the leg muscles to move.

Method of transmitting information

According to this principle, there are reflex and neurohumoral systems. The first is the spinal cord, which is able to respond to stimuli without the participation of the brain.

Interesting! A person does not control the reflex function, since the spinal cord makes decisions on its own. For example, when you touch a hot surface, your hand immediately withdraws, and at the same time you did not even think about making this movement - your reflexes worked.

The neurohumoral system, which includes the brain, must initially process the information; you can control this process. After this, the signals are sent to the PNS, which carries out the commands of your brain center.

Functional affiliation

Speaking about parts of the nervous system, one cannot fail to mention the autonomic one, which in turn is divided into sympathetic, somatic and parasympathetic.

The autonomic system (ANS) is the department that is responsible for regulation of work lymph nodes, blood vessels, organs and glands(external and internal secretion).

The somatic system is a collection of nerves that are found in bones, muscles and skin. They are the ones who react to all environmental factors and send data to the brain center, and then carry out its orders. Absolutely every muscle movement is controlled by somatic nerves.

Interesting! The right side of the nerves and muscles is controlled by the left hemisphere, and the left by the right.

The sympathetic system is responsible for the release of adrenaline into the blood, controls heart function, lungs and the supply of nutrients to all parts of the body. In addition, it regulates body saturation.

The parasympathetic is responsible for reducing the frequency of movements and also controls the functioning of the lungs, some glands, and the iris. An equally important task is regulating digestion.

Control type

Another clue to the question “how the nervous system works” can be given by a convenient classification by type of control. It is divided into higher and lower activities.

Higher activity controls behavior in the environment. All intellectual and creative activity also belongs to the highest.

Lower activity is the regulation of all functions within the human body. This type of activity makes all body systems a single whole.

Structure and functions of the NS

We have already figured out that the entire NS should be divided into peripheral, central, autonomic and all of the above, but much more needs to be said about their structure and functions.

Spinal cord

This organ is located in the spinal canal and in essence is a kind of “rope” of nerves. It is divided into gray and white matter, where the former is completely covered by the latter.

Interesting! In cross-section, it is noticeable that the gray matter is woven from nerves in such a way that it resembles a butterfly. This is why it is often called “butterfly wings”.

Total the spinal cord consists of 31 sections, each of which is responsible for a separate group of nerves that control specific muscles.

The spinal cord, as already mentioned, can work without the participation of the brain - we are talking about reflexes that cannot be regulated. In the same turn, it is under the control of the organ of thinking and performs a conductive function.

Brain

This organ is the least studied; many of its functions still raise many questions in scientific circles. It is divided into five departments:

• cerebral hemispheres(forebrain);
• intermediate;
• oblong;
• rear;
• average.

The first section makes up 4/5 of the entire mass of the organ. It is responsible for vision, smell, movement, thinking, hearing, and sensitivity. The medulla oblongata is an incredibly important center that regulates processes such as heartbeat, breathing, protective reflexes, selection gastric juice and others.

The middle department controls a function such as. The intermediate plays a role in the formation emotional state. There are also centers responsible for thermoregulation and metabolism in the body.

Brain structure

Nerve structure

The NS is a collection of billions of specific cells. To understand how the nervous system works, it is necessary to talk about its structure.

A nerve is a structure that consists of a certain number of fibers. These, in turn, consist of axons - they are the conductors of all impulses.

The number of fibers in one nerve can vary significantly. Usually it is about one hundred, but V human eye there are more than 1.5 million fibers.

The axons themselves are covered with a special sheath, which significantly increases the speed of the signal - this allows a person to react to stimuli almost instantly.

The nerves themselves are also different, and therefore they are classified into the following types:

• motor (transmits information from the central nervous system to the muscular system);
• cranial (this includes optic, olfactory and other types of nerves);
• sensitive (transmit information from the PNS to the CNS);
• dorsal (located in and control parts of the body);
• mixed (capable of transmitting information in two directions).

Structure of the nerve trunk

We have already dealt with topics such as “Types of the human nervous system” and “How the nervous system works,” but there is a lot left aside interesting facts that are worthy of mention:

1. The amount in our body is greater than the number of people on the entire planet Earth.
2. The brain contains about 90–100 billion neurons. If you connect them all into one line, it will reach about 1 thousand km.
3. The speed of the pulses reaches almost 300 km/h.
4. After the onset of puberty, the mass of the thinking organ increases every year decreases by approximately one gram.
5. Men's brains are approximately 1/12 larger than women's.
6. The largest organ of thinking was recorded in a mentally ill person.
7. The cells of the central nervous system are practically irreparable, and severe stress and anxiety can seriously reduce their number.
8. Until now, science has not determined what percentage we use our main thinking organ. There are well-known myths that there are no more than 1%, and geniuses - no more than 10%.
9. The size of the thinking organ is not at all does not affect mental activity. Previously, it was believed that men are smarter than the fair sex, but this statement was refuted at the end of the twentieth century.
10. Alcoholic drinks greatly suppress the function of synapses (the place of contact between neurons), which significantly slows down mental and motor processes.

We learned what the human nervous system is - it is a complex collection of billions of cells that interact with each other at a speed equal to the movement of the fastest cars in the world.

A person learns about this even in his school years. Biology lessons provide general information about the body in general and individual organs in particular. As part of the school curriculum, children learn that the normal functioning of the body depends on the state of the nervous system. When malfunctions occur in it, the work of other organs is also disrupted. There are various factors that, to one degree or another, influence this influence. Nervous system characterized as one of the most important parts of the body. It determines the functional unity of a person’s internal structures and the connection of the body with the external environment. Let's take a closer look at what it is

Structure

To understand what the nervous system is, it is necessary to study all its elements separately. The structural unit is a neuron. It is a cell with processes. Neurons form circuits. Speaking about what the nervous system is, it should also be said that it consists of two sections: central and peripheral. The first includes the spinal cord and brain, the second includes the nerves and nodes extending from them. Conventionally, the nervous system is divided into autonomic and somatic.

Cells

They are divided into 2 large groups: afferent and efferent. Activity of the nervous system starts with receptors. They perceive light, sound, smells. Efferent - motor - cells generate and direct impulses to certain organs. They consist of a body and a nucleus, numerous processes called dendrites. A fiber is isolated - an axon. Its length can be 1-1.5 mm. Axons ensure the transmission of impulses. The membranes of cells responsible for the perception of smell and taste contain special compounds. They react to certain substances by changing their state.

Vegetative department

Activity of the nervous system ensures the functioning of internal organs, glands, lymphatic and blood vessels. To a certain extent, it also determines the functioning of muscles. IN autonomic system There are parasympathetic and sympathetic divisions. The latter ensures dilation of the pupil and small bronchi, increased blood pressure, increased heart rate, etc. The parasympathetic department is responsible for the functioning of the genital organs, bladder, and rectum. Impulses emanate from it, activating other glossopharyngeal, for example). The centers are located in the trunk of the head and sacral part spinal cord.

Pathologies

Diseases of the autonomic system can be caused by various factors. Quite often, disorders are a consequence of other pathologies, such as head injury, poisoning, and infections. Failures in the autonomic system can be caused by a lack of vitamins and frequent stress. Often diseases are “masked” by other pathologies. For example, if there is a malfunction of the breast or cervical nodes trunk, there is pain in the sternum, radiating to the shoulder. Such symptoms are characteristic of heart disease, so patients often confuse the pathologies.

Spinal cord

Outwardly, it resembles a heavy metal. The length of this section in an adult is about 41-45 cm. There are two thickenings in the spinal cord: lumbar and cervical. The so-called innervation structures of the lower and upper extremities are formed in them. The following sections are distinguished: sacral, lumbar, thoracic, cervical. Throughout its entire length it is covered with soft, hard and arachnoid membranes.

Brain

It is located in the skull. The brain consists of the right and left hemispheres, brainstem and cerebellum. It has been established that its weight is greater in men than in women. The brain begins its development in the embryonic period. The organ reaches its actual size by about 20 years of age. Towards the end of life, the weight of the brain decreases. It contains departments:

1. Finite.
2. Intermediate.
3. Average.
4. Rear.
5. Oblong.

Hemispheres

They also contain an olfactory center. The outer shell of the hemispheres has a rather complex pattern. This is due to the presence of ridges and grooves. They form something like "convolutions". Each person's drawing is individual. However, there are several grooves that are the same for everyone. They allow us to distinguish five lobes: frontal, parietal, occipital, temporal and hidden.

Unconditioned reflexes

Nervous system processes- response to stimuli. Unconditioned reflexes were studied by such a prominent Russian scientist as I.P. Pavlov. These reactions are focused mainly on the self-preservation of the body. The main ones are food, orientation, and defensive. Unconditioned reflexes are innate.

Classification

Unconditioned reflexes were studied by Simonov. The scientist identified 3 classes of innate reactions corresponding to the development of a specific area of ​​the environment:

Orienting reflex

It is expressed in involuntary sensory attention, accompanied by an increase in muscle tone. The reflex is triggered by a new or unexpected stimulus. Scientists call this reaction “wariness,” anxiety, or surprise. There are three phases of its development:

1. Stopping the current activity, fixing the posture. Simonov calls this general (preventive) inhibition. It occurs upon the appearance of any stimulus with an unknown signal.
2. Transition to the “activation” reaction. At this stage, the body is put into reflexive readiness for a likely encounter with an emergency situation. This manifests itself in general increase muscle tone. At this phase, a multicomponent reaction takes place. It involves turning the head and eyes towards the stimulus.
3. Fixing the stimulus field to begin differentiated analysis of signals and select a response.

Meaning

The orienting reflex is part of the structure of exploratory behavior. This is especially evident in a new environment. Research activities can be focused both on mastering novelty and on searching for an object that can satisfy curiosity. In addition, it can also provide analysis of the significance of the stimulus. In such a situation, there is an increase in the sensitivity of the analyzers.

Mechanism

The implementation of the orientation reflex is a consequence of the dynamic interaction of many formations of nonspecific and specific elements of the central nervous system. The general activation phase, for example, is associated with the launch and onset of generalized excitation of the cortex. When analyzing a stimulus, cortical-limbic-thalamic integration is of primary importance. The hippocampus plays an important role in this.

Conditioned reflexes

At the turn of the 19th-20th centuries. Pavlov, who studied the work of the digestive glands for a long time, revealed the following phenomenon in experimental animals. An increase in the secretion of gastric juice and saliva occurred regularly not only when food entered the gastrointestinal tract directly, but also when waiting for it to be received. At that time, the mechanism of this phenomenon was not known. Scientists explained it by “mental stimulation” of the glands. In subsequent studies, Pavlov classified this reaction as a conditioned (acquired) reflex. They can appear and disappear during a person's life. For a conditioned reaction to occur, two stimuli must coincide. One of them, under any conditions, provokes a natural response - an unconditioned reflex. The second, due to its routineness, does not provoke any reaction. It is defined as indifferent (indifferent). For a conditioned reflex to occur, the second stimulus must begin to act earlier than the unconditioned one, by several seconds. In this case, the biological significance of the first should be less.

Nervous system protection

As you know, the body is affected by a variety of factors. State of the nervous system affects the functioning of other organs. Even seemingly insignificant failures can cause serious illnesses. However, they will not always be associated with the activity of the nervous system. In this regard, great attention should be paid preventive measures. First of all, it is necessary to reduce irritating factors. It is known that constant stress and anxiety are one of the causes of heart pathologies. Treatment of these diseases includes not only medications, but also physiotherapy, exercise therapy, etc. Diet is of particular importance. From proper nutrition depends on the condition of all human systems and organs. Food must contain sufficient amounts of vitamins. Experts recommend including in the diet herbal products, greens, vegetables and fruits.

Vitamin C

It has a beneficial effect on all body systems, including the nervous system. Vitamin C ensures energy production at the cellular level. This compound is involved in the synthesis of ATP (adenosine triphosphoric acid). Vitamin C is considered one of the strongest antioxidants; it neutralizes negative impact free radicals by binding them. In addition, the substance can enhance the activity of other antioxidants. These include vitamin E and selenium.

Lecithin

It provides normal course processes in the nervous system. Lecithin - main nutrient for cells. The content in the peripheral region is about 17%, in the brain - 30%. With insufficient lecithin intake, nervous exhaustion occurs. The person becomes irritable, which often leads to nervous breakdowns. Lecithin is necessary for all cells of the body. It is included in the group of B-vitamins and promotes energy production. In addition, lecithin is involved in the production of acetylcholine.

Music that calms the nervous system

As mentioned above, for diseases of the central nervous system therapeutic measures may include more than just taking medications. The therapeutic course is selected depending on the severity of the disorders. Meanwhile, relaxation of the nervous system This can often be achieved without visiting a doctor. A person can independently find ways to relieve irritation. For example, there are different melodies. As a rule, these are slow compositions, often without words. However, some people may find marching to be calming. When choosing melodies, you should focus on your own preferences. You just need to make sure that the music is not depressing. Today, a special relaxing genre has become quite popular. It combines classics and folk melodies. The main sign of relaxing music is quiet monotony. It “envelops” the listener, creating a soft but durable “cocoon” that protects a person from external irritations. Relaxation music can be classical, but not symphonic. It is usually performed by one instrument: piano, guitar, violin, flute. It can also be a song with a repetitive chant and simple words.

The sounds of nature are very popular - the rustling of leaves, the sound of rain, birdsong. In combination with the melody of several instruments, they take a person away from the everyday hustle and bustle, the rhythm of the metropolis, and relieve nervous and muscle tension. When listening, thoughts are organized, excitement is replaced by calm.

In the human body, the work of all its organs is closely interconnected, and therefore the body functions as a single whole. The coordination of the functions of internal organs is ensured by the nervous system, which, in addition, communicates the body as a whole with the external environment and controls the functioning of each organ.

Distinguish central nervous system (brain and spinal cord) and peripheral, represented by nerves extending from the brain and spinal cord and other elements lying outside the spinal cord and brain. The entire nervous system is divided into somatic and autonomic (or autonomic). Somatic nervous the system primarily communicates the body with the external environment: perception of irritations, regulation of movements of the striated muscles of the skeleton, etc., vegetative - regulates metabolism and the functioning of internal organs: heartbeat, peristaltic contractions of the intestines, secretion of various glands, etc. Both of them function in close interaction, but the autonomic nervous system has some independence (autonomy), controlling many involuntary functions.

A cross-section of the brain shows that it consists of gray and white matter. Gray matter is a collection of neurons and their short processes. In the spinal cord it is located in the center, surrounding the spinal canal. In the brain, on the contrary, gray matter is located along its surface, forming a cortex and separate clusters called nuclei, concentrated in the white matter. White matter is located under the gray and is composed of nerve fibers covered with membranes. Nerve fibers connect to form nerve bundles, and several such bundles form individual nerves. The nerves through which excitation is transmitted from the central nervous system to the organs are called centrifugal, and the nerves that conduct excitation from the periphery to the central nervous system are called centripetal.

The brain and spinal cord are covered with three membranes: dura mater, arachnoid membrane and vascular membrane. Solid - external, connective tissue, lining the internal cavity of the skull and spinal canal. Arachnoid located under solid ~ this thin shell with a small number of nerves and blood vessels. Vascular the membrane is fused with the brain, extends into the grooves and contains many blood vessels. Between the choroid and arachnoid membranes, cavities filled with brain fluid are formed.

In response to irritation, the nervous tissue enters a state of excitation, which is a nervous process that causes or enhances the activity of the organ. The property of nervous tissue to transmit excitation is called conductivity. The speed of excitation is significant: from 0.5 to 100 m/s, therefore, interaction is quickly established between organs and systems that meets the needs of the body. Excitation is carried out along the nerve fibers in isolation and does not pass from one fiber to another, which is prevented by the membranes covering the nerve fibers.

The activity of the nervous system is reflexive character. The response to stimulation carried out by the nervous system is called reflex. The path along which nervous excitation is perceived and transmitted to the working organ is called reflex arc. It consists of five sections: 1) receptors that perceive irritation; 2) sensitive (centripetal) nerve, transmitting excitation to the center; 3) the nerve center, where excitation switches from sensory neurons to motor neurons; 4) motor (centrifugal) nerve, carrying excitation from the central nervous system to the working organ; 5) a working organ that reacts to the received irritation.

The process of inhibition is the opposite of excitation: it stops activity, weakens or prevents its occurrence. Excitation in some centers of the nervous system is accompanied by inhibition in others: nerve impulses entering the central nervous system can delay certain reflexes. Both processes are excitation And braking - are interconnected, which ensures coordinated activity of organs and the entire organism as a whole. For example, during walking, contraction of the flexor and extensor muscles alternates: when the flexion center is excited, impulses follow to the flexor muscles, at the same time, the extension center is inhibited and does not send impulses to the extensor muscles, as a result of which the latter relax, and vice versa.

Spinal cord is located in the spinal canal and has the appearance of a white cord stretching from the occipital foramen to the lower back. There are longitudinal grooves along the anterior and posterior surfaces of the spinal cord; the spinal canal runs in the center, around which the Gray matter - an accumulation of a huge number of nerve cells that form a butterfly outline. By outer surface The spinal cord contains white matter - a collection of bundles of long processes of nerve cells.

In the gray matter, anterior, posterior and lateral horns are distinguished. They lie in the anterior horns motor neurons, in the rear - insert, which communicate between sensory and motor neurons. Sensory neurons lie outside the cord, in the spinal ganglia along the sensory nerves. Long processes extend from the motor neurons of the anterior horns - anterior roots, forming motor nerve fibers. Axons of sensory neurons approach the dorsal horns, forming back roots, which enter the spinal cord and transmit excitation from the periphery to the spinal cord. Here the excitation is switched to the interneuron, and from it to the short processes of the motor neuron, from which it is then communicated to the working organ along the axon.

In the intervertebral foramina, the motor and sensory roots are connected, forming mixed nerves, which then split into front and rear branches. Each of them consists of sensory and motor nerve fibers. Thus, at the level of each vertebra from the spinal cord in both directions only 31 pairs leave spinal nerves mixed type. The white matter of the spinal cord forms pathways that stretch along the spinal cord, connecting both its individual segments with each other and the spinal cord with the brain. Some pathways are called ascending or sensitive, transmitting excitation to the brain, others - downward or motor, which conduct impulses from the brain to certain segments of the spinal cord.

Function of the spinal cord. The spinal cord performs two functions - reflex and conduction.

Each reflex is carried out by a strictly defined part of the central nervous system - the nerve center. A nerve center is a collection of nerve cells located in one of the parts of the brain and regulating the activity of an organ or system. For example, the center of the knee reflex is located in lumbar region spinal cord, the center of urination is in the sacral, and the center of pupil dilation is in the upper thoracic segment of the spinal cord. The vital motor center of the diaphragm is localized in the III-IV cervical segments. Other centers - respiratory, vasomotor - are located in the medulla oblongata. In the future, some more nerve centers that control certain aspects of the body’s life will be considered. The nerve center consists of many interneurons. It processes information that comes from the corresponding receptors, and generates impulses that are transmitted to the executive organs - heart, blood vessels, skeletal muscles, glands, etc. As a result of them functional state changes. To regulate the reflex and its accuracy, the participation of the higher parts of the central nervous system, including the cerebral cortex, is necessary.

The nerve centers of the spinal cord are directly connected to the receptors and executive organs of the body. Motor neurons of the spinal cord provide contraction of the muscles of the trunk and limbs, as well as the respiratory muscles - the diaphragm and intercostal muscles. In addition to the motor centers of skeletal muscles, the spinal cord contains a number of autonomic centers.

Another function of the spinal cord is conduction. Bundles of nerve fibers that form white matter connect various parts of the spinal cord to each other and the brain to the spinal cord. There are ascending pathways that carry impulses to the brain, and descending pathways that carry impulses from the brain to the spinal cord. According to the first, excitation arising in the receptors of the skin, muscles, and internal organs is carried along the spinal nerves to the dorsal roots of the spinal cord, perceived by sensitive neurons of the spinal nodes and from here sent either to the dorsal horns of the spinal cord, or as part of the white matter reaches the trunk, and then the cerebral cortex. Descending pathways carry excitation from the brain to the motor neurons of the spinal cord. From here, excitation is transmitted along the spinal nerves to the executive organs.

The activity of the spinal cord is controlled by the brain, which regulates spinal reflexes.

Brain located in the brain part of the skull. Its average weight is 1300-1400 g. After a person is born, brain growth continues up to 20 years. It consists of five sections: the anterior (cerebral hemispheres), intermediate, middle "hindbrain and medulla oblongata. Inside the brain there are four interconnected cavities - cerebral ventricles. They are filled with cerebrospinal fluid. The first and second ventricles are located in the cerebral hemispheres, the third - in the diencephalon, and the fourth - in the medulla oblongata. The hemispheres (the newest part in evolutionary terms) reach a high level of development in humans, making up 80% of the mass of the brain. The phylogenetically more ancient part is the brain stem. The trunk includes the medulla oblongata, pons, midbrain and diencephalon. The white matter of the trunk contains numerous nuclei of gray matter. The nuclei of 12 pairs of cranial nerves also lie in the brain stem. The brainstem is covered by the cerebral hemispheres.

The medulla oblongata is a continuation of the spinal cord and repeats its structure: there are also grooves on the anterior and posterior surfaces. It consists of white matter (conducting bundles), where clusters of gray matter are scattered - the nuclei from which cranial nerves originate - from the IX to the XII pairs, including the glossopharyngeal (IX pair), vagus (X pair), innervating the respiratory organs, blood circulation, digestion and other systems, sublingual (XII pair).. At the top, the medulla oblongata continues into a thickening - pons, and from the sides why the lower cerebellar peduncles extend. From above and from the sides, almost the entire medulla oblongata is covered by the cerebral hemispheres and the cerebellum.

The gray matter of the medulla oblongata contains vital centers that regulate cardiac activity, breathing, swallowing, carrying out protective reflexes (sneezing, coughing, vomiting, lacrimation), secretion of saliva, gastric and pancreatic juice, etc. Damage to the medulla oblongata can cause death due to cessation of cardiac activity and respiration.

The hindbrain includes the pons and cerebellum. Pons It is bounded below by the medulla oblongata, from above it passes into the cerebral peduncles, and its lateral sections form the middle cerebellar peduncles. The substance of the pons contains the nuclei of the V to VIII pairs of cranial nerves (trigeminal, abducens, facial, auditory).

Cerebellum located posterior to the pons and medulla oblongata. Its surface consists of gray matter (cortex). Under the cerebellar cortex there is white matter, in which there are accumulations of gray matter - the nuclei. The entire cerebellum is represented by two hemispheres, the middle part - the vermis and three pairs of legs formed by nerve fibers, through which it is connected to other parts of the brain. The main function of the cerebellum is unconditioned reflex coordination of movements, determining their clarity, smoothness and maintaining body balance, as well as maintaining muscle tone. Through the spinal cord, along the pathways, impulses from the cerebellum enter the muscles.

The cerebral cortex controls the activity of the cerebellum. The midbrain is located in front of the pons and is represented by quadrigeminal And legs of the brain. In its center there is a narrow canal (brain aqueduct), which connects the III and IV ventricles. The cerebral aqueduct is surrounded by gray matter, in which the nuclei of the III and IV pairs of cranial nerves lie. In the cerebral peduncles the pathways from the medulla oblongata continue; pons to the cerebral hemispheres. The midbrain plays an important role in the regulation of tone and in the implementation of reflexes that make standing and walking possible. The sensitive nuclei of the midbrain are located in the quadrigeminal tubercles: the upper ones contain nuclei associated with the organs of vision, and the lower ones contain nuclei associated with the organs of hearing. With their participation, orienting reflexes to light and sound are carried out.

The diencephalon occupies the highest position in the brainstem and lies anterior to the cerebral peduncles. Consists of two visual tuberosities, supracubertal, subtubercular region and geniculate bodies. On the periphery diencephalon there is white matter, and in its thickness there are nuclei of gray matter. Visual tuberosities - main subcortical sensitivity centers: here by upward paths impulses arrive from all receptors of the body, and from here to the cerebral cortex. In the sub-hillock part (hypothalamus) there are centers, the totality of which represents the highest subcortical center of the autonomic nervous system, regulating metabolism in the body, heat transfer, and the constancy of the internal environment. The parasympathetic centers are located in the anterior parts of the hypothalamus, and the sympathetic centers in the posterior parts. The subcortical visual and auditory centers are concentrated in the nuclei of the geniculate bodies.

The second pair of cranial nerves, the optic ones, goes to the geniculate bodies. The brain stem is connected to the environment and to the organs of the body by cranial nerves. By their nature they can be sensitive (I, II, VIII pairs), motor (III, IV, VI, XI, XII pairs) and mixed (V, VII, IX, X pairs).

Autonomic nervous system. Centrifugal nerve fibers are divided into somatic and autonomic. Somatic conduct impulses to skeletal striated muscles, causing them to contract. They originate from motor centers located in the brainstem, in the anterior horns of all segments of the spinal cord and, without interruption, reach the executive organs. Centrifugal nerve fibers going to internal organs and systems, to all tissues of the body, are called vegetative. Centrifugal neurons of the autonomic nervous system lie outside the brain and spinal cord - in the peripheral nerve nodes - ganglia. The processes of ganglion cells end in smooth muscle, cardiac muscle and glands.

The function of the autonomic nervous system is to regulate physiological processes in the body, to ensure the body's adaptation to changing environmental conditions.

The autonomic nervous system does not have its own special sensory pathways. Sensitive impulses from organs are sent along sensory fibers common to the somatic and autonomic nervous systems. The regulation of the autonomic nervous system is carried out by the cerebral cortex.

The autonomic nervous system consists of two parts: sympathetic and parasympathetic. Nuclei of the sympathetic nervous system located in the lateral horns of the spinal cord, from the 1st thoracic to the 3rd lumbar segments. Sympathetic fibers leave the spinal cord as part of the anterior roots and then enter the nodes, which, connected by short bundles in a chain, form a paired border trunk located on both sides of the spinal column. Next, from these nodes, the nerves go to the organs, forming plexuses. Impulses entering the organs through sympathetic fibers provide reflex regulation of their activity. They strengthen and increase heart rate, cause rapid redistribution of blood by narrowing some vessels and dilating others.

Parasympathetic nerve nuclei lie in the middle, medulla oblongata and sacral parts of the spinal cord. Unlike the sympathetic nervous system, all parasympathetic nerves reach peripheral nerve nodes located in the internal organs or on the approaches to them. The impulses conducted by these nerves cause a weakening and slowing of cardiac activity, a narrowing of the coronary vessels of the heart and brain vessels, dilation of the vessels of the salivary and other digestive glands, which stimulates the secretion of these glands, and increases the contraction of the muscles of the stomach and intestines.

Most internal organs receive dual autonomic innervation, that is, they are approached by both sympathetic and parasympathetic nerve fibers, which function in close interaction, exerting the opposite effect on the organs. It has great importance in adapting the body to constantly changing environmental conditions.

The forebrain consists of highly developed hemispheres and the middle part connecting them. Right and left hemisphere separated from each other by a deep fissure at the bottom of which lies the corpus callosum. Corpus callosum connects both hemispheres through long processes of neurons that form pathways. The cavities of the hemispheres are represented lateral ventricles(I and II). The surface of the hemispheres is formed by gray matter or the cerebral cortex, represented by neurons and their processes; under the cortex lies white matter - pathways. Pathways connect individual centers within one hemisphere, or the right and left halves of the brain and spinal cord, or different floors of the central nervous system. The white matter also contains clusters of nerve cells that form the subcortical nuclei of the gray matter. Part of the cerebral hemispheres is the olfactory brain with a pair of olfactory nerves extending from it (I pair).

The total surface of the cerebral cortex is 2000 - 2500 cm 2, its thickness is 2.5 - 3 mm. The cortex includes more than 14 billion nerve cells arranged in six layers. In a three-month-old embryo, the surface of the hemispheres is smooth, but the cortex grows faster than the braincase, so the cortex forms folds - convolutions, limited by grooves; they contain about 70% of the surface of the cortex. Furrows divide the surface of the hemispheres into lobes. Each hemisphere has four lobes: frontal, parietal, temporal And occipital, The deepest grooves are the central ones, separating the frontal lobes from the parietal lobes, and the lateral ones, which delimit the temporal lobes from the rest; The parieto-occipital sulcus separates the parietal lobe from the occipital lobe (Fig. 85). Anterior to the central sulcus in the frontal lobe is the anterior central gyrus, behind it is the posterior central gyrus. The lower surface of the hemispheres and the brain stem is called base of the brain.

To understand how the cerebral cortex functions, you need to remember that the human body has a large number of a variety of highly specialized receptors. Receptors are capable of detecting the most minor changes in the external and internal environment.

Receptors located in the skin respond to changes in the external environment. In muscles and tendons there are receptors that signal to the brain about the degree of muscle tension and joint movements. There are receptors that respond to changes in the chemical and gas composition of the blood, osmotic pressure, temperature, etc. In the receptor, irritation is converted into nerve impulses. For sensitive nerve pathways impulses are conducted to the corresponding sensitive areas of the cerebral cortex, where a specific sensation is formed - visual, olfactory, etc.

The functional system, consisting of a receptor, a sensitive pathway and a zone of the cortex where this type of sensitivity is projected, was called by I. P. Pavlov analyzer.

Analysis and synthesis of the received information is carried out in a strictly defined area - the zone of the cerebral cortex. The most important areas of the cortex are motor, sensitive, visual, auditory, and olfactory. Motor the zone is located in the anterior central gyrus in front of the central sulcus of the frontal lobe, the zone skin-muscular sensitivity - behind the central sulcus, in the posterior central gyrus of the parietal lobe. Visual the zone is concentrated in the occipital lobe, auditory - in the superior temporal gyrus temporal lobe, A olfactory And gustatory zones - in the anterior temporal lobe.

The activity of analyzers reflects the external material world in our consciousness. This enables mammals to adapt to environmental conditions by changing behavior. Man, learning natural phenomena, the laws of nature and creating tools, actively changes the external environment, adapting it to his needs.

Many neural processes take place in the cerebral cortex. Their purpose is twofold: interaction of the body with the external environment (behavioral reactions) and the unification of body functions, nervous regulation of all organs. The activity of the cerebral cortex of humans and higher animals was defined by I. P. Pavlov as higher nervous activity, representing conditioned reflex function cerebral cortex. Even earlier, the main principles about the reflex activity of the brain were expressed by I. M. Sechenov in his work “Reflexes of the Brain.” However, the modern idea of ​​higher nervous activity was created by I.P. Pavlov, who, by studying conditioned reflexes, substantiated the mechanisms of adaptation of the body to changing environmental conditions.

Conditioned reflexes are developed during the individual life of animals and humans. Therefore, conditioned reflexes are strictly individual: some individuals may have them, while others may not. For such reflexes to occur, the action of the conditioned stimulus must coincide in time with the action of the unconditioned stimulus. Only the repeated coincidence of these two stimuli leads to the formation of a temporary connection between the two centers. According to the definition of I.P. Pavlov, reflexes acquired by the body during its life and resulting from the combination of indifferent stimuli with unconditioned ones are called conditioned.

In humans and mammals, new conditioned reflexes are formed throughout life; they are locked in the cerebral cortex and are temporary in nature, since they represent temporary connections of the organism with the environmental conditions in which it is located. Conditioned reflexes in mammals and humans are very complex to develop, since they cover a whole complex of stimuli. In this case, connections arise between different departments cortex, between the cortex and subcortical centers, etc. The reflex arc becomes significantly more complex and includes receptors that perceive conditioned stimulation, a sensory nerve and the corresponding pathway with subcortical centers, a section of the cortex that perceives conditioned stimulation, a second section associated with the center unconditioned reflex, unconditioned reflex center, motor nerve, working organ.

During the individual life of an animal and a person, countless formed conditioned reflexes serve as the basis for his behavior. Animal training is also based on the development of conditioned reflexes, which arise as a result of combination with unconditioned ones (giving treats or encouraging affection) when jumping through a burning ring, lifting on their paws, etc. Training is important in the transportation of goods (dogs, horses), border protection, hunting (dogs), etc.

Various environmental stimuli acting on the body can cause not only the formation of conditioned reflexes in the cortex, but also their inhibition. If inhibition occurs immediately upon the first action of the stimulus, it is called unconditional. When braking, suppression of one reflex creates conditions for the emergence of another. For example, the smell of a predatory animal inhibits the consumption of food by a herbivore and causes an orienting reflex, in which the animal avoids meeting the predator. In this case, in contrast to unconditional inhibition, the animal develops conditioned inhibition. It occurs in the cerebral cortex when a conditioned reflex is reinforced by an unconditioned stimulus and ensures the animal’s coordinated behavior in constantly changing environmental conditions, when useless or even harmful reactions are excluded.

Higher nervous activity. Human behavior is associated with conditional-unconditional reflex activity. Based on unconditioned reflexes, starting from the second month after birth, the child develops conditioned reflexes: as he develops, communicates with people and is influenced by the external environment, temporary connections constantly arise in the cerebral hemispheres between their various centers. The main difference between human higher nervous activity is thinking and speech, which appeared as a result of labor social activity. Thanks to the word, generalized concepts and ideas arise, the ability to logical thinking. As a stimulus, a word evokes a large number of conditioned reflexes in a person. They are the basis for training, education, and the development of work skills and habits.

Based on the development of speech function in people, I. P. Pavlov created the doctrine of first and second signaling systems. The first signaling system exists in both humans and animals. This system, the centers of which are located in the cerebral cortex, perceives through receptors direct, specific stimuli (signals) of the external world - objects or phenomena. In humans, they create the material basis for sensations, ideas, perceptions, impressions about the surrounding nature and social environment, and this constitutes the basis concrete thinking. But only in humans there is a second signaling system associated with the function of speech, with the word audible (speech) and visible (writing).

A person can be distracted from the characteristics of individual objects and find common properties in them, which are generalized in concepts and united by one word or another. For example, the word “birds” summarizes representatives of various genera: swallows, tits, ducks and many others. Likewise, every other word acts as a generalization. For a person, a word is not only a combination of sounds or an image of letters, but first of all a form of representing material phenomena and objects of the surrounding world in concepts and thoughts. With the help of words they are formed general concepts. Through the word, signals about specific stimuli are transmitted, and in this case the word serves as a fundamentally new stimulus - signal signals.

When generalizing various phenomena, a person discovers natural connections between them - laws. A person’s ability to generalize is the essence abstract thinking, which distinguishes him from animals. Thinking is the result of the function of the entire cerebral cortex. The second signaling system arose as a result of the joint work of people, in which speech became a means of communication between them. On this basis, verbal human thinking arose and developed further. The human brain is the center of thinking and the center of speech associated with thinking.

The dream and its meaning. According to the teachings of I.P. Pavlov and other domestic scientists, sleep is a deep protective inhibition that prevents overwork and exhaustion of nerve cells. It covers the cerebral hemispheres, midbrain and diencephalon. In

During sleep, the activity of many physiological processes drops sharply; only the parts of the brain stem that regulate vital functions continue to function. important functions, - breathing, heartbeat, but their function is also reduced. The sleep center is located in the hypothalamus of the diencephalon, in the anterior nuclei. The posterior nuclei of the hypothalamus regulate the state of awakening and wakefulness.

Monotonous speech, quiet music, general silence, darkness, and warmth help the body fall asleep. During partial sleep, some “sentinel” points of the cortex remain free from inhibition: the mother sleeps soundly when there is noise, but the slightest rustle of the child wakes her up; soldiers sleep with the roar of guns and even on the march, but immediately respond to the orders of the commander. Sleep reduces the excitability of the nervous system, and therefore restores its functions.

Sleep occurs quickly if stimuli that interfere with the development of inhibition, such as loud music, bright lights, etc., are eliminated.

Using a number of techniques, preserving one excited area, it is possible to induce artificial inhibition in the cerebral cortex (dream-like state) in a person. This condition is called hypnosis. I.P. Pavlov considered it as a partial inhibition of the cortex limited to certain zones. With the onset of the deepest phase of inhibition, weak stimuli (for example, a word) are more effective than strong ones (pain), and high suggestibility is observed. This state of selective inhibition of the cortex is used as therapeutic appointment, during which the doctor instills in the patient that it is necessary to eliminate harmful factors - smoking and drinking alcohol. Sometimes hypnosis can be caused by a strong, unusual stimulus under given conditions. This causes “numbness,” temporary immobilization, and concealment.

Dreams. Both the nature of sleep and the essence of dreams are revealed on the basis of the teachings of I.P. Pavlov: during a person’s wakefulness, excitation processes predominate in the brain, and when all areas of the cortex are inhibited, complete deep sleep develops. With such sleep there are no dreams. In the case of incomplete inhibition, individual uninhibited brain cells and areas of the cortex enter into various interactions with each other. Unlike normal connections in the waking state, they are characterized by quirkiness. Every dream is a more or less vivid and complex event, a picture, a living image that periodically arises in a sleeping person as a result of the activity of cells that remain active during sleep. According to I.M. Sechenov, “dreams are unprecedented combinations of experienced impressions.” Often, external irritations are included in the content of a dream: a warmly covered person sees himself in hot countries, the cooling of his feet is perceived by him as walking on the ground, in the snow, etc. Scientific analysis of dreams from a materialistic point of view has shown the complete failure of the predictive interpretation of “prophetic dreams.”

Hygiene of the nervous system. The functions of the nervous system are carried out by balancing excitatory and inhibitory processes: excitation at some points is accompanied by inhibition at others. At the same time, the functionality of the nervous tissue is restored in the areas of inhibition. Fatigue is promoted by low mobility during mental work and monotony during physical work. Fatigue of the nervous system weakens its regulatory function and can provoke the occurrence of a number of diseases: cardiovascular, gastrointestinal, skin, etc.

The most favorable conditions for the normal functioning of the nervous system are created with the correct alternation of work, active rest and sleep. Elimination of physical fatigue and nervous fatigue occurs when switching from one type of activity to another, in which the load will be experienced alternately different groups nerve cells. In conditions of high automation of production, the prevention of overwork is achieved by the personal activity of the employee, his creative interest, and the regular alternation of moments of work and rest.

Drinking alcohol and smoking cause great harm to the nervous system.

Nervous system (sustema nervosum) is a complex of anatomical structures that ensure the individual adaptation of the body to the external environment and the regulation of the activity of individual organs and tissues.

Only a biological system can exist that is capable of acting in accordance with external conditions in close connection with the capabilities of the organism itself. It is this single goal - establishing behavior and state of the body that is adequate to the environment - are subordinated to the functions of individual systems and organs at each moment of time. In this regard, the biological system acts as a single whole.

The nervous system, together with the endocrine glands, is the main integrating and coordinating apparatus, which, on the one hand, ensures the integrity of the body, and on the other, its behavior adequate to the external environment.

The nervous system includes the brain and spinal cord, as well as nerves, ganglia, plexuses, etc. All these formations are predominantly built from nervous tissue, which
- capable get excited under the influence of irritation from the environment internal or external to the body and
- excite in the form of a nerve impulse to various nerve centers for analysis, and then
- transmit the “order” developed at the center to the executive bodies to perform a response of the body in the form of movement (movement in space) or changes in the function of internal organs.

Excited e tion - active physiological process , with which some types of cells respond to external influences. The ability of cells to generate excitation is called excitability. Excitable cells include nerve, muscle and glandular cells.
All other cells have only irritability, i.e. the ability to change their metabolic processes when exposed to any factors (irritants).
In excitable tissues, especially nervous tissues, excitation can spread along the nerve fiber and is a carrier of information about the properties of the stimulus . In muscle and glandular cells, excitation is a factor that triggers their specific activity - contraction, secretion.

Braking e tion in the central nervous system - active physiological process , the result of which is a delay in the excitation of the nerve cell.
Together with excitation, inhibition forms the basis of the integrative activity of the nervous system and ensures the coordination of all functions of the body.

The human nervous system is classified according to the conditions of formation and type of management as: - Lower nervous activity - Higher nervous activity According to the method of transmitting information as: - Neurohumoral regulation - Reflex regulation By area of ​​localization as: - central nervous system - Peripheral nervous system By functional affiliation as: - Autonomic nervous system - Somatic nervous system - Sympathetic nervous system - Parasympathetic nervous system

The anatomical and functional unit of the nervous system is the nerve cell - neuron. Neurons have processes with which they connect with each other and with innervated formations (muscle fibers, blood vessels, glands). The processes of a nerve cell are not functionally equivalent: some of them conduct stimulation to the neuron body - This dendrites, and only one shoot - axon - from the nerve cell body to other neurons or organs .

The processes of neurons are surrounded by membranes and combined into bundles, which form nerves. The membranes isolate the processes of different neurons from each other and contribute to the conduction of excitation. The sheathed processes of nerve cells are called. The number of nerve fibers in different nerves ranges from 102 to 105. Most nerves contain processes of both sensory and motor neurons. Interneurons are predominantly located in the spinal cord and brain, their processes form the pathways of the central nervous system.
Most nerves in the human body mixed, that is, they contain both sensory and motor nerve fibers. That is why, when nerves are damaged, sensory disorders are almost always combined with motor disorders.

Irritation is perceived by the nervous system through the sense organs (eye, ear, organs of smell and taste) and special sensitive nerve endings - receptors located in the skin, internal organs, blood vessels, skeletal muscles and joints.

The functioning of the nervous system is based on neurohumoral regulation And reflex regulation .

Neurohumoral regulation (Greek neuron nerve + lat. humor fluid) - regulating and coordinating influence of the nervous system and those contained in the blood, lymph and tissue fluid biologically active substances on the vital processes of the human and animal body. Numerous specific and nonspecific metabolic products (metabolites) are involved in the neurohumoral regulation of functions. N.r.f. is important for maintaining the relative constancy of the composition and properties of the internal environment of the body, as well as for adapting the body to changing conditions of existence. Interacting with the somatic (animal) nervous system and the endocrine system, the neurohumoral regulatory function ensures the maintenance of constant homeostasis And adaptation in changing environmental conditions.

For a long time, nervous regulation was actively opposed to humoral regulation. Modern physiology has completely rejected the opposition of individual types of regulation (for example, reflex - humoral-hormonal or other). At the early stages of the evolutionary development of animals, the nervous system was in its infancy. Communication between individual cells or organs in such organisms was carried out using various chemical substances , secreted by working cells or organs (i.e., was humoral in nature). As the nervous system improved, humoral regulation gradually came under the controlling influence of a more advanced nervous system. At the same time, many transmitters of nervous excitation (acetylcholine, norepinephrine, gemma-aminobutyric acid, serotonin, etc.), having fulfilled their main role - the role mediators and, having avoided enzymatic inactivation or reuptake by nerve endings, enter the blood, carrying out a distant (non-mediator) effect. In this case, biologically active substances penetrate through histohematic barriers into organs and tissues, direct and regulate their vital functions.

Reflex regulation
Reflex(lat. reflexus turned back, reflected) is the body’s response to external or internal irritation with the participation of the nervous system, ensuring the occurrence, change or cessation functional activity organs, tissues or the whole organism, carried out with the participation of the central nervous system in response to irritation of the body’s receptors.
The reflex pathway in the body is a chain of sequentially interconnected neurons , transmitting irritation from the receptor to the spinal cord or brain, and from there to the working organ (muscle, gland). It is called reflex arc .

Each neuron in the reflex arc performs its own function. There are three types of neurons:
irritable- sensitive ( afferent) neuron,
conveying irritation to the working organ - motor ( efferent) neuron,
connecting sensory and motor neurons - intercalary ( association neuron). In this case, excitation is always carried out in one direction: from sensory to motor neuron.

Reflex is the elementary unit of nervous action . Under natural conditions, reflexes are not carried out in isolation, but are combined (integrated) into complex reflex acts, having a certain biological orientation. The biological significance of reflex mechanisms lies in the regulation of the work of organs and the coordination of their functional interaction in order to ensure the constancy of the internal environment of the body, maintaining its integrity and the ability to adapt to constantly changing environmental conditions.

Reflexes are grouped into different groups depending on the leading feature taken as the basis for their division. A fairly common characteristic of reflexes along individual links of the reflex arc. By receptor location reflexes are divided into extero-, intero- and proprioceptive, according to the location of the central link- spinal, bulbar, mesencephalic, cerebellar, diencephalic, cortical; by localization of the efferent part- somatic and vegetative; according to the reaction caused - swallowing, blinking, coughing, etc.
According to the classification of I.I. Pavlov, all reflexes are divided into innate, or unconditional(they are species-specific and relatively constant), and individually acquired, or conditional reflexes (are changeable and temporary in nature and are developed in the process of interaction of the body with the environment).

Unconditioned reflexes are divided into simple (food, defensive, sexual, visceral, tendon) and complex reflexes (instincts, emotions). Some researchers also classify indicative (orientative-exploratory) reflexes as unconditioned reflexes. The instinctive activity of animals (instincts) includes several stages of animal behavior, and the individual stages of its implementation are sequentially related to each other according to the type chain reflex.

Based on the provisions of I.P. Pavlova about nerve center as a morphofunctional set nerve formations, located in various sections of the central nervous system, the concept of the structural and functional architecture of the unconditioned reflex was developed. The central part of the arc B.r. does not pass through any one part of the central nervous system, but is multi-storey and multi-branched. Each branch passes through some important department nervous system: spinal cord, medulla oblongata, midbrain, cerebral cortex. The higher branch, in the form of the cortical representation of one or another unconditioned reflex, serves as the basis for the formation of conditioned reflexes.

Makes up the so-called lower nervous activity animals.
Evolutionarily more primitive species of animals are characterized by simple unconditioned reflexes and instincts, for example, in animals in which the role of acquired, individually developed reactions is still relatively small and innate, albeit complex forms of behavior predominate, dominance of tendon and labyrinthine reflexes is observed. With the complication of the structural organization of the c.s.s. and the progressive development of the cerebral cortex, complex unconditioned reflexes and, in particular, emotions acquire a significant role.


Conditioned reflexes - body reactions (reflexes), produced under certain conditions during the life of a person or animal on the basis of innate unconditioned reflexes. Unlike unconditioned reflexes, conditioned reflexes have the ability to quickly form (when the body needs it in a given situation) and to the same rapid fading (when the need for them disappears).

Conditioned reflex excitation occurs when any indifferent stimulus(lat. indifferens - indifferent) reinforced by unconditional. Thanks to temporary connections of varying complexity, previously indifferent stimuli preceding a particular activity become a signal (condition) of this activity. Having acquired a signal value, the conditioned stimulus leads to the emergence of a signal in the central nervous system. excitation that outstrips the activity of brain structures that ensure the formation of future behavior. Such anticipatory excitation not only ensures a biologically expedient adaptation of the organism to the environment, but also underlies the active influence on this environment.

Thus, the conditioned reflex is one of the main types of adaptive activity of the body, carried out by the higher departments of the central nervous system. by the formation of temporary connections between signal stimulation and unconditioned (innate) reaction of the body.
The classification of conditioned reflexes may be based on the nature of the response (motor, secretory, etc.); method of formation (UR of the first, second and other orders, associative, imitation, etc.), biological significance (nutritional, defensive, orientation-research, etc.).
A set of unconditioned reflexes amounts to higher nervous activity .

Higher nervous activity - integrative activity of the higher parts of the central nervous system (cerebral cortex and subcortical centers), ensuring the most perfect adaptation of animals and humans to the environment.

As a result of long evolutionary development, the nervous system turned out to be represented by two sections. They are clearly different in appearance, but structurally and functionally they form a single whole. This central nervous system in the form of the brain and spinal cord and peripheral nervous system , represented by nerves, nerve plexuses and nodes.

The central nervous system (systema nervosum centrale) is represented by head And spinal cord. In their thickness, areas of gray color (gray matter) are clearly visible, this is the appearance of clusters of neuron bodies, and white matter, formed by the processes of nerve cells, through which they establish connections with each other. The number of neurons and the degree of their concentration are much higher in upper section, which as a result takes the form of a three-dimensional brain.

Spinal cord located in the spinal canal from the first cervical to the second lumbar vertebra. Externally, the spinal cord resembles a cylindrical cord. 31 pairs of spinal nerves depart from the spinal cord, which leave the spinal canal through the corresponding intervertebral foramina and branch symmetrically in the right and left halves of the body. The spinal cord is divided into cervical, thoracic, lumbar, sacral and coccygeal sections, respectively; among the spinal nerves, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1-3 coccygeal nerves are considered. The section of the spinal cord corresponding to a pair (right and left) of the spinal nerves is called segment of the spinal cord .

Every spinal nerve is formed as a result of the fusion of the anterior and posterior roots extending from the spinal cord. On the dorsal root there is a thickening - the spinal ganglion, where the bodies of sensory neurons are located. The processes of sensory neurons carry excitation from the receptors to the spinal cord.
The anterior roots of the spinal nerves are formed by processes of motor neurons, which transmit commands from the central nervous system to skeletal muscles and internal organs.
They close at the level of the spinal cord reflex arcs, providing the simplest reflex reactions, such as tendon reflexes (for example, the knee reflex), flexion reflexes when irritating pain receptors of the skin, muscles and internal organs. An example of a simple spinal reflex is the withdrawal of a hand when it touches a hot object. The reflex activity of the spinal cord is associated with maintaining posture, maintaining a stable body position when turning and tilting the head, alternating flexion and extension of paired limbs when walking, running, etc. In addition, the spinal cord plays an important role in regulating the activity of internal organs, in particular the intestines, bladder, and blood vessels.

Peripheral nervous system Basically it is a connecting link between the central nervous system and organs. The nerves that make up the peripheral nervous system are not independent structures; they are formed by processes of motor neurons, the bodies of which are located in the brain and spinal cord, and processes of sensory neurons that carry information to the central nervous system. Thus, from the point of view of functions and structure, the division of the nervous system into central and peripheral is relative; the nervous system is one.
The nerves that make up the peripheral nervous system are formed motor, sensitive And vegetative fibers .

Motor fibers are long processes (axons) of neurons, the bodies of which are located in the spinal cord and in parts of the brain, they follow to striated fibers of body muscles.

Sensitive fibers - processes of neurons of the same name, whose bodies are located in the form of clusters ( sensitive nodes) inside the nerves in close proximity to the central nervous system, they carry information to the centers spinal and brain.

The peripheral nervous system is represented :
a) 12th cranial nerves(on both sides), which provide brain control over the head and neck areas;
b) the 31st pair of spinal nerves, through which the spinal cord controls the torso, limbs, and organs of the thoracic and abdominal cavities.

Schematic representation of the structure of the human autonomic nervous system and the organs innervated by it (shown in red sympathetic nervous system, blue - parasympathetic; connections between cortical and subcortical centers and spinal cord formations are indicated by a dotted line). 1 And 2 - cortical and subcortical centers; 3 - oculomotor nerve; 4 - facial nerve; 5 - glossopharyngeal nerve; 6 - nervus vagus; 7 - superior cervical sympathetic node; 8 - star knot; 9 - nodes (ganglia) of the sympathetic trunk; 10 - sympathetic nerve fibers (vegetative branches) of the spinal nerves; 11 - celiac (solar) plexus; 12 - superior mesenteric node; 13 - inferior mesenteric node; 14 - hypogastric plexus; 15 - sacral parasympathetic nucleus of the spinal cord; 16 - pelvic splanchnic nerve; 17 - hypogastric nerve; 18 - rectum; 19 - uterus; 20 - bladder; 21 - small intestine; 22 - large intestine; 23 - stomach; 24 - spleen; 25 - liver; 26 - heart; 27 - lung; 28 - esophagus; 29 - larynx; 30 - pharynx; 31 and 32 - salivary glands; 33 - language; 34 - parotid salivary gland; 35 - eyeball; 36 - lacrimal gland; 37 - ciliary node; 38 - pterygopalatine node; 39 - ear node; 40 - submandibular node.

The nervous system is also divided into somatic and autonomic (autonomic).

TO somatic nervous system include those parts that innervate the organs of the musculoskeletal system and the skin (Greek sō ma, sō matos - body, “relating to the body”).

The autonomic nervous system (systema nervosum autonomicum; synonym: autonomic nervous system, involuntary nervous system, visceral nervous system) is a part of the nervous system that ensures the activity of internal organs, regulation of vascular tone, innervation of glands, trophic innervation of skeletal muscles, receptors and the nervous system itself.

Autonomic fibers emerge from the central nervous system and, subsequently leaving the main nerve trunks, through the system of vegetative nodes regulate the functioning of internal organs . Such relationships between the peripheral and central nervous systems indicate their functional and structural unity.

The autonomic nervous system has central and peripheral sections.
IN central department There are suprasegmental (higher) and segmental (lower) vegetative centers.
Suprasegmental autonomic centers concentrated in brain- in the cerebral cortex (mainly in the frontal and parietal lobes), hypothalamus, olfactory brain, subcortical structures (striatum), in the brain stem (reticular formation), cerebellum, etc.
Segmental autonomic centers located and in the brain and spinal cord.

The autonomic centers of the brain are conventionally divided into midbrain and bulbar (autonomic nuclei of the oculomotor, facial, glossopharyngeal and vagus nerves), and the spinal cord into lumbosternal and sacral.

Motor centers innervation of non-striated (smooth) muscles of internal organs and vessels are located in precentral And frontal areas. There are also reception centers from internal organs and blood vessels, centers of sweating, nervous trophism, and metabolism. The centers of thermoregulation, salivation and lacrimation are concentrated in the striatum. The participation of the cerebellum in the regulation of such autonomic functions as pupillary reflex, skin trophism. The nuclei of the reticular formation constitute the suprasegmental centers of vital functions - respiratory, vasomotor, cardiac activity, swallowing, etc.

Peripheral department The autonomic nervous system is represented by nerves and nodes located near internal organs (extramural) or in their thickness (intramural).

The autonomic nodes are connected to each other by nerves, forming plexuses, for example pulmonary, cardiac, abdominal aortic plexus.

Sympathetic nervous system (pars sympathica, Greek sympathēs - experiencing a similar feeling), part of the autonomic nervous system, including nerve cells thoracic and upper lumbar spinal cord and nerve cells of the border sympathetic trunk, solar plexus, mesenteric nodes, the processes of which innervate all organs.
The influence of the sympathetic nervous system on the central nervous system. is manifested by a change in its bioelectrical activity, as well as its conditioned and unconditioned reflex activity.
With increased tonesympathetic nervous system are intensifying heart contractions and their rhythm become more frequent, the speed of excitation through the heart muscle increases, blood vessels constrict, blood pressure increases, metabolism increases, blood glucose increases, bronchi and pupils dilate, the secretory activity of the adrenal medulla increases, the tone of the gastrointestinal tract decreases etc.

Parasympathetic nervous system (pars parasympathica, Greek raga- - prefix meaning “retreat, deviation from something”, etc.) - part of the autonomic nervous system, represented by the oculomotor, facial, glossopharyngeal, vagus nerves and their nuclei, neurons of the lateral horns of the spinal cord at the level of the II-IV sacral segments, as well as associated ganglia, pre- and postganglionic fibers.
Increased tone parasympathetic nervous system accompanied by decrease strength and frequency of heart contractions, slowing down the speed of excitation through the myocardium, reducing blood pressure, increased insulin secretion and decreased blood glucose concentration, increased secretory and motor activity of the gastrointestinal tract.

Many internal organs receive both sympathetic and parasympathetic innervation. The influence of these two departments is often antagonistic, but there are many examples where both departments act synergistic(so-called functional synergy).
In many organs having both sympathetic and parasympathetic innervation , under physiological conditions the regulatory influences of the parasympathetic nerves predominate. These organs include the bladder and some exocrine glands (lacrimal, digestive, etc.).
There are also organs supplied only by sympathetic or only parasympathetic nerves ; These include almost all blood vessels, the spleen, smooth muscles of the eyes, some exocrine glands (sweat glands) and smooth muscles of the hair follicles.

The transmission pathways of adaptation-trophic influences are based on straight And indirect types of sympathetic innervation . There are tissues endowed with direct sympathetic innervation (cardiac muscle, uterus and other smooth muscle formations), but the bulk of tissues (skeletal muscles, glands) have indirect adrenergic innervation. In this case, the transmission of the adaptation-trophic influence occurs humorally: the mediator is transferred to the effector cells by the blood stream or reaches them by diffusion.