What is the nervous system of organs. The structure and functions of the human nervous system
In the human body, the work of all its organs is closely interconnected, and therefore the body functions as a whole. Function Consistency internal organs provides 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 departing from the head and spinal cord nerves 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 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 organism. 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 bark hemispheres. 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, constancy 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 associated with environment and with the organs of the body 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 executive bodies. 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 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 area where it is projected this species sensitivity, 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.
Many neural processes take place in the cerebral cortex. 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 idea of higher nervous activity created by I. P. Pavlov, who, exploring 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 whole complex irritants. 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 in the cortex not only the formation of conditioned reflexes, 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, the animal produces conditional 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 nature and the public 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 general properties, which 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. Words are used to form general concepts. 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, on snow, etc. Scientific analysis dreams from a materialistic position showed 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 activity of the nervous system are created with the correct alternation of labor, active rest 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.
All organs and systems of the human body are closely interconnected, they interact with the help of the nervous system, which regulates all the mechanisms of life, from digestion to the process of reproduction. It is known that a person (NS) provides communication human body with the external environment. The unit of the NS is the neuron, which is a nerve cell that conducts impulses to other cells of the body. Connecting into neural circuits, they form a whole system, both somatic and vegetative.
We can say that the NS is plastic, as it is able to restructure its work in the event that changes occur in the needs of the human body. This mechanism is especially relevant when one of the parts of the brain is damaged.
Since the human nervous system coordinates the work of all organs, its damage affects the activity of both nearby and distant structures, and is accompanied by the failure of the functions of organs, tissues and body systems. The causes of disruption of the nervous system may lie in the presence of infections or poisoning of the body, in the occurrence of a tumor or injury, in diseases of the National Assembly and metabolic disorders.
Thus, the human NS plays a conducting role in the formation and development of the human body. Thanks to the evolutionary improvement of the nervous system, the human psyche and consciousness developed. The nervous system is a vital mechanism for regulating the processes that occur in the human body.
a set of nerve formations in vertebrates and humans, through which the perception of stimuli acting on the body is realized, the processing of the resulting excitation impulses, the formation of responses. Thanks to it, the functioning of the body as a whole is ensured:
1) contacts with the outside world;
2) implementation of goals;
3) coordination of the work of internal organs;
4) holistic adaptation of the body.
The neuron acts as the main structural and functional element of the nervous system. Stand out:
1) the central nervous system - which consists of the brain and spinal cord;
2) peripheral nervous system - which consists of nerves extending from the brain and spinal cord, from intervertebral nerve nodes, as well as from the peripheral part of the autonomic nervous system;
3) vegetative nervous system - structures of the nervous system that provide control of the vegetative functions of the body.
NERVOUS SYSTEM
English nervous system) - a set of nerve formations in the human body and vertebrates. Its main functions are: 1) ensuring contacts with the outside world (perception of information, organization of body reactions - from simple responses to stimuli to complex behavioral acts); 2) realization of the goals and intentions of a person; 3) integration of internal organs into systems, coordination and regulation of their activities (see Homeostasis); 4) organization of integral functioning and development of the organism.
Structural and functional element of N. with. is a neuron - a nerve cell consisting of a body, dendrites (the receptor and integrating apparatus of the neuron) and an axon (its efferent part). On the terminal branches of the axon there are special formations that are in contact with the body and dendrites of other neurons - synapses. Synapses are of 2 types - excitatory and inhibitory, with their help, respectively, the transmission or blockade of the impulse message passing through the fiber to the destination neuron occurs.
The interaction of postsynaptic excitatory and inhibitory effects on one neuron creates a multi-conditioning response of the cell, which is the simplest element of integration. Neurons, differentiated in structure and function, are combined into neural modules (neural ensembles) - next. a stage of integration that ensures high plasticity in the organization of brain functions (see Plasticity n. s).
N. s. divided into central and peripheral. C. n. with. It consists of the brain, which is located in the cranial cavity, and the spinal cord, located in the spine. The brain, especially its cortex, is the most important organ of mental activity. The spinal cord carries out g. inborn behaviors. Peripheral N. with. consists of nerves extending from the brain and spinal cord (the so-called cranial and spinal nerves), intervertebral ganglions, and also from the peripheral part of the autonomic N. with. - accumulations of nerve cells (ganglia) with nerves approaching them (preganglionic) and departing from them (postganglionic) nerves.
The vegetative functions of the body (digestion, blood circulation, respiration, metabolism, etc.) are controlled by vegetative nervous system, which is divided into sympathetic and parasympathetic sections: the 1st section mobilizes the functions of the body in a state of increased mental stress, the 2nd - ensures the functioning of internal organs in normal conditions. Si. Blocks of the brain, Deep structures of the brain, Cortex, Neuron-detector, Properties n. with. (N. V. Dubrovinskaya, D. A. Farber.)
NERVOUS SYSTEM
nervous system) - a set of anatomical structures formed by nervous tissue. The nervous system consists of many neurons that transmit information in the form of nerve impulses to various parts of the body and receive it from them to maintain the active life of the body. The nervous system is divided into central and peripheral. The brain and spinal cord form the central nervous system; peripheral nerves include paired spinal and cranial nerves with their roots, their branches, nerve endings and ganglia. There is another classification, according to which the unified nervous system is also conventionally divided into two parts: somatic (animal) and autonomic (autonomous). The somatic nervous system innervates mainly the organs of the soma (body, striated, or skeletal, muscles, skin) and some internal organs (tongue, larynx, pharynx), provides a connection between the body and the external environment. The autonomic (autonomous) nervous system innervates all the viscera, glands, including endocrine, smooth muscles of organs and skin, blood vessels and the heart, regulates metabolic processes in all organs and tissues. The autonomic nervous system, in turn, is divided into two parts: parasympathetic and sympathetic. In each of them, as in the somatic nervous system, the central and peripheral sections are distinguished (ed.). The main structural and functional unit of the nervous system is the neuron (nerve cell).
Nervous system
Word formation. Comes from the Greek. neuron - vein, nerve and systema - connection.
Specificity. Her work provides:
Contacts with the outside world;
Realization of goals;
Coordination of the work of internal organs;
Whole body adaptation.
The neuron is the main structural and functional element of the nervous system.
The central nervous system, which consists of the brain and spinal cord,
Peripheral nervous system, consisting of nerves extending from the brain and spinal cord, intervertebral ganglions;
Peripheral division of the autonomic nervous system.
NERVOUS SYSTEM
Collective designation of a complete system of structures and organs, consisting of nervous tissue. Depending on what is in the center of attention, various schemes for isolating parts of the nervous system are used. The most common is the anatomical division into the central nervous system (the brain and spinal cord) and the peripheral nervous system (everything else). Another taxonomy is based on functions, dividing the nervous system into the somatic nervous system and the autonomic nervous system, the first serves to carry out voluntary, conscious sensory and motor functions, and the last - for visceral, automatic, involuntary.
Source: Nervous system
A system that ensures the integration of the functions of all organs and tissues, their trophism, communication with the outside world, sensitivity, movement, consciousness, alternation of wakefulness and sleep, the state of emotional and mental processes, including manifestations of higher nervous activity, the development of which determines the characteristics of a person's personality. S.n. It is divided primarily into central, represented by the brain tissue (brain and spinal cord), and peripheral, which includes all other structures of the nervous system.
NERVOUS SYSTEM
a complex network of structures that permeates the entire body and ensures self-regulation of its vital activity due to the ability to respond to external and internal influences (stimuli). The main functions of the nervous system are the receipt, storage and processing of information from the external and internal environment, the regulation and coordination of the activities of all organs and organ systems. In humans, as in all mammals, the nervous system includes three main components: 1) nerve cells (neurons); 2) glial cells associated with them, in particular neuroglial cells, as well as cells that form neurilemma; 3) connective tissue. Neurons provide the conduction of nerve impulses; neuroglia performs supporting, protective and trophic functions both in the brain and spinal cord, and neurilemma, which consists mainly of specialized, so-called. Schwann cells, participates in the formation of sheaths of peripheral nerve fibers; connective tissue supports and links together the various parts of the nervous system. The human nervous system is divided in different ways. Anatomically, it consists of the central nervous system (CNS) and the peripheral nervous system (PNS). The central nervous system includes the brain and spinal cord, and the PNS, which provides communication between the central nervous system and various parts of the body, includes cranial and spinal nerves, as well as nerve nodes (ganglia) and nerve plexuses that lie outside the spinal cord and brain.
Neuron. The structural and functional unit of the nervous system is a nerve cell - a neuron. It is estimated that there are more than 100 billion neurons in the human nervous system. A typical neuron consists of a body (i.e., a nuclear part) and processes, one usually non-branching process, an axon, and several branching ones, dendrites. The axon carries impulses from the cell body to the muscles, glands, or other neurons, while the dendrites carry them to the cell body. In a neuron, as in other cells, there is a nucleus and a number of tiny structures - organelles (see also CELL). These include the endoplasmic reticulum, ribosomes, Nissl bodies (tigroid), mitochondria, the Golgi complex, lysosomes, filaments (neurofilaments and microtubules).
Nerve impulse. If the stimulation of a neuron exceeds a certain threshold value, then a series of chemical and electrical changes occur at the point of stimulation, which spread throughout the neuron. Transmitted electrical changes are called nerve impulses. Unlike a simple electric discharge, which, due to the resistance of the neuron, will gradually weaken and be able to overcome only a short distance, a much slower "running" nerve impulse in the process of propagation is constantly restored (regenerates). The concentration of ions (electrically charged atoms) - mainly sodium and potassium, as well as organic matter- outside the neuron and inside it are not the same, so the nerve cell at rest is negatively charged from the inside, and positively from the outside; as a result, a potential difference arises on the cell membrane (the so-called "resting potential" is approximately -70 millivolts). Any change that reduces the negative charge inside the cell and thereby the potential difference across the membrane is called depolarization. The plasma membrane surrounding a neuron is a complex formation consisting of lipids (fats), proteins and carbohydrates. It is practically impermeable to ions. But some of the protein molecules in the membrane form channels through which certain ions can pass. However, these channels, called ionic channels, are not always open, but, like gates, they can open and close. When a neuron is stimulated, some of the sodium (Na +) channels open at the point of stimulation, due to which sodium ions enter the cell. The influx of these positively charged ions reduces the negative charge of the inner surface of the membrane in the region of the channel, which leads to depolarization, which is accompanied by abrupt change voltage and discharge - there is a so-called. "action potential", i.e. nerve impulse. The sodium channels then close. In many neurons, depolarization also causes potassium (K+) channels to open, causing potassium ions to flow out of the cell. The loss of these positively charged ions again increases the negative charge on the inner surface of the membrane. The potassium channels then close. Other membrane proteins also begin to work - the so-called. potassium-sodium pumps that ensure the movement of Na + from the cell, and K + into the cell, which, along with the activity of potassium channels, restores the initial electrochemical state (resting potential) at the point of stimulation. Electrochemical changes at the point of stimulation cause depolarization at the adjacent point of the membrane, triggering the same cycle of changes in it. This process is constantly repeated, and at each new point where depolarization occurs, an impulse of the same magnitude is born as at the previous point. Thus, along with the renewed electrochemical cycle, the nerve impulse propagates through the neuron from point to point. Nerves, nerve fibers and ganglia. A nerve is a bundle of fibers, each of which functions independently of the others. The fibers in a nerve are organized into groups surrounded by a specialized connective tissue, in which the vessels pass, supplying the nerve fibers with nutrients and oxygen and removing carbon dioxide and decay products. Nerve fibers along which impulses propagate from peripheral receptors to the central nervous system (afferent) are called sensitive or sensory. Fibers that transmit impulses from the central nervous system to muscles or glands (efferent) are called motor or motor. Most nerves are mixed and consist of both sensory and motor fibers. A ganglion (ganglion) is a cluster of neuron bodies in the peripheral nervous system. Axon fibers in the PNS are surrounded by a neurilemma - a sheath of Schwann cells that are located along the axon, like beads on a thread. A significant number of these axons are covered with an additional sheath of myelin (a protein-lipid complex); they are called myelinated (meaty). Fibers that are surrounded by neurilemma cells, but not covered with a myelin sheath, are called unmyelinated (non-myelinated). Myelinated fibers are found only in vertebrates. The myelin sheath is formed from the plasma membrane of the Schwann cells, which winds around the axon like a roll of ribbon, forming layer upon layer. The area of the axon where two adjacent Schwann cells touch each other is called the node of Ranvier. In the CNS, the myelin sheath of nerve fibers is formed by a special type of glial cells - oligodendroglia. Each of these cells forms the myelin sheath of several axons at once. Unmyelinated fibers in the CNS lack sheaths of any special cells. The myelin sheath speeds up the conduction of nerve impulses that "jump" from one node of Ranvier to another, using this sheath as a connecting electrical cable. The speed of impulse conduction increases with the thickening of the myelin sheath and ranges from 2 m/s (along unmyelinated fibers) to 120 m/s (along fibers especially rich in myelin). For comparison: the propagation speed electric current on metal wires - from 300 to 3000 km / s.
Synapse. Each neuron has a specialized connection to muscles, glands, or other neurons. The zone of functional contact between two neurons is called a synapse. Interneuronal synapses are formed between different parts of two nerve cells: between an axon and a dendrite, between an axon and a cell body, between a dendrite and a dendrite, between an axon and an axon. A neuron that sends an impulse to a synapse is called presynaptic; the neuron receiving the impulse is postsynaptic. The synaptic space is slit-shaped. A nerve impulse propagating along the membrane of a presynaptic neuron reaches the synapse and stimulates the release of a special substance - a neurotransmitter - into a narrow synaptic cleft. Neurotransmitter molecules diffuse through the cleft and bind to receptors on the membrane of the postsynaptic neuron. If the neurotransmitter stimulates the postsynaptic neuron, its action is called excitatory; if it suppresses, it is called inhibitory. The result of the summation of hundreds and thousands of excitatory and inhibitory impulses simultaneously flowing to a neuron is the main factor determining whether this postsynaptic neuron will generate a nerve impulse in this moment. In a number of animals (for example, in the spiny lobster), a particularly close connection is established between the neurons of certain nerves with the formation of either an unusually narrow synapse, the so-called. gap junction, or, if neurons are in direct contact with each other, tight junction. Nerve impulses pass through these connections not with the participation of a neurotransmitter, but directly, by electrical transmission. A few dense junctions of neurons are also found in mammals, including humans.
Regeneration. By the time a person is born, all his neurons and most of interneuronal connections have already been formed, and in the future only single new neurons are formed. When a neuron dies, it is not replaced by a new one. However, the remaining ones can take over the functions of the lost cell, forming new processes that form synapses with those neurons, muscles or glands with which the lost neuron was connected. Cut or damaged PNS neuron fibers surrounded by neurilemma can regenerate if the cell body remains intact. Below the site of transection, the neurilemma is preserved as a tubular structure, and that part of the axon that remains connected with the cell body grows along this tube until it reaches the nerve ending. Thus, the function of the damaged neuron is restored. Axons in the CNS that are not surrounded by a neurilemma are apparently unable to grow back to the site of their former termination. However, many CNS neurons can give rise to new short processes - branches of axons and dendrites that form new synapses.
CENTRAL NERVOUS SYSTEM
The CNS consists of the brain and spinal cord and their protective membranes. The outermost is the dura mater, under it is the arachnoid (arachnoid), and then the pia mater, fused with the surface of the brain. Between the soft and arachnoid membranes is the subarachnoid (subarachnoid) space containing the cerebrospinal (cerebrospinal) fluid, in which both the brain and the spinal cord literally float. The action of the buoyancy force of the fluid leads to the fact that, for example, the brain of an adult, having an average mass of 1500 g, actually weighs 50-100 g inside the skull. The meninges and cerebrospinal fluid also play the role of shock absorbers, softening all kinds of shocks and shocks that experiences the body and which could cause damage to the nervous system. The CNS is made up of gray and white matter. Gray matter is made up of cell bodies, dendrites, and unmyelinated axons, organized into complexes that include countless synapses and serve as information processing centers for many of the functions of the nervous system. White matter consists of myelinated and unmyelinated axons, which act as conductors that transmit impulses from one center to another. The composition of gray and white matter also includes glial cells. CNS neurons form many circuits that perform two main functions: they provide reflex activity, as well as complex information processing in higher brain centers. These higher centers, such as the visual cortex (visual cortex), receive incoming information, process it, and transmit a response signal along the axons. The result of the activity of the nervous system is one or another activity, which is based on the contraction or relaxation of muscles or the secretion or cessation of secretion of glands. It is with the work of muscles and glands that any way of our self-expression is connected. Incoming sensory information is processed by passing through a sequence of centers connected by long axons, which form specific pathways, such as pain, visual, auditory. Sensitive (ascending) pathways go in an ascending direction to the centers of the brain. Motor (descending) pathways connect the brain with the motor neurons of the cranial and spinal nerves. Pathways are usually organized in such a way that information (for example, pain or tactile) from the right side of the body goes to the left side of the brain and vice versa. This rule also applies to descending motor pathways: the right half of the brain controls the movements of the left half of the body, and the left half controls the right. From this general rule however, there are a few exceptions. The brain consists of three main structures: the cerebral hemispheres, the cerebellum, and the brainstem. The large hemispheres are the most large part brain - contain higher nerve centers that form the basis of consciousness, intellect, personality, speech, understanding. In each of the large hemispheres, the following formations are distinguished: isolated accumulations (nuclei) of gray matter lying in the depths, which contain many important centers; a large array of white matter located above them; covering the hemispheres from the outside, a thick layer of gray matter with numerous convolutions, constituting the cerebral cortex. The cerebellum also consists of a deep gray matter, an intermediate array of white matter, and an outer thick layer of gray matter that forms many convolutions. The cerebellum provides mainly coordination of movements. The brain stem is formed by a mass of gray and white matter, not divided into layers. The trunk is closely connected with the cerebral hemispheres, cerebellum and spinal cord and contains numerous centers of sensory and motor pathways. The first two pairs of cranial nerves depart from the cerebral hemispheres, the remaining ten pairs from the trunk. The trunk regulates such vital functions as breathing and blood circulation.
see also HUMAN BRAIN.
Spinal cord. Located inside the spinal column and protected by its bone tissue, the spinal cord has a cylindrical shape and is covered with three membranes. On a transverse section, the gray matter has the shape of the letter H or a butterfly. Gray matter is surrounded by white matter. The sensory fibers of the spinal nerves end in the dorsal (posterior) sections of the gray matter - the posterior horns (at the ends of H facing the back). The bodies of motor neurons of the spinal nerves are located in the ventral (anterior) sections of the gray matter - the anterior horns (at the ends of H, remote from the back). In the white matter, there are ascending sensory pathways ending in the gray matter of the spinal cord, and descending motor pathways coming from the gray matter. In addition, many fibers in the white matter connect the different parts of the gray matter of the spinal cord.
PERIPHERAL NERVOUS SYSTEM
The PNS provides a two-way connection between the central parts of the nervous system and the organs and systems of the body. Anatomically, the PNS is represented by cranial (cranial) and spinal nerves, as well as a relatively autonomous enteric nervous system localized in the intestinal wall. All cranial nerves (12 pairs) are divided into motor, sensory or mixed. The motor nerves originate in the motor nuclei of the trunk, formed by the bodies of the motor neurons themselves, and the sensory nerves are formed from the fibers of those neurons whose bodies lie in the ganglia outside the brain. 31 pairs of spinal nerves depart from the spinal cord: 8 pairs of cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. They are designated according to the position of the vertebrae adjacent to the intervertebral foramen from which these nerves emerge. Each spinal nerve has an anterior and a posterior root that merges to form the nerve itself. The back root contains sensory fibers; it is closely related to the spinal ganglion (posterior root ganglion), which consists of the bodies of neurons whose axons form these fibers. The anterior root consists of motor fibers formed by neurons whose cell bodies lie in the spinal cord.
AUTONOMIC SYSTEM
The autonomic, or autonomic, nervous system regulates the activity of the involuntary muscles, the heart muscle, and various glands. Its structures are located both in the central nervous system and in the peripheral. The activity of the autonomic nervous system is aimed at maintaining homeostasis, i.e. a relatively stable state of the internal environment of the body, such as a constant body temperature or blood pressure corresponding to the needs of the body. Signals from the CNS arrive at the working (effector) organs through pairs of series-connected neurons. The bodies of neurons of the first level are located in the CNS, and their axons terminate in the autonomic ganglia lying outside the CNS, and here they form synapses with the bodies of neurons of the second level, the axons of which directly contact the effector organs. The first neurons are called preganglionic, the second - postganglionic. In that part of the autonomic nervous system, which is called the sympathetic, the bodies of preganglionic neurons are located in the gray matter of the thoracic (thoracic) and lumbar (lumbar) spinal cord. Therefore, the sympathetic system is also called the thoraco-lumbar system. The axons of its preganglionic neurons terminate and form synapses with postganglionic neurons in the ganglia located in a chain along the spine. Axons of postganglionic neurons are in contact with effector organs. The endings of postganglionic fibers secrete norepinephrine (a substance close to adrenaline) as a neurotransmitter, and therefore the sympathetic system is also defined as adrenergic. The sympathetic system is complemented by the parasympathetic nervous system. The bodies of its pregangliar neurons are located in the brainstem (intracranial, i.e. inside the skull) and the sacral (sacral) section of the spinal cord. Therefore, the parasympathetic system is also called the craniosacral system. Axons of preganglionic parasympathetic neurons terminate and form synapses with postganglionic neurons in the ganglia located near the working organs. The endings of postganglionic parasympathetic fibers release the neurotransmitter acetylcholine, on the basis of which the parasympathetic system is also called the cholinergic system. As a rule, the sympathetic system stimulates those processes that are aimed at mobilizing the body's forces in extreme situations or under stress. The parasympathetic system contributes to the accumulation or restoration of the body's energy resources. The reactions of the sympathetic system are accompanied by the consumption of energy resources, an increase in the frequency and strength of heart contractions, an increase in blood pressure and blood sugar, as well as an increase in blood flow to skeletal muscles due to a decrease in its flow to internal organs and skin. All of these changes are characteristic of the "fright, flight or fight" response. The parasympathetic system, on the contrary, reduces the frequency and strength of heart contractions, lowers blood pressure, stimulates digestive system. The sympathetic and parasympathetic systems act in a coordinated manner and cannot be regarded as antagonistic. Together they support the functioning of internal organs and tissues at a level corresponding to the intensity of stress and the emotional state of a person. Both systems function continuously, but their activity levels fluctuate depending on the situation.
REFLEXES
When an adequate stimulus acts on the receptor of a sensory neuron, a volley of impulses arises in it, triggering a response action called a reflex act (reflex). Reflexes underlie most of the manifestations of the vital activity of our body. The reflex act is carried out by the so-called. reflex arc; this term refers to the path of transmission of nerve impulses from the point of initial stimulation on the body to the organ that performs the response. The arc of the reflex that causes contraction of the skeletal muscle consists of at least two neurons: a sensory neuron, whose body is located in the ganglion, and the axon forms a synapse with the neurons of the spinal cord or brain stem, and the motor (lower, or peripheral, motor neuron), whose body is located in gray matter, and the axon terminates in a motor end plate on skeletal muscle fibers. The reflex arc between the sensory and motor neurons can also include a third, intermediate, neuron located in the gray matter. The arcs of many reflexes contain two or more intermediate neurons. Reflex actions are carried out involuntarily, many of them are not realized. The knee jerk, for example, is elicited by tapping the quadriceps tendon at the knee. This is a two-neuron reflex, its reflex arc consists of muscle spindles (muscle receptors), a sensory neuron, a peripheral motor neuron, and a muscle. Another example is the reflex withdrawal of a hand from a hot object: the arc of this reflex includes a sensory neuron, one or more intermediate neurons in the gray matter of the spinal cord, a peripheral motor neuron, and a muscle. Many reflex acts have a much more complex mechanism. The so-called intersegmental reflexes are made up of combinations of simpler reflexes, in the implementation of which many segments of the spinal cord take part. Thanks to such reflexes, for example, coordination of the movements of the arms and legs when walking is ensured. The complex reflexes that close in the brain include movements associated with maintaining balance. Visceral reflexes, i.e. reflex reactions of internal organs mediated by the autonomic nervous system; they provide emptying of the bladder and many processes in the digestive system.
see also REFLEX.
DISEASES OF THE NERVOUS SYSTEM
Damage to the nervous system occurs with organic diseases or injuries of the brain and spinal cord, meninges, peripheral nerves. Diagnosis and treatment of diseases and injuries of the nervous system is the subject of a special branch of medicine - neurology. Psychiatry and clinical psychology are mainly concerned with mental disorders. The areas of these medical disciplines often overlap. See individual diseases of the nervous system: ALZHEIMER'S DISEASE;
STROKE ;
MENINGITIS;
NEURITIS;
PARALYSIS;
PARKINSON'S DISEASE;
POLIO;
MULTIPLE SCLEROSIS ;
TENETIS;
CEREBRAL PALSY ;
CHOREA;
ENCEPHALITIS;
EPILEPSY.
see also
ANATOMY COMPARATIVE;
HUMAN ANATOMY .
LITERATURE
Bloom F., Leizerson A., Hofstadter L. Brain, mind and behavior. M., 1988 Human Physiology, ed. R. Schmidt, G. Tevsa, vol. 1. M., 1996
Collier Encyclopedia. - Open Society. 2000 .
Include organs of the central nervous system (brain and spinal cord) and organs of the peripheral nervous system (peripheral ganglions, peripheral nerves, receptor and effector nerve endings).
Functionally, the nervous system is divided into somatic, which innervates skeletal muscle tissue, i.e., controlled by consciousness, and vegetative (autonomous), which regulates the activity of internal organs, blood vessels and glands, i.e. does not depend on consciousness.
The functions of the nervous system are regulatory and integrating.
It is laid on the 3rd week of embryogenesis in the form of a neural plate, which is transformed into a neural groove, from which a neural tube is formed. There are 3 layers in its wall:
Internal - ependymal:
Medium - raincoat. Later it turns into gray matter.
External - edge. It produces white matter.
In the cranial part of the neural tube, an extension is formed, from which 3 cerebral vesicles are formed at the beginning, and later - five. The latter give rise to five parts of the brain.
The spinal cord is formed from the trunk of the neural tube.
In the first half of embryogenesis, there is an intensive proliferation of young glial and nerve cells. Subsequently, a radial glia is formed in the mantle layer of the cranial region. Its thin long processes penetrate the wall of the neural tube. Young neurons migrate along these processes. There is a formation of centers of the brain (especially intensively from 15 to 20 weeks - a critical period). Gradually, in the second half of embryogenesis, proliferation and migration fade. After birth, division stops. When the neural tube is formed, cells that are located between the ectoderm and the neural tube are evicted from the neural folds (interlocking areas), forming the neural crest. The latter is split into 2 sheets:
1 - under the ectoderm, pigmentocytes (skin cells) are formed from it;
2 - around the neural tube - ganglionic plate. Peripheral nerve nodes (ganglia), the adrenal medulla, and sections of chromaffin tissue (along the spine) are formed from it. After birth, there is an intensive growth of the processes of nerve cells: axons and dendrites, synapses between neurons, neural circuits (a strictly ordered interneuronal connection) are formed, which make up reflex arcs (successively located cells that transmit information) that provide reflex activity of a person (especially the first 5 years of life child, so stimuli are needed to form bonds). Also in the first years of a child's life, myelination is the most intensive - the formation of nerve fibers.
PERIPHERAL NERVOUS SYSTEM (PNS).
Peripheral nerve trunks are part of the neurovascular bundle. They are mixed in function, contain sensory and motor nerve fibers (afferent and efferent). Myelinated nerve fibers predominate, and non-myelinated ones are in small quantities. Around each nerve fiber is a thin layer of loose connective tissue with blood and lymphatic vessels - endoneurium. Around the bundle of nerve fibers is a sheath of loose fibrous connective tissue - the perineurium - with a small number of vessels (it mainly performs a frame function). Around the entire peripheral nerve there is a sheath of loose connective tissue with larger vessels - the epineurium. Peripheral nerves regenerate well, even after complete damage. Regeneration is carried out due to the growth of peripheral nerve fibers. The growth rate is 1-2 mm per day (the ability to regenerate is a genetically fixed process).
spinal node
It is a continuation (part) of the posterior root of the spinal cord. Functionally sensitive. Outside covered with a connective tissue capsule. Inside - connective tissue layers with blood and lymphatic vessels, nerve fibers (vegetative). In the center - myelinated nerve fibers of pseudo-unipolar neurons located along the periphery of the spinal ganglion. Pseudo-unipolar neurons have a large rounded body, a large nucleus, well-developed organelles, especially the protein-synthesizing apparatus. A long cytoplasmic outgrowth departs from the body of the neuron - this is part of the body of the neuron, from which one dendrite and one axon depart. Dendrite - long, forms a nerve fiber that goes as part of a peripheral mixed nerve to the periphery. Sensitive nerve fibers end at the periphery with a receptor, i.e. sensitive nerve ending. Axons are short and form the posterior root of the spinal cord. In the posterior horns of the spinal cord, axons form synapses with interneurons. Sensitive (pseudo-unipolar) neurons constitute the first (afferent) link of the somatic reflex arc. All cell bodies are located in ganglia.
Spinal cord
Outside, it is covered with a pia mater, which contains blood vessels that penetrate into the substance of the brain. Conventionally, 2 halves are distinguished, which are separated by the anterior median fissure and the posterior median connective tissue septum. In the center is the central canal of the spinal cord, which is located in the gray matter, lined with ependyma, contains cerebrospinal fluid, which is in constant motion. Along the periphery is white matter, where there are bundles of nerve myelin fibers that form pathways. They are separated by glial-connective tissue septa. In the white matter, the anterior, lateral and posterior cords are distinguished.
In the middle part there is a gray matter, in which the posterior, lateral (in the thoracic and lumbar segments) and anterior horns are distinguished. The halves of the gray matter are connected by the anterior and posterior commissures of the gray matter. The gray matter contains a large number of glial and nerve cells. Gray matter neurons are divided into:
1) Internal neurons, completely (with processes) located within the gray matter, are intercalated and are located mainly in the posterior and lateral horns. There are:
a) Associative. located within one half.
b) Commissural. Their processes extend into the other half of the gray matter.
2) Beam neurons. They are located in the posterior horns and in the lateral horns. They form nuclei or are located diffusely. Their axons enter the white matter and form bundles of nerve fibers in an ascending direction. They are inserts.
3) Radicular neurons. They are located in the lateral nuclei (kernels of the lateral horns), in the anterior horns. Their axons extend beyond the spinal cord and form the anterior roots of the spinal cord.
In the superficial part of the posterior horns there is a spongy layer, which contains a large number of small intercalary neurons.
Deeper than this strip is a gelatinous substance containing mainly glial cells, small neurons (the latter in small quantities).
In the middle part is the own nucleus of the posterior horns. It contains large beam neurons. Their axons go to the white matter of the opposite half and form the dorsal-cerebellar anterior and dorsal-thalamic posterior pathways.
The cells of the nucleus provide exteroceptive sensitivity.
At the base of the posterior horns is the thoracic nucleus (Clark-Shutting column), which contains large bundle neurons. Their axons go to the white matter of the same half and participate in the formation of the posterior spinal cerebellar tract. Cells in this pathway provide proprioceptive sensitivity.
AT intermediate zone are the lateral and medial nuclei. The medial intermediate nucleus contains large bundle neurons. Their axons go to the white matter of the same half and form the anterior spinal cerebellar tract, which provides visceral sensitivity.
The lateral intermediate nucleus refers to the autonomic nervous system. Thoracic and upper lumbar regions is the sympathetic nucleus, and in the sacral - the nucleus of the parasympathetic nervous system. It contains an intercalary neuron, which is the first neuron of the efferent link of the reflex arc. This is a radicular neuron. Its axons exit as part of the anterior roots of the spinal cord.
In the anterior horns are large motor nuclei, which contain motor radicular neurons with short dendrites and a long axon. The axon exits as part of the anterior roots of the spinal cord, and then goes as part of the peripheral mixed nerve, represents motor nerve fibers and is pumped at the periphery by a neuromuscular synapse on skeletal muscle fibers. They are effectors. Forms the third effector link of the somatic reflex arc.
In the anterior horns, a medial group of nuclei is isolated. It is developed in the thoracic region and provides innervation to the muscles of the body. The lateral group of nuclei is located in the cervical and lumbar regions and innervates the upper and lower extremities.
In the gray matter of the spinal cord there is a large number of diffuse bundle neurons (in the posterior horns). Their axons go into the white matter and immediately divide into two branches that go up and down. Branches through 2-3 segments of the spinal cord return back to the gray matter and form synapses on the motor neurons of the anterior horns. These cells form their own apparatus of the spinal cord, which provides a connection between neighboring 4-5 segments of the spinal cord, which ensures the response of a muscle group (an evolutionarily developed protective reaction).
The white matter contains ascending (sensitive) pathways, which are located in the posterior cords and in the peripheral part of the lateral horns. Descending nerve pathways (motor) are located in the anterior cords and in the inner part of the lateral cords.
Regeneration. Very poorly regenerates gray matter. Regeneration of white matter is possible, but the process is very long.
Histophysiology of the cerebellum. The cerebellum refers to the structures of the brain stem, i.e. is a more ancient formation that is part of the brain.
Performs a number of functions:
balance;
The centers of the autonomic nervous system (ANS) (intestinal motility, blood pressure control) are concentrated here.
Outside covered with meninges. The surface is embossed due to deep furrows and convolutions, which are deeper than in the cerebral cortex (CBC).
On the cut is represented by the so-called "tree of life".
The gray matter is located mainly along the periphery and inside, forming nuclei.
In each gyrus, the central part is occupied by white matter, in which 3 layers are clearly visible:
1 - surface - molecular.
2 - medium - ganglionic.
3 - internal - granular.
1. The molecular layer is represented by small cells, among which basket and stellate (small and large) cells are distinguished.
Basket cells are located closer to the ganglion cells of the middle layer, i.e. inside the layer. They have small bodies, their dendrites branch in the molecular layer, in a plane transverse to the course of the gyrus. The neurites run parallel to the plane of the gyrus above the bodies of the pear-shaped cells (the ganglion layer), forming numerous branches and contacts with the dendrites of the pear-shaped cells. Their branches are braided around the bodies of pear-shaped cells in the form of baskets. Excitation of basket cells leads to inhibition of pear-shaped cells.
Outwardly, stellate cells are located, the dendrites of which branch out here, and the neurites participate in the formation of the basket and communicate by synapses with the dendrites and bodies of the pear-shaped cells.
Thus, the basket and stellate cells of this layer are associative (connecting) and inhibitory.
2. Ganglion layer. Here are located large ganglion cells (diameter = 30-60 microns) - Purkin' cells. These cells are located strictly in one row. The cell bodies are pear-shaped, there is a large nucleus, the cytoplasm contains EPS, mitochondria, the Golgi complex is poorly expressed. One neurite departs from the base of the cell, which passes through the granular layer, then into the white matter and ends at the cerebellar nuclei with synapses. This neurite is the first link in the efferent (descending) pathways. 2-3 dendrites depart from the apical part of the cell, which branch intensively in the molecular layer, while the branching of the dendrites occurs in a plane transverse to the course of the gyrus.
Pear-shaped cells are the main effector cells of the cerebellum, where an inhibitory impulse is produced.
3. Granular layer, saturated with cellular elements, among which cells - grains stand out. These are small cells, with a diameter of 10-12 microns. They have one neurite, which goes into the molecular layer, where it comes into contact with the cells of this layer. Dendrites (2-3) are short and branch into numerous "bird's foot" branches. These dendrites come into contact with afferent fibers called bryophytes. The latter also branch out and come into contact with the branching of the dendrites of cells - grains, forming glomeruli of thin weaves like moss. In this case, one mossy fiber is in contact with many cells - grains. And vice versa - the cell - the grain is also in contact with many mossy fibers.
Mossy fibers come here from the olives and the bridge, i.e. they bring here the information that comes through the associative neurons to the pear-shaped neurons. Large stellate cells are also found here, which lie closer to the pear-shaped cells. Their processes contact the granule cells proximal to the mossy glomeruli and in this case block the impulse transmission.
Other cells can also be found in this layer: stellate with a long neurite extending into the white matter and further into the adjacent gyrus (Golgi cells are large stellate cells).
Afferent climbing fibers - liana-like - enter the cerebellum. They come here as part of the spinal tracts. Then they crawl along the bodies of pear-shaped cells and along their processes, with which they form numerous synapses in the molecular layer. Here they carry an impulse directly to the pear-shaped cells.
Efferent fibers come out of the cerebellum, which are the axons of the piriform cells.
The cerebellum has a large number of glial elements: astrocytes, oligodendrogliocytes, which perform supporting, trophic, restrictive and other functions. A large amount of serotonin is released in the cerebellum, thus. the endocrine function of the cerebellum can also be distinguished.
Cerebral cortex (CBC)
This is a newer part of the brain. (It is believed that the CBP is not a vital organ.) It has great plasticity.
Thickness can be 3-5mm. The area occupied by the cortex increases due to furrows and convolutions. CBP differentiation ends by the age of 18, and then there are processes of accumulation and use of information. The mental abilities of an individual also depend on the genetic program, but in the end it all depends on the number of synaptic connections formed.
There are 6 layers in the cortex:
1. Molecular.
2. External granular.
3. Pyramidal.
4. Internal grainy.
5. Ganglionic.
6. Polymorphic.
Deeper than the sixth layer is the white matter. The bark is divided into granular and agranular (according to the severity of granular layers).
In KBP cells have different shape and different sizes, in diameter from 10-15 to 140 microns. The main cellular elements are pyramidal cells, which have a pointed apex. Dendrites extend from the lateral surface, and one neurite from the base. Pyramidal cells can be small, medium, large, giant.
In addition to pyramidal cells, there are arachnids, cells - grains, horizontal.
The arrangement of cells in the cortex is called cytoarchitectonics. The fibers that form myelin pathways or various systems of associative, commissural, etc. form the myeloarchitectonics of the cortex.
1. In the molecular layer, cells are found in small numbers. The processes of these cells: the dendrites go here, and the neurites form an external tangential path, which also includes the processes of the underlying cells.
2. Outer granular layer. There are many small cellular elements of pyramidal, stellate and other forms. The dendrites either branch here or pass into another layer; neurites go to the tangential layer.
3. Pyramid layer. Quite extensive. Basically, small and medium pyramidal cells are found here, the processes of which also branch out in the molecular layer, and the neurites of large cells can go into the white matter.
4. Inner granular layer. It is well expressed in the sensitive zone of the cortex (granular type of cortex). Represented by many small neurons. The cells of all four layers are associative and transmit information to other departments from the underlying departments.
5. Ganglion layer. Here are located mainly large and giant pyramidal cells. These are mainly effector cells, tk. the neurites of these neurons go into the white matter, being the first links of the effector pathway. They can give off collaterals, which can return to the cortex, forming associative nerve fibers. Some processes - commissural - go through the commissure to the neighboring hemisphere. Some neurites switch either on the nuclei of the cortex, or in the medulla oblongata, in the cerebellum, or they can reach the spinal cord (Ir. congestion-motor nuclei). These fibers form the so-called. projection paths.
6. The layer of polymorphic cells is located on the border with the white matter. There are large neurons of various shapes. Their neurites can return in the form of collaterals to the same layer, or to another gyrus, or to myelin pathways.
The entire cortex is divided into morpho-functional structural units - columns. 3-4 million columns are distinguished, each of which contains about 100 neurons. The column passes through all 6 layers. The cellular elements of each column are concentrated around the top column, which includes a group of neurons capable of processing a unit of information. This includes afferent fibers from the thalamus, and cortico-cortical fibers from the adjacent column or from the adjacent gyrus. This is where the efferent fibers come out. Due to collaterals in each hemisphere, 3 columns are interconnected. Through commissural fibers, each column is connected to two columns of the adjacent hemisphere.
All organs of the nervous system are covered with membranes:
1. The pia mater is formed by loose connective tissue, due to which furrows are formed, carries blood vessels and is delimited by glial membranes.
2. The arachnoid meninges are represented by delicate fibrous structures.
Between the soft and arachnoid membranes there is a subarachnoid space filled with cerebral fluid.
3. Dura mater, formed from coarse fibrous connective tissue. It is fused with bone tissue in the region of the skull, and is more mobile in the region of the spinal cord, where there is a space filled with cerebrospinal fluid.
The gray matter is located on the periphery, and also forms nuclei in the white matter.
Autonomic nervous system (ANS)
Subdivided into:
sympathetic part,
parasympathetic part.
The central nuclei are distinguished: the nuclei of the lateral horns of the spinal cord, the medulla oblongata, and the midbrain.
On the periphery, nodes can form in organs (paravertebral, prevertebral, paraorganic, intramural).
The reflex arc is represented by the afferent part, which is common, and the efferent part is the preganglionic and postganglionic link (they can be multi-storied).
In the peripheral ganglia of the ANS, various cells can be located in structure and function:
Motor (according to Dogel - type I):
Associative (type II)
Sensitive, the processes of which reach the neighboring ganglia and extend far beyond.