Nervous regulation- this is an electrophysiological regulation carried out with the help of nerve impulses and is characterized by a quick, specific, short-term, local effect on organs. Features of nervous regulation are determined by the structure and properties of the nervous system.

The main structural and functional elements of the activity of the nervous system are neurons, which together with neuroglia form nervous tissue, the main properties of which are excitability and conductivity.

Neuron - nerve cell, which is the structural unit of the nervous system. Neuron body has a nucleus, mitochondria, ribosomes and other organelles. Short processes extend from the body - dendrites, that receive nerve impulses from other neurons. long tail - axon, conducts nerve impulses away from the body of the neuron. Axons may be covered myelin sheath, which ensures their isolation and protection. Myelin fibers have interceptions of Ranvier, increase the speed of transmission of nerve impulses. Neurons communicate with each other and with organs synoptic endings. The bodies of motor and insertion neurons and dendrites form Gray matter, and long processes of neurons - white matter. According to the number of processes, neurons are multipolar- with numerous processes; bipolar - with two processes; unipolar- with one branch. According to their functions, neurons are divided into: sensitive(receptor, afferent) - transmit signals from receptors to the central nervous system; plug-in(intermediate) - transmit impulses within the CNS motor(effector, efferent) - transmit impulses from the central nervous system to the working organs. Neurons provide the perception of stimuli from the environment and their transformation into nerve impulses. [receptor function), transmission of nerve impulses throughout the body ( leading function), pulse formation ( impulsive function, for example, for the neurons of the respiratory center, which form impulses for the regulation of respiratory movements), the formation of neurohormones ( neurohormonal function, for example, for hypothalamic neurons that produce releasing hormones).

Neuroglia - a collection of nerve cells, along with neurons, form the nervous tissue. The proportion of neuroglia in the human nervous system is about 40%. The size of neuroglial cells, which are astrocytes, oligodendrocytes, ependymal cells and microglial cells, is smaller than neurons by 3-4 times, and the number is 10 times more. With age, their number increases because, unlike neurons, they can divide. The main functions of neuroglia are supporting, protective, trophic, secretory, etc.

All nervous activity is carried out with the help of reflexes, which are based on reflex arcs .

Reflex- the response of the body to the influence of the environment, which is carried out with the participation of the nervous system. According to the moment of occurrence, reflexes are divided into unconditional (congenital, hereditary, permanent reactions) and conditional (acquired, individual reactions). Reflexes provide regulation of all physiological functions of the body and adaptation of the activities of individual organs and systems to its needs.

reflex arc- the path along which the nerve impulse passes during the implementation of the reflex. There are 5 links in the reflex arc: 1) receptor- sensitive nerve ending that perceives irritation; 2) afferent(centripetal, sensitive) -

centripetal nerve fiber that transmits excitation to the central nervous system 3) central - a section of the central nervous system where excitation switches from a centripetal neuron to a centrifugal one; four) efferent(centrifugal, motor) - centrifugal nerve fiber, carries a nerve impulse from the center to the periphery; 5) effector(working) - a motor ending that transmits a nerve impulse to the working organ. Reflex arcs are simple(2 neurons) take into account that the basis of the activity of the nervous system is not an open reflex arc, but a closed reflex ring, that is, there are feedback circuits through which nerve impulses from effectors again enter the central nervous system and inform it about the state of the organ at the moment.

Neurons in the nervous system combine with synapses, and their processes (fibers) combined into pathways nerves .

Synapses - formations that provide communication between neurons. The term "synapse" was introduced into scientific circulation by C. Sherrington in 1897 to denote the anatomical contact between two neurons. In the human nervous system, chemical and electrical synapses are distinguished. Chemical synapses are complex systems of the following components; terminal plaque(thickened part of the terminal branches of axons, which has synaptic vesicles with mediators, and mitochondria that provide synaptic processes with energy), presynaptic membrane(transmits excitement) postsyoptic membrane(feels excited) synoptic gap(space between membranes). The mediators of synaptic excitation and inhibition include acetylcholine, norepinephrine, adrenaline, serotonin, glutamic and aspartic acids, etc. Electrical synapses differ from chemical synapses in that they have a very narrow synaptic cleft through which ions are transmitted through ordered protein tunnels almost without delay in both directions .

Nerves- a set of nerve fibers that connect the central nervous system with organs and tissues of the body. Outwardly, the nerves are covered with a connective tissue sheath (epineurium), in the thickness of the nerve there are separate nerve bundles, covered with an inner membrane (perineurium). Nerve bundles are formed nerve fibers, which are affected and motorized. In the connective tissue sheath pass circulatory and lymphatic vessels. Nerves are divided into cranial (12 pairs) and spinal (31 pairs). Depending on the nature of the nerve fibers that make up the composition, the nerves are divided into motor(consists only of motor fibers), sensitive(consisting only of sensitive fibers) and mixed(composed of sensory and motor fibers). The longest and longest nerve of the human body is the sciatic nerve, the diameter of which at the point of origin from the spinal cord is 2 cm. Nerve nodes can be located along the course of the nerves. nerve nodes (ganglia) - an accumulation of gray matter outside the central nervous system, consisting of neurons, the processes of which are part of the nerves and nerve plexuses. The entire set of nerves, nerve nodes and nerve plexuses forms the peripheral nervous system

Coordination of nervous activity occurs at the level nervous centers whose functioning is based on the interaction of two processes: arousal and braking .

Nerve center- this is a set of neurons that is necessary for the implementation of the reflex and sufficient for the regulation of a specific physiological function. Nerve centers have certain properties (for example, unilateral conduction of excitation, delayed conduction of excitation, dominant), due to the structure of neural circuits within the center and the characteristics of the synaptic conduction of nerve impulses. Nerve centers are located in certain parts of the central nervous system. For example, the respiratory center is contained in the medulla oblongata, the knee-jerk reflex center is in the lumbar spinal cord. The activity of the nerve centers is based on the interaction of the processes of excitation and inhibition.

Excitation - an active nervous process by which nerve cells respond to external influences. Braking - an active nervous process that leads to a decrease or cessation of excitation in a certain area of ​​\u200b\u200bthe nervous tissue.

The human nervous system combines organs and systems and ensures the existence of the body as a whole, performing the following functions: regulatory- the work of other organs and systems is ensured (for example, it changes breathing) coordinating- the relationship of organs to each other when performing certain functions (for example, the work of organs while running) connection with the environment- perceives the impact of the external and internal environment; carries out higher nervous activity and ensures the existence of man as a social being.

Lesson topic: Nervous regulation. The structure and significance of the nervous system.
Target:
To form knowledge about the structure of the nervous system, its functions.
Tasks:
To reveal the dependence of the functions performed on the characteristics of nerve cells, the reflex principle of the nervous system, the mechanism of nervous regulation;
Continue developing the skills and techniques of mental activity of students: comparison, analysis, generalization, self-observation.
Equipment: Computer, multimedia projector, screen.

During the classes:
1. Updating knowledge about the nervous system, structural features, and the principle of operation; about reflex.
What types of nervous system are shown in the picture?
What are the structural features of each type of nervous system?
What is a reflex?

2. Learning new material.

2.1. The neuron is the basis of the nervous system. Types of neurons, properties and functions. Synapse.
You already know that the existence of an organism in a complex, constantly changing world is impossible without coordination and regulation of its activities. This is primarily done by the nervous system. The nervous system is a set of structures in the human body that unites the activity of all organs and systems and ensures the functioning of the body as a whole in its constant interaction with the external environment. The nervous system perceives external and internal stimuli, analyzes this information, selects and processes it, and in accordance with this regulates and coordinates the functions of the body.
NS value:
1. ensures the maintenance of homeostasis
2. ensures the coordinated work of all organs and systems of the body
3. carries out the orientation of the organism in the external environment and adaptive reactions to its changes
4. forms the basis of mental activity: speech, thinking, social behavior.
The nervous system is formed mainly by nervous tissue, the main element of which is a nerve cell with processes (axon and dendrites), which has high excitability and the ability to quickly conduct excitation.
A, dendrites. B is the body of the nerve cell. C - axon.
Neurons are the basis of the nervous system. The nervous system is a neuron consisting of a body of a nerve cell and processes - an axon and dendrites. In addition to nerve cells, the structure of the nervous system includes neuroglial cells, which perform a supporting function in it, and also participate in the metabolism of nerve cells.
The interaction between neurons is carried out due to the contacts between them.
These contacts are called synapses. (recording the definition in a notebook) In the area of ​​contact between the end of one neuron and the surface of another, in most cases a special space is preserved - the synaptic cleft.
The main functions of neurons are the perception of stimuli, their processing, the transmission of this information and the formation of a response.
Depending on the type and course of the nerve processes (fibers), as well as their functions, neurons are divided into: a) sensitive, receptor (afferent), the fibers of which conduct nerve impulses from receptors to the central nervous system; their bodies are in the spinal ganglia or ganglia of the cranial nerves; b) motor (efferent), connecting the central nervous system with effectors; their bodies and dendrites are located in the central nervous system, and axons go beyond its limits (with the exception of efferent neurons of the autonomic nervous system, whose bodies are located in the peripheral ganglia); c) intercalary (associative) neurons, serving as connecting links between afferent and efferent neurons; their bodies and processes are located in the central nervous system.
2.2. The structure and significance of the nervous system (conversation with the elements of the story, work with the textbook drawing up diagrams). (reference diagrams in the notebook).
The nervous system, depending on its location, is conditionally divided into central and peripheral. The central nervous system includes the brain and spinal cord, while the peripheral nervous system includes nerves (cranial and spinal), nerve nodes and nerve endings.
Nerves are bundles of long processes of nerve cells that extend beyond the brain and spinal cord. The bundles are covered with connective tissue that forms the sheaths of the nerves.
Nerve ganglions are clusters of neuron bodies outside the central nervous system.
Receptors are the nerve endings of the branches of the processes.
The development and differentiation of the structures of the human nervous system led to its division into the somatic and autonomic nervous systems.
The somatic nervous system regulates the work of skeletal muscles, skin, and communicates the body with the environment.
The peculiarity of the structure of the autonomic nervous system is that its fibers extending from the central nervous system do not reach directly to the working organ, but first enter the peripheral ganglia, where they end on cells that give off axons directly to the innervated organ.
Depending on where the ganglia of the autonomic nervous system are located, and some of its functional features, the autonomic nervous system is divided into 2 parts: parasympathetic and sympathetic.
2.3. The reflex principle of the activity of the nervous system. Reflex, types of reflexes, instincts .. Examples of conditioned and unconditioned reflexes).
The main regularities of the activity of the central nervous system are associated primarily with the features of the reflex arc - the structural basis of each reflex act. A reflex arc is the path along which a nerve impulse travels.
For simplicity, the reflex arc is usually depicted as a chain of a number of single cells of various kinds: a receptor cell, a sensitive (afferent), intercalary and motor (efferent) nerve cells, and an executive cell. In fact, the reflex arc combines many such chains, the specific links of which are not a single cell of one kind or another, but an ensemble of interconnected homogeneous cells.
The reflex arc can be simple or complex.
The entire set of reflex reactions of the body is divided into two main groups: unconditioned reflexes - congenital, carried out along hereditarily fixed nerve pathways, and conditioned reflexes acquired during the individual life of the organism through the formation of temporary connections in the central nervous system.
Questions for conversation:
What unconditioned and conditioned reflexes do you know?
What is a necessary condition for the formation of conditioned reflexes in animals?
Congenital forms of behavior (unconditioned reflexes) have been developed in the process of evolution and are the same result of natural selection, as well as morphological, physiological and other signs of an organism. They are genetically rigidly defined, therefore, in taxonomy, one of the species criteria is behavioral. Unconditioned reflexes are very diverse. They can be classified as follows.
1. Reflexes aimed at preserving the internal environment of the body. These are food, drink, as well as homeostatic reflexes (maintaining a constant body temperature, optimal breathing and heart rates, etc.).
2. Reflexes that occur when the conditions of the external environment of the body change. These are situational reflexes (behavior in a flock, building nests, exploratory and imitative reflexes) and defensive reactions.
3. Reflexes associated with the preservation of the species - sexual and parental
Such reflexes are species-specific; characteristic of all representatives of this species. The range of stimuli triggering them is genetically rigidly defined (food, pain, smell of an individual of the opposite sex, etc.). I.P. Pavlov called such reflexes unconditioned, and the stimuli that triggered them were reinforcements.
The second group of reflexes are acquired responses that are formed as a result of the repeated combination of any indifferent (initially insignificant) stimulus with reinforcement. Such reflexes are individual; they are developed under certain conditions in each individual, may disappear during life or be replaced by other similar reflexes and are not transmitted to offspring. Formation of writing skills, the use of tools.

The ability to form such connections is inherent only in the cerebral cortex. The formation of conditioned reflex connections allows the organism to most perfectly and subtly adapt to constantly changing conditions of existence. Conditioned reflexes were discovered and studied by IP Pavlov in the late 19th and early 20th centuries. The study of the conditioned reflex activity of animals and humans led him to the creation of the doctrine of higher nervous activity (HNA) and analyzers. Each analyzer consists of a perceiving part - a receptor, pathways and analyzing structures of the CNS, which necessarily include its higher department. The cerebral cortex in humans and higher animals is a set of cortical ends of analyzers; it carries out the highest forms of analyzer and integrative activity, providing the most perfect and subtlest forms of interaction between the organism and the external environment.
The reflex arc conducts excitation in only one direction - from the receptor end to the executive organ. This is due to the structural and functional polarization inherent in all nerve cells: on the terminal branches of the axons of each neuron, there are microstructural formations, the so-called. synapses, through which it contacts the bodies or dendrites of other neurons and unilaterally transmits its activity to them. Diverse external and internal receptors of the body, specialized in the process of evolution to a subtle and perfect perception of individual, qualitatively specific types of energy - light, sound, thermal, mechanical and chemical, transform them into a process of nervous excitation, which in the form of rhythmic impulses is transmitted sequentially from one link reflex arc to others. Excitation on its multi-stage path to the final link undergoes significant changes in rhythm, intensity, speed and character. In the executive organs, reflex excitation can generate diverse effects due to the specific features of the structure and functions of the executive organs themselves (muscles, glands, blood vessels, etc.).
2.4. The principle of direct and feedback in the work of the nervous system.
Important for the normal course of reflex activity is the mechanism of the so-called feedback, afferentation - information about the result of the implementation of this reflex reaction, coming through the afferent pathways from the executive organs. Based on this information, if the result is unsatisfactory, in the formed functional system, the activity of individual elements can be rearranged until the result corresponds to the level required for the organism.
2.5. The role of I.M. Sechenov and I.P. Pavlov in the development of the doctrine of reflexes. (student messages). (If there is a resource of time in the lesson)
Materials for student reports about scientists I.M. Sechenov and I.P. Pavlov are on the site http://window.edu.ru/ Single window of access to educational resources. Russian education. The system of federal educational portals.
4. Consolidation of knowledge.
Conversation on the questions "Test your knowledge"
Independent work on the drawing of the textbook p. 52-53
5. Homework. P.50 - 55, notes in a notebook.
6. Reflection.

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

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

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

General characteristics of the nervous system

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

The impact of stimuli is perceived by specialized sensory receptors. Examples of such stimuli can be light quanta, sounds, heat, cold, mechanical 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 material basis of mental activity: speech, thinking, social behavior.

Structure of the nervous system

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

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

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

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

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

According to their functional significance, neurons are divided into three groups: sensitive (sensory, receptor); intercalary (associative); motor (effector, motor).

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

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

Functions of the central nervous system

The central nervous system performs several functions.

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

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

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

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

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

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

Reflex regulation of nervous activity

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

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

Reflex in Latin means "reflection". The term "reflex" was first proposed by the Czech researcher I.G. Prohaska, who developed the doctrine of reflective actions. The further development of the reflex theory is associated with the name of I.M. Sechenov. He believed that everything unconscious and conscious is accomplished by the type of reflex. But then there were no methods for an objective assessment of brain activity that could confirm this assumption. Later, an objective method for assessing brain activity was developed by Academician I.P. Pavlov, and he received the name of the method of conditioned reflexes. Using this method, the scientist proved that the basis of the higher nervous activity of animals and humans are conditioned reflexes, which are formed on the basis of unconditioned reflexes 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 by a large number of intercalary and motor neurons.

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

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

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

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

Unconditioned reflexes - congenital, hereditary reactions. Unconditioned reflexes are carried out through reflex arcs already formed in the body. Unconditioned reflexes are species-specific, i.e. common to all animals of this species. They are constant throughout life and arise in response to adequate stimulation of the receptors. Unconditioned reflexes are 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 feedback link in the form of reverse afferentation, which is an essential component of reflex activity. The principle of reverse afferentation in reflex activity was developed by P.K. Anokhin and is based on the fact that the structural basis of the reflex is not a reflex arc, but a reflex ring, which includes the following links: receptor, afferent nerve pathway, nerve center, efferent nerve pathway, working organ , reverse afferentation.

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

Properties of nerve centers

Nerve centers have a number of characteristic functional properties.

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

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

In the nerve centers, summation of excitations can occur.

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

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

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

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

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

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

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

CNS coordination activity and its principles

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

An example 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 food or liquid from entering the airways. The coordination function of the central nervous system is fundamentally important for the implementation of complex movements carried out with the participation of many muscles. Examples of such movements are the articulation of speech, the act of swallowing, gymnastic movements that require the coordinated contraction and relaxation of many muscles.

Principles of coordination activity

• Reciprocity - mutual inhibition of antagonistic groups of neurons (flexor and extensor motoneurons)
• Terminal neuron - activation of an efferent neuron from different receptive fields and competition between different afferent impulses for a given motor neuron
• Switching - the process of transferring activity from one nerve center to the antagonist nerve center
• Induction - change of excitation by inhibition or vice versa
• Feedback is a mechanism that ensures the need for signaling from 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.

The principle of a common final path follows from the principle of convergence and is close in essence. It is understood as the possibility of implementing the same reaction triggered by the final efferent neuron in the hierarchical nervous circuit, to which the axons of many other nerve cells converge. An example of a classic final pathway is the 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, signals are widely distributed (irradiated) and many centers located at different levels of the CNS are quickly involved in the response.

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

The participation of feedback can be considered on the example of the implementation of the flexion reflex caused by mechanical action on skin receptors (Fig. 5). With reflex contraction of the flexor muscle, the activity of proprioreceptors and the frequency of sending nerve impulses along the afferent fibers to the a-motoneurons of the spinal cord, which innervate this muscle, change. As a result, a closed 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 (center 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.

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? This 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 changes in the conditions of the external and internal environment. This system combines sensitization, motor activity and the correct functioning of such systems as 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 ability to transform and generate the energies of the external and internal environment and transform 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 (there are two smaller hemispheres of the cerebellum in the occipital region of the skull). 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. The whole integral system is conditionally formed: 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, among other things, can cause an increase in heart rate, an increase in blood pressure, and excitation of the senses 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 side of the cell membrane does not lead to the appearance of an 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 rises, 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 how a nerve impulse travels 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.