Development of a lesson on the topic "Structure and meaning nervous system. Nervous regulation", introduces students to the structure and classification of the nervous system, determines the relationship between the nervous system and the work of internal organs. Children learn to work independently with the text of the textbook, think logically and form the results of logical operations in oral and written form.

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The structure and significance of the nervous system. nervous regulation.

Goals: learn the structure and classification of the nervous system; the structure of the nervous tissue, neuron, gray and white matter, nerves, nerve nodes; the essence of the concepts of "reflex", "reflex arc" and their classification. Form concepts: independently work with the text of the textbook, extract the necessary information from it; think logically and form results mental operations in oral and written form.

Tasks: show the leading role of the nervous system in regulating the work of organs and ensuring a unified system of the body; form an idea of ​​​​the structure and functions spinal cord; show the connection between the concepts of "reflex" and "function of the spinal cord"; develop the ability to apply knowledge to explain phenomena.

Equipment: tables: diagram of the structure of the nervous system, "Nerve cells and reflex arc diagram"; video "Reflex arc"

During the classes:

1. Organizing time.
2. Biological dictation.

Students give definitions to the concepts from the previous lesson.

1. Learning new material.

1. The value of the nervous system.

A conversation summarizing the knowledge of students received at different lessons and in various articles of the textbook "Biology: Man".

The functions of the nervous system are written on the blackboard. Students must support each point with examples, facts from previously studied topics.

1. Anatomical classification of parts of the nervous system.

Story with elements of conversation. Drawing up a diagram of the "Nervous system"

1. Spinal cord

The structure of the spinal cord (teacher's explanation)

Spinal cord lies in the spinal canal and in adults it is a long (45 cm in men and 41-42 cm in women), somewhat flattened from front to back, cylindrical cord, which at the top directly passes into the medulla oblongata, and at the bottom ends with a conical sharpening at the level of the II lumbar vertebra. Knowledge of this fact is of practical importance (in order not to damage the spinal cord during a lumbar puncture for the purpose of taking cerebrospinal fluid or for the purpose of spinal anesthesia, it is necessary to insert a syringe needle between the spinous processes of the III and IV lumbar vertebrae).

Internal structure of the spinal cord.The spinal cord is made up of gray matter, which contains nerve cells, and white matter, which is made up of myelinated nerve fibers. Gray matter , is embedded inside the spinal cord and surrounded on all sides by white matter. Gray matter forms two vertical columns placed in the right and left halves of the spinal cord. In the middle of it lies a narrow central canal, the spinal cord, which runs the entire length of the latter and contains cerebrospinal fluid. white matter consists of nerve processes that make up three systems of nerve fibers:

1. Short bundles of associative fibers connecting parts of the spinal cord at different levels (afferent and intercalary neurons).
2. Long centripetal (sensitive, afferent).
3. Long centrifugal (motor, efferent).

Functions of the spinal cord (Teacher's story, demonstration of the unconditioned knee jerk, picture of the reflex arc of the knee jerk)

Reflex - an involuntary act, a quick response of the body to the action of an irritant, carried out with the participation of the central nervous system and under its control. This is the main form of nervous activity of the organism of multicellular animals, including humans.

You know from a zoology course that an organism is born with a large set of ready-made, innate reflexes. Part of the reflexes is developed during life under certain conditions of the action of the environment. What are such reflexes called (unconditional and conditional, respectively).

Let's consider the mechanism of implementation of the reflex using the example of the knee reflex. In all organs of the body there are receptors - sensitive nerve endings that convert irritations into nerve impulses. They are also present in the thigh muscle. If you hit the tendon ligament just below the knee, then the muscle is stretched and excitation occurs in its receptors, which is transmitted through the sensory (afferent) nerve to the motor (efferent) nerve, whose body is located in the spinal cord. Through this neuron, the nerve impulse reaches the same muscle (working organ), and it contracts, extending the leg at the knee joint. Accumulations of neurons of the central nervous system that cause a certain reflex action are calledreflex centersthese reflexes. The knee jerk occurs when not one, but many receptors located in one area of ​​the body are irritated -reflexogenic zone (receptive field).

Thus, the material basis of the reflex isreflex arc- a chain of neurons that forms the path of a nerve impulse during the implementation of a reflex.

Using this example, fill in the table "Links of the reflex arc" from memory:

Watching the video "Reflex arc"

1. The connection between the spinal cord and the brain(teacher's explanation)

1. Consolidation of knowledge.

Frontal writing.

Add definitions.

Nerve ganglions are clusters of ______________

Nerves are clusters of ___________________

A reflex is a __________________ of an organism on _____________________, which is carried out with the help of _______________.

1. What is called a reflex?
2. In the dark, entering your room, you accurately locate the switch and turn on the light. Is your movement towards the switch an unconditioned or conditioned reflex? Justify the answer.
3. How many links does the reflex arc include?
4. What anatomical structures are represented by each section of the reflex arc?
5. Is it possible to implement a reflex in case of violation of one of the links of the reflex arc? Why?
6. In some people, the knee jerk is mild. To strengthen it, they offer to clasp hands in front of the chest and pull them in different directions. Why does this lead to an increase in the reflex?

HomeworkTextbook A.G. Dragomilova, R.D. Masha § 46, 49. Workbook#2 assignments 150-153, 158, 181.

1 Physiological regulation- this is an active control of the body's functions and its behavior to maintain an optimal level of vital activity, the constancy of the internal environment and metabolic processes in order to adapt the body to changing environmental conditions.

Physiological regulation mechanisms :

1. humoral.

Humoral physiological regulation uses body fluids (blood, lymph, cerebrospinal fluid, etc.) to transmit information. Signals are transmitted through chemicals: hormones, mediators, biologically active substances (BAS), electrolytes, etc.

Features of humoral regulation :

does not have an exact addressee - with the current of biological fluids, substances can be delivered to any cells of the body;

the speed of information delivery is low - it is determined by the flow rate of biological fluids - 0.5-5 m / s;

duration of action.

Nervous physiological regulation for processing and transmitting information is mediated through the central and peripheral nervous system. Signals are transmitted using nerve impulses.

Features of nervous regulation:

has an exact addressee - signals are delivered to strictly defined organs and tissues;

high speed of information delivery - the speed of transmission of a nerve impulse - up to 120 m / s;

short duration of action.

There is no sharp boundary between nervous and hormonal regulation. For example, the transfer of excitation from one nerve cell to another or an executive organ occurs through a mediator, which is similar to humoral regulation (similar to hormones); in addition, some nerve endings release active substances into the blood. And finally, the closest connection between these mechanisms can be traced at the level of the hypothalamic-pituitary system. So, nervous and humoral regulation have mutual influence on each other and are combined into a single neurohumoral regulation system.

3 Reflex- this is a strictly predetermined reaction of the body to external or internal irritation, carried out with the obligatory participation of the central nervous system. The reflex is a functional unit of nervous activity.

Types of reflexes by the nature of the response(on a biological basis) are divided into food, sexual, defensive, motor, etc.

According to the level of closure of the reflex arc reflexes are divided into:

spinal - close at the level of the spinal cord;

bulbar - close at the level of the medulla oblongata;

mesencephalic - close at the level of the midbrain;

diencephalic - close at the level of the diencephalon;

subcortical - close at the level of subcortical structures;

cortical - close at the level of the cortex of the cerebral hemispheres.

Depending on the nature of the response reflexes can be:

somatic - motor response;

vegetative - the response affects the internal organs, blood vessels, etc.

According to I.P. Pavlov, reflexes are distinguished unconditional and conditional.

For the occurrence of a reflex, 2 prerequisites are necessary:

a sufficiently strong stimulus that exceeds the threshold of excitability

reflex arc

Principles of reflex regulation according to Pavlov I.P. The elementary form of nervous activity is reflex- the body's response to irritation of receptors, which consists in the occurrence, change or termination of the functional activity of organs, tissues or the whole organism and is carried out with the participation of the central nervous system. I.P. Pavlov formulated the basic principles of the reflex theory: determinism, analysis and synthesis, and structure: 1) principle of determinism(principle of causality) - any reflex reaction is causally conditioned. Every activity of the organism, every act of nervous activity is caused by a certain cause, an influence from the external world or the internal environment of the organism; 2) the principle of unity of the processes of analysis and synthesis as part of a reflex reaction, the nervous system analyzes, i.e. distinguishes, with the help of receptors, all acting external and internal stimuli and, on the basis of this analysis, forms a holistic response - synthesis; 3) structural principle- an absolutely necessary condition for the implementation of the reflex is the structural and functional integrity of all links of the reflex arc. Below we consider the structure of the para- and sympathetic reflex arcs.

4 Somatic (animal) reflex arc

The receptor link is formed by afferent pseudo-unipolar neurons, the bodies of which are located in the spinal ganglia. The dendrites of these cells form sensitive nerve endings in the skin or skeletal muscles, and the axons enter the spinal cord as part of the posterior roots and go to the posterior horns of its gray matter, forming synapses on the bodies and dendrites of intercalary neurons. Some branches (collaterals) of the axons of pseudounipolar neurons pass (without forming connections in the posterior horns) directly to the anterior horns, where they terminate on motor neurons (forming two-neuron reflex arcs with them).

The associative link is represented by multipolar intercalary neurons, the dendrites and bodies of which are located in the posterior horns of the spinal cord, and the axons are directed to the anterior horns, transmitting impulses to the bodies and dendrites of effector neurons.

The effector link is formed by multipolar motor neurons, the bodies and dendrites of which lie in the anterior horns, and the axons leave the spinal cord as part of the anterior roots, go to the spinal ganglion and then, as part of the mixed nerve, to the skeletal muscle, on the fibers of which their branches form neuromuscular synapses (motor, or motor, plaques).

5 Autonomic reflexes

The autonomic nervous system does not have its own afferent nerve pathways. Reflex excitation of the efferent autonomic pathways is caused by irritation of the same receptors and afferent pathways, the irritation of which causes motor reflexes. However, irritation of the reflexogenic zones and afferent fibers of the internal organs, which are characterized by a particularly slow conduction of excitation, in most cases causes reflexes of the internal organs, or autonomic reflexes. Most of the afferent fibers of the internal organs enter the spinal cord through the posterior roots.

The reflexes of the sympathetic system, due to the distribution of sympathetic fibers throughout the body, are not limited, but widespread, capturing many organs.

The autonomic nervous system carries out two kinds of reflexes: functional and trophic. The functional effect on the organs is that irritation of the autonomic nerves either causes the function of the organ or inhibits it (the “starting” function). The trophic influence consists in the fact that the metabolism in the organs is directly regulated and thereby the level of their activity is determined (the “corrective” function). The reflex activity of the autonomic nervous system includes autonomic segmental reflexes, axon reflexes, the arc of which closes outside the spinal cord, within the branches of one nerve (such reflexes are characteristic of vascular reactions), as well as viscero-visceral reflexes (for example, cardiopulmonary, viscerocutaneous, which, in particular, cause the appearance of areas of skin hyperesthesia in diseases of internal organs) and skin-visceral reflexes (which are used when applying local thermal procedures, reflexology, etc.). The autonomic nervous system includes segmental apparatuses (spinal cord, autonomic nodes, sympathetic trunk), as well as suprasegmental apparatuses - the limbic-reticular complex, hypothalamus.

Membrane receptor- a molecule (usually a protein) on the surface of a cell, cell organelles or dissolved in the cytoplasm, specifically reacting by changing its spatial configuration to the addition of a molecule of a certain chemical substance to it, which transmits an external regulatory signal and, in turn, transmits this signal inside the cell or cell organelle , often with the help of so-called secondary mediators or transmembrane ion currents.

6 The simplest reflex arc in humans is formed by two neurons - sensory and motor (motor neuron). An example of a simple reflex is the knee jerk. In other cases, three (or more) neurons are included in the reflex arc - sensory, intercalary and motor. In a simplified form, this is the reflex that occurs when a finger is pricked with a pin. This is a spinal reflex, its arc passes not through the brain, but through the spinal cord. The processes of sensory neurons enter the spinal cord as part of the posterior root, and the processes of motor neurons exit the spinal cord as part of the anterior root. The bodies of sensory neurons are located in the spinal node of the posterior root (in the dorsal ganglion), and the intercalary and motor neurons are located in the gray matter of the spinal cord.

The simple reflex arc described above allows a person to automatically (involuntarily) adapt to change. environment, for example, withdraw your hand from a painful stimulus, change the size of the pupil depending on the lighting conditions. It also helps to regulate the processes occurring inside the body. All this contributes to maintaining the constancy of the internal environment, that is, maintaining homeostasis. In many cases, a sensory neuron transmits information (usually through several interneurons) to the brain. The brain processes incoming sensory information and stores it for later use. Along with this, the brain can send motor nerve impulses along the descending path directly to the spinal motor neurons; spinal motor neurons initiate the effector response.

7 Excitability is the ability of highly organized tissues (nervous, muscular, glandular) to respond to irritation by changing physiological properties and generating the excitation process. The nervous system has the highest excitability, then muscle tissue, and finally glandular cells. Excitation is a reaction of a living cell to irritation, developed in the process of evolution. With V., the living system passes from a state of relative physiological rest to activity (for example, contraction of a muscle fiber, secretion by glandular cells, etc. The threshold of irritation is a measure excitability tissue that can be measured with an oscilloscope.

Basic physiological properties of excitable tissues Excitability- the ability of a tissue to respond to stimulation with excitation. Excitability of envy on the level of metabolic processes and the charge of the cell membrane. The index of excitability - the threshold of irritation - is the minimum strength of the stimulus that causes the first visible response of the tissue. Irritants are: subthreshold, threshold, suprathreshold. Excitability and irritation threshold are inversely proportional values. Conductivity- the ability of the tissue to conduct excitation along its entire length. The conductivity index is the rate of excitation. The speed of excitation through the skeletal tissue is 6-13 m/s, through the nervous tissue up to 120 m/s. Conductivity depends on the intensity of metabolic processes, on excitability (in direct proportion). refractoriness(non-excitability) - the ability of a tissue to sharply reduce its excitability when excited. At the moment of the most active response, the tissue becomes non-excitable. Distinguish:

absolutely refractory period - the time during which the tissue does not respond to absolutely any pathogens;

relative refractory period - the tissue is relatively unexcitable - excitability is restored to its original level.

Refractory index - the duration of the refractory period (t). The duration of the refractory period in skeletal muscle is 35-50 ms, and in nervous tissue - 0.5-5 ms. Tissue refractoriness depends on the level of metabolic processes and functional activity (inverse relationship). Lability(functional mobility) - the ability of a tissue to reproduce a certain number of excitation waves per unit of time in exact accordance with the rhythm of the applied stimuli. This property characterizes the rate of occurrence of excitation. Lability index: the maximum number of excitation waves in a given tissue: nerve fibers - 500-1000 impulses per second, muscle tissue - 200-250 impulses per second, synapse - 100-125 impulses per second. Lability depends on the level of metabolic processes in the tissue, excitability, refractoriness. For muscle tissue, a fifth property is added to the four listed properties - contractility.

The human nervous system is a stimulator of the muscular system, which we talked about in. As we already know, muscles are needed to move parts of the body in space, and we even studied specifically which muscles are designed for which work. But what powers the muscles? What and how makes them work? About this and will be discussed in this article, from which you will draw the necessary theoretical minimum for mastering the topic indicated in the title of the article.

First of all, it is worth saying that the nervous system is designed to transmit information and commands to our body. The main functions of the human nervous system are the perception of changes within the body and the space surrounding it, the interpretation of these changes and the response to them in the form of a certain form (including muscle contraction).

Nervous system- a set of different, interacting nervous structures, which, along with the endocrine system, provides coordinated regulation of the work of most of the body's systems, as well as a response to changing conditions of the external and internal environment. This system combines sensitization, motor activity and the correct functioning of such systems as the endocrine, immune and not only.

The structure of the nervous system

Excitability, irritability and conductivity are characterized as functions of time, that is, it is a process that occurs from irritation to the appearance of an organ response. The propagation of a nerve impulse in the nerve fiber occurs due to the transition of local foci of excitation to neighboring inactive areas of the nerve fiber. The human nervous system has the property of transforming and generating the energies of the external and internal environment and transforming them into a nervous process.

The structure of the human nervous system: 1- brachial plexus; 2- musculocutaneous nerve; 3- radial nerve; 4- median nerve; 5- ilio-hypogastric nerve; 6- femoral-genital nerve; 7- locking nerve; 8- ulnar nerve; 9- common peroneal nerve; 10 - deep peroneal nerve; 11- superficial nerve; 12- brain; 13- cerebellum; 14- spinal cord; 15- intercostal nerves; 16 - hypochondrium nerve; 17- lumbar plexus; 18 - sacral plexus; 19- femoral nerve; 20 - sexual nerve; 21- sciatic nerve; 22 - muscular branches of the femoral nerves; 23 - saphenous nerve; 24- tibial nerve

The nervous system functions as a whole with the sense organs and is controlled by the brain. The largest part of the latter is called the cerebral hemispheres (in the occipital region of the skull there are two smaller hemispheres of the cerebellum). The brain is connected to the spinal cord. The right and left cerebral hemispheres are interconnected by a compact bundle of nerve fibers called the corpus callosum.

Spinal cord- the main nerve trunk of the body - passes through the canal formed by the openings of the vertebrae, and stretches from the brain to the sacral spine. From each side of the spinal cord, nerves depart symmetrically to different parts of the body. Touch in general terms is provided by certain nerve fibers, the innumerable endings of which are located in the skin.

Classification of the nervous system

The so-called types of the human nervous system can be represented as follows. All complete system conditionally form: the central nervous system - CNS, which includes the brain and spinal cord, and the peripheral nervous system - PNS, which includes numerous nerves extending from the brain and spinal cord. The skin, joints, ligaments, muscles, internal organs and sensory organs send input signals to the CNS via PNS neurons. At the same time, outgoing signals from the central NS, the peripheral NS sends to the muscles. As a visual material, below, in a logically structured way, the entire human nervous system (diagram) is presented.

central nervous system- the basis of the human nervous system, which consists of neurons and their processes. The main and characteristic function of the central nervous system is the implementation of reflective reactions of various degrees of complexity, which are called reflexes. The lower and middle sections of the central nervous system - the spinal cord, medulla oblongata, midbrain, diencephalon and cerebellum - control the activity of individual organs and systems of the body, implement communication and interaction between them, ensure the integrity of the body and its correct functioning. The highest department of the central nervous system - the cerebral cortex and the nearest subcortical formations - for the most part controls the communication and interaction of the body as an integral structure with the outside world.

Peripheral nervous system- is a conditionally allocated part of the nervous system, which is located outside the brain and spinal cord. Includes nerves and plexuses of the autonomic nervous system, connecting the central nervous system with the organs of the body. Unlike the CNS, the PNS is not protected by bones and can be subject to mechanical damage. In turn, the peripheral nervous system itself is divided into somatic and autonomic.

• somatic nervous system- part of the human nervous system, which is a complex of sensory and motor nerve fibers responsible for the excitation of muscles, including skin and joints. She also manages the coordination of body movements, and the receipt and transmission of external stimuli. This system performs actions that a person controls consciously.
• autonomic nervous system divided into sympathetic and parasympathetic. The sympathetic nervous system governs the response to danger or stress, and can cause an increase in heart rate, blood pressure, and sensory stimulation, among other things, by increasing the level of adrenaline in the blood. The parasympathetic nervous system, in turn, controls the state of rest, and regulates pupillary contraction, slowing of the heart rate, dilation of blood vessels, and stimulation of the digestive and genitourinary systems.

Above you can see a logically structured diagram, which shows the parts of the human nervous system, in the order corresponding to the above material.

The structure and functions of neurons

All movements and exercises are controlled by the nervous system. The main structural and functional unit of the nervous system (both central and peripheral) is the neuron. Neurons are excitable cells that are capable of generating and transmitting electrical impulses (action potentials).

The structure of the nerve cell: 1- cell body; 2- dendrites; 3- cell nucleus; 4- myelin sheath; 5- axon; 6- end of the axon; 7- synaptic thickening

The functional unit of the neuromuscular system is the motor unit, which consists of a motor neuron and the muscle fibers innervated by it. Actually, the work of the human nervous system on the example of the process of muscle innervation occurs as follows.

The cell membrane of the nerve and muscle fiber is polarized, that is, there is a potential difference across it. Inside the cell contains a high concentration of potassium ions (K), and outside - sodium ions (Na). At rest, the potential difference between the inner and outer sides of the cell membrane does not lead to electric charge. This defined value is the resting potential. Due to changes in the external environment of the cell, the potential on its membrane constantly fluctuates, and if it increases, and the cell reaches its electrical threshold of excitation, there is a sharp change in the electrical charge of the membrane, and it begins to conduct an action potential along the axon to the innervated muscle. By the way, in large muscle groups, one motor nerve can innervate up to 2-3 thousand muscle fibers.

In the diagram below, you can see an example of what path a nerve impulse takes from the moment a stimulus occurs to receiving a response to it in each individual system.

Nerves are connected to each other through synapses, and to muscles through neuromuscular junctions. Synapse- this is the place of contact between two nerve cells, and - the process of transmitting an electrical impulse from a nerve to a muscle.

synaptic connection: 1- neural impulse; 2- receiving neuron; 3- axon branch; 4- synaptic plaque; 5- synaptic cleft; 6 - neurotransmitter molecules; 7- cell receptors; 8 - dendrite of the receiving neuron; 9- synaptic vesicles

Neuromuscular contact: 1 - neuron; 2- nerve fiber; 3- neuromuscular contact; 4- motor neuron; 5- muscle; 6- myofibrils

Thus, as we have already said, the process of physical activity in general and muscle contraction in particular is completely controlled by the nervous system.

Conclusion

Today we learned about the purpose, structure and classification of the human nervous system, as well as how it is related to its motor activity and how it affects the work of the whole organism as a whole. Since the nervous system is involved in the regulation of the activity of all organs and systems of the human body, including, and possibly, first of all, the cardiovascular system, in the next article from the series on the systems of the human body, we will move on to its consideration.

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

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

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

General characteristics of the nervous system

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

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

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

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

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

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

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

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

The structure of the nervous system

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

Rice. 1. The structure of the nervous system

Rice. 2. Functional division of the nervous system

Significance of the nervous system:

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

Structure of the nervous system

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

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

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

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

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

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

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

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

Functions of the central nervous system

The central nervous system performs several functions.

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

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

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

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

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

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

Reflex regulation of nervous activity

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Properties of nerve centers

Nerve centers have a number of characteristic functional properties.

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

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

In the nerve centers, summation of excitations can occur.

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

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

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

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

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

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

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

CNS coordination activity and its principles

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

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

Principles of coordination activities

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

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

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

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

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

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

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

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

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

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

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

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

Dominant Properties

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

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