How the nervous system works. Nervous System (NS): functions, structure and diseases

Nervous system The human body is made up of tiny cells called nerve cells. Through circuits made up of these cells, nerve impulses go to the brain, and the response - to the muscles. There are over 10 billion in total in the human body. nerve cells.

Different areas of the brain are responsible for a variety of feelings, sensations and moods.

Nerve cells are called neurons. Outwardly, neurons have a variety of shapes: some are star-shaped, others are triangles or spirals. But even such a small detail of the body as neuron, consists of several parts: body, long process - axon and shorter and thinner processes - dendrites. Thanks to the processes, the cells are attached to each other and their interaction. The body of a neuron, like any other cell, consists of a nucleus surrounded by cytoplasm and covered with a membrane.

The central organ of the human nervous system that controls its functioning is brain. The human brain is able to perform much more processes associated with thinking, feelings, emotions than the brain of other living beings. The surface of the human brain is covered with shallow furrows - convolutions. It consists of white and gray matter. With the help of the first there is a connection between the spinal cord and the brain, and the second makes up the cerebral cortex.

The human brain is made up of several sections.

medulla oblongata and pons serve to communicate with the spinal cord. They control the work of the digestive and respiratory systems, the work of the heart.

Cerebellum coordinates all human movements. It is the activity of this part of the brain that ensures the accuracy and speed of movements.

midbrain responsible for responding to external stimuli, that is, responsible for the sensory system.

diencephalon regulates metabolism and body temperature.

The largest parts of the brain are two cerebral hemispheres. The hemispheres of the brain allow a person to analyze the sensations received through the senses (for example, the taste of food). The hemispheres of the brain are also responsible for speech, thinking, emotions.

brain weight- on average, it is 1360-1375 grams for men, 1220-1245 grams for women. After rapid growth during the first year of life (the brain of a newborn is 410 grams - 1/8 of the body weight; the brain weight at the end of the first year is 900 grams - 1/14 of the body weight), the brain grows slowly and between 20-30 years reaches the limit of its growth, up to 50 years does not change, and then begins to decrease in weight. Among animals, man has the greatest weight of the brain, not only relative, but also absolute. Only the whale has a slightly heavier brain than a human (2816). The brain of a horse weighs 680 g; lion - 250 g; anthropomorphic monkeys 350-400, rarely more.

More or less brain weight various people by itself cannot serve as an indication of the size of their mental capacity. On the other hand, people of outstanding ability often have a brain weight that far exceeds the average. The richness of mental organization depends on the quantity and quality of nerve cells in the cortical layer of the hemispheres and, probably, on the number of association fibers of the large brain.

The second most important organ of the nervous system is spinal cord. It is located inside the dorsal and cervical vertebrae. The spinal cord is responsible for all human movements and is connected to the brain, which coordinates these movements. The spinal cord together with the brain make up the central nervous system, and the nerve processes make up the peripheral nervous system.

The structure and functions of the human nervous system are so complex that a separate section of anatomy called neuroanatomy is devoted to their study. The central nervous system is responsible for everything, for the very life of a person - and this is not an exaggeration. If there is a deviation in the functional activity of one of the departments, the integrity of the system is violated, and human health is endangered.

The nervous system is a collection of anatomically and functionally interconnected nerve cells with their processes. Distinguish between the central and peripheral nervous systems. The central nervous system includes the brain and spinal cord, and the peripheral nervous system includes cranial and spinal nerves and related roots, spinal nodes and plexuses.

The main function of the nervous system is the regulation of the vital activity of the body, maintaining the constancy of the internal environment, metabolic processes, as well as communicating with the outside world.

The nervous system is made up of nerve cells nerve fibers and neuroglial cells.

You will learn more about the structure and functions of the nervous system from this article.

Neuron as a structural and functional unit of the human nervous system

A nerve cell - a neuron - is a structural and functional unit of the nervous system. A neuron is a cell capable of perceiving irritation, becoming excited, generating nerve impulses and transmitting them to other cells.

That is, the neuron of the nervous system performs two functions:

1. Processes incoming information and transmits a nerve impulse
2. Maintains its vitality

A neuron, as a structural unit of the nervous system, consists of a body and processes - short, branching (dendrites) and one long (axon), which can give rise to numerous branches. The point of contact between neurons is called a synapse. Synapses can be between an axon and the body of a nerve cell, an axon and a dendrite, two axons, and less often between two Dendrites. In synapses, impulses are transmitted bioelectrically or through chemically active substances of mediators (acetylcholine, norepinephrine, dopamine, serotonin, etc.). Numerous neuropeptides (enkephalins, endorphins, etc.) also participate in synaptic transmission.

Transportation of biologically active substances along the axon from the body of a neuron in the central nervous system to the synapse and back (axonal transport) ensures the supply and renewal of mediators, as well as the formation of new processes - axons and dendrites. Thus, two interconnected processes are constantly going on in the brain - the emergence of new processes and synapses and the partial disintegration of those that already existed. And this underlies learning, adaptation, as well as restoration and compensation of impaired functions.

The cell membrane (cell membrane) is a thin lipoprotein plate penetrated by channels through which K, Na, Ca, C1 ions selectively flow. Functions cell wall human nervous system - creation electric charge cells, due to which there is excitation and impulse.

Neuroglia is a connective tissue supporting structure of the nervous system (stroma) that performs a protective function.

Interlacing of axons, dendrites and processes of glial cells create a picture of a neuropil.

The nerve fiber in the structure of the nervous system is a process of the nerve cell (axial cylinder), covered to a greater or lesser extent by myelin and surrounded by the Schwann sheath, which performs protective and trophic functions. In myelin fibers, the impulse moves at a speed of up to 100 m/sec.

The accumulation of bodies of neurons in the human nervous system forms the gray matter of the brain, and their processes form the white matter. The collection of neurons located outside the central nervous system is called the ganglion. A nerve is a trunk of combined nerve fibers. Depending on the function, motor, sensory, autonomic and mixed nerves are distinguished.

Speaking about the structure of the human nervous system, a set of neurons that regulate any function is called the nerve center. The complex of physiological mechanisms associated with the performance of a particular function is called a functional system.

It includes cortical and subcortical nerve centers, pathways, peripheral nerves, and executive organs.

The basis of the functional activity of the nervous system is a reflex. A reflex is the body's response to a stimulus. A reflex is carried out through a chain of neurons (at least two), called a reflex arc. The neuron that perceives irritation is the afferent part of the arc; the neuron that carries out the response is the efferent part. But the reflex act does not end with a one-time response of the working body. There is a feedback that affects muscle tone - a self-regulatory ring in the form of a gamma loop.

The reflex activity of the nervous system ensures that the body perceives any changes in the external world.

The ability to perceive external phenomena is called reception. Sensitivity is the ability to feel stimuli perceived by the nervous system. The formations of the central and peripheral nervous system that perceive and analyze information about phenomena both inside the body and in the environment are called analyzers. There are visual, auditory, gustatory, olfactory, sensory and motor analyzers. Each analyzer consists of a peripheral (receptor) section, a conductive part and a cortical section, in which the analysis and synthesis of perceived stimuli takes place.

Since the central sections of various analyzers are located in the cerebral cortex, all information coming from the external and internal environment is concentrated in it, which is the basis for the higher mental nervous activity. Analysis of the information received by the cortex is recognition, gnosis. The functions of the cerebral cortex also include the development of action plans (programs) and their implementation - praxis.

The following describes how the spinal cord of the human nervous system is arranged.

The human central nervous system: how the spinal cord works (with photo)

The spinal cord as part of the central nervous system is a cylindrical cord 41-45 cm long, located in the spinal canal from the first cervical vertebra to the second lumbar. It has two thickenings - cervical and lumbosacral, providing innervation of the limbs. The lumbosacral thickening passes into the medullary cone, ending in a filiform continuation - the terminal thread, reaching the end of the spinal canal. The spinal cord performs conduction and reflex functions.

The spinal cord of the nervous system has a segmental structure. A segment is a section of the spinal cord with two pairs of spinal roots. In total, the spinal cord has 31-32 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1-2 coccygeal (rudimentary). The anterior and posterior horns of the spinal cord, the anterior and posterior spinal roots, spinal nodes and spinal nerves make up the segmental apparatus of the spinal cord. As the spine develops, it becomes longer than the spinal cord, so the roots, lengthening, form a ponytail.

On a section of the spinal cord of the human nervous system, gray and white matter can be seen. The gray matter consists of cells, looks like the letter "H" with anterior - motor horns, posterior - sensitive and lateral - vegetative. The central canal of the spinal cord runs through the center of the gray matter. The median fissure (front) and the median sulcus (rear) divide the spinal cord into left and right halves, interconnected by white and gray patches.

The gray matter is surrounded by nerve fibers - conductors that form the white matter, in which the anterior, lateral and posterior columns are distinguished. The anterior pillars are located between the anterior horns, the posterior ones between the posterior ones, and the lateral ones between the anterior and posterior horns of each side.

These photos show the structure of the spinal cord of the human nervous system:

Spinal nerves in the nervous system

The spinal nerves in the human nervous system are formed by the fusion of the anterior (motor) and posterior (sensory) roots of the spinal cord and exit the spinal canal through the intervertebral foramens. Each pair of these nerves innervates a certain part of the body - the metamere.

Leaving the spinal canal, the spinal nerves of the nervous system are divided into four branches:

1. Front, innervating the skin and muscles of the limbs and the anterior surface of the body;
2. Rear, innervating the skin and muscles of the back surface of the body;
3. Meningeal heading to the hard shell of the spinal cord;
4. connecting, next to the sympathetic nodes.

Front branches spinal nerves form plexuses: cervical, brachial, lumbar, sacral and coccygeal.

cervical plexus formed by the anterior branches of the cervical nerves C:-C4; innervates the skin of the back of the head, the lateral surface of the face, the supra-, subclavian and upper scapular regions, the diaphragm.

Brachial plexus formed by the anterior branches of C4-T1; innervates the skin and muscles of the upper limb.

Front branches T2-T11, without forming a plexus, together with the posterior branches provide innervation of the skin and muscles of the chest, back and abdomen.

Lumbosacral plexus is a combination of the lumbar and sacral.

Lumbar plexus formed by the anterior branches of T12 -L 4; innervates the skin and muscles of the lower abdomen, anterior and lateral thighs.

sacral plexus formed by the anterior branches of the L5-S4 nerves; innervates the skin and muscles of the gluteal region, perineum, back of the thigh, lower leg and foot. From it departs the largest nerve of the body - the sciatic.

coccygeal plexus formed by the anterior branches of S5-C0C2; innervates the perineum.

The next section of the article is devoted to the structure and functions of the main parts of the brain.

The human nervous system: the structure and functions of the main parts of the brain

The brain, which is part of the nervous system, is located in the cranium, covered with the meninges, between which cerebrospinal fluid (CSF) circulates. Through the foramen magnum, the brain is connected to the spinal cord. The mass of the brain of an adult is on average 1300-1500 g. The function of the human brain is to regulate all processes occurring in the body.

The brain as part of the nervous system consists of the following sections: two hemispheres, the cerebellum and the trunk.

In the brain stem, the medulla oblongata, the pons, the legs of the brain (midbrain), as well as the base and the tire are isolated.

The medulla oblongata is like a continuation of the spinal cord. The intersection of the pyramidal tracts serves as a conditional border between the medulla oblongata and the spinal cord. In the medulla oblongata there are vital centers that regulate breathing, blood circulation, swallowing; it contains all the motor and sensory pathways connecting the spinal cord and brain.

The structure of the bridge of the nervous system of the brain includes the nuclei of the V, VI, VII and VIII pairs of cranial nerves, sensory pathways as part of the medial loop, fibers of the auditory pathway in the form of a lateral loop, etc.

The cerebral peduncles are part of the midbrain, they connect the bridge to the hemispheres and include ascending and descending pathways. The roof of the midbrain has a plate on which the quadrigemina is located. In the upper colliculus is the primary subcortical center of vision, in the lower colliculus - the primary subcortical center of hearing. Thanks to the mounds, the orientation and protective reactions of the body are carried out, which occur under the influence of visual and auditory stimuli. Under the roof of the midbrain is the aqueduct of the midbrain, which connects the III and IV ventricles hemispheres.

The diencephalon consists of the thalamus (thalamus), epithalamus, metathalamus, and hypothalamus. The cavity of the diencephalon is the third ventricle. The thalamus is a cluster of nerve cells located on both sides of the third ventricle. The thalamus is one of the subcortical centers of vision and the center of afferent impulses from the whole body, heading to the cerebral cortex. In the thalamus, the formation of sensations and the transmission of impulses to the extra-pyramidal system take place.

Metathalamus in the brain of the human nervous system also contains one of the subcortical centers of vision and the subcortical center of hearing (medial and lateral geniculate body).

The epithalamus includes the pineal gland, which is an endocrine gland that regulates the function of the adrenal cortex and the development of sexual characteristics.

The hypothalamus consists of a gray tubercle, funnel, cerebral appendage (neurohypophysis) and paired mastoid bodies. In the hypothalamus there are accumulations of gray matter in the form of nuclei, which are the centers of the autonomic nervous system that regulate all types of metabolism, respiration, blood circulation, the activity of internal organs and endocrine glands. The hypothalamus maintains the constancy of the internal environment in the body (homeostasis) and, thanks to connections with the limbic system, participates in the formation of emotions, carrying out their vegetative coloring.

Along the entire length of the brain stem is located and occupies central position phylogenetically ancient formation of gray matter in the form of a dense network of nerve cells with many processes - the reticular formation. Branches from all types of sensitive systems are sent to the reticular formation, so any irritation coming from the periphery is transmitted by it along ascending paths to the cerebral cortex, activating its activity. Thus, the reticular formation is involved in the implementation of normal biological rhythms of wakefulness and sleep, is an ascending, activating system of the brain - an "energy generator".

Together with the limbic structures, the reticular formation provides normal cortical-subcortical relationships and behavioral responses. It is also involved in the regulation of muscle tone, and its descending pathways provide reflex activity of the spinal cord.

The cerebellum is located under the occipital lobes of the brain and is separated from them by the dura mater - cerebellar tenon. It distinguishes the central part - the cerebellar vermis and the lateral sections - the hemispheres. In the depths of the white matter of the cerebellar hemispheres are the dentate nucleus and smaller nuclei - corky and spherical. The nucleus of the roof is located in the middle part of the cerebellum. The cerebellar nuclei are involved in the coordination of movements and balance, as well as in the regulation of muscle tone. Three pairs of legs connect the cerebellum with all parts of the brain stem, providing its connection with the extrapyramidal system, the cerebral cortex and the spinal cord.

The structure and main functions of the cerebral hemispheres

The structure of the cerebrum includes two hemispheres, interconnected by a large white commissure - the corpus callosum, consisting of fibers that connect the lobes of the brain of the same name. The surface of each hemisphere is covered with a bark consisting of cells and separated by many furrows. The areas of the cortex located between the furrows are called convolutions. The deepest furrows divide each hemisphere into lobes: frontal, parietal, occipital and temporal. The central (Roland) sulcus separates the parietal lobe from the frontal; in front of it is the precentral gyrus. The frontal lobe is divided by horizontal grooves into the superior, middle, and inferior gyrus.

Behind the central sulcus in the structure of the cerebral hemispheres is the postcentral gyrus. The parietal lobe is divided by a transverse intraparietal sulcus into superior and inferior parietal lobules.

A deep lateral (Sylvian) furrow separates the temporal lobe from the frontal and parietal. On the lateral surface of the temporal lobe, the superior, middle, and inferior temporal gyrus are located longitudinally. On the inner surface The temporal lobe contains a gyrus called the hippocampus.

On the inner surface of the hemispheres, the parietal-occipital sulcus separates the parietal lobe from the occipital one, and the spur sulcus divides the occipital lobe into two gyri - the precuneus and the wedge.

On the medial surface of the hemispheres above the corpus callosum, the cingulate gyrus is located arcuately, passing into the parahippocampal gyrus.

The cerebral cortex is the youngest evolutionary part of the central nervous system, consisting of neurons. It is most developed in humans. The cortex is a layer of gray matter 1.3-4 mm thick, covering the white matter of the hemispheres, consisting of axons, dendrites of nerve cells and neuroglia.

The cortex plays a very important role in the regulation of vital important processes in the body, the implementation of behavioral acts and mental activity.

The function of the cortex of the frontal lobe is the organization of movements, motor skills of speech, complex shapes behavior and thinking. In the precentral gyrus is the center of voluntary movements, from here the pyramidal path begins.

The parietal lobe contains the centers of the analyzer of general sensitivity, gnosis, praxis, writing, counting.

The functions of the temporal lobe of the large brain are the perception and processing of auditory, gustatory and olfactory sensations, the analysis and synthesis of speech sounds, and memory mechanisms. The basal parts of the cerebral hemispheres are connected with the higher autonomic centers.

In the occipital lobe are the cortical centers of vision.

Not all functions of the cerebral hemispheres are represented symmetrically in the cortex. For example, speech, reading and writing in most people are functionally related to the left hemisphere.

The right hemisphere provides orientation in time, place, connected with the emotional sphere.

The axons and dendrites of the nerve cells of the cortex make up the pathways that connect the various sections of the cortex, the cortex and other sections of the brain and spinal cord. The pathways form a radiant crown, consisting of fan-shaped diverging fibers, and an internal capsule located between the basal (subcortical) nuclei.

Subcortical nuclei (caudate, lenticular, amygdala, fence) are located deep in the white matter around the ventricles of the brain. Morphologically and functionally, the caudate nucleus and the shell are combined into the striatum (striatum). Pale ball, red core black matter and the reticular formation of the midbrain is combined into a pale body (pallidum). The striatum and pallidum form a very important functional system- striopallidar or extrapyramidal. The extrapyramidal system provides training for various muscle groups to perform a holistic movement, also provides mimic, auxiliary and friendly movements, gestures, automated motor acts (grimaces, whistles, etc.).

A special role is played by the most evolutionarily ancient sections of the cerebral cortex, located on the inner surface of the hemispheres - the cingulate and parahippocampal gyrus. Together with the amygdala, olfactory bulb and olfactory tract, they form the limbic system, which is closely connected with the reticular formation of the brain stem and constitutes a single functional system - the limbic-reticular complex (LRK). Speaking about the structure and functions of the large brain, it should be noted that the limbic-reticular complex is involved in the formation of instinctive and emotional reactions (food, sexual, defensive instincts, anger, rage, pleasure) of human behavior. LRK also takes part in the regulation of the tone of the cerebral cortex, the processes of sleep, wakefulness, and adaptation.

See how the large brain of the human nervous system works in these photos:

12 pairs of cranial nerves of the nervous system and their functions (with video)

At the base of the brain, 12 pairs of cranial nerves emerge from the medulla. By function, they are divided into sensitive, motor and mixed. In the proximal direction, the cranial nerves are associated with the nuclei of the brainstem, subcortical nuclei, the cerebral cortex and the cerebellum. In the distal direction, the cranial nerves are associated with various functional structures(eyes, ears, muscles of the face, tongue, glands, etc.).

I pair - olfactory nerve ( n. olfactorius) . The receptors are located in the mucous membrane of the turbinates, connected to the sensory neurons of the olfactory bulb. Along the olfactory tract, signals enter the primary olfactory centers (the nuclei of the olfactory triangle) and further to the internal parts of the temporal lobe (hippocampus), where the cortical centers of smell are located.

II pair - optic nerves ( n. opticus) . The receptors of this pair of craniocerebral nerves are the cells of the retina, from the ganglionic layer of which the nerves themselves begin. Passing on the basis of the frontal lobes in front of the Turkish saddle, the optic nerves partially cross, forming a chiasma, and are sent as part of the visual tracts to the subcortical visual centers, and from them to the occipital lobes.

III pair - oculomotor nerves ( n. oculomotorius) . They contain motor and parasympathetic fibers that innervate the muscles that lift the upper eyelids, constrict the pupil, and the muscles of the eyeball, with the exception of the superior oblique and abductor.

IV pair - trochlear nerves ( n. trochlearis) . This pair of cranial nerves innervates the superior oblique muscles of the eyes.

V pair - trigeminal nerves ( n. trigeminus) . They are mixed nerves. Sensory neurons of the trigeminal (Gasser) node form three large branches: the ophthalmic, maxillary and mandibular nerves, which exit the cranial cavity and innervate the frontoparietal part of the scalp, facial skin, eyeballs, mucous membranes of the nasal cavities, mouth, anterior two-thirds of the tongue, teeth, dura mater. The central processes of the cells of the Gasser ganglion go deep into the brain stem and connect with the second sensitive neurons, forming a chain of nuclei. Signals from the stem nuclei through the thalamus go to the postcentral gyrus (fourth neuron) of the opposite hemisphere. Peripheral innervation corresponds to the branches of the nerve, segmental - has the form of ring zones. The motor fibers of the trigeminal nerve regulate the masticatory muscles.

VI pair - abducens nerves ( n. abducens) . Innervates the abductor muscles of the eye.

VII pair - facial nerves ( n. facialis) . They innervate the mimic muscles of the face. When leaving the bridge, the intermediate nerve joins the facial nerve, providing taste innervation of the anterior two-thirds of the tongue, parasympathetic innervation of the submandibular and sublingual glands, and lacrimal glands.

VIII pair - cochleovestibular (auditory, vestibulocochlear) nerve ( n. vestibulo-cochlearis) . This pair of cranial nerves provides the function of hearing and balance, has extensive connections with the structures of the extrapyramidal system, cerebellum, spinal cord, and cortex.

IX pair - glossopharyngeal nerves ( n. glossopharyngeus).

They function in close connection with the X-pair - vagus nerves ( n. vagus) . These nerves have a number of common nuclei in the medulla oblongata, performing sensory, motor and secretory functions. They innervate the soft palate, pharynx, upper esophagus, parotid salivary gland, posterior third of the tongue. The vagus nerve carries out parasympathetic innervation of all internal organs up to the level of the pelvis.

XI pair - accessory nerves ( n. accessorius) . Innervate the sternocleidomastoid and trapezius muscles.

XII pair - hypoglossal nerves ( n. hypoglossus) . Innervate the muscles of the tongue.

Vegetative department of the human nervous system: structure and main functions

Autonomic nervous system (ANS) It is the part of the nervous system that keeps the body alive. It innervates the heart, blood vessels, internal organs, and also provides tissue trophism, ensures the constancy of the internal environment of the body. In the autonomic nervous system, there are sympathetic and parasympathetic parts. They interact as antagonists and synergists. Thus, the sympathetic nervous system dilates the pupil, increases the heart rate, constricts blood vessels, increases blood pressure, reduces the secretion of glands, slows down the peristalsis of the stomach and intestines, and reduces sphincters. Parasympathetic, on the contrary, constricts the pupil, slows down the heartbeat, dilates blood vessels, lowers blood pressure, increases the secretion of glands and intestinal motility, and relaxes the sphincters.

The sympathetic autonomic nervous system performs a trophic function, enhances oxidative processes, nutrient intake, respiratory and cardiovascular activity, changes permeability cell membrane. The role of the parasympathetic system is protective. At rest, the vital activity of the body is provided by the parasympathetic system, while under tension, the sympathetic system.

In the structure of the autonomic nervous system, segmental and suprasegmental sections are distinguished.

The segmental part of the ANS is represented by sympathetic and parasympathetic formations at the spinal and stem levels.

The centers of the human sympathetic autonomic nervous system are located in the lateral columns of the spinal cord at the C8-L3 level. Sympathetic fibers exit the spinal cord with anterior roots, interrupt at the nodes of the paired sympathetic trunk, which is located on the anterior surface of the spinal column and consists of 20-25 pairs of nodes, containing sympathetic cells. Fibers depart from the nodes of the sympathetic trunk, forming sympathetic plexuses and nerves, which are directed to organs and vessels.

The centers of the parasympathetic nervous system are located in the brainstem and in the sacral segments S2-S4 of the spinal cord. The processes of the cells of the parasympathetic nuclei of the brain stem as part of the oculomotor, facial, glossopharyngeal and vagus nerves provide innervation of the glands and smooth muscles of all internal organs, with the exception of the pelvic organs. The fibers of the cells of the parasympathetic nuclei of the sacral segments form the pelvic splanchnic nerves leading to the bladder, rectum, and genitals.

Both sympathetic and parasympathetic fibers are interrupted in the peripheral vegetative nodes located near the innervated organs or in their walls.

The fibers of the autonomic nervous system form a number of plexuses: solar, pericardial, mesenteric, pelvic, which innervate the internal organs and regulate their function.

The higher suprasegmental division of the autonomic nervous system includes the nuclei of the hypothalamus, the limbic-reticular complex, the basal structures of the temporal lobe, and some sections of the associative zone of the cerebral cortex. The role of these formations is to integrate the basic mental and somatic functions.

At rest, the vital activity of the body is provided by the parasympathetic system, while under tension, the sympathetic system.

The centers of the sympathetic nervous system are located in the lateral columns of the spinal cord at the level of C8-L3; sympathetic fibers exit the spinal cord with anterior roots, interrupted at the nodes of the paired sympathetic trunk.

Here you can watch the video "Human Nervous System" to better understand how it works:

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Useful articles

With the evolutionary complication of multicellular organisms, the functional specialization of cells, the need arose for the regulation and coordination of life processes at the supracellular, tissue, organ, systemic and organismal levels. These new regulatory mechanisms and systems should have appeared along with the preservation and complication of the mechanisms for regulating the functions of individual cells with the help of signaling molecules. The adaptation of multicellular organisms to changes in the environment of existence could be carried out on the condition that new regulatory mechanisms would be able to provide fast, adequate, targeted responses. These mechanisms must be able to memorize and retrieve from the memory apparatus information about previous effects on the body, as well as have other properties that ensure effective adaptive activity of the body. They were the mechanisms of the nervous system that appeared in complex, highly organized organisms.

Nervous system is a set of special structures that unites and coordinates the activity of all organs and systems of the body in constant interaction with the external environment.

The central nervous system includes the brain and spinal cord. The brain is subdivided into the hindbrain (and the pons), the reticular formation, subcortical nuclei,. The bodies form the gray matter of the CNS, and their processes (axons and dendrites) form the white matter.

General characteristics of the nervous system

One of the functions of the nervous system is perception various signals (stimuli) of the external and internal environment of the body. Recall that any cells can perceive various signals of the environment of existence with the help of specialized cellular receptors. However, they are not adapted to the perception of a number of vital signals and cannot instantly transmit information to other cells that perform the function of regulators of integral adequate reactions of the body to the action of stimuli.

The impact of stimuli is perceived by specialized sensory receptors. Examples of such stimuli can be light quanta, sounds, heat, cold, mechanical effects (gravity, pressure change, vibration, acceleration, compression, stretching), as well as signals complex nature(Colour, complex sounds, word).

To assess the biological significance of the perceived signals and organize an adequate response to them in the receptors of the nervous system, their transformation is carried out - coding into a universal form of signals understandable to the nervous system - into nerve impulses, holding (transferred) which along the nerve fibers and pathways to the nerve centers are necessary for their analysis.

The signals and the results of their analysis are used by the nervous system to response organization to changes in the external or internal environment, regulation and coordination functions of cells and supracellular structures of the body. Such responses are carried out by effector organs. The most common variants of responses to influences are motor (motor) reactions of skeletal or smooth muscles, changes in the secretion of epithelial (exocrine, endocrine) cells initiated by the nervous system. Taking a direct part in the formation of responses to changes in the environment of existence, the nervous system performs the functions homeostasis regulation, ensure functional interaction organs and tissues and their integration into a single whole body.

Thanks to the nervous system, an adequate interaction of the organism with the environment is carried out not only through the organization of responses by effector systems, but also through its own mental reactions - emotions, motivations, consciousness, thinking, memory, higher cognitive and creative processes.

The nervous system is divided into central (brain and spinal cord) and peripheral - nerve cells and fibers outside the cranial cavity and spinal canal. The human brain contains over 100 billion nerve cells. (neurons). Accumulations of nerve cells that perform or control the same functions form in the central nervous system nerve centers. The structures of the brain, represented by the bodies of neurons, form the gray matter of the CNS, and the processes of these cells, uniting into pathways, form the white matter. Besides, structural part CNS are glial cells that form neuroglia. The number of glial cells is about 10 times the number of neurons, and these cells make up the majority of the mass of the central nervous system.

According to the features of the functions performed and the structure, the nervous system is divided into somatic and autonomous (vegetative). Somatic structures include the structures of the nervous system, which provide the perception of sensory signals mainly from the external environment through the sense organs, and control the work of the striated (skeletal) muscles. The autonomic (vegetative) nervous system includes structures that provide the perception of signals mainly from the internal environment of the body, regulate the work of the heart, other internal organs, smooth muscles, exocrine and part of the endocrine glands.

In the central nervous system, it is customary to distinguish structures located at different levels, which are characterized by specific functions and a role in the regulation of life processes. Among them, the basal nuclei, brain stem structures, spinal cord, peripheral nervous system.

The structure of the nervous system

The nervous system is divided into central and peripheral. The central nervous system (CNS) includes the brain and spinal cord, and the peripheral nervous system includes the nerves extending from the central nervous system to various organs.

Rice. 1. The structure of the nervous system

Rice. 2. Functional division of the nervous system

Significance of the nervous system:

• unites the organs and systems of the body into a single whole;
• regulates the work of all organs and systems of the body;
• carries out the connection of the organism with the external environment and its adaptation to environmental conditions;
• forms the material basis of mental activity: speech, thinking, social behavior.

Structure of the nervous system

The structural and physiological unit of the nervous system is - (Fig. 3). It consists of a body (soma), processes (dendrites) and an axon. Dendrites strongly branch and form many synapses with other cells, which determines their leading role in the perception of information by the neuron. The axon starts from the cell body with the axon mound, which is the generator of a nerve impulse, which is then carried along the axon to other cells. The axon membrane in the synapse contains specific receptors that can respond to various mediators or neuromodulators. Therefore, the process of mediator release by presynaptic endings can be influenced by other neurons. Also, the membrane of the endings contains a large number of calcium channels through which calcium ions enter the ending when it is excited and activate the release of the mediator.

Rice. 3. Scheme of a neuron (according to I.F. Ivanov): a - structure of a neuron: 7 - body (pericaryon); 2 - core; 3 - dendrites; 4.6 - neurites; 5.8 - myelin sheath; 7- collateral; 9 - node interception; 10 — a kernel of a lemmocyte; 11 - nerve endings; b — types of nerve cells: I — unipolar; II - multipolar; III - bipolar; 1 - neuritis; 2 - dendrite

Usually, in neurons, the action potential occurs in the region of the axon hillock membrane, the excitability of which is 2 times higher than the excitability of other areas. From here, the excitation spreads along the axon and the cell body.

Axons, in addition to the function of conducting excitation, serve as channels for the transport of various substances. Proteins and mediators synthesized in the cell body, organelles and other substances can move along the axon to its end. This movement of substances is called axon transport. There are two types of it - fast and slow axon transport.

Each neuron in the central nervous system performs three physiological roles: it receives nerve impulses from receptors or other neurons; generates its own impulses; conducts excitation to another neuron or organ.

By functional value neurons are divided into three groups: sensitive (sensory, receptor); intercalary (associative); motor (effector, motor).

In addition to neurons in the central nervous system, there are glial cells, occupying half the volume of the brain. Peripheral axons are also surrounded by a sheath of glial cells - lemmocytes (Schwann cells). Neurons and glial cells are separated by intercellular clefts that communicate with each other and form a fluid-filled intercellular space of neurons and glia. Through this space there is an exchange of substances between nerve and glial cells.

Neuroglial cells perform many functions: supporting, protective and trophic role for neurons; maintain a certain concentration of calcium and potassium ions in the intercellular space; destroy neurotransmitters and other biologically active substances.

Functions of the central nervous system

The central nervous system performs several functions.

Integrative: The organism of animals and humans is a complex highly organized system consisting of functionally interconnected cells, tissues, organs and their systems. This relationship, the unification of the various components of the body into a single whole (integration), their coordinated functioning is provided by the central nervous system.

Coordinating: the functions of various organs and systems of the body must proceed in a coordinated manner, since only with this way of life it is possible to maintain the constancy of the internal environment, as well as successfully adapt to changing environmental conditions. The coordination of the activity of the elements that make up the body is carried out by the central nervous system.

Regulatory: the central nervous system regulates all the processes occurring in the body, therefore, with its participation, the most adequate changes in the work of various organs occur, aimed at ensuring one or another of its activities.

Trophic: the central nervous system regulates trophism, the intensity of metabolic processes in the tissues of the body, which underlies the formation of reactions that are adequate to the ongoing changes in the internal and external environment.

Adaptive: the central nervous system communicates the body with the external environment by analyzing and synthesizing various information coming to it from sensory systems. This makes it possible to restructure the activities of various organs and systems in accordance with changes in the environment. It performs the functions of a regulator of behavior necessary in specific conditions of existence. This ensures adequate adaptation to the surrounding world.

Formation of non-directional behavior: the central nervous system forms a certain behavior of the animal in accordance with the dominant need.

Reflex regulation of nervous activity

The adaptation of the vital processes of an organism, its systems, organs, tissues to changing environmental conditions is called regulation. The regulation provided jointly by the nervous and hormonal systems is called neurohormonal regulation. Thanks to the nervous system, the body carries out its activities on the principle of a reflex.

The main mechanism of the activity of the central nervous system is the response of the body to the actions of the stimulus, carried out with the participation of the central nervous system and aimed at achieving a useful result.

Reflex in Latin means "reflection". The term "reflex" was first proposed by the Czech researcher I.G. Prohaska, who developed the doctrine of reflective actions. The further development of the reflex theory is associated with the name of I.M. Sechenov. He believed that everything unconscious and conscious is accomplished by the type of reflex. But then there were no methods for an objective assessment of brain activity that could confirm this assumption. Later, an objective method for assessing brain activity was developed by Academician I.P. Pavlov, and he received the name of the method of conditioned reflexes. Using this method, the scientist proved that the basis of the higher nervous activity of animals and humans are conditioned reflexes, which are formed on the basis of unconditioned reflexes through the formation of temporary bonds. Academician P.K. Anokhin showed that the whole variety of animal and human activities is carried out on the basis of the concept of functional systems.

The morphological basis of the reflex is , consisting of several nerve structures, which ensures the implementation of the reflex.

Three types of neurons are involved in the formation of a reflex arc: receptor (sensitive), intermediate (intercalary), motor (effector) (Fig. 6.2). They are combined into neural circuits.

Rice. 4. Scheme of regulation according to the reflex principle. Reflex arc: 1 - receptor; 2 - afferent path; 3 - nerve center; 4 - efferent path; 5 - working body (any organ of the body); MN, motor neuron; M - muscle; KN — command neuron; SN — sensory neuron, ModN — modulatory neuron

The receptor neuron's dendrite contacts the receptor, its axon goes to the CNS and interacts with the intercalary neuron. From the intercalary neuron, the axon goes to the effector neuron, and its axon goes to the periphery to the executive organ. Thus, a reflex arc is formed.

Receptor neurons are located on the periphery and in internal organs, while intercalary and motor neurons are located in the central nervous system.

In the reflex arc, five links are distinguished: the receptor, the afferent (or centripetal) path, the nerve center, the efferent (or centrifugal) path and the working organ (or effector).

The receptor is a specialized formation that perceives irritation. The receptor consists of specialized highly sensitive cells.

The afferent link of the arc is a receptor neuron and conducts excitation from the receptor to the nerve center.

The nerve center is formed by a large number of intercalary and motor neurons.

This link of the reflex arc consists of a set of neurons located in different parts of the central nervous system. The nerve center receives impulses from receptors along the afferent pathway, analyzes and synthesizes this information, and then transmits the generated action program along the efferent fibers to the peripheral executive organ. And the working body carries out its characteristic activity (the muscle contracts, the gland secretes a secret, etc.).

A special link of reverse afferentation perceives the parameters of the action performed by the working organ and transmits this information to the nerve center. The nerve center is the action acceptor of the back afferent link and receives information from the working organ about the completed action.

The time from the beginning of the action of the stimulus on the receptor until the appearance of a response is called the reflex time.

All reflexes in animals and humans are divided into unconditioned and conditioned.

Unconditioned reflexes - congenital, hereditary reactions. Unconditioned reflexes are carried out through reflex arcs already formed in the body. Unconditioned reflexes are species-specific, i.e. common to all animals of this species. They are constant throughout life and arise in response to adequate stimulation of the receptors. Unconditioned reflexes are classified according to biological significance: food, defensive, sexual, locomotor, orientation. According to the location of the receptors, these reflexes are divided into: exteroceptive (temperature, tactile, visual, auditory, gustatory, etc.), interoceptive (vascular, cardiac, gastric, intestinal, etc.) and proprioceptive (muscular, tendon, etc.). By the nature of the response - to motor, secretory, etc. By finding the nerve centers through which the reflex is carried out - to the spinal, bulbar, mesencephalic.

Conditioned reflexes - reflexes acquired by the body in the course of its individual life. Conditioned reflexes are carried out through newly formed reflex arcs on the basis of reflex arcs of unconditioned reflexes with the formation of a temporary connection between them in the cerebral cortex.

Reflexes in the body are carried out with the participation of endocrine glands and hormones.

At the heart of modern ideas about the reflex activity of the body is the concept of a useful adaptive result, to achieve which any reflex is performed. Information about the achievement of a useful adaptive result enters the central nervous system through the feedback link in the form of reverse afferentation, which is an essential component of reflex activity. The principle of reverse afferentation in reflex activity was developed by P.K. Anokhin and is based on the fact that the structural basis of the reflex is not a reflex arc, but a reflex ring, which includes the following links: receptor, afferent nerve pathway, nerve center, efferent nerve pathway, working organ , reverse afferentation.

When any link of the reflex ring is turned off, the reflex disappears. Therefore, the integrity of all links is necessary for the implementation of the reflex.

Properties of nerve centers

Nerve centers have a number of characteristic functional properties.

Excitation in the nerve centers spreads unilaterally from the receptor to the effector, which is associated with the ability to conduct excitation only from the presynaptic membrane to the postsynaptic one.

Excitation in the nerve centers is carried out more slowly than along the nerve fiber, as a result of slowing down the conduction of excitation through the synapses.

In the nerve centers, summation of excitations can occur.

There are two main ways of summation: temporal and spatial. At temporary summation several excitatory impulses come to the neuron through one synapse, are summed up and generate an action potential in it, and spatial summation manifests itself in the case of receipt of impulses to one neuron through different synapses.

In them, the rhythm of excitation is transformed, i.e. a decrease or increase in the number of excitation impulses leaving the nerve center compared to the number of impulses coming to it.

The nerve centers are very sensitive to the lack of oxygen and the action of various chemicals.

Nerve centers, unlike nerve fibers, are capable of rapid fatigue. Synaptic fatigue during prolonged activation of the center is expressed in a decrease in the number of postsynaptic potentials. This is due to the consumption of the mediator and the accumulation of metabolites that acidify the environment.

The nerve centers are in a state of constant tone, due to the continuous flow of a certain number of impulses from the receptors.

Nerve centers are characterized by plasticity - the ability to increase their functionality. This property may be due to synaptic facilitation - improved conduction in synapses after a short stimulation of the afferent pathways. With frequent use of synapses, the synthesis of receptors and mediator is accelerated.

Along with excitation, inhibitory processes occur in the nerve center.

CNS coordination activity and its principles

One of the important functions of the central nervous system is the coordination function, which is also called coordination activities CNS. It is understood as the regulation of the distribution of excitation and inhibition in neuronal structures, as well as the interaction between nerve centers, which ensure the effective implementation of reflex and voluntary reactions.

An example coordination activities The central nervous system may have a reciprocal relationship between the centers of respiration and swallowing, when during swallowing the center of respiration is inhibited, the epiglottis closes the entrance to the larynx and prevents food or liquid from entering the airways. The coordination function of the central nervous system is fundamentally important for the implementation of complex movements carried out with the participation of many muscles. Examples of such movements can be the articulation of speech, the act of swallowing, gymnastic movements that require the coordinated contraction and relaxation of many muscles.

Principles of coordination activities

• Reciprocity - mutual inhibition of antagonistic groups of neurons (flexor and extensor motoneurons)
• Terminal neuron - activation of an efferent neuron from different receptive fields and competition between different afferent impulses for a given motor neuron
• Switching - the process of transferring activity from one nerve center to the antagonist nerve center
• Induction - change of excitation by inhibition or vice versa
• Feedback is a mechanism that ensures the need for signaling from receptors executive bodies for the successful implementation of the function
• Dominant - a persistent dominant focus of excitation in the central nervous system, subordinating the functions of other nerve centers.

The coordination activity of the central nervous system is based on a number of principles.

Convergence principle is realized in convergent chains of neurons, in which the axons of a number of others converge or converge on one of them (usually efferent). Convergence ensures that the same neuron receives signals from different nerve centers or receptors of different modalities (different sense organs). On the basis of convergence, a variety of stimuli can cause the same type of response. For example, the watchdog reflex (turning the eyes and head - alertness) can be caused by light, sound, and tactile influences.

The principle of a common final path follows from the principle of convergence and is close in essence. It is understood as the possibility of implementing the same reaction triggered by the final efferent neuron in the hierarchical nervous circuit, to which the axons of many other nerve cells converge. An example of a classic final pathway is the motoneurons of the anterior horns of the spinal cord or the motor nuclei of the cranial nerves, which directly innervate the muscles with their axons. The same motor response (for example, bending the arm) can be triggered by the receipt of impulses to these neurons from the pyramidal neurons of the primary motor cortex, neurons of a number of motor centers of the brainstem, interneurons of the spinal cord, axons of sensitive neurons of the spinal ganglia in response to the action of signals perceived by different sense organs (to light, sound, gravitational, pain or mechanical effects).

Principle of divergence is realized in divergent chains of neurons, in which one of the neurons has a branching axon, and each of the branches forms a synapse with another nerve cell. These circuits perform the functions of simultaneously transmitting signals from one neuron to many other neurons. Due to divergent connections, there is a wide distribution (irradiation) of signals and a rapid involvement in the response of many centers located on different levels CNS.

The principle of feedback (reverse afferentation) It consists in the possibility of transmitting information about the ongoing reaction (for example, about movement from muscle proprioceptors) back to the nerve center that triggered it, via afferent fibers. Thanks to feedback, a closed neural circuit (circuit) is formed, through which it is possible to control the progress of the reaction, adjust the strength, duration and other parameters of the reaction, if they have not been implemented.

The participation of feedback can be considered on the example of the implementation of the flexion reflex caused by mechanical action on skin receptors (Fig. 5). With reflex contraction of the flexor muscle, the activity of proprioreceptors and the frequency of sending nerve impulses along the afferent fibers to the a-motoneurons of the spinal cord, which innervate this muscle, change. As a result, a closed loop regulation, in which the role of the feedback channel is performed by afferent fibers that transmit information about the contraction to the nerve centers from muscle receptors, and the role of the direct connection channel is performed by efferent fibers of motor neurons going to the muscles. Thus, the nerve center (its motor neurons) receives information about the change in the state of the muscle caused by the transmission of impulses along the motor fibers. Thanks to the feedback, a kind of regulatory nerve ring is formed. Therefore, some authors prefer to use the term "reflex ring" instead of the term "reflex arc".

The presence of feedback is important in the mechanisms of regulation of blood circulation, respiration, body temperature, behavioral and other reactions of the body and is discussed further in the relevant sections.

Rice. 5. Feedback scheme in neural circuits of the simplest reflexes

The principle of reciprocal relations is realized in the interaction between the nerve centers-antagonists. For example, between a group of motor neurons that control arm flexion and a group of motor neurons that control arm extension. Due to reciprocal relationships, excitation of neurons in one of the antagonistic centers is accompanied by inhibition of the other. In the given example, the reciprocal relationship between the flexion and extension centers will be manifested by the fact that during the contraction of the flexor muscles of the arm, an equivalent relaxation of the extensor muscles will occur, and vice versa, which ensures smooth flexion and extension movements of the arm. Reciprocal relations are carried out due to the activation of inhibitory interneurons by the neurons of the excited center, the axons of which form inhibitory synapses on the neurons of the antagonistic center.

Dominant principle is also realized on the basis of the characteristics of the interaction between the nerve centers. The neurons of the dominant, most active center (focus of excitation) have a stable high activity and suppress excitation in other nerve centers, subjecting them to their influence. Moreover, the neurons of the dominant center attract afferent nerve impulses addressed to other centers and increase their activity due to the receipt of these impulses. The dominant center can be in a state of excitation for a long time without signs of fatigue.

An example of a state caused by the presence of a dominant focus of excitation in the central nervous system is the state after an important event experienced by a person, when all his thoughts and actions somehow become connected with this event.

Dominant Properties

• Hyperexcitability
• Excitation persistence
• Excitation inertia
• Ability to suppress subdominant foci
• Ability to sum excitations

The considered principles of coordination can be used, depending on the processes coordinated by the CNS, separately or together in various combinations.

Very clear, concise and clear. Posted as a keepsake.

1. What is the nervous system

One of the components of a person is his nervous system. It is reliably known that diseases of the nervous system adversely affect the physical condition of the entire human body. With a disease of the nervous system, both the head and the heart (the “motor” of a person) begin to hurt.

Nervous system is a system that regulates the activity of all human organs and systems. This system causes:

1) the functional unity of all human organs and systems;

2) the connection of the whole organism with the environment.

The nervous system has its own structural unit which is called a neuron. Neurons are cells that have special processes. It is neurons that build neural circuits.

The entire nervous system is divided into:

1) central nervous system;

2) peripheral nervous system.

The central nervous system includes the brain and spinal cord, and the peripheral nervous system includes the cranial and spinal nerves and nerve nodes extending from the brain and spinal cord.

Also conditionally, the nervous system can be divided into two large sections:

1) somatic nervous system;

2) autonomic nervous system.

somatic nervous system associated with the human body. This system is responsible for the fact that a person can move independently, it also determines the connection of the body with the environment, as well as sensitivity. Sensitivity is provided with the help of human sense organs, as well as with the help of sensitive nerve endings.

The movement of a person is ensured by the fact that with the help of the nervous system, skeletal muscle mass is controlled. Scientists-biologists call the somatic nervous system in another way animal, because movement and sensitivity are peculiar only to animals.

Nerve cells can be divided into two large groups:

1) afferent (or receptor) cells;

2) efferent (or motor) cells.

Receptor nerve cells perceive light (using visual receptors), sound (using sound receptors), smells (using olfactory and taste receptors).

Motor nerve cells generate and transmit impulses to specific executing organs. The motor nerve cell has a body with a nucleus, numerous processes called dendrites. A nerve cell also has a nerve fiber called an axon. The length of these axons ranges from 1 to 1.5 mm. With their help, electrical impulses are transmitted to specific cells.

In the cell membranes that are responsible for the sensation of taste and smell, there are special biological compounds that react to a particular substance by changing their state.

In order for a person to be healthy, he must first of all monitor the state of his nervous system. Today, people sit in front of a computer a lot, stand in traffic jams, and also get into various stressful situations (for example, a student received a negative grade at school or an employee received a reprimand from his immediate superiors) - all this negatively affects our nervous system. Today, enterprises and organizations create rest rooms (or relaxation rooms). Arriving in such a room, the worker mentally disconnects from all problems and just sits and relaxes in a favorable environment.

Employees of law enforcement agencies (police, prosecutors, etc.) have created, one might say, their own system to protect their own nervous system. Victims often come to them and talk about the misfortune that happened to them. If a law enforcement officer, as they say, takes to heart what happened to the victims, then he will retire as an invalid, if at all his heart can withstand until retirement. Therefore, law enforcement officers put, as it were, a “protective screen” between themselves and the victim or the criminal, that is, the problems of the victim, the criminal are listened to, but an employee, for example, of the prosecutor’s office, does not express any human participation in them. Therefore, it is not uncommon to hear that all law enforcement officers are heartless and very evil people. In fact, they are not like that - they just have such a method of protecting their own health.

2. Autonomic nervous system

autonomic nervous system is one of the parts of our nervous system. The autonomic nervous system is responsible for: the activity of the internal organs, the activity of the endocrine and external secretion glands, the activity of the blood and lymphatic vessels, and also, to some extent, the muscles.

The autonomic nervous system is divided into two sections:

1) sympathetic section;

2) parasympathetic section.

Sympathetic nervous system dilates the pupil, it also causes an increase in heart rate, an increase in blood pressure, expands the small bronchi, etc. This nervous system is carried out by sympathetic spinal centers. It is from these centers that peripheral sympathetic fibers begin, which are located in the lateral horns of the spinal cord.

parasympathetic nervous system is responsible for the activity of the bladder, genitals, rectum, and it also “irritates” a number of other nerves (for example, glossopharyngeal, oculomotor nerve). Such a "diverse" activity of the parasympathetic nervous system is explained by the fact that its nerve centers are located both in the sacral spinal cord and in the brain stem. Now it becomes clear that those nerve centers that are located in the sacral spinal cord control the activity of organs located in the small pelvis; nerve centers located in the brain stem regulate the activity of other organs through a number of special nerves.

How is the control over the activity of the sympathetic and parasympathetic nervous system carried out? Control over the activity of these sections of the nervous system is carried out by special autonomic apparatus, which are located in the brain.

Diseases of the autonomic nervous system. The causes of diseases of the autonomic nervous system are as follows: a person does not tolerate hot weather or, conversely, feels uncomfortable in winter. A symptom may be that a person, when excited, quickly begins to blush or turn pale, his pulse quickens, he begins to sweat a lot.

It should be noted that diseases of the autonomic nervous system occur in people from birth. Many believe that if a person gets excited and blushes, then he is simply too modest and shy. Few people would think that this person has some kind of autonomic nervous system disease.

Also, these diseases can be acquired. For example, due to a head injury, chronic poisoning with mercury, arsenic, due to a dangerous infectious disease. They can also occur when a person is overworked, with a lack of vitamins, with severe mental disorders and experiences. Also, diseases of the autonomic nervous system can be the result of non-compliance with safety regulations at work with dangerous working conditions.

The regulatory activity of the autonomic nervous system may be impaired. Diseases can "mask" as other diseases. For example, when sick solar plexus there may be bloating, poor appetite; with a disease of the cervical or thoracic nodes of the sympathetic trunk, chest pains can be observed, which can radiate to the shoulder. These pains are very similar to heart disease.

To prevent diseases of the autonomic nervous system, a person should follow a number of simple rules:

1) avoid nervous fatigue, colds;

2) observe safety precautions in production with hazardous working conditions;

3) eat well;

4) go to the hospital in a timely manner, complete the entire prescribed course of treatment.

Moreover, the last point, timely admission to the hospital and complete completion of the prescribed course of treatment, is the most important. This follows from the fact that delaying your visit to the doctor for too long can lead to the most unfortunate consequences.

Good nutrition also plays important role, because a person "charges" his body, gives him new strength. Having refreshed, the body begins to fight diseases several times more actively. In addition, fruits contain many beneficial vitamins that help the body fight disease. The most useful fruits are in their raw form, because when they are harvested, many beneficial features may disappear. A number of fruits, in addition to containing vitamin C, also have a substance that enhances the action of vitamin C. This substance is called tannin and is found in quinces, pears, apples, and pomegranates.

3. Central nervous system

The human central nervous system consists of the brain and spinal cord.

The spinal cord looks like a cord, it is somewhat flattened from front to back. Its size in an adult is approximately 41 to 45 cm, and its weight is about 30 gm. It is "surrounded" by the meninges and is located in the brain canal. Throughout its length, the thickness of the spinal cord is the same. But it has only two thickenings:

1) cervical thickening;

2) lumbar thickening.

It is in these thickenings that the so-called innervation nerves of the upper and lower extremities are formed. Dorsal brain is divided into several departments:

1) cervical;

2) thoracic region;

3) lumbar;

4) sacral department.

The human brain is located in the cranial cavity. It has two cerebral hemispheres: the right hemisphere and left hemisphere. But, in addition to these hemispheres, the trunk and cerebellum are also isolated. Scientists have calculated that the brain of a man is heavier than the brain of a woman by an average of 100 gm. They explain this by the fact that most men are much larger than women in terms of their physical parameters, that is, all parts of a man's body are larger than parts of a woman's body. The brain actively begins to grow even when the child is still in the womb. The brain reaches its "real" size only when a person reaches the age of twenty. At the very end of a person's life, his brain becomes a little lighter.

There are five main divisions in the brain:

1) telencephalon;

2) diencephalon;

3) midbrain;

4) hindbrain;

5) medulla oblongata.

If a person has suffered a traumatic brain injury, then this always negatively affects both his central nervous system and his mental state.

When the psyche is disturbed, a person can hear voices inside the head that command him to do this or that. All attempts to drown out these voices are futile and in the end the person goes and does what the voices ordered him to do.

In the hemisphere, the olfactory brain and basal nuclei are distinguished. Also, everyone knows this joke phrase: "Strain your brains", that is, think. Indeed, the "drawing" of the brain is very complex. The complexity of this "pattern" is predetermined by the fact that furrows and ridges go along the hemispheres, which form a kind of "gyrus". Despite the fact that this "drawing" is strictly individual, there are several common furrows. Thanks to these common furrows, biologists and anatomists have identified 5 lobes of the hemispheres:

1) frontal lobe;

2) parietal lobe;

3) occipital lobe;

4) temporal lobe;

5) hidden share.

The brain and spinal cord are covered with membranes:

1) dura mater;

2) arachnoid;

3) soft shell.

Hard shell. The hard shell covers the outside of the spinal cord. In its shape, it most of all resembles a bag. It should be said that the outer hard shell of the brain is the periosteum of the bones of the skull.

Arachnoid. The arachnoid is a substance that is almost closely adjacent to the hard shell of the spinal cord. The arachnoid membrane of both the spinal cord and the brain does not contain any blood vessels.

Soft shell. The pia mater of the spinal cord and brain contains nerves and blood vessels, which, in fact, feed both brains.

Despite the fact that hundreds of works have been written on the study of the functions of the brain, its nature has not been fully elucidated. One of the most important mysteries that the brain “guesses” is vision. Rather, how and with what help we see. Many mistakenly assume that vision is the prerogative of the eyes. This is not true. Scientists are more inclined to believe that the eyes simply perceive the signals that our environment sends us. Eyes pass them on "by authority". The brain, having received this signal, builds a picture, i.e. we see what our brain “shows” to us. Similarly, the issue with hearing should be resolved: it is not the ears that hear. Rather, they also receive certain signals that the environment sends us.

In general, what the brain is, mankind will not find out to the end soon. It is constantly evolving and developing. It is believed that the brain is the "residence" of the human mind.

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 fiber membranes peripheral nerves; 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 CNS includes the brain and spinal cord, and the PNS, which provides communication between the CNS and various parts body - 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 endoplasmic reticulum, ribosomes, Nissl bodies (tigroid), mitochondria, 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 called a nerve impulse. Unlike a simple electrical discharge, which, due to the resistance of the neuron, will gradually weaken and will be able to overcome only short distance, a much slower "running" nerve impulse in the process of propagation is constantly restored (regenerates). The concentrations of ions (electrically charged atoms) - mainly sodium and potassium, as well as organic substances - 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, together with the renewed electrochemical cycle, the nerve impulse propagates along 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 clusters surrounded by specialized connective tissue, which contains vessels that supply the nerve fibers with nutrients and oxygen and remove carbon dioxide and waste 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 special type glial cells - oligodendroglia. Each of these cells forms the myelin sheath of several axons at once. Unmyelinated fibers in the CNS lack a sheath of any special cells. The myelin sheath accelerates 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 at a given moment. In a number of animals (for example, in the lobster) between the neurons of certain nerves, a special close connection 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 cerebral hemispheres - the largest part of the brain - contain higher nerve centers that form the basis of consciousness, intellect, personality, speech, and 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 one, 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 a 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, peripheral motor neuron and 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 deal mainly 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 .