Nervous system consists of tortuous networks of nerve cells that make up various interconnected structures and control all the activities of the body, both desired and conscious actions, and reflexes and automatic actions; the nervous system allows us to interact with the outside world, and is also responsible for mental activity.

The nervous system consists of various interconnected structures that together make up an anatomical and physiological unit. consists of organs located inside the skull (brain, cerebellum, brain stem) and spine (spinal cord); is responsible for interpreting the state and various needs of the body based on the information received, in order to then generate commands designed to obtain appropriate responses.

consists of many nerves that go to the brain (brain pairs) and spinal cord (vertebral nerves); acts as a transmitter of sensory stimuli to the brain and commands from the brain to the organs responsible for their execution. The autonomic nervous system controls the functions of numerous organs and tissues through antagonistic effects: the sympathetic system is activated during anxiety, while the parasympathetic system is activated at rest.

central nervous system
Includes the spinal cord and brain structures.

Topic. Structure and functions of the human nervous system

1 What is the nervous system

2 Central nervous system

Brain

Spinal cord

CNS

3 Autonomic nervous system

4 Development of the nervous system in ontogeny. Characteristics of the three-bubble and five-bubble stages of brain formation

What is the nervous system

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.

Nervous system controls the activity of various organs, systems and apparatuses that make up the body. It regulates the functions of movement, digestion, respiration, blood supply, metabolic processes, etc. The nervous system establishes the relationship of the body with the external environment, unites all parts of the body into a single whole.

The nervous system according to the topographic principle is divided into central and peripheral ( rice. one).

central nervous system(CNS) includes the brain and spinal cord.

To peripheral part of the nervoussystems include spinal and cranial nerves with their roots and branches, nerve plexuses, nerve nodes, nerve endings.

In addition, the nervous system containstwo special parts : somatic (animal) and vegetative (autonomous).

somatic nervous system innervates mainly the organs of the soma (body): striated (skeletal) muscles (face, trunk, limbs), skin and some internal organs (tongue, larynx, pharynx). The somatic nervous system primarily performs the functions of connecting the body with the external environment, providing sensitivity and movement, causing contraction of the skeletal muscles. Since the functions of movement and feeling are characteristic of animals and distinguish them from plants, this part of the nervous system is calledanimal(animal). The actions of the somatic nervous system are controlled by human consciousness.

autonomic nervous system innervates the viscera, glands, smooth muscles of organs and skin, blood vessels and the heart, regulates metabolic processes in tissues. The autonomic nervous system influences the processes of the so-called plant life, common to animals and plants(metabolism, respiration, excretion, etc.), which is why its name comes from ( vegetative- vegetable).

Both systems are closely related, but the autonomic nervous system has some degree of autonomy and does not depend on our will, as a result of which it is also called autonomic nervous system.

She is being divided into two parts sympathetic and parasympathetic. The allocation of these departments is based both on the anatomical principle (differences in the location of the centers and the structure of the peripheral part of the sympathetic and parasympathetic nervous system), and on functional differences.

Excitation of the sympathetic nervous system contributes to the intensive activity of the body; excitation of the parasympathetic On the contrary, it helps to restore the resources expended by the body.

The sympathetic and parasympathetic systems have opposite influence on many organs, being functional antagonists. Yes, under influence of impulses coming along the sympathetic nerves, heart contractions become more frequent and intensified, blood pressure in the arteries rises, glycogen in the liver and muscles breaks down, blood glucose increases, pupils dilate, sensitivity of the sense organs and the efficiency of the central nervous system increase, bronchi narrow, contractions of the stomach and intestines are inhibited, secretion decreases gastric juice and pancreatic juice, the bladder relaxes and its emptying is delayed. Under the influence of impulses coming through the parasympathetic nerves, heart contractions slow down and weaken, blood pressure decreases, blood glucose decreases, contractions of the stomach and intestines are stimulated, secretion of gastric juice and pancreatic juice increases, etc.

central nervous system

Central nervous system (CNS)- the main part of the nervous system of animals and humans, consisting of a cluster of nerve cells (neurons) and their processes.

central nervous system consists of the brain and spinal cord and their protective membranes.

The outermost is dura mater , below it is located arachnoid (arachnoid ), and then pia mater fused to the surface of the brain. Between the soft and arachnoid membranes is subarachnoid (subarachnoid) space , containing cerebrospinal fluid, in which both the brain and spinal cord literally float. The action of the buoyancy force of the fluid leads to the fact that, for example, the adult brain, which has 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.

CNS formed from gray and white matter .

Gray matter make up 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 that act as conductors that transmit impulses from one center to another. The gray and white matter also contain glial cells.

CNS neurons form many circuits that perform two main functions: 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- this or that 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 upward direction to the centers of the brain. Motor (descending)) paths 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. There are a few exceptions to this general rule, however.

Brain

consists of three main structures: the cerebral hemispheres, the cerebellum and the trunk.

Large hemispheres - the largest part of the brain - contain higher nerve centers that form the basis of consciousness, intellect, personality, speech, understanding. In each of the large hemispheres, the following formations are distinguished: isolated accumulations (nuclei) of gray matter lying in the depths, which contain many important centers; a large array of white matter located above them; covering the hemispheres from the outside, a thick layer of gray matter with numerous convolutions, constituting the cerebral cortex.

Cerebellum also consists of a deep gray matter, an intermediate array of white matter and an outer thick layer of gray matter, forming many convolutions. The cerebellum provides mainly coordination of movements.

Trunk The brain 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, while the remaining ten pairs from the trunk. The trunk regulates such vital functions as breathing and blood circulation.

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.

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.

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.

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 brainis divided into several departments:

1) cervical;

2) thoracic region;

3) lumbar;

4) sacral department.

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.

Main and specific CNS function- the implementation of simple and complex highly differentiated reflective reactions, called reflexes. In higher animals and humans, the lower and middle sections of the central nervous system - the spinal cord, medulla oblongata, midbrain, diencephalon and cerebellum - regulate the activity of individual organs and systems of a highly developed organism, communicate and interact between them, ensure the unity of the organism and the integrity of its activity. The highest department of the central nervous system - the cerebral cortex and the nearest subcortical formations - mainly regulates the connection and relationship of the body as a whole with the environment.

The main features of the structure and function CNS

connected with all organs and tissues through the peripheral nervous system, which in vertebrates includes cranial nerves from the brain, and spinal nerves- from the spinal cord, intervertebral nerve nodes, as well as the peripheral part of the autonomic nervous system - nerve nodes, with nerve fibers approaching them (preganglionic) and departing from them (postganglionic) nerve fibers.

Sensory, or afferent, nervous adductor fibers carry excitation to the central nervous system from peripheral receptors; by diverting efferent (motor and autonomic) nerve fibers excitation from the central nervous system is sent to the cells of the executive working apparatus (muscles, glands, blood vessels, etc.). In all parts of the CNS there are afferent neurons that perceive stimuli coming from the periphery, and efferent neurons that send nerve impulses to the periphery to various executive organs.

Afferent and efferent cells with their processes can contact each other and make up two-neuron reflex arc, carrying out elementary reflexes (for example, tendon reflexes of the spinal cord). But, as a rule, interneurons, or interneurons, are located in the reflex arc between the afferent and efferent neurons. Communication between different parts of the central nervous system is also carried out with the help of many processes of afferent, efferent and intercalary neurons of these departments, forming intracentral short and long pathways. The CNS also includes neuroglial cells, which perform a supporting function in it, and also participate in the metabolism of nerve cells.

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.

autonomic nervous system

autonomic nervous system It 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 the 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, with a disease of the solar plexus, bloating, poor appetite can be observed; 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 an 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 useful properties can 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.

Development of the nervous system in ontogeny. Characteristics of the three-bubble and five-bubble stages of brain formation

Ontogeny, or the individual development of an organism, is divided into two periods: prenatal (intrauterine) and postnatal (after birth). The first continues from the moment of conception and the formation of the zygote until birth; the second - from the moment of birth to death.

prenatal period in turn is divided into three periods: initial, embryonic and fetal. The initial (pre-implantation) period in humans covers the first week of development (from the moment of fertilization to implantation in the uterine mucosa). Embryonic (prefetal, embryonic) period - from the beginning of the second week to the end of the eighth week (from the moment of implantation to the completion of organ laying). The fetal (fetal) period begins from the ninth week and lasts until birth. At this time, there is an increased growth of the body.

postnatal period ontogenesis is divided into eleven periods: 1st - 10th day - newborns; 10th day - 1 year - infancy; 1-3 years - early childhood; 4-7 years - the first childhood; 8-12 years - the second childhood; 13-16 years - adolescence; 17-21 years old - youthful age; 22-35 years - the first mature age; 36-60 years - the second mature age; 61-74 years - old age; from 75 years old - senile age, after 90 years old - long-livers.

Ontogeny ends with natural death.

The nervous system develops from three main formations: neural tube, neural crest and neural placodes. The neural tube is formed as a result of neurulation from the neural plate - a section of the ectoderm located above the notochord. According to the theory of Shpemen's organizers, chord blastomeres are capable of releasing substances - inductors of the first kind, as a result of which the neural plate bends inside the body of the embryo and a neural groove is formed, the edges of which then merge, forming a neural tube. The closure of the edges of the neural groove begins in the cervical region of the body of the embryo, spreading first to the caudal part of the body, and later to the cranial.

The neural tube gives rise to the central nervous system, as well as neurons and gliocytes of the retina. Initially, the neural tube is represented by a multi-row neuroepithelium, the cells in it are called ventricular. Their processes, facing the cavity of the neural tube, are connected by nexuses, the basal parts of the cells lie on the subpial membrane. The nuclei of neuro-epithelial cells change their location depending on the phase of the cell life cycle. Gradually, towards the end of embryogenesis, ventricular cells lose their ability to divide and give rise to neurons and various types of gliocytes in the postnatal period. In some areas of the brain (germinal or cambial zones), ventricular cells do not lose their ability to divide. In this case, they are called subventricular and extraventricular. Of these, in turn, neuroblasts differentiate, which, no longer having the ability to proliferate, undergo changes during which they turn into mature nerve cells - neurons. The difference between neurons and other cells of their differon (cell row) is the presence of neurofibrils in them, as well as processes, while the axon (neuritis) appears first, and later - dendrites. The processes form connections - synapses. In total, the differon of the nervous tissue is represented by neuroepithelial (ventricular), subventricular, extraventricular cells, neuroblasts and neurons.

Unlike macroglial gliocytes, which develop from ventricular cells, microglial cells develop from the mesenchyme and enter the macrophage system.

The cervical and trunk parts of the neural tube give rise to the spinal cord, the cranial part differentiates into the head. The cavity of the neural tube turns into a spinal canal connected to the ventricles of the brain.

The brain undergoes several stages in its development. Its departments develop from the primary cerebral vesicles. At first there are three of them: front, middle and diamond-shaped. By the end of the fourth week, the anterior cerebral vesicle is divided into the rudiments of the telencephalon and diencephalon. Shortly thereafter, the rhomboid bladder also divides, giving rise to the hindbrain and medulla oblongata. This stage of brain development is called the stage of five brain bubbles. The time of their formation coincides with the time of the appearance of the three bends of the brain. First of all, a parietal bend is formed in the region of the middle cerebral bladder, its bulge is turned dorsally. After it, an occipital bend appears between the rudiments of the medulla oblongata and spinal cord. Its convexity is also turned dorsally. The last to form a bridge bend between the two previous ones, but it bends ventrally.

The cavity of the neural tube in the brain is transformed first into the cavity of three, then five bubbles. The cavity of the rhomboid bladder gives rise to the fourth ventricle, which is connected through the aqueduct of the midbrain (the cavity of the middle cerebral bladder) with the third ventricle, formed by the cavity of the rudiment of the diencephalon. The cavity of the initially unpaired rudiment of the telencephalon is connected through the interventricular opening with the cavity of the rudiment of the diencephalon. In the future, the cavity of the terminal bladder will give rise to the lateral ventricles.

The walls of the neural tube at the stages of formation of the cerebral vesicles will thicken most evenly in the region of the midbrain. The ventral part of the neural tube is transformed into the legs of the brain (midbrain), gray tubercle, funnel, posterior pituitary gland (midbrain). Its dorsal part turns into a plate of the roof of the midbrain, as well as the roof of the third ventricle with the choroid plexus and the epiphysis. The lateral walls of the neural tube in the region of the diencephalon grow, forming visual tubercles. Here, under the influence of inductors of the second kind, protrusions are formed - eye vesicles, each of which will give rise to an eye cup, and later - the retina. Inducers of the third kind, located in the eyecups, affect the ectoderm above itself, which laces up inside the glasses, giving rise to the lens.

LECTURE ON THE TOPIC: HUMAN NERVOUS SYSTEM

Nervous system is a system that regulates the activity of all human organs and systems. This system determines: 1) the functional unity of all human organs and systems; 2) the connection of the whole organism with the environment.

From the point of view of maintaining homeostasis, the nervous system provides: maintaining the parameters of the internal environment at a given level; inclusion of behavioral responses; adaptation to new conditions if they persist for a long time.

Neuron(nerve cell) - the main structural and functional element of the nervous system; Humans have over 100 billion neurons. The neuron consists of a body and processes, usually one long process - an axon and several short branched processes - dendrites. Along the dendrites, impulses follow to the cell body, along the axon - from the cell body to other neurons, muscles or glands. Thanks to the processes, neurons contact each other and form neural networks and circles through which nerve impulses circulate.

A neuron is the functional unit of the nervous system. Neurons are susceptible to stimulation, that is, they are able to be excited and transmit electrical impulses from receptors to effectors. In the direction of impulse transmission, afferent neurons (sensory neurons), efferent neurons (motor neurons) and intercalary neurons are distinguished.

Nervous tissue is called excitable tissue. In response to some influence, the process of excitation arises and spreads in it - the rapid recharging of cell membranes. The emergence and spread of excitation (nerve impulse) is the main way the nervous system implements its control function.

The main prerequisites for the occurrence of excitation in cells: the existence of an electrical signal on the membrane at rest - the resting membrane potential (RMP);

the ability to change the potential by changing the permeability of the membrane for certain ions.

The cell membrane is a semi-permeable biological membrane, it has channels for potassium ions to pass through, but there are no channels for intracellular anions that are held at the inner surface of the membrane, while creating a negative charge of the membrane from the inside, this is the resting membrane potential, which is on average - - 70 millivolts (mV). There are 20-50 times more potassium ions in the cell than outside, this is maintained throughout life with the help of membrane pumps (large protein molecules capable of transporting potassium ions from the extracellular environment to the inside). The MPP value is due to the transfer of potassium ions in two directions:

1. outside into the cage under the action of pumps (with a large expenditure of energy);

2. out of the cell by diffusion through membrane channels (without energy costs).

In the process of excitation, the main role is played by sodium ions, which are always 8-10 times more outside the cell than inside. Sodium channels are closed when the cell is at rest, in order to open them, it is necessary to act on the cell with an adequate stimulus. If the stimulation threshold is reached, sodium channels open and sodium enters the cell. In thousandths of a second, the membrane charge will first disappear, and then change to the opposite - this is the first phase of the action potential (AP) - depolarization. The channels close - the peak of the curve, then the charge is restored on both sides of the membrane (due to potassium channels) - the stage of repolarization. Excitation stops and while the cell is at rest, the pumps change the sodium that has entered the cell for the potassium that has left the cell.

AP evoked at any point of the nerve fiber itself becomes an irritant for neighboring sections of the membrane, causing AP in them, and they, in turn, excite more and more new sections of the membrane, thus spreading throughout the cell. In myelin-coated fibers, PD will only occur in myelin-free areas. Therefore, the speed of signal propagation increases.

The transfer of excitation from a cell to another occurs with the help of a chemical synapse, which is represented by the point of contact between two cells. The synapse is formed by the presynaptic and postsynaptic membranes and the synaptic cleft between them. Excitation in the cell resulting from AP reaches the area of ​​the presynaptic membrane, where synaptic vesicles are located, from which a special substance, the mediator, is ejected. The neurotransmitter enters the gap, moves to the postsynaptic membrane and binds to it. Pores for ions open in the membrane, they move inside the cell and a process of excitation occurs.

Thus, in the cell, the electrical signal is converted into a chemical one, and the chemical signal is again converted into an electrical one. Signal transmission in the synapse is slower than in the nerve cell, and also one-sided, since the mediator is released only through the presynaptic membrane, and can only bind to the receptors of the postsynaptic membrane, and not vice versa.

Mediators can cause in cells not only excitation, but also inhibition. At the same time, pores are opened on the membrane for such ions, which increase the negative charge that existed on the membrane at rest. One cell can have many synaptic contacts. An example of a mediator between a neuron and a skeletal muscle fiber is acetylcholine.

The nervous system is divided into central nervous system and peripheral nervous system.

In the central nervous system, the brain is distinguished, where the main nerve centers and the spinal cord are concentrated, here there are centers of a lower level and there are pathways to peripheral organs.

Peripheral - nerves, ganglia, ganglia and plexuses.

The main mechanism of activity of the nervous system - reflex. A reflex is any response of the body to a change in the external or internal environment, which is carried out with the participation of the central nervous system in response to irritation of the receptors. The structural basis of the reflex is the reflex arc. It includes five consecutive links:

1 - Receptor - a signaling device that perceives the impact;

2 - Afferent neuron - leads the signal from the receptor to the nerve center;

3 - Intercalary neuron - the central part of the arc;

4 - Efferent neuron - the signal comes from the central nervous system to the executive structure;

5 - Effector - a muscle or gland that performs a certain type of activity

Brain consists of accumulations of bodies of nerve cells, nerve tracts and blood vessels. Nerve tracts form the white matter of the brain and consist of bundles of nerve fibers that conduct impulses to or from different parts of the gray matter of the brain - the nuclei or centers. Pathways connect the various nuclei, as well as the brain with the spinal cord.

Functionally, the brain can be divided into several sections: the forebrain (consisting of the telencephalon and diencephalon), the midbrain, the hindbrain (consisting of the cerebellum and the pons), and the medulla oblongata. The medulla oblongata, pons, and midbrain are collectively referred to as the brainstem.

Spinal cord located in the spinal canal, reliably protecting it from mechanical damage.

The spinal cord has a segmental structure. Two pairs of anterior and posterior roots depart from each segment, which corresponds to one vertebra. There are 31 pairs of nerves in total.

The posterior roots are formed by sensitive (afferent) neurons, their bodies are located in the ganglia, and the axons enter the spinal cord.

The anterior roots are formed by axons of efferent (motor) neurons whose bodies lie in the spinal cord.

The spinal cord is conditionally divided into four sections - cervical, thoracic, lumbar and sacral. It closes a huge number of reflex arcs, which ensures the regulation of many body functions.

The gray central substance is nerve cells, the white one is nerve fibers.

The nervous system is divided into somatic and autonomic.

To somatic nervous system (from the Latin word "soma" - body) refers to the part of the nervous system (both cell bodies and their processes), which controls the activity of skeletal muscles (body) and sensory organs. This part of the nervous system is largely controlled by our consciousness. That is, we are able to bend or unbend an arm, a leg, and so on at will. However, we are unable to consciously stop perceiving, for example, sound signals.

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

The autonomic nervous system is practically not controlled by consciousness, that is, we are not able to relieve gallbladder spasm at will, stop cell division, stop intestinal activity, expand or narrow blood vessels

The nervous system is the highest integrating and coordinating system of the human body, which ensures the coordinated activity of internal organs and the connection of the body with the external environment.

Anatomically, the nervous system is divided into the central (brain and spinal cord); and peripheral, including 12 pairs of cranial nerves, 31 pairs of spinal nerves and nerve nodes located outside the brain and spinal cord.

The function of the nervous system is divided into:

the somatic nervous system - mainly carries out the connection of the body with the external environment: the perception of irritations, the regulation of movements of the striated muscles, etc.

autonomic (autonomous) nervous system - regulates metabolism and the functioning of internal organs: heartbeat, vascular tone, peristaltic contractions of the intestine, secretion of various glands, etc. The autonomic nervous system is divided into parasympathetic and sympathetic nervous systems.

Both of them function in close interaction, however, the autonomic nervous system has some independence, controlling involuntary functions.

The nervous system is made up of nerve cells called neurons. There are 25 billion neurons in the brain, and 25 million cells in the periphery. The bodies of neurons are located mainly in the CNS. Gray matter is a collection of neurons. In the spinal cord, it is located in the center, surrounding the spinal canal. In the brain, on the contrary, the gray matter is located on the surface, forming a cortex and separate clusters - nuclei concentrated in the white matter.

White matter is under gray and is composed of nerve fibers (neuronal processes) covered with sheaths. Nerve ganglions also consist of bodies of neurons. Nerve fibers that extend beyond the CNS and nerve nodes, connecting, compose nerve bundles, and several such bundles form individual nerves.

Centripetal, or sensitive - nerves that conduct excitation from the periphery to the central nervous system. For example, visual, olfactory, auditory.

Centrifugal, or motor - nerves through which excitation is transmitted from the central nervous system to the organs. For example, oculomotor.

Mixed (wandering, spinal), if excitation goes in one direction along one fiber, and in the other direction along the other.

Functions nervous system: regulates the activity of all organs and organ systems, communicates with the external environment through the sense organs; is the material basis for higher nervous activity, thinking, behavior and speech.

The structure and function of the spinal cord.

The spinal cord is located in the spinal canal from the 1st cervical vertebra to the 1st - 2nd lumbar, its length is about 45 cm, thickness is about 1 cm. The anterior and posterior longitudinal grooves divide it into two symmetrical halves. In the center is the spinal canal, which contains the cerebrospinal fluid. In the middle part of the spinal cord, near the spinal canal, there is gray matter, which in cross section resembles the contour of a butterfly. The gray matter is formed by the bodies of neurons, it distinguishes between the anterior and posterior horns. The bodies of intercalary neurons are located in the posterior horns of the spinal cord, and the bodies of motor neurons are located in the anterior horns. In the thoracic region, lateral horns are also distinguished, in which the neurons of the sympathetic part of the autonomic nervous system are located. Surrounding the gray matter is the white matter formed by the nerve fibers. The spinal cord is covered by three membranes:

hard shell - outer, connective tissue, lining the inner cavity of the skull and spinal canal;

arachnoid - located under the solid. This is a thin shell with a small number of nerves and vessels;

the choroid is fused with the brain, enters the furrows and contains many blood vessels.

Fluid-filled cavities form between the vascular and arachnoid membranes.

31 pairs of mixed spinal nerves leave the spinal cord. Each nerve begins with two roots: the anterior (motor), in which the processes of motor neurons and autonomic fibers are located, and the posterior (sensory), through which excitation is transmitted to the spinal cord. In the posterior roots are the spinal nodes - clusters of sensory neuron bodies.

Transection of the posterior roots leads to a loss of sensation in those areas that are innervated by the corresponding roots, and transection of the anterior roots leads to paralysis of the innervated muscles.

The functions of the spinal cord are reflex and conduction. As a reflex center, the spinal cord takes part in motor (conducts nerve impulses to the skeletal muscles) and autonomic reflexes. The most important vegetative reflexes of the spinal cord are vasomotor, food, respiratory, defecation, urination, sexual. The reflex function of the spinal cord is under the control of the brain.

The reflex functions of the spinal cord can be examined on the spinal preparation of a frog (without a brain), which retains the simplest motor reflexes. She withdraws her paw in response to mechanical and chemical stimuli. In humans, the brain is of decisive importance in the implementation of the coordination of motor reflexes.

The conduction function is carried out due to the ascending and descending paths of the white matter. Excitation from the muscles and internal organs is transmitted along the ascending paths to the brain, along the descending paths - from the brain to the organs.

The structure and functions of the brain.

There are five sections in the brain: the medulla oblongata; the hindbrain, which includes the bridge and the cerebellum; midbrain; diencephalon and forebrain, represented by the large hemispheres. Up to 80% of the mass of the brain falls on the cerebral hemispheres. The central canal of the spinal cord continues into the brain, where it forms four cavities (ventricles). Two ventricles are located in the hemispheres, the third - in the diencephalon, the fourth - at the level of the medulla oblongata and the bridge. They contain cranial fluid. The brain, as well as the spinal cord, is surrounded by three membranes - connective tissue, arachnoid and vascular.

The medulla oblongata is a continuation of the spinal cord, performs reflex and conduction functions. Reflex functions are associated with the regulation of the work of the respiratory, digestive, and circulatory organs. Here are the centers of protective reflexes - coughing, sneezing, vomiting.

The bridge connects the cerebral cortex with the spinal cord and cerebellum, performing mainly a conductive function.

The cerebellum is formed by two hemispheres, externally covered with a bark of gray matter, under which is white matter. The white matter contains nuclei. The middle part of the cerebellum - the worm - connects its hemispheres. The cerebellum is responsible for coordination, balance and influences muscle tone. When the cerebellum is damaged, there is a decrease in muscle tone and a disorder in the coordination of movements, but after a while other parts of the nervous system begin to perform the functions of the cerebellum, and the lost functions are partially restored. Together with the bridge, the cerebellum is part of the hindbrain.

The midbrain connects all parts of the brain. Here are the centers of skeletal muscle tone, the primary centers of visual and auditory orienting reflexes, which are manifested in the movements of the eyes and head towards stimuli.

Three parts are distinguished in the diencephalon: the visual tubercles (thalamus), the epithalamic region (epithalamus), which includes the pineal gland, and the hypothalamic region (hypothalamus). The subcortical centers of all types of sensitivity are located in the thalamus, excitation from the sense organs comes here, and from here it is transmitted to various parts of the cerebral cortex. The hypothalamus contains the highest regulatory centers of the autonomic nervous system. It controls the constancy of the internal environment of the body. Here are the centers of appetite, thirst, sleep, thermoregulation, i.e. regulation of all types of metabolism. Neurons of the hypothalamus produce neurohormones that regulate the functioning of the endocrine system. In the diencephalon there are also emotional centers: centers of pleasure, fear, aggression. Together with the hindbrain and medulla, the diencephalon is part of the brainstem.

The forebrain is represented by the cerebral hemispheres connected by the corpus callosum. The surface of the forebrain is formed by the cortex, the area of ​​which is about 2200 cm 2. Numerous folds, convolutions and furrows significantly increase the surface of the cortex. The surface of the convolutions is more than two times smaller than the surface of the furrows. The human cortex has from 14 to 17 billion nerve cells arranged in 6 layers, the thickness of the cortex is 2-4 mm. Accumulations of neurons in the depths of the hemispheres form subcortical nuclei. The cerebral cortex consists of 4 lobes: frontal, parietal, temporal and occipital, separated by furrows. In the cortex of each hemisphere, the central sulcus separates the frontal lobe from the parietal, the lateral sulcus separates the temporal lobe, and the parietal-occipital sulcus separates the occipital lobe from the parietal.

In the cortex, sensory, motor and associative zones are distinguished. Sensitive zones are responsible for the analysis of information coming from the sense organs: occipital - for vision, temporal - for hearing, smell and taste; parietal - for skin and joint-muscular sensitivity. Moreover, each hemisphere receives impulses from the opposite side of the body. The motor zones are located in the posterior regions of the frontal lobes, from here come the commands for contraction of the skeletal muscles, their defeat leads to muscle paralysis. Associative zones are located in the frontal lobes of the brain and are responsible for the development of programs for behavior and management of human labor activity; their mass in humans is more than 50% of the total mass of the brain.

A person is characterized by a functional asymmetry of the hemispheres: the left hemisphere is responsible for abstract-logical thinking, speech centers are also located there (Brock's center is responsible for pronunciation, Wernicke's center for understanding speech), the right hemisphere is for figurative thinking, musical and artistic creativity.

Due to the strong development of the cerebral hemispheres, the average mass of the human brain is 1400 g on average.

a set of nerve formations in vertebrates and humans, through which the perception of stimuli acting on the body is realized, the processing of the resulting excitation impulses, the formation of responses. Thanks to it, the functioning of the body as a whole is ensured:

1) contacts with the outside world;

2) implementation of goals;

3) coordination of the work of internal organs;

4) holistic adaptation of the organism.

The neuron acts as the main structural and functional element of the nervous system. Stand out:

1) the central nervous system - which consists of the brain and spinal cord;

2) peripheral nervous system - which consists of nerves extending from the brain and spinal cord, from intervertebral nerve nodes, as well as from the peripheral part of the autonomic nervous system;

3) vegetative nervous system - structures of the nervous system that provide control of the vegetative functions of the body.

NERVOUS SYSTEM

English nervous system) - a set of nerve formations in the human body and vertebrates. Its main functions are: 1) ensuring contacts with the outside world (perception of information, organization of body reactions - from simple responses to stimuli to complex behavioral acts); 2) realization of the goals and intentions of a person; 3) integration of internal organs into systems, coordination and regulation of their activities (see Homeostasis); 4) organization of integral functioning and development of the organism.

Structural and functional element of N. with. is a neuron - a nerve cell consisting of a body, dendrites (the receptor and integrating apparatus of the neuron) and an axon (its efferent part). On the terminal branches of the axon there are special formations that are in contact with the body and dendrites of other neurons - synapses. Synapses are of 2 types - excitatory and inhibitory, with their help, respectively, the transmission or blockade of the impulse message passing through the fiber to the destination neuron occurs.

The interaction of postsynaptic excitatory and inhibitory effects on one neuron creates a multi-conditioning response of the cell, which is the simplest element of integration. Neurons, differentiated in structure and function, are combined into neural modules (neural ensembles) - next. a stage of integration that ensures high plasticity in the organization of brain functions (see Plasticity n. s).

N. s. divided into central and peripheral. C. n. With. It consists of the brain, which is located in the cranial cavity, and the spinal cord, located in the spine. The brain, especially its cortex, is the most important organ of mental activity. The spinal cord carries out g. inborn behaviors. Peripheral N. with. consists of nerves extending from the brain and spinal cord (the so-called cranial and spinal nerves), intervertebral ganglions, and also from the peripheral part of the autonomic N. with. - accumulations of nerve cells (ganglia) with nerves approaching them (preganglionic) and departing from them (postganglionic) nerves.

The vegetative functions of the body (digestion, blood circulation, respiration, metabolism, etc.) are controlled by vegetative nervous system, which is divided into sympathetic and parasympathetic sections: the 1st section mobilizes the functions of the body in a state of increased mental stress, the 2nd - ensures the functioning of internal organs under normal conditions. Si. Blocks of the brain, Deep structures of the brain, Cortex, Neuron-detector, Properties n. With. (N. V. Dubrovinskaya, D. A. Farber.)

NERVOUS SYSTEM

nervous system) - a set of anatomical structures formed by nervous tissue. The nervous system consists of many neurons that transmit information in the form of nerve impulses to various parts of the body and receive it from them to maintain the active life of the body. The nervous system is divided into central and peripheral. The brain and spinal cord form the central nervous system; peripheral nerves include paired spinal and cranial nerves with their roots, their branches, nerve endings and ganglia. There is another classification, according to which the unified nervous system is also conventionally divided into two parts: somatic (animal) and autonomic (autonomous). The somatic nervous system innervates mainly the organs of the soma (body, striated, or skeletal, muscles, skin) and some internal organs (tongue, larynx, pharynx), provides a connection between the body and the external environment. The autonomic (autonomous) nervous system innervates all the viscera, glands, including endocrine, smooth muscles of organs and skin, blood vessels and the heart, regulates metabolic processes in all organs and tissues. The autonomic nervous system, in turn, is divided into two parts: parasympathetic and sympathetic. In each of them, as in the somatic nervous system, the central and peripheral sections are distinguished (ed.). The main structural and functional unit of the nervous system is the neuron (nerve cell).

Nervous system

Word formation. Comes from the Greek. neuron - vein, nerve and systema - connection.

Specificity. Her work provides:

Contacts with the outside world;

Realization of goals;

Coordination of the work of internal organs;

Whole body adaptation.

The neuron is the main structural and functional element of the nervous system.

The central nervous system, which consists of the brain and spinal cord,

Peripheral nervous system, consisting of nerves extending from the brain and spinal cord, intervertebral ganglions;

Peripheral division of the autonomic nervous system.

NERVOUS SYSTEM

Collective designation of a complete system of structures and organs, consisting of nervous tissue. Depending on what is in the center of attention, various schemes for isolating parts of the nervous system are used. The most common is the anatomical division into the central nervous system (the brain and spinal cord) and the peripheral nervous system (everything else). Another taxonomy is based on functions, dividing the nervous system into the somatic nervous system and the autonomic nervous system, the former for voluntary, conscious sensory and motor functions, and the latter for visceral, automatic, involuntary ones.

Source: Nervous system

A system that ensures the integration of the functions of all organs and tissues, their trophism, communication with the outside world, sensitivity, movement, consciousness, alternation of wakefulness and sleep, the state of emotional and mental processes, including manifestations of higher nervous activity, the development of which determines the characteristics of a person's personality. S.n. It is divided primarily into central, represented by the brain tissue (brain and spinal cord), and peripheral, which includes all other structures of the nervous system.