The names of the three parts of the nervous system. Parts of the nervous system

The human nervous system is an important part of the body, which is responsible for many processes that occur. Its diseases have a bad effect on the human condition. It regulates the activity and interaction of all systems and organs. Given the current environmental background and constant stress it is necessary to pay serious attention to the daily routine and proper nutrition to avoid potential health problems.

General information

The nervous system influences the functional interaction of all human systems and organs, as well as the body’s connection with the outside world. Its structural unit, the neuron, is a cell with specific processes. Neural circuits are built from these elements. The nervous system is divided into central and peripheral. The first includes the brain and spinal cord, and the second includes all the nerves and nerve nodes extending from them.

Somatic nervous system

Besides this, nervous system divided into somatic and vegetative. The somatic system is responsible for the interaction of the body with the outside world, for the ability to move independently and for sensitivity, which is provided with the help of sense organs and some nerve endings. A person’s ability to move is ensured by the control of the skeletal and muscle mass, which is carried out using the nervous system. Scientists also call this system animal, since only animals can move and have sensitivity.

Autonomic nervous system

This system is responsible for the internal state of the body, that is, for:

The human autonomic nervous system, in turn, is divided into sympathetic and parasympathetic. The first is responsible for pulse, blood pressure, bronchi, and so on. Its work is controlled by spinal centers, from which come sympathetic fibers located in the lateral horns. The parasympathetic is responsible for the functioning of the bladder, rectum, genitals and a number of nerve endings. This multifunctionality of the system is explained by the fact that its work is carried out both with the help of the sacral part of the brain and through its trunk. These systems are controlled by specific autonomic apparatuses located in the brain.

Diseases

The human nervous system is extremely susceptible to external influence, there are the most various reasons which can cause her illness. Most often, the vegetative system suffers due to the weather, and a person can feel unwell both in too hot weather and cold winter. There are a number of characteristic symptoms for such diseases. For example, a person turns red or pale, their heart rate increases, or they begin to sweat excessively. In addition, such diseases can be acquired.

How do these diseases appear?

They can develop due to head trauma, or arsenic, as well as due to complex and dangerous infectious disease. Such diseases can also develop due to overwork, due to a lack of vitamins, mental disorders or constant stress.

You also need to be careful in hazardous working conditions, which can also affect the development of diseases of the autonomic nervous system. In addition, such diseases can masquerade as others, some of which resemble heart disease.

Central nervous system

It is formed from two elements: the spinal cord and the brain. The first of them looks like a cord, slightly flattened in the middle. In an adult, its size varies from 41 to 45 cm, and its weight reaches only 30 grams. The spinal cord is completely surrounded by membranes that are located in a specific canal. The thickness of the spinal cord does not change along its entire length, except in two places called the cervical and lumbar enlargements. It is here that the nerves of the upper, as well as lower limbs. It is divided into sections such as cervical, lumbar, thoracic and sacral.

Brain

It is located in the human skull and is divided into two components: the left and right hemisphere. In addition to these parts, the trunk and cerebellum are also distinguished. Biologists have been able to determine that the brain of an adult male is 100 mg heavier than a female one. This is explained solely by the fact that all parts of the body of a representative of the stronger sex are larger than female ones. physical parameters thanks to evolution.

The fetal brain begins to actively grow even before birth, in the womb. It stops developing only when a person reaches 20 years of age. In addition, in old age, towards the end of life, it becomes a little easier.

Divisions of the brain

There are five main parts of the brain:

In the event of a traumatic brain injury, a person's central nervous system can be seriously damaged, and this has a negative impact on the person's mental state. With such disorders, patients may experience voices in their heads that are not so easy to get rid of.

Meninges

The brain and spinal cord are covered by three types of membranes:

• The hard shell covers the outside of the spinal cord. It is shaped very much like a bag. It also functions as the periosteum of the skull.
• The arachnoid membrane is a substance that is practically adjacent to the hard tissue. Neither the dura mater nor the arachnoid membrane contains blood vessels.
• The pia mater is a collection of nerves and vessels that supply both brains.

Brain functions

This is very the hard part organism, on which the entire human nervous system depends. Even taking into account that a huge number of scientists are studying the problems of the brain, all its functions have not yet been fully studied. The most difficult mystery for science is the study of the features of the visual system. It is still unclear how and with the help of which parts of the brain we have the ability to see. People far from science mistakenly believe that this happens solely with the help of the eyes, but this is absolutely not the case.

Scientists studying this issue believe that the eyes only perceive the signals that the the world around us, and in turn transmit them to the brain. Receiving a signal, it creates a visual picture, that is, in fact, we see what our brain shows. The same thing happens with hearing; in fact, the ear only perceives sound signals received through the brain.

Conclusion

Currently, diseases of the autonomic system are very common among the younger generation. This is due to many factors, for example, poor condition environment, improper daily routine or irregular and unhealthy diet. To avoid such problems, it is recommended to carefully monitor your routine and avoid various stresses and overwork. After all, the health of the central nervous system is responsible for the condition of the entire body, otherwise such problems can provoke serious disruptions in the functioning of other important organs.

Subject. 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 ontogenesis. Characteristics of the three-vesicle and five-vesicle stages of brain formation

What is the nervous system

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

1) functional unity of all human organs and systems;

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

Nervous system controls the activities 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 external environment, unites all parts of the body into a single whole.

The nervous system is divided according to topographic principle into central and peripheral ( rice. 1).

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 ganglia, and nerve endings.

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

Somatic nervous system innervates primarily the organs of the soma (body): striated (skeletal) muscles (face, torso, limbs), skin and some internal organs (tongue, larynx, pharynx). The somatic nervous system primarily carries out the functions of connecting the body with the external environment, providing sensitivity and movement, causing contraction of 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 insides, 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 so-called plant life, common to animals and plants(metabolism, respiration, excretion, etc.), which is where its name comes from ( vegetative- vegetable).

Both systems are closely related, but the autonomic nervous system has some degree of independence 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 identification of these departments is based both on an anatomical principle (differences in the location of centers and the structure of the peripheral parts of the sympathetic and parasympathetic nervous system) and on functional differences.

Stimulation of the sympathetic nervous system promotes intense activity of the body; parasympathetic stimulation , on the contrary, helps restore the resources expended by the body.

The sympathetic and parasympathetic systems have opposite effects 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 increases, glycogen is broken down in the liver and muscles, the glucose content in the blood increases, the pupils dilate, the sensitivity of the sensory organs and the performance of the central nervous system increases, the 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 levels decrease, contractions of the stomach and intestines are stimulated, the 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 nerve cells(neurons) and their processes.

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

The outermost one is dura mater , underneath it is located arachnoid (arachnoid ), and then pia mater fused to the surface of the brain. Between the soft and arachnoid membranes there is subarachnoid (subarachnoid) space , containing cerebrospinal fluid, in which both the brain and spinal cord literally float. The action of the buoyant 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 blows and shocks that tests the body and which could lead to damage to the nervous system.

The central nervous system is formed of gray and white matter .

Gray matter consist of cell bodies, dendrites and unmyelinated axons, organized into complexes that include countless synapses and serve as information processing centers, providing many functions of the nervous system.

White matter consists of myelinated and unmyelinated axons that act as conductors transmitting impulses from one center to another. The gray and white matter also contains 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 through a sequence of centers connected by long axons that form specific pathways, for example pain, visual, auditory. Sensitive (ascending) pathways go in an ascending direction to the centers of the brain. Motor (descending) pathways connect the brain with motor neurons of the cranial and spinal nerves. The pathways are usually organized in such a way that information (for example, pain or tactile) from the right side of the body enters the left side of the brain and vice versa. This rule also applies to the 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 movements of the right. There are, however, a few exceptions to this general rule.

Brain

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

Large hemispheres - the largest part of the brain - contain higher nerve centers that form the basis of consciousness, intelligence, personality, speech, and understanding. In each of the cerebral hemispheres, the following formations are distinguished: underlying isolated accumulations (nuclei) of gray matter, which contain many important centers; a large mass of white matter located above them; covering the outside of the hemispheres is a thick layer of gray matter with numerous convolutions that makes up the cerebral cortex.

Cerebellum also consists of a deep gray matter, an intermediate mass of white matter and an outer thick layer of gray matter, forming many convolutions. The cerebellum primarily provides 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, the cerebellum and the spinal cord and contains numerous centers of sensory and motor pathways. The first two pairs of cranial nerves arise from cerebral hemispheres, the remaining ten pairs are from the trunk. The trunk regulates such vital important functions like breathing and blood circulation.

Scientists have calculated that a man's brain is heavier than a woman's brain by an average of 100 gm. They explain this by the fact that most men, in terms of their physical parameters, are much more women, i.e. 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 “true” size only when a person reaches twenty years of age. At the very end of a person's life, his brain becomes a little lighter.

The brain has five main sections:

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 “pattern” of the brain is very complex. The complexity of this “pattern” is determined by the fact that furrows and ridges run along the hemispheres, which form a kind of “convolutions”. Despite the fact that this “pattern” is strictly individual, several common grooves are distinguished. Thanks to these common grooves, biologists and anatomists have identified 5 hemisphere lobes:

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 to study the functions of the brain, its nature has not been fully elucidated. One of the most important riddles that the brain “makes” is vision. Or rather, how and with what help we see. Many people mistakenly assume that vision is the prerogative of the eyes. This is wrong. Scientists are more inclined to believe that the eyes simply perceive signals that the environment around us sends us. The eyes transmit them further “up the chain of command.” The brain, having received this signal, builds a picture, i.e. we see what our brain “shows” us. The issue of hearing should be resolved similarly: it is not the ears that hear. Or 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 medullary canal. Throughout its entire 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 region;

2) thoracic region;

3) lumbar region;

4) sacral section.

Located inside the spinal column and protected by its bone tissue, the spinal cord has a cylindrical shape and is covered with three membranes. In a cross section, the gray matter is shaped like the letter H or a butterfly. Gray matter is surrounded by white matter. Sensitive fibers of the spinal nerves end in the dorsal (posterior) parts of the gray matter - the dorsal horns (at the ends of the H, facing the back). The bodies of motor neurons of the spinal nerves are located in the ventral (anterior) parts of the gray matter - the anterior horns (at the ends of the H, distant 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 different parts of the gray matter of the spinal cord.

Home and specific central nervous system function- 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, carry out communication and interaction between them, ensure the unity of the organism and the integrity of its activities. The higher 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.

Main structural features and functions CNS

connected to all organs and tissues through the peripheral nervous system, which in vertebrates includes cranial nerves emanating 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 extending from them (postganglionic).

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

Afferent and efferent cells with their processes can contact each other and form two-neuron reflex arc, carrying out elementary reflexes (for example, tendon reflexes of the spinal cord). But, as a rule, intercalary nerve cells, 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 using many afferent, efferent and interneurons of these sections, 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 membrane;

3) soft shell.

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

Arachnoid. The arachnoid membrane 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 soft membrane of the spinal cord and brain contains nerves and vessels, which, in fact, nourish both brains.

Autonomic nervous system

Autonomic nervous system - This is one of the parts of our nervous system. The autonomic nervous system is responsible for: the activity of internal organs, the activity of glands of the internal and external secretion, the activity of 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 increased heart rate, increased blood pressure, dilates small bronchi, etc. This nervous system is carried out by sympathetic spinal centers. It is from these centers that the 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, the glossopharyngeal, oculomotor nerve). This “diverse” activity of the parasympathetic nervous system is explained by the fact that its nerve centers are located both in the sacral part of the spinal cord and in the brain stem. Now it becomes clear that those nerve centers that are located in the sacral part of the spinal cord control the activity of organs located in the pelvis; nerve centers, which are located in the brain stem, regulate the activity of other organs through a number of special nerves.

How is the activity of the sympathetic and parasympathetic nervous system controlled? The activity of these sections of the nervous system is controlled by special autonomic apparatuses located in the brain.

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

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

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

The regulatory activity of the autonomic nervous system may be impaired. Diseases can “masquerade” as other diseases. For example, with a disease of the solar plexus, bloating and poor appetite may be observed; with a disease of the cervical or thoracic nodes of the sympathetic trunk, chest pain may be observed, which can radiate to the shoulder. Such pain is 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 and colds;

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

3) eat well;

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

Moreover, the last point, timely access 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 dire consequences.

Good nutrition also plays an important role, because a person “charges” his body and gives it new strength. Having refreshed yourself, 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 prepared, many beneficial properties may disappear. A number of fruits, in addition to containing vitamin C, also contain a substance that enhances the effect of vitamin C. This substance is called tannin and is found in quince, pears, apples, and pomegranate.

Development of the nervous system in ontogenesis. Characteristics of the three-vesicle and five-vesicle stages of brain formation

Ontogenesis, or individual development The body is divided into two periods: prenatal (intrauterine) and postnatal (after birth). The first lasts 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 (preimplantation) period in humans covers the first week of development (from the moment of fertilization to implantation into the uterine mucosa). The embryonic (prefetal, embryonic) period is from the beginning of the second week to the end of the eighth week (from the moment of implantation until the completion of organ formation). The fetal period begins in the ninth week and lasts until birth. At this time, increased growth of the body occurs.

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 - first childhood; 8-12 years old - second childhood; 13-16 years - adolescence; 17-21 years - adolescence; 22-35 years old - the first mature age; 36-60 years - second mature age; 61-74 years- old age; from 75 years old - old age, after 90 years old - long-livers.

Ontogenesis ends with natural death.

The nervous system develops from three main structures: neural tube, neural crest and neural placodes. The neural tube is formed as a result of neurulation from the neural plate, a section of ectoderm located above the notochord. According to the theory of Spemen's organizers, notochord blastomeres are capable of secreting substances - inductors of the first kind, as a result of which the neural plate bends into the body of the embryo and a neural groove is formed, the edges of which then merge, forming the 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 part.

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 multirow 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 neuroepithelial cells change their location depending on the phase of the cell's life cycle. Gradually, towards the end of embryogenesis, ventricular cells lose the ability to divide and in the postnatal period give rise to neurons and various types of gliocytes. 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 series) is the presence in them of neurofibrils, as well as processes, with the axon (neurite) appearing first, and dendrites later. The processes form connections - synapses. In total, the differentiation of 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 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 brain. The cavity of the neural tube turns into the spinal canal, connected to the ventricles of the brain.

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

The cavity of the neural tube in the brain is transformed first into the cavities of three, then five vesicles. The cavity of the rhomboid vesicle gives rise to the fourth ventricle, which connects through the midbrain aqueduct (the cavity of the mesencephalon) with the third ventricle, formed by the cavity of the diencephalon rudiment. The cavity of the initially unpaired rudiment of the telencephalon is connected through the interventricular foramen with the cavity of the rudiment of the diencephalon. Subsequently, 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 brain vesicles will thicken most evenly in the region of the midbrain. The ventral part of the neural tube is transformed into the cerebral peduncles (midbrain), gray tubercle, infundibulum, and posterior lobe of the pituitary gland (diencephalon). Its dorsal part turns into the 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 area of ​​the diencephalon grow, forming the visual thalamus. Here, under the influence of inductors of the second kind, protrusions are formed - eye vesicles, each of which will give rise to the optic cup, and later - the retina. Inductors of the third kind, located in the optic cups, influence the ectoderm above them, which is laced into the cups, giving rise to the lens.

The human nervous system is similar in structure to the nervous system higher mammals, but differs in significant brain development. The main function of the nervous system is to control the vital functions of the entire organism.

Neuron

All organs of the nervous system are built from nerve cells called neurons. A neuron is capable of receiving and transmitting information in the form of a nerve impulse.

Rice. 1. Structure of a neuron.

The body of a neuron has processes with which it communicates with other cells. The short processes are called dendrites, the long ones are called axons.

The structure of the human nervous system

The main organ of the nervous system is the brain. Connected to it is the spinal cord, which looks like a cord about 45 cm long. Together, the spinal cord and brain make up the central nervous system (CNS).

Rice. 2. Scheme of the structure of the nervous system.

The nerves leaving the central nervous system make up the peripheral part of the nervous system. It consists of nerves and ganglia.

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Nerves are formed from axons, the length of which can exceed 1 m.

Nerve endings contact each organ and transmit information about their condition to the central nervous system.

There is also a functional division of the nervous system into somatic and autonomic (autonomic).

The part of the nervous system that innervates the striated muscles is called somatic. Her work is associated with the conscious efforts of a person.

The autonomic nervous system (ANS) regulates:

• circulation;
• digestion;
• selection;
• breath;
• metabolism;
• smooth muscle function.

Thanks to the work of the autonomic nervous system, many processes of normal life occur that we do not consciously regulate and usually do not notice.

The importance of the functional division of the nervous system in ensuring the normal functioning of finely tuned work mechanisms, independent of our consciousness internal organs.

The highest organ of the ANS is the hypothalamus, located in the intermediate part of the brain.

The VNS is divided into 2 subsystems:

• sympathetic;
• parasympathetic.

Sympathetic nerves activate organs and control them in situations that require action and increased attention.

Parasympathetic slows down the functioning of organs and turns on during rest and relaxation.

For example, sympathetic nerves dilate the pupil and stimulate the secretion of saliva. Parasympathetic, on the contrary, constrict the pupil and slow down salivation.

Reflex

This is the body's response to irritation from the external or internal environment.

The main form of activity of the nervous system is a reflex (from the English reflection - reflection).

An example of a reflex is withdrawing a hand from a hot object. The nerve ending senses high temperature and transmits a signal about it to the central nervous system. A response impulse arises in the central nervous system, going to the muscles of the arm.

Rice. 3. Reflex arc diagram.

The sequence: sensory nerve - CNS - motor nerve is called a reflex arc.

Brain

The brain is distinguished by the strong development of the cerebral cortex, in which the centers of higher nervous activity are located.

The characteristics of the human brain sharply distinguished it from the animal world and allowed it to create a rich material and spiritual culture.

What have we learned?

The structure and functions of the human nervous system are similar to those of mammals, but differ in the development of the cerebral cortex with the centers of consciousness, thinking, memory, and speech. The autonomic nervous system controls the body without the participation of consciousness. The somatic nervous system controls body movement. The principle of activity of the nervous system is reflex.

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Includes the organs of the central nervous system (brain and spinal cord) and organs of the peripheral nervous system (peripheral nerve ganglia, peripheral nerves, receptor and effector nerve endings).

Functionally, the nervous system is divided into somatic, which innervates the skeletal muscle tissue, i.e. controlled by consciousness and vegetative (autonomous), which regulates the activity of internal organs, blood vessels and glands, i.e. does not depend on consciousness.

The functions of the nervous system are regulatory and integrating.

It is formed in the 3rd week of embryogenesis in the form of a neural plate, which transforms into the neural groove, from which the neural tube is formed. There are 3 layers in its wall:

Internal - ependymal:

The middle one is raincoat. It is subsequently converted into gray matter.

Outer - edge. A white substance is formed from it.

In the cranial part of the neural tube, an expansion is formed, from which 3 brain vesicles are initially formed, and later - five. The latter give rise to five parts of the brain.

The spinal cord is formed from the trunk portion of the neural tube.

In the first half of embryogenesis, intensive proliferation of young glial and nerve cells occurs. Subsequently, radial glia are formed in the mantle layer of the cranial region. Its thin long processes penetrate the wall of the neural tube. Young neurons migrate along these processes. The formation of brain centers occurs (especially intensively from 15 to 20 weeks - the critical period). Gradually, in the second half of embryogenesis, proliferation and migration die out. After birth, division stops. During the formation of the neural tube, cells are evicted from the neural folds (closing areas), which are located between the ectoderm and the neural tube, forming the neural crest. The latter splits into 2 leaves:

1 - under the ectoderm, pigmentocytes (skin cells) are formed from it;

2 - around the neural tube - ganglion plate. From it, peripheral nerve nodes (ganglia), the adrenal medulla, and sections of chromaffin tissue (along the spine) are formed. After birth, there is an intensive growth of nerve cell processes: axons and dendrites are formed, synapses between neurons, neural chains (strictly ordered interneuronal communication), which make up reflex arcs (successively arranged cells that transmit information), ensuring human reflex activity (especially the first 5 years of life child, therefore stimuli are needed to form connections). Also, in the first years of a child’s life, myelination occurs most intensively - the formation of nerve fibers.

PERIPHERAL NERVOUS SYSTEM (PNS).

Peripheral nerve trunks are part of the neurovascular bundle. They are mixed in function, containing sensory and motor nerve fibers (afferent and efferent). Myelinated nerve fibers predominate, and non-myelinated nerve fibers are present in small quantities. Around each nerve fiber there is a thin layer of loose connective tissue with blood and lymphatic vessels - the endoneurium. Around the bundle of nerve fibers there is a sheath of loose fibrous connective tissue - perineurium - with a small number of vessels (mainly performs a frame function). Around the entire peripheral nerve there is a sheath of loose connective tissue with larger vessels - epineurium. Peripheral nerves regenerate well, even after complete damage. Regeneration is carried out due to the growth of peripheral nerve fibers. The growth rate is 1-2 mm per day (the ability to regenerate is a genetically fixed process).

Spinal ganglion

It is a continuation (part) of the dorsal root of the spinal cord. Functionally sensitive. The outside is covered with a connective tissue capsule. Inside there are connective tissue layers with blood and lymphatic vessels, nerve fibers (vegetative). In the center are the myelinated nerve fibers of pseudounipolar neurons located along the periphery of the spinal ganglion. Pseudounipolar neurons have a large rounded body, a large nucleus, and well-developed organelles, especially the protein-synthesizing apparatus. A long cytoplasmic process extends from the neuron body - this is part of the neuron body, from which one dendrite and one axon extend. The dendrite is long, forms a nerve fiber that goes as part of the peripheral mixed nerve to the periphery. Sensitive nerve fibers end at the periphery with a receptor, i.e. sensory nerve ending. The axons are short and form the dorsal root of the spinal cord. In the dorsal horn of the spinal cord, axons form synapses with interneurons. Sensitive (pseudo-unipolar) neurons constitute the first (afferent) link of the somatic reflex arc. All cell bodies are located in ganglia.

Spinal cord

The outside is covered with the pia mater, which contains blood vessels that penetrate into the substance of the brain. Conventionally, there are 2 halves, which are separated by the anterior median fissure and the posterior median connective tissue septum. In the center is the central canal of the spinal cord, which is located in the gray matter, lined with ependyma, and contains cerebrospinal fluid, which is in constant motion. Along the periphery there is white matter, where there are bundles of myelinated nerve fibers that form pathways. They are separated by glial connective tissue septa. The white matter is divided into anterior, lateral and posterior cords.

In the middle part there is gray matter, in which the posterior, lateral (in the thoracic and lumbar segments) and anterior horns are distinguished. The halves of the gray matter are connected by the anterior and posterior commissure of the gray matter. In the gray matter there are large quantities glial and nerve cells. Gray matter neurons are divided into:

1) Internal neurons, completely (with processes) located within the gray matter, are intercalary and are located mainly in the posterior and lateral horns. There are:

a) Associative. Located within one half.

b) Commissural. Their processes extend into the other half of the gray matter.

2) Tufted neurons. They are located in the posterior horns and lateral horns. They form nuclei or are located diffusely. Their axons enter the white matter and form bundles of ascending nerve fibers. They are intercalary.

3) Root neurons. They are located in the lateral nuclei (nuclei of the lateral horns), in the anterior horns. Their axons extend beyond the spinal cord and form the anterior roots of the spinal cord.

In the superficial part of the posterior horns there is a spongy layer, which contains big number small interneurons.

Deeper than this strip is a gelatinous substance containing mainly glial cells and small neurons (the latter in small quantities).

In the middle part there is its own nucleus of the posterior horns. It contains large tufted neurons. Their axons go into the white matter of the opposite half and form the spinocerebellar anterior and spinothalamic posterior tracts.

Nuclear cells provide exteroceptive sensitivity.

At the base of the posterior horns is the thoracic nucleus (Clark-Schutting column), which contains large fascicular neurons. Their axons go into the white matter of the same half and participate in the formation of the posterior spinocerebellar tract. Cells in this pathway provide proprioceptive sensitivity.

The intermediate zone contains the lateral and medial nuclei. The medial intermediate nucleus contains large fasciculate neurons. Their axons go into the white matter of the same half and form the anterior spinocerebellar tract, which provides visceral sensitivity.

The lateral intermediate nucleus belongs to the autonomic nervous system. In the thoracic and upper lumbar regions it is the sympathetic nucleus, and in the sacral region it is the nucleus of the parasympathetic nervous system. It contains an interneuron, which is the first neuron of the efferent link of the reflex arc. This is a root neuron. Its axons emerge as part of the anterior roots of the spinal cord.

The anterior horns contain large motor nuclei that contain motor root neurons with short dendrites and a long axon. The axon emerges as part of the anterior roots of the spinal cord, and subsequently goes as part of the peripheral mixed nerve, represents motor nerve fibers and is pumped to the periphery by the neuromuscular synapse on skeletal muscle fibers. They are effectors. Forms the third effector link of the somatic reflex arc.

In the anterior horns, a medial group of nuclei is distinguished. It is developed in the thoracic region and provides innervation to the muscles of the trunk. The lateral group of nuclei is located in the cervical and lumbar regions and innervates the upper and lower extremities.

The gray matter of the spinal cord contains a large number of diffuse tufted neurons (in the dorsal horns). Their axons go into the white matter and immediately divide into two branches that extend upward and downward. The branches return through 2-3 segments of the spinal cord to the gray matter and form synapses on the motor neurons of the anterior horns. These cells form their own apparatus of the spinal cord, which provides communication between the neighboring 4-5 segments of the spinal cord, due to which the response of the muscle group is ensured (an evolutionarily developed protective reaction).

The white matter contains ascending (sensitive) pathways, which are located in the posterior funiculi and in the peripheral part of the lateral horns. Descending nerve tracts (motor) are located in the anterior cords and in the inner part of the lateral cords.

Regeneration. Gray matter regenerates very poorly. Regeneration of white matter is possible, but the process is very long.

Histophysiology of the cerebellum. The cerebellum belongs to the structures of the brain stem, i.e. is a more ancient formation that is part of the brain.

Performs a number of functions:

Equilibrium;

The centers of the autonomic nervous system (ANS) (intestinal motility, blood pressure control) are concentrated here.

The outside is covered with meninges. The surface is embossed due to deep grooves and convolutions, which are deeper than in the cerebral cortex (CBC).

The cross-section is represented by the so-called “tree of life”.

Gray matter is located mainly along the periphery and inside, forming nuclei.

In each gyrus, the central part is occupied by white matter, in which 3 layers are clearly visible:

1 - surface - molecular.

2 - medium - ganglionic.

3 - internal - granular.

1. The molecular layer is represented by small cells, among which basket and stellate (small and large) cells are distinguished.

Basket cells are located closer to the ganglion cells of the middle layer, i.e. in the inner part of the layer. They have small bodies, their dendrites branch in the molecular layer, in a plane transverse to the course of the gyrus. The neurites run parallel to the plane of the gyrus above the piriform cell bodies (ganglionic layer), forming numerous branches and contacts with the dendrites of the piriform cells. Their branches are woven around the bodies of pear-shaped cells in the form of baskets. Excitation of basket cells leads to inhibition of piriform cells.

Outside there are stellate cells, the dendrites of which branch here, and the neurites participate in the formation of the basket and synapse with the dendrites and bodies of the piriform cells.

Thus, basket and stellate cells of this layer are associative (connecting) and inhibitory.

2. Ganglion layer. Large ganglion cells (diameter = 30-60 µm) - Purkine cells - are located here. These cells are located strictly in one row. The cell bodies are pear-shaped, there is a large nucleus, the cytoplasm contains EPS, mitochondria, the Golgi complex is poorly expressed. A single neurite emerges from the base of the cell, passes through the granular layer, then into the white matter and ends at the cerebellar nuclei at synapses. This neurite is the first link of the efferent (descending) pathways. 2-3 dendrites extend from the apical part of the cell, which intensively branch in the molecular layer, while the branching of the dendrites occurs in a plane transverse to the course of the gyrus.

Pear-shaped cells are the main effector cells of the cerebellum, where inhibitory impulses are produced.

3. The granular layer is saturated with cellular elements, among which cells - grains - stand out. These are small cells with a diameter of 10-12 microns. They have one neurite, which goes into the molecular layer, where it comes into contact with the cells of this layer. Dendrites (2-3) are short and branch in numerous branches in a bird's foot fashion. These dendrites make contact with afferent fibers called mossy fibers. The latter also branch and come into contact with the branching dendrites of cells - grains, forming balls of thin weaves like moss. In this case, one mossy fiber comes into contact with many cells - grains. And vice versa - the grain cell also comes into contact with many mossy fibers.

Mossy fibers come here from olives and bridge, i.e. bring here information that passes through associative neurons to the piriform neurons. Large stellate cells are also found here, which lie closer to the pyriform cells. Their processes contact granule cells proximal to the mossy glomeruli and in this case block impulse transmission.

Other cells may also be found in this layer: stellate with a long neurite extending into the white matter and further into the adjacent gyrus (Golgi cells - large stellate cells).

Afferent climbing fibers - liana-like - enter the cerebellum. They come here as part of the spinocerebellar tracts. Then they crawl along the bodies of the piriform cells and along their processes, with which they form numerous synapses in the molecular layer. Here they carry an impulse directly to the piriform cells.

Efferent fibers emerge from the cerebellum, which are the axons of the piriform cells.

The cerebellum has a large number of glial elements: astrocytes, oligodendrogliocytes, which perform supporting, trophic, restrictive and other functions. The cerebellum secretes a large amount of serotonin, i.e. The endocrine function of the cerebellum can also be distinguished.

Cerebral cortex (CBC)

This is a newer part of the brain. (It is believed that the KBP is not a vital organ.) It has great plasticity.

The thickness can be 3-5 mm. The area occupied by the cortex increases due to grooves and convolutions. The differentiation of the KBP ends by the age of 18, and then there are processes of accumulation and use of information. The mental abilities of an individual also depend on the genetic program, but ultimately everything depends on the number of synaptic connections formed.

There are 6 layers in the cortex:

1. Molecular.

2. External granular.

3. Pyramid.

4. Internal granular.

5. Ganglionic.

6. Polymorphic.

Deeper than the sixth layer is the white matter. The bark is divided into granular and agranular (according to the severity of the granular layers).

In KBP cells have different shapes and different sizes, in diameter from 10-15 to 140 microns. The main cellular elements are pyramidal cells, which have a pointed apex. Dendrites extend from the lateral surface, and one neurite extends from the base. Pyramidal cells can be small, medium, large, or giant.

In addition to pyramidal cells, there are arachnids, grain cells, and horizontal cells.

The arrangement of cells in the cortex is called cytoarchitecture. Fibers forming myelin tracts or various systems of associative, commissural, etc. form the myeloarchitecture of the cortex.

1. In the molecular layer, cells are found in small quantity. The processes of these cells: dendrites go here, and neurites form an external tangential path, which also includes the processes of underlying cells.

2. Outer granular layer. There are many small cellular elements of pyramidal, stellate and other shapes. Dendrites either branch here or extend into another layer; neurites extend into the tangential layer.

3. Pyramid layer. Quite extensive. Mostly small and medium-sized pyramidal cells are found here, the processes of which branch in the molecular layer, and the neurites large cells may go into the white matter.

4. Inner granular layer. Well expressed in the sensitive zone of the cortex (granular type of cortex). Represented by many small neurons. The cells of all four layers are associative and transmit information to other sections from the underlying sections.

5. Ganglion layer. Mostly large and giant pyramidal cells are located here. These are mainly effector cells, because the neurites of these neurons extend into the white matter, being the first links in the effector pathway. They can give off collaterals, which can return to the cortex, forming associative nerve fibers. Some processes - commissural - go through the commissure to the neighboring hemisphere. Some neurites switch either on the nuclei of the cortex, or in the medulla oblongata, in the cerebellum, or can reach the spinal cord (1g. conglomerate-motor nuclei). These fibers form the so-called. projection paths.

6. A layer of polymorphic cells is located at the border with the white matter. There are large neurons of different shapes here. Their neurites can return in the form of collaterals to the same layer, or to another gyrus, or to the myelin tracts.

The entire cortex is divided into morpho-functional structural units - columns. There are 3-4 million columns, each of which has about 100 neurons. The column passes through all 6 layers. The cellular elements of each column are concentrated around the gland, and the column contains a group of neurons capable of processing a unit of information. This includes afferent fibers from the thalamus, and cortico-cortical fibers from the adjacent column or from the neighboring gyrus. Efferent fibers emerge from here. Due to collaterals in each hemisphere, 3 columns are interconnected. Through commissural fibers, each column is connected to two columns of the adjacent hemisphere.

All organs of the nervous system are covered with membranes:

1. The pia mater is formed by loose connective tissue, due to which the grooves are formed, carries blood vessels and is delimited by glial membranes.

2. The arachnoid mater is represented by delicate fibrous structures.

Between the soft and arachnoid membranes there is a subarachnoid space filled with cerebral fluid.

3. The dura mater is formed from rough fibrous connective tissue. It is fused with bone tissue in the area of ​​the skull, and is more mobile in the area of ​​the spinal cord, where there is a space filled with cerebrospinal fluid.

Gray matter is located along the periphery, and also forms nuclei in the white matter.

Autonomic nervous system (ANS)

Divided into:

The sympathetic part

Parasympathetic part.

The central nuclei are distinguished: the nuclei of the lateral horns of the spinal cord, the medulla oblongata, and the midbrain.

On the periphery, nodes can form in organs (paravertebral, prevertebral, paraorgan, intramural).

The reflex arc is represented by the afferent part, which is common, and the efferent part - this is the preganglionic and postganglionic link (can be multi-storeyed).

In the peripheral ganglia of the ANS, various cells can be located in structure and function:

Motor (according to Dogel - type I):

Associative (type II)

Sensitive, the processes of which reach neighboring ganglia and spread far beyond.

This section will describe common diseases of the human nervous system. But, first, let us briefly recall the composition and functions of the human nervous system.

The human nervous system is a collection of receptors, nerves, ganglia, and brain. The nervous system perceives stimuli acting on the body, conducts and processes the resulting excitation, and forms responses adaptive reactions. The nervous system also regulates and coordinates all functions of the body in its interaction with the external environment.

The functional unit of the human nervous system is neuron- the longest cell in our body. The length of a neuron reaches one and a half meters, and its lifespan can be the same as the life of the entire organism. The human nervous system has up to 15 billion neurons - this is a huge number. The total length of all neurons in one person is approximately equal to the distance from the Earth to the Moon.

A neuron consists of a body and processes:

• axon- a non-branching process that conducts nerve impulses from the cell body to muscles and glands;
• dendrites- branching processes that transmit nerve impulses to other neurons.

The central organ of the nervous system is brain- the most “voracious” organ of the human body, since with a weight of about 1.5 kg it consumes up to 20% of all oxygen circulating in the blood.

The brain consists of two hemispheres - left and right. Moreover, the left hemisphere is responsible for the work of the organs of the right half of our body, and the right hemisphere is responsible for the work of the left half.

The surface area of ​​the cerebral cortex is covered with multiple grooves and convolutions, which significantly increase its surface area. Certain areas of the brain are responsible for certain abilities: speaking, seeing, hearing... 12 pairs of cranial nerves and many nerve conductors depart from the brain, which carry out a “dialogue” of the brain with the tissues and muscles of the whole body.

With the help of the brain stem, the brain connects to the spinal cord, from which 31 pairs of spinal nerves arise, covering our entire body.

Some muscles of our body work outside of our consciousness, as if “by themselves” - these are the heart muscle, the pulmonary muscles. The work of such muscles is regulated autonomic nervous system, which is part of the sympathetic and parasympathetic nervous systems.

Sympathetic nervous system consists of two chains of nerve nodes (ganglia), which are located along the spine and regulate the functioning of internal organs: stomach, heart, intestines.

Center parasympathetic system located in the upper part of the spinal cord, and the nerve nodes are located directly in the internal organs.

ATTENTION! The information provided on this site is for reference only. Only a specialist doctor in a specific field can make a diagnosis and prescribe treatment.