Nerves. Three types of human nervous system

In the human body, the work of all its organs is closely interconnected, and therefore the body functions as a whole. The coordination of the functions of the internal organs is provided by the nervous system, which, in addition, communicates the body as a whole with the external environment and controls the work 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 that lie outside the spinal cord and brain. The entire nervous system is divided into somatic and autonomic (or autonomic). Somatic nervous the system mainly carries out the connection of the organism with the external environment: the perception of stimuli, the 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, however, the autonomic nervous system has some independence (autonomy), managing many involuntary functions.

A 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, the gray matter is located on its surface, forming a cortex and separate clusters, called nuclei, concentrated in the white matter. white matter is under gray and is made up of nerve fibers covered with sheaths. Nerve fibers, connecting, compose 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 dressed in three layers: hard, arachnoid and vascular. Solid - external, connective tissue, lines the internal cavity of the skull and spinal canal. gossamer located under the hard ~ it is a thin shell with a small number of nerves and blood vessels. Vascular the membrane is fused with the brain, enters the furrows and contains many blood vessels. Cavities filled with cerebral fluid form between the vascular and arachnoid membranes.

In response to irritation, the nervous tissue enters a state of excitation, which is a nervous process that causes or enhances the activity of an 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 sheaths covering the nerve fibers.

The activity of the nervous system is reflex character. The response to a stimulus 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 the excitation switches from sensory to motor neurons; 4) motor (centrifugal) nerve, which carries excitation from the central nervous system to the working organ; 5) a working body that reacts to the irritation received.

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 - interrelated, which ensures the coordinated activity of organs and the whole organism as a whole. For example, while walking, the contraction of the flexor and extensor muscles alternates: when the flexion center is excited, the 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 located in the spinal canal and has the appearance of a white cord, stretching from the occipital foramen to the lower back. Along the anterior and posterior surfaces of the spinal cord there are longitudinal grooves, in the center there is a spinal canal, around which is concentrated Gray matter - the accumulation of a huge number of nerve cells that form the contour of a butterfly. On the outer surface of the cord of the spinal cord is white matter - an accumulation of bundles of long processes of nerve cells.

The gray matter is divided into anterior, posterior and lateral horns. In the anterior horns lie motor neurons, in the back - intercalary, which communicate between sensory and motor neurons. Sensory neurons lie outside the cord, in the spinal nodes along the sensory nerves. Long processes extend from the motor neurons of the anterior horns - front roots, forming motor nerve fibers. Axons of sensory neurons approach the posterior horns, forming back roots, which enter the spinal cord and transmit excitation from the periphery to the spinal cord. Here, excitation switches to the intercalary neuron, and from it to short processes of the motor neuron, from which it is then transmitted along the axon to the working organ.

In the intervertebral foramen, the motor and sensory roots are connected, forming mixed nerves, which then split into anterior and posterior 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 leaving only 31 pairs spinal nerves of mixed type. The white matter of the spinal cord forms pathways that stretch along the spinal cord, connecting both its individual segments to each other, and the spinal cord to the brain. Some pathways are called ascending or sensitive transmitting excitation to the brain, others - descending or motor, which conduct impulses from the brain to certain segments of the spinal cord.

The 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. The nerve center is a collection of nerve cells located in one of the parts of the brain and regulating the activity of any organ or system. For example, the center of the knee-jerk reflex is located in the lumbar 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 life of the body will be considered. The nerve center consists of many intercalary neurons. It processes information that comes from the corresponding receptors, and impulses are formed that are transmitted to the executive organs - the heart, blood vessels, skeletal muscles, glands, etc. As a result, their functional state changes. To regulate the reflex, its accuracy requires the participation of the higher parts of the central nervous system, including the cerebral cortex.

The nerve centers of the spinal cord are directly connected with the receptors and executive organs of the body. The 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 intercostals. In addition to the motor centers of skeletal muscles, there are a number of autonomic centers in the spinal cord.

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

The activity of the spinal cord is under the control of the brain, which regulates spinal reflexes.

Brain located in the medulla of the skull. Its average weight is 1300-1400 g. After the birth of a person, brain growth continues up to 20 years. It consists of five sections: the anterior (large hemispheres), intermediate, middle "hind and medulla oblongata. Inside the brain there are four interconnected cavities - cerebral ventricles. They are filled with cerebrospinal fluid. I and II ventricles are located in the cerebral hemispheres, III - in the diencephalon, and IV - in the medulla oblongata. The hemispheres (the newest part in evolutionary terms) reach high development in humans, accounting for 80% of the mass of the brain. The phylogenetically older part is the brain stem. The trunk includes the medulla oblongata, the medullary (varoli) bridge, the midbrain and the diencephalon. Numerous nuclei of gray matter lie in the white matter of the trunk. The nuclei of 12 pairs of cranial nerves also lie in the brainstem. The brain stem is covered by the cerebral hemispheres.

The medulla oblongata is a continuation of the spinal cord and repeats its structure: furrows also lie on the anterior and posterior surfaces. It consists of white matter (conducting bundles), where clusters of gray matter are scattered - the nuclei from which the cranial nerves originate - from the IX to XII pair, 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 legs of the cerebellum depart. From above and from the sides, almost the entire medulla oblongata is covered by the cerebral hemispheres and the cerebellum.

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

The hindbrain includes the pons and cerebellum. Pons from below it is limited by the medulla oblongata, from above it passes into the legs of the brain, its lateral sections form the middle legs of the cerebellum. In the substance of the pons, there are nuclei from the V to VIII pair of cranial nerves (trigeminal, abducent, facial, auditory).

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

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

The diencephalon occupies the highest position in the trunk and lies anterior to the legs of the brain. It consists of two visual hillocks, supratuberous, hypothalamic region and geniculate bodies. On the periphery of the diencephalon is white matter, and in its thickness - the nuclei of gray matter. Visual tubercles - the main subcortical centers of sensitivity: impulses from all the receptors of the body arrive here along the ascending paths, and from here to the cerebral cortex. In the hypothalamus (hypothalamus) there are centers, the totality of which is the highest subcortical center of the autonomic nervous system, which regulates the metabolism in the body, heat transfer, and the constancy of the internal environment. Parasympathetic centers are located in the anterior hypothalamus, and sympathetic centers in the posterior. The subcortical visual and auditory centers are concentrated in the nuclei of the geniculate bodies.

The 2nd pair of cranial nerves - optic nerves - 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 the motor centers located in the brain stem, in the anterior horns of all segments of the spinal cord and, without interruption, reach the executive organs. Centrifugal nerve fibers that go to internal organs and systems, to all tissues of the body, are called vegetative. The 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 muscles, in the heart muscle and in the glands.

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

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

The autonomic nervous system consists of two parts: sympathetic and parasympathetic. Nuclei of the sympathetic nervous system are 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, connecting in short bundles into a chain, form a paired border trunk located on both sides of the spinal column. Further from these nodes, the nerves go to the organs, forming plexuses. The impulses coming through the sympathetic fibers to the organs provide reflex regulation of their activity. They increase and speed up heart contractions, cause a rapid redistribution of blood by constricting some vessels and expanding others.

Nuclei of the parasympathetic nerves lie in the middle, oblong sections of the brain and sacral spinal cord. Unlike the sympathetic nervous system, all parasympathetic nerves reach the peripheral nerve nodes located in the internal organs or on the outskirts of them. The impulses carried out by these nerves cause weakening and slowing of cardiac activity, constriction 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 of the internal organs receive a double autonomic innervation, that is, both sympathetic and parasympathetic nerve fibers approach them, which function in close interaction, having the opposite effect on the organs. This is of great importance in adapting the body to constantly changing environmental conditions.

The forebrain consists of strongly developed hemispheres and the median part connecting them. The right and left hemispheres are 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 the same hemisphere, or the right and left halves of the brain and spinal cord, or different floors of the central nervous system. In the white matter there are also 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 brain box, so the cortex forms folds - convolutions, limited by furrows; they contain about 70% of the surface of the cortex. Furrows divide the surface of the hemispheres into lobes. There are four lobes in each hemisphere: frontal, parietal, temporal and occipital, The deepest furrows are central, separating the frontal lobes from the parietal, and lateral, which delimit the temporal lobes from the rest; the parietal-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 highly specialized receptors. Receptors are able to capture the most insignificant changes in the external and internal environment.

Receptors located in the skin respond to changes in the external environment. Muscles and tendons contain 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. Through sensitive nerve pathways, impulses are conducted to the corresponding sensitive areas of the cerebral cortex, where a specific sensation is formed - visual, olfactory, etc.

A functional system consisting of a receptor, a sensitive pathway and a cortical zone where this type of sensitivity is projected, I. P. Pavlov called analyzer.

The 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, sensory, visual, auditory, olfactory. Motor the zone is located in the anterior central gyrus in front of the central sulcus of the frontal lobe, the zone musculoskeletal 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 of the temporal lobe, and olfactory and taste zones - in the anterior part of the temporal lobe.

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

In the cerebral cortex, many nervous processes are carried out. Their purpose is twofold: the interaction of the body with the external environment (behavioral reactions) and the unification of body functions, the nervous regulation of all organs. The activity of the cerebral cortex of humans and higher animals is defined by I.P. Pavlov as higher nervous activity representing conditioned reflex function cerebral cortex. Even earlier, the main provisions on the reflex activity of the brain were expressed by I. M. Sechenov in his work "Reflexes of the Brain". However, the modern concept of higher nervous activity was created by IP 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 the occurrence of such reflexes, 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 arising as a result of a 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 difficult to develop, since they cover a whole range of stimuli. In this case, connections arise between different parts of the cortex, between the cortex and subcortical centers, etc. The reflex arc becomes much more complicated 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 irritation, the second site associated with the center of the unconditioned reflex, the center of the unconditioned reflex, the motor nerve, the working organ.

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

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

Higher nervous activity. Human behavior is associated with conditionally unconditioned reflex activity. On the basis of unconditioned reflexes, starting from the second month after birth, the child develops conditioned reflexes: as it 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 the higher nervous activity of a person is thinking and speech that emerged as a result of labor social activity. Thanks to the word, generalized concepts and representations, the ability to think logically arise. As an irritant, a word causes a large number of conditioned reflexes in a person. Training, education, development of labor skills and habits are based on them.

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

A person can be distracted from the features of individual objects and find in them common properties that are generalized in concepts and united by one word or another. For example, the word "birds" generalizes representatives of various genera: swallows, tits, ducks, and many others. Similarly, 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 displaying material phenomena and objects of the surrounding world in concepts and thoughts. With the help of words, general concepts are formed. Signals about specific stimuli are transmitted through the word, and in this case the word serves as a fundamentally new stimulus - signals signal.

When summarizing various phenomena, a person discovers regular connections between them - laws. The ability of a person 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 labor activity 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.

Sleep and its meaning. According to the teachings of IP 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 - breathing, heartbeat, continue their activity, 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, warmth contribute to falling asleep of the body. During partial sleep, some "sentinel" points of the cortex remain free from inhibition: the mother sleeps soundly with noise, but she is awakened by the slightest rustle of the child; soldiers sleep at the roar of guns and even on the march, but immediately react to the orders of the commander. Sleep reduces the excitability of the nervous system, and therefore restores its functions.

Sleep sets in quickly if stimuli preventing the development of inhibition, such as loud music, bright lights, etc., are eliminated.

With the help of a number of techniques, retaining one excited area, it is possible to induce artificial inhibition in the cerebral cortex in a person (a dream-like state). Such a state is called hypnosis. IP 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) act more efficiently than strong ones (pain), and high suggestibility is observed. This state of selective inhibition of the cortex is used as a therapeutic technique, during which the doctor suggests to the patient that it is necessary to exclude harmful factors - smoking and drinking alcohol. Sometimes hypnosis can be caused by a strong, unusual stimulus under the given conditions. This causes "numbness", temporary immobilization, hiding.

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 parts of the cortex are inhibited, complete deep sleep develops. With such a dream, there are no dreams. In the case of incomplete inhibition, individual non-inhibited 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. Each 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. In the words of I. M. Sechenov, "dreams are unprecedented combinations of experienced impressions." Often, external stimuli are included in the content of sleep: a warmly sheltered person sees himself in hot countries, cooling his feet is perceived by him as walking on the ground, in snow, etc. A scientific analysis of dreams from a materialistic position 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 efficiency of the nervous tissue is restored in the areas of inhibition. Fatigue is facilitated by low mobility during mental work and monotony during physical work. Fatigue of the nervous system weakens its regulatory function and can provoke 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, outdoor activities and sleep. The elimination of physical fatigue and nervous fatigue occurs when switching from one type of activity to another, in which different groups of nerve cells will alternately experience the load. In conditions of high automation of production, the prevention of overwork is achieved by the personal activity of the worker, his creative interest, regular alternation of moments of work and rest.

The use of alcohol and smoking brings great harm to the nervous system.

Nerves branch off from the central nervous system. A nerve is made up of long bundles of nerve fibers. Nerve fibers, no matter how long they are, have a microscopic thickness, but sometimes it can reach a large size. The diameter of the sciatic nerve is 1 cm.

Outside, the nerve is covered with a white connective tissue sheath. On the transverse section, cut bundles of nerve fibers, surrounded by layers of connective tissue, and blood vessels are clearly visible.

Types of nerves

The composition of the nerves may include centrifugal or centripetal nerve fibers, or both. Depending on this, three types of nerves are distinguished.

Centripetal nerves transmit excitation from the organs to the central nervous system, informing it of all changes inside and outside the body. Therefore, they are also called sensitive and "informative." Such, for example, is the auditory nerve.

Centrifugal nerves conduct impulses from the central nervous system to organs. They are called motor, "command". An example is the oculomotor nerve.

mixed nerves make up most of the nerves in the human body. So, all spinal nerves consist of sensory (centripetal) and motor (centrifugal) nerve fibers. On them, impulses move simultaneously both centrifugally and centripetally, but only along the nerve fibers of the same name.

Nerve center

Certain parts of the neutral nervous system that control any activity of the body are called nerve centers. Each nerve center consists of several groups of neurons and nerve fibers. All together they ensure the normal implementation of certain funktsionalizma. So, a person has centers of speech, writing, breathing, etc.

"Human Anatomy and Physiology", M.S. Milovzorova

The autonomic nervous system is part of the nervous system. Her work is subordinated to the central nervous system. The centers of the autonomic nervous system are located in the brain and spinal cord. The fibers of the autonomic nervous system are part of the spinal and cranial nerves. They innervate all organs of the body without exception. Some organs are approached by two autonomic nerves: sympathetic and parasympathetic. Typically, they…

Autonomic nerve fibers, leaving the central nervous system, do not immediately reach the organ, but end at the nodes. These fibers are called prenodular (2). In the nodes there are neurons (1), the processes of which form post-node fibers (3), which are pumped into the organs. Pre-nodal fibers in the nodes come into contact with several post-nodal fibers, and they branch out, innervating several organs at once. Therefore, the excitement that arises ...

Previously, it was believed that the autonomic nervous system affects only the viscera - "organs of plant life." Hence the name - "vegetative". In fact, it also innervates the skeletal muscles. Active muscular work makes great demands on the body as a whole. Muscles need an increased supply of oxygen, sugar and other substances, and decay products must be quickly removed from them. Autonomic nervous...

Nerve endings are located throughout the human body. They carry the most important function and are an integral part of the entire system. The structure of the human nervous system is a complex branched structure that runs through the entire body.

The physiology of the nervous system is a complex composite structure.

The neuron is considered the basic structural and functional unit of the nervous system. Its processes form fibers that are excited when exposed and transmit an impulse. The impulses reach the centers where they are analyzed. After analyzing the received signal, the brain transmits the necessary reaction to the stimulus to the appropriate organs or parts of the body. The human nervous system is briefly described by the following functions:

• providing reflexes;
• regulation of internal organs;
• ensuring the interaction of the organism with the external environment, by adapting the body to changing external conditions and stimuli;
• interaction of all organs.

The value of the nervous system is to ensure the vital activity of all parts of the body, as well as the interaction of a person with the outside world. The structure and functions of the nervous system are studied by neurology.

Structure of the CNS

Anatomy of the central nervous system (CNS) is a collection of neuronal cells and neuronal processes of the spinal cord and brain. A neuron is a unit of the nervous system.

The function of the central nervous system is to provide reflex activity and process impulses coming from the PNS.

Structural features of the PNS

Thanks to the PNS, the activity of the entire human body is regulated. The PNS is made up of cranial and spinal neurons and fibers that form ganglia.

The structure and functions are very complex, so any slightest damage, for example, damage to the vessels in the legs, can cause serious disruption of its work. Thanks to the PNS, control is exercised over all parts of the body and the vital activity of all organs is ensured. The importance of this nervous system for the body cannot be overestimated.

The PNS is divided into two divisions - the somatic and autonomic systems of the PNS.

It performs double work - collecting information from the sense organs, and further transferring this data to the central nervous system, as well as ensuring the motor activity of the body, by transmitting impulses from the central nervous system to the muscles. Thus, it is the somatic nervous system that is the instrument of human interaction with the outside world, since it processes the signals received from the organs of vision, hearing and taste buds.

Ensures the performance of the functions of all organs. It controls the heartbeat, blood supply, and respiratory activity. It contains only motor nerves that regulate muscle contraction.

To ensure the heartbeat and blood supply, the efforts of the person himself are not required - it is the vegetative part of the PNS that controls this. The principles of the structure and function of the PNS are studied in neurology.

Departments of the PNS

The PNS also consists of an afferent nervous system and an efferent division.

The afferent section is a collection of sensory fibers that process information from receptors and transmit it to the brain. The work of this department begins when the receptor is irritated due to any impact.

The efferent system differs in that it processes impulses transmitted from the brain to effectors, that is, muscles and glands.

One of the important parts of the autonomic division of the PNS is the enteric nervous system. The enteric nervous system is formed from fibers located in the gastrointestinal tract and urinary tract. The enteric nervous system controls the motility of the small and large intestines. This department also regulates the secretion secreted in the gastrointestinal tract and provides local blood supply.

The value of the nervous system is to ensure the work of internal organs, intellectual function, motor skills, sensitivity and reflex activity. The central nervous system of a child develops not only in the prenatal period, but also during the first year of life. The ontogenesis of the nervous system begins from the first week after conception.

The basis for the development of the brain is formed already in the third week after conception. The main functional nodes are indicated by the third month of pregnancy. By this time, the hemispheres, trunk and spinal cord have already been formed. By the sixth month, the higher parts of the brain are already better developed than the spinal region.

By the time the baby is born, the brain is the most developed. The size of the brain in a newborn is approximately one eighth of the weight of the child and fluctuates within 400 g.

The activity of the central nervous system and PNS is greatly reduced in the first few days after birth. This may be in the abundance of new irritating factors for the baby. This is how the plasticity of the nervous system is manifested, that is, the ability of this structure to rebuild. As a rule, the increase in excitability occurs gradually, starting from the first seven days of life. The plasticity of the nervous system deteriorates with age.

CNS types

In the centers located in the cerebral cortex, two processes simultaneously interact - inhibition and excitation. The rate at which these states change determines the types of the nervous system. While one section of the CNS center is excited, the other is slowed down. This is the reason for the peculiarities of intellectual activity, such as attention, memory, concentration.

Types of the nervous system describe the differences between the speed of the processes of inhibition and excitation of the central nervous system in different people.

People may differ in character and temperament, depending on the characteristics of the processes in the central nervous system. Its features include the speed of switching neurons from the process of inhibition to the process of excitation, and vice versa.

Types of the nervous system are divided into four types.

• The weak type, or melancholic, is considered the most prone to the occurrence of neurological and psycho-emotional disorders. It is characterized by slow processes of excitation and inhibition. A strong and unbalanced type is a choleric. This type is distinguished by the predominance of excitatory processes over inhibition processes.
• Strong and mobile - this is the type of sanguine. All processes occurring in the cerebral cortex are strong and active. Strong, but inert, or phlegmatic type, characterized by a low rate of switching of nervous processes.

Types of the nervous system are interconnected with temperaments, but these concepts should be distinguished, because temperament characterizes a set of psycho-emotional qualities, and the type of the central nervous system describes the physiological features of the processes occurring in the central nervous system.

CNS protection

The anatomy of the nervous system is very complex. The CNS and PNS suffer from the effects of stress, overexertion, and malnutrition. Vitamins, amino acids and minerals are necessary for the normal functioning of the central nervous system. Amino acids take part in the work of the brain and are the building material for neurons. Having figured out why and what vitamins and amino acids are needed for, it becomes clear how important it is to provide the body with the necessary amount of these substances. Glutamic acid, glycine and tyrosine are especially important for humans. The scheme of taking vitamin-mineral complexes for the prevention of diseases of the central nervous system and PNS is selected individually by the attending physician.

Beam damage, congenital pathologies and anomalies in the development of the brain, as well as the action of infections and viruses - all this leads to disruption of the central nervous system and PNS and the development of various pathological conditions. Such pathologies can cause a number of very dangerous diseases - immobilization, paresis, muscle atrophy, encephalitis and much more.

Malignant neoplasms in the brain or spinal cord lead to a number of neurological disorders. If you suspect an oncological disease of the central nervous system, an analysis is prescribed - the histology of the affected departments, that is, an examination of the composition of the tissue. A neuron, as part of a cell, can also mutate. Such mutations can be detected by histology. Histological analysis is carried out according to the testimony of a doctor and consists in collecting the affected tissue and its further study. With benign formations, histology is also performed.

There are many nerve endings in the human body, damage to which can cause a number of problems. Damage often leads to a violation of the mobility of a part of the body. For example, an injury to the hand can lead to pain in the fingers and impaired movement. Osteochondrosis of the spine provoke the occurrence of pain in the foot due to the fact that an irritated or transmitted nerve sends pain impulses to receptors. If the foot hurts, people often look for the cause in a long walk or injury, but the pain syndrome can be triggered by damage to the spine.

If you suspect damage to the PNS, as well as any related problems, you should be examined by a specialist.

Nervous system- an integral morphological and functional set of various interconnected nervous structures, which, together with the humoral system, provides an interconnected regulation of the activity of all body systems and a response to changes in the conditions of the internal and external environment. The nervous system acts as an integrative system, linking sensitivity, motor activity and the work of other regulatory systems (endocrine and immune) into one whole.

General characteristics of the nervous system

All the variety of meanings of the nervous system follows from its properties.

1. , irritability and conductivity are characterized as functions of time, that is, it is a process that occurs from irritation to the manifestation of the response activity of the organ. According to the electrical theory of propagation of a nerve impulse in a nerve fiber, it propagates due to the transition of local foci of excitation to neighboring inactive regions of the nerve fiber or the process of propagating depolarization, which is similar to an electric current. Another chemical process takes place in synapses, in which the development of an excitation-polarization wave belongs to the mediator acetylcholine, that is, a chemical reaction.
2. The nervous system has the property of transforming and generating the energies of the external and internal environment and converting them into a nervous process.
3. A particularly important property of the nervous system is the property of the brain to store information in the process of not only ontogenesis, but also phylogenesis.

The nervous system consists of neurons, or nerve cells, and, or neuroglial cells. Neurons are the main structural and functional elements in both 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 shapes and sizes, form processes of two types: axons and dendrites. A neuron usually has several short branched dendrites, along which impulses follow to the body of the neuron, and one long axon, along which impulses go from the body of the neuron to other cells (neurons, muscle or glandular cells). The transfer of excitation from one neuron to other cells occurs through specialized contacts - synapses.

Morphology of neurons

The structure of nerve cells is different. There are numerous classifications of nerve cells based on the shape of their body, the length and shape of the dendrites, and other features. According to their functional significance, nerve cells are divided into motor (motor), sensory (sensory) and interneurons. The nerve cell performs two main functions: a) specific - processing the information received by the neuron and transmitting the nerve impulse; b) biosynthetic to maintain their vital activity. This finds expression in the ultrastructure of the nerve cell. The transfer of information from one cell to another, the unification of nerve cells into systems and complexes of varying complexity determine the characteristic structures of a nerve cell - axons, dendrites, synapses. Organelles associated with the provision of energy metabolism, the protein-synthesizing function of the cell, etc., are found in most cells; in nerve cells, they are subordinate to the performance of their main functions - processing and transmitting information. The body of a nerve cell at the microscopic level is a round and oval formation. The nucleus is located in the center of the cell. It contains a nucleolus and is surrounded by nuclear membranes. In the cytoplasm of nerve cells there are elements of the granular and non-granular cytoplasmic reticulum, polysomes, ribosomes, mitochondria, lysosomes, multibubbly bodies and other organelles. In the functional morphology of the cell body, attention is primarily drawn to the following ultrastructures: 1) mitochondria, which determine energy metabolism; 2) nucleus, nucleolus, granular and non-granular cytoplasmic reticulum, lamellar complex, polysomes and ribosomes, which mainly provide the protein-synthesizing function of the cell; 3) lysosomes and phagosomes - the main organelles of the "intracellular digestive tract"; 4) axons, dendrites and synapses, providing the morphofunctional connection of individual cells.

Microscopic examination reveals that the body of nerve cells, as it were, gradually passes into a dendrite, a sharp boundary and pronounced differences in the ultrastructure of the soma and the initial section of a large dendrite are not observed. Large trunks of dendrites give off large branches, as well as small twigs and spines. Axons, like dendrites, play an important role in the structural and functional organization of the brain and the mechanisms of its systemic activity. As a rule, one axon departs from the body of a nerve cell, which can then give off numerous branches. Axons are covered with a myelin sheath to form myelin fibers. The fiber bundles make up the white matter of the brain, cranial and peripheral nerves. Interweaving of axons, dendrites and processes of glial cells create complex, non-repeating patterns of the neuropil. Interconnections between nerve cells are carried out by interneuronal contacts, or synapses. Synapses are divided into axosomatic, formed by an axon with a neuron body, axodendritic, located between an axon and a dendrite, and axo-axonal, located between two axons. Dendro-dendritic synapses located between dendrites are much less common. In the synapse, a presynaptic process containing presynaptic vesicles and a postsynaptic part (dendrite, cell body, or axon) are isolated. The active zone of synaptic contact, in which the mediator is released and the impulse is transmitted, is characterized by an increase in the electron density of the presynaptic and postsynaptic membranes separated by the synaptic cleft. According to the mechanisms of impulse transmission, synapses are distinguished in which this transmission is carried out with the help of mediators, and synapses in which the impulse is transmitted electrically, without the participation of mediators.

Axonal transport plays an important role in interneuronal connections. Its principle is that in the body of a nerve cell, due to the participation of the rough endoplasmic reticulum, the lamellar complex, the nucleus and enzyme systems dissolved in the cytoplasm of the cell, a number of enzymes and complex molecules are synthesized, which are then transported along the axon to its terminal sections - synapses. The axonal transport system is the main mechanism that determines the renewal and supply of mediators and modulators in presynaptic endings, and also underlies the formation of new processes, axons and dendrites.

neuroglia

Glial 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, delimiting and protective functions.

Comparative neuroanatomy

Types of nervous systems

There are several types of organization of the nervous system, presented in various systematic groups of animals.

• Diffuse nervous system - presented in the coelenterates. Nerve cells form a diffuse nerve plexus in the ectoderm throughout the body of the animal, and with strong irritation of one part of the plexus, a generalized response occurs - the whole body reacts.
• Stem nervous system (orthogon) - some nerve cells are collected in the nerve trunks, along with which the diffuse subcutaneous plexus is also preserved. This type of nervous system is presented in flatworms and nematodes (in the latter, the diffuse plexus is greatly reduced), as well as in many other groups of protostomes - for example, gastrotrichs and cephalopods.

• The nodal nervous system, or complex ganglionic system, is present in annelids, arthropods, molluscs, and other groups of invertebrates. Most of the cells of the central nervous system are collected in nerve nodes - ganglia. In many animals, the cells in them are specialized and serve individual organs. In some mollusks (for example, cephalopods) and arthropods, a complex association of specialized ganglia with developed connections between them arises - a single brain or cephalothoracic nerve mass (in spiders). In insects, some sections of the protocerebrum (“mushroom bodies”) have a particularly complex structure.
• The tubular nervous system (neural tube) is characteristic of chordates.

Nervous system of various animals

Nervous system of cnidarians and ctenophores

Cnidarians are considered the most primitive animals that have a nervous system. In polyps, it is a primitive subepithelial neural network ( nervous plexus), braiding the entire body of the animal and consisting of neurons of different types (sensitive and ganglion cells), connected to each other by processes ( diffuse nervous system), especially dense plexuses are formed at the oral and aboral poles of the body. Irritation causes a rapid conduction of excitation through the body of the hydra and leads to a contraction of the entire body, due to the contraction of the epithelial-muscular cells of the ectoderm and at the same time their relaxation in the endoderm. Jellyfish are more complicated than polyps; in their nervous system, the central section begins to separate. In addition to the subcutaneous nerve plexus, they have ganglia along the marginal umbrella, connected by processes of nerve cells in nerve ring, from which the muscle fibers of the sail are innervated and ropalia- structures containing various ( diffuse-nodular nervous system). Greater centralization is observed in scyphomedusa and especially cube jellyfish. Their 8 ganglia, corresponding to 8 ropalia, reach a fairly large size.

The nervous system of ctenophores includes a subepithelial nerve plexus with thickening along rows of rowing plates that converge to the base of a complex aboral sensory organ. In some ctenophores, nerve ganglia located next to it are described.

Nervous system of protostomes

flatworms have already divided into central and peripheral parts of the nervous system. In general, the nervous system resembles a regular lattice - this type of structure was called orthogonal. It consists of a brain ganglion, in many groups surrounding the statocyst (endon brain), which is connected to nerve trunks orthogonal, running along the body and connected by annular transverse bridges ( commissures). Nerve trunks consist of nerve fibers extending from nerve cells scattered along their course. In some groups, the nervous system is rather primitive and close to diffuse. Among flatworms, the following trends are observed: ordering of the subcutaneous plexus with isolation of trunks and commissures, an increase in the size of the cerebral ganglion, which turns into a central control apparatus, immersion of the nervous system into the thickness of the body; and, finally, a decrease in the number of nerve trunks (in some groups, only two abdominal (lateral) trunk).

In nemerteans, the central part of the nervous system is represented by a pair of connected double ganglia located above and below the proboscis sheath, connected by commissures and reaching a significant size. Nerve trunks go back from the ganglia, usually a pair of them and they are located on the sides of the body. They are also connected by commissures, they are located in the skin-muscular sac or in the parenchyma. Numerous nerves depart from the head node, the spinal nerve (often double), abdominal and pharyngeal nerves are most strongly developed.

Gastrociliary worms have a supraesophageal ganglion, a peripharyngeal nerve ring, and two superficial lateral longitudinal trunks connected by commissures.

Nematodes have parapharyngeal nerve ring, forward and backward from which 6 nerve trunks depart, the largest - the abdominal and dorsal trunks - stretch along the corresponding hypodermal ridges. Between themselves, the nerve trunks are connected by semi-annular jumpers; they innervate the muscles of the abdominal and dorsal lateral bands, respectively. The nervous system of the nematode Caenorhabditis elegans been mapped at the cellular level. Every neuron has been registered, traced back to its origin, and most, if not all, neural connections are known. In this species, the nervous system is sexually dimorphic: the male and hermaphrodite nervous systems have different numbers of neurons and groups of neurons to perform sex-specific functions.

In kinorhynchus, the nervous system consists of a peripharyngeal nerve ring and a ventral (abdominal) trunk, on which, in accordance with their inherent body segmentation, ganglion cells are located in groups.

The nervous system of hairballs and priapulids is similar, but their ventral nerve trunk is devoid of thickenings.

Rotifers have a large supraglottic ganglion, from which nerves depart, especially large ones - two nerves that run through the entire body on the sides of the intestine. Smaller ganglia lie in the foot (pedal ganglion) and next to the masticatory stomach (mastax ganglion).

The acanthocephalans have a very simple nervous system: inside the proboscis sheath there is an unpaired ganglion, from which thin branches extend forward to the proboscis and two thicker lateral trunks back, they exit the proboscis sheath, cross the body cavity, and then go back along its walls.

Annelids have a paired supraesophageal ganglion, peripharyngeal connectives(connectives, unlike commissures, connect opposite ganglia) connected to the abdominal part of the nervous system. In primitive polychaetes, it consists of two longitudinal nerve cords, in which nerve cells are located. In more highly organized forms, they form paired ganglia in each body segment ( nervous staircase), and the nerve trunks converge. In most polychaetes, the paired ganglia merge ( ventral nerve cord), some of them merge and their connectives. Numerous nerves depart from the ganglia to the organs of their segment. In a series of polychaetes, the nervous system is immersed from under the epithelium into the thickness of the muscles or even under the skin-muscle sac. Ganglia of different segments can concentrate if their segments merge. Similar trends are observed in oligochaetes. In leeches, the nerve chain lying in the abdominal lacunar canal consists of 20 or more ganglia, and the first 4 ganglia are combined into one ( subpharyngeal ganglion) and the last 7.

In Echiurids, the nervous system is poorly developed - the peripharyngeal nerve ring is connected to the ventral trunk, but the nerve cells are scattered evenly over them and do not form knots anywhere.

Sipunculids have a supraoesophageal nerve ganglion, a peripharyngeal nerve ring, and an abdominal trunk devoid of nerve ganglions, lying on the inside of the body cavity.

Tardigrades have a supraesophageal ganglion, peripharyngeal connectives, and a ventral chain with 5 paired ganglia.

Onychophorans have a primitive nervous system. The brain consists of three sections: the protocerebrum innervates the eyes, the deutocerebrum innervates the antennae, and the tritocerebrum innervates the foregut. From the circumpharyngeal connectives, nerves depart to the jaws and oral papillae, and the connectives themselves pass into abdominal trunks far from each other, evenly covered with nerve cells and connected by thin commissures.

Nervous system of arthropods

In arthropods, the nervous system is composed of a paired supraesophageal ganglion, consisting of several connected ganglions (the brain), peripharyngeal connectives, and an abdominal nerve cord, consisting of two parallel trunks. In most groups, the brain is divided into three sections - proto-, deuto- and tritocerebrum. Each segment of the body has a pair of nerve ganglia, but ganglia often merge to form large ones; for example, the subesophageal ganglion consists of several pairs of fused ganglia - it controls the salivary glands and some muscles of the esophagus.

In a number of crustaceans, in general, the same tendencies are observed as in annelids: the convergence of a pair of abdominal nerve trunks, the fusion of paired nodes of one segment of the body (that is, the formation of the abdominal nerve chain), and the merger of its nodes in the longitudinal direction as the segments of the body merge. So, crabs have only two nerve masses - the brain and the nerve mass in the chest, while in copepods and shell crayfish, a single compact formation is formed, penetrated by the canal of the digestive system. The brain of crayfish consists of paired lobes - the protocerebrum, from which the optic nerves depart, having ganglionic clusters of nerve cells, and the deutocerebrum, which innervates antennas I. Usually, tritocerebrum is also added, formed by merged nodes of the antenna segment II, the nerves to which usually depart from the peripharyngeal connectives. Crustaceans have a developed sympathetic nervous system, consisting of the medulla and unpaired sympathetic nerve, which has several ganglia and innervates the intestines. play an important role in cancer physiology neurosecretory cells located in different parts of the nervous system and secrete neurohormones.

The centipede brain has a complex structure, most likely formed by many ganglia. The subpharyngeal ganglion innervates all the oral limbs, a long paired longitudinal nerve trunk begins from it, on which there is one paired ganglion in each segment (in bipedal centipedes in each segment, starting from the fifth, there are two pairs of ganglia located one after the other).

The nervous system of insects, also consisting of the brain and the ventral nerve chain, can achieve significant development and specialization of individual elements. The brain consists of three typical sections, each of which consists of several ganglia, separated by layers of nerve fibers. An important associative center are "mushroom bodies" protocerebrum. Particularly developed brain in social insects (ants, bees, termites). The abdominal nerve cord consists of the subpharyngeal ganglion that innervates the mouth limbs, three large thoracic nodes and abdominal nodes (no more than 11). In most species, more than 8 ganglia are not found in the adult state; in many, they merge, giving large ganglionic masses. It can reach the formation of only one ganglionic mass in the chest, which innervates both the chest and the abdomen of the insect (for example, in some flies). In ontogenesis, ganglia often unite. Sympathetic nerves leave the brain. Practically in all departments of the nervous system there are neurosecretory cells.

In horseshoe crabs, the brain is not externally dissected, but has a complex histological structure. Thickened peripharyngeal connectives innervate chelicerae, all limbs of the cephalothorax, and gill covers. The abdominal nerve chain consists of 6 ganglia, the posterior one is formed by the fusion of several. The nerves of the abdominal limbs are connected by longitudinal lateral trunks.

The nervous system of arachnids has a clear tendency to concentrate. The brain consists only of the protocerebrum and tritocerebrum due to the absence of structures that the deutocerebrum innervates. The metamerism of the ventral nerve chain is most clearly preserved in scorpions - they have a large ganglionic mass in the chest and 7 ganglia in the abdomen, in salpugs there is only 1 of them, and in spiders all ganglia have merged into the cephalothoracic nerve mass; in haymakers and ticks there is no distinction between it and the brain.

Sea spiders, like all chelicerae, do not have a deutocerebrum. The abdominal nerve cord in different species contains from 4-5 ganglia to one continuous ganglionic mass.

Nervous system of molluscs

In primitive molluscs of chitons, the nervous system consists of a peripharyngeal ring (innervates the head) and 4 longitudinal trunks - two pedal(innervate the leg, which are connected in no particular order by numerous commissures, and two pleurovisceral, which are located outward and above the pedal (innervate the visceral sac, connect above the powder). The pedal and pleurovisceral trunks of one side are also connected by many bridges.

The nervous system of monoplacophores is similar, but the pedal shafts are connected by only one bridge.

In more developed forms, as a result of the concentration of nerve cells, several pairs of ganglia are formed, which are displaced towards the anterior end of the body, with the supraesophageal ganglion (brain) receiving the greatest development.

Morphological division

The nervous system of mammals and humans according to morphological features is divided into:

• peripheral nervous system

The peripheral nervous system includes spinal nerves and nerve plexuses

Functional division

• Somatic (animal) nervous system
• Autonomic (vegetative) nervous system
  • Sympathetic division of the autonomic nervous system
  • Parasympathetic division of the autonomic nervous system
  • Metasympathetic division of the autonomic nervous system (enteric nervous system)

Ontogenesis

Models

At present, there is no single provision on the development of the nervous system in ontogeny. The main problem is to assess the level of determinism (predestination) in the development of tissues from germ cells. The most promising models are mosaic model and regulatory model. Neither one nor the other can fully explain the development of the nervous system.

• The mosaic model assumes the complete determination of the fate of an individual cell throughout the entire ontogeny.
• The regulatory model assumes the random and variable development of individual cells, with only the neural direction determined (that is, any cell of a certain group of cells can become anything within the limits of the possibility of development for this group of cells).

For invertebrates, the mosaic model is practically flawless - the degree of determination of their blastomeres is very high. But for vertebrates, things are much more complicated. A certain role of determination here is undoubted. Already at the sixteen-cell stage of development of the vertebrate blastula, it is possible to say with a sufficient degree of certainty which blastomere is not precursor of a particular organ.

Marcus Jacobson in 1985 introduced a clonal model of brain development (close to regulatory). He suggested that the fate of individual groups of cells, which are the offspring of an individual blastomere, that is, “clones” of this blastomere, is determined. Moody and Takasaki (independently) developed this model in 1987. A map of the 32-cell stage of blastula development was made. For example, it has been established that the descendants of the D2 blastomere (vegetative pole) are always found in the medulla oblongata. On the other hand, the descendants of almost all blastomeres of the animal pole do not have a pronounced determination. In different organisms of the same species, they may or may not occur in certain parts of the brain.

Regulatory mechanisms

It was found that the development of each blastomere depends on the presence and concentration of specific substances - paracrine factors, which are secreted by other blastomeres. For example, in experience in vitro with the apical part of the blastula, it turned out that in the absence of activin (the paracrine factor of the vegetative pole), the cells develop into a normal epidermis, and in its presence, depending on the concentration, as it increases: mesenchymal cells, smooth muscle cells, cells of the notochord or cells of the heart muscle.

In recent years, thanks to the emergence of new research methods, a branch called veterinary psychoneurology has begun to develop in veterinary medicine, which studies the systemic relationships between the activity of the nervous system as a whole and other organs and systems.

Professional communities and magazines

The Society for Neuroscience (SfN, the Society for Neuroscience) is the largest non-profit international organization that brings together more than 38 thousand scientists and doctors involved in the study of the brain and nervous system. The Society was founded in 1969 and is headquartered in Washington DC. Its main purpose is the exchange of scientific information between scientists. To this end, an international conference is held annually in various US cities and the Journal of Neuroscience is published. The society conducts enlightenment and educational work.

The Federation of European Neuroscience Societies (FENS, the Federation of European Neuroscience Societies) unites a large number of professional societies from European countries, including Russia. The federation was founded in 1998 and is a partner of the American Society for Neuroscience (SfN). The federation holds an international conference in different European cities every 2 years and publishes the European Journal of Neuroscience (European Journal of Neuroscience)

Interesting Facts

American Harriet Cole (1853-1888) died at the age of 35 from tuberculosis and bequeathed her body to science. Then pathologist Rufus B. Univer of the Hahnemann College of Medicine in Philadelphia spent 5 months carefully removing, dissecting and fixing Harriet's nerves. He even managed to keep the eyeballs that remained attached to the optic nerves.

About that, a person learns in his school years. Biology lessons provide general information about the body in general and about 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 failures occur in it, the work of other organs is disrupted. There are various factors that, to one degree or another, influence. nervous system characterized as one of the most important parts of the body. It determines the functional unity of the internal structures of a person and the connection of the organism with the external environment. Let's take a closer look at what is

Structure

To understand what the nervous system is, it is necessary to study all its elements separately. The neuron acts as a structural unit. It is a cell with processes. Circuits are formed from neurons. 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 - 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. The 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. In isolated fiber - axon. Its length can be 1-1.5 mm. Axons provide the transmission of impulses. In the cell membranes responsible for the perception of smell and taste, there are special compounds. They react to certain substances by changing their state.

Vegetative department

The activity of the nervous system provides the work of internal organs, glands, lymphatic and blood vessels. To a certain extent, it also determines the functioning of the muscles. In the autonomic system, parasympathetic and sympathetic divisions are distinguished. The latter provides for the expansion of the pupil and small bronchi, increased pressure, increased heart rate, etc. The parasympathetic department is responsible for the functioning of the genitals, 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 of the spinal cord.

Pathologies

Diseases of the autonomic system can be caused by various factors. Quite often, disorders are the result of other pathologies, such as TBI, poisoning, infections. Failures in the vegetative system can be caused by a lack of vitamins, frequent stress. Often diseases are "masked" by other pathologies. For example, if the functioning of the thoracic or cervical nodes of the trunk is disturbed, pain in the sternum is noted, radiating to the shoulder. Such symptoms are characteristic of heart disease, so patients often confuse the pathology.

Spinal cord

Outwardly, it resembles a heavy. The length of this section in an adult is about 41-45 cm. There are two thickenings in the spinal cord: lumbar and cervical. They form the so-called innervation structures of the lower and upper limbs. In the following departments are distinguished: sacral, lumbar, thoracic, cervical. Throughout its length, it is covered with soft, hard and arachnoid shells.

Brain

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

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

hemispheres

They also have an olfactory center. The outer shell of the hemispheres has a rather complex pattern. This is due to the presence of ridges and furrows. They form a kind of "convolutions". Each person has a unique drawing. However, there are several furrows that are the same for everyone. They allow you 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 IP Pavlov. These reactions are focused mainly on the self-preservation of the organism. The main ones are food, orientation, defensive. Unconditioned reflexes are innate.

Classification

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

Orienting reflex

It is expressed in involuntary sensory attention, accompanied by an increase in muscle tone. A reflex is evoked by a new or unexpected stimulus. Scientists call this reaction "alarming", anxiety, surprise. There are three phases of its development:

1. Cessation of current activity, fixation of posture. Simonov calls this general (preventive) inhibition. It occurs on the appearance of any stimulus with an unknown signal.
2. Transition to the "activation" reaction. At this stage, the body is transferred to a reflex readiness for a likely meeting with an emergency. This is manifested in a general increase in muscle tone. In this phase, a multicomponent reaction takes place. It includes turning the head, eyes towards the stimulus.
3. Fixation of the stimulus field to start a differentiated analysis of signals and select a response.

Meaning

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

Mechanism

The implementation of the orienting reflex is a consequence of the dynamic interaction of many formations of nonspecific and specific elements of the CNS. The general activation phase, for example, is associated with the initiation and onset of generalized cortical excitation. When analyzing the 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 directly entered the gastrointestinal tract, but also while 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 the course of subsequent research, Pavlov attributed such a reaction to conditioned (acquired) reflexes. They can come and go over the course of a person's life. For a conditioned response to occur, two stimuli must coincide. One of them in any conditions provokes a natural response - an unconditioned reflex. The second, due to its routine, does not provoke any reaction. It is defined as indifferent (indifferent). In order for a conditioned reflex to arise, the second stimulus must begin to act earlier than the unconditioned reflex by a few seconds. At the same time, the biological significance of the former should be less.

Nervous system protection

As you know, a variety of factors affect the body. State of the nervous system affects other organs. Even seemingly minor failures can cause serious illness. At the same time, they will not always be associated with the activity of the nervous system. In this regard, much attention should be paid to preventive measures. First of all, it is necessary to reduce irritating factors. It is known that constant stress, experiences are one of the causes of cardiac pathologies. The treatment of these diseases includes not only medicines, but also physiotherapy, exercise therapy, etc. Diet is of particular importance. The state of all human systems and organs depends on proper nutrition. Food should contain enough vitamins. Experts recommend including plant foods, herbs, vegetables and fruits in the diet.

Vitamin C

It has a beneficial effect on all body systems, including the nervous system. Vitamin C provides energy 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 the negative effects of free radicals by binding them. In addition, the substance is able to enhance the activity of other antioxidants. These include vitamin E and selenium.

Lecithin

It ensures the normal course of processes in the nervous system. Lecithin is the main nutrient for cells. The content in the peripheral section is about 17%, in the brain - 30%. With insufficient intake of lecithin, 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 B-vitamin group and promotes energy production. In addition, lecithin is involved in the production of acetylcholine.

Music that calms the nervous system

As mentioned above, in diseases of the central nervous system, therapeutic measures may include not only taking medications. The therapeutic course is selected depending on the severity of the violations. Meanwhile, relaxation of the nervous system often achieved without consulting 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, a march can also calm some people. 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 classical, folk melodies. The main sign of relaxing music is a quiet monotony. It "envelops" the listener, creating a soft but strong "cocoon" that protects the person from external irritations. Relaxing music can be classical, but not symphonic. Usually it is performed by one instrument: piano, guitar, violin, flute. It can also be a song with repeated recitative and simple words.

The sounds of nature are very popular - the rustle of leaves, the sound of rain, bird singing. In combination with the melody of several instruments, they take a person away from the daily hustle and bustle, the rhythm of the metropolis, and relieve nervous and muscular tension. When listening, thoughts are ordered, excitement is replaced by calmness.