In order for a person's behavior to be successful, it is necessary that his internal states, the external conditions in which the person is located, and the practical actions taken by him correspond to each other. At the physiological level, the function of combining (integrating) all of the above factors is provided by nervous system. Its device has access to both internal organs and the external environment. Its function is to connect them and control the organs * of movement.

In this way, main function of the nervous system- integration of external influence with the corresponding adaptive reaction of the organism.

The entire nervous system is divided into central and peripheral. The central nervous system consists of the forebrain, midbrain, hindbrain and spinal cord. It is in these main parts of the central nervous system that the most important structures are located that are directly related to mental processes, states and properties of a person: thalamus, hypothalamus, bridge, cerebellum and medulla oblongata... Nerve fibers diverge from the spinal cord and brain throughout the body - this peripheral nervous system. It connects the brain with the sense organs and with the executive organs - the muscles and glands.

All living organisms have the ability to respond to physical and chemical changes in the environment. The stimuli of the external environment (light, sound, smell, touch, etc.) are transformed

PRINCIPLES AND LAWS OF HIGHER NERVOUS ACTIVITY

The processes of inhibition and excitation are subject to the following laws.

The law of irradiation of excitation. Very strong stimuli with prolonged exposure to the body cause irradiation - the spread of excitation over a significant part of the cerebral cortex. Only optimal stimuli of medium strength cause strictly localized foci of excitation, which is the most important condition for successful activity.

The law of concentration of excitation. Excitation that has spread from a certain point to other areas of the cortex, over time, is concentrated in the place of its primary occurrence. This law underlies the main condition of our activity - attention. When excitation is concentrated in certain areas of the cerebral cortex, its functional interaction with inhibition occurs, which ensures normal analytical and synthetic activity.

The law of mutual induction of nervous processes. On the periphery of the focus of one nervous process, a process with the opposite sign always occurs. If the process of excitation is concentrated in one area of ​​the cortex, then the process of inhibition inductively arises around it. The more intense the concentrated excitation, the more intense and widespread the process of inhibition. Along with simultaneous induction, there is a successive induction of nervous processes - a successive change of nervous processes in the same parts of the brain.

STRUCTURE OF THE NERVOUS SYSTEM

Structural unit of the nervous system is a nerve cell neuron. It consists of a cell body, a nucleus, branched processes - dendrites, along which nerve impulses go to the cell body, and one long process - axon. It carries the nerve impulse from the cell body to other cells or effectors.

The processes of two neighboring neurons are connected by a special formation - synapse. It plays an essential role in filtering nerve impulses: it passes some impulses and delays others. Neurons are connected to each other and carry out joint activities.

The central nervous system is made up of brain and spinal cord. The brain is divided into brain stem and anterior brain. The brain stem is made up of medulla oblongata and midbrain. The forebrain is divided into intermediate and finite.

All parts of the brain have their own functions. Thus, the diencephalon consists of the hypothalamus - the center of emotions and vital needs, the limbic system, and the thalamus.

Humans are especially developed cerebral cortex - organ of higher mental functions. It has a thickness of 3-4 mm, and its total area is on average 0.25 square meters. m. The bark consists of six layers. The cells of the cerebral cortex are interconnected. There are about 15 billion of them.

Different cortical neurons have their own specific function. One group of neurons performs the function of analysis, the other group performs synthesis, combines impulses coming from various or-

sensory organs and brain regions. There is a system of neurons that keeps traces of previous influences and compares new influences with existing traces.

According to the features of the microscopic structure, the entire cortex divided into several dozen structural units - fields, and according to the location of its parts - into four lobes: 1) occipital; 2) temporal; 3) parietal; 4) frontal.

The human cerebral cortex is a holistically working organ, although some of its parts are functionally specialized: 1) the occipital region of the cortex performs complex visual functions; 2) frontotemporal - speech; 3) temporal - auditory.

The largest part of the motor cortex of the human cerebral cortex is associated with regulation of the movement of labor and speech organs.

All parts of the cerebral cortex are interconnected; they are also connected to the underlying parts of the brain, which carry out the most important vital functions. The human brain contains all the structures that arose at various stages of the evolution of living organisms. They contain the "experience" accumulated in the process of the entire evolutionary development. This testifies to the common origin of man and animals.

As the organization of animals at various stages of evolution becomes more complex, the importance of the cerebral cortex grows more and more. If, for example, the cerebral cortex of a frog is removed, the frog hardly changes its behavior. Deprived of the cerebral cortex, the dove flies, maintains balance, but already loses a number of vital functions. A dog with a removed cerebral cortex becomes completely unadapted to the environment.

Generally excitation is a property of living organisms, an active response of excitable tissue to irritation. For the nervous system, excitation - main function. The cells that form the nervous system have the property of conducting excitation from one area where it arose to other areas and to neighboring cells. Thus, excitement is a carrier of information about properties coming from outside.

Braking is an active process, inextricably linked with excitation, leading to a delay in the activity of nerve centers or working organs. In the first case, braking is called vaetsyatsentralnoy, vtorom-peripheral.

Only a normal ratio of excitation and inhibition processes provides behavior that is adequate (corresponding) to the environment. The imbalance between these processes, the predominance of one of them causes significant disturbances in the mental regulation of conduction.

Braking happens external and internal. So, if some new strong stimulus suddenly acts on the animal, then the previous activity of the animal at the moment will slow down. This is external (unconditional) inhibition. In this case, the emergence of a focus of excitation, according to the law of negative induction, causes inhibition of other parts of the cortex.

One of the types of internal, or conditional, inhibition is extinction of the conditioned reflex, if it is not reinforced by an unconditioned stimulus (extinguishing inhibition). This type of inhibition causes the cessation of previously developed reactions if they become useless under new conditions.

are fused by special sensitive cells (receptors) into nerve impulses - a series of electrical and chemical changes in the nerve fiber. Nerve impulses are transmitted along sensitive (afferent) nerve fibers to the spinal cord and brain. Here, the corresponding command impulses are generated, which are transmitted along the motor (efferent) nerve fibers to the executive organs (muscles, glands). These executive bodies are called effectors.

The activity of the nervous system is directly subordinated to the work of the brain. Consider the activity of the human cerebral cortex.

The activity of the cerebral cortex is subject to a number of principles and laws. The main ones were first established I. P. Pavlov. At present, some provisions of the teachings of IP Pavlov have been clarified and developed, and some parts have been revised. However, in order to master the basics of modern neurophysiology, it is necessary to familiarize yourself with the fundamental provisions of the doctrine.

As established by I.P. Pavlov, the main fundamental principle of the work of the cerebral cortex is analytic-synthetic principle. Orientation in the environment is associated with isolating its individual properties, aspects, features (analysis) and combining, linking these features with what is beneficial or harmful to the body (synthesis).

Synthesis - is the closure of connections, and analysis- this is an increasingly subtle separation of one stimulus from another. The analytical and synthetic activity of the cerebral cortex is carried out by the interaction of two nervous processes: arousal and braking.

3 1 . REFLEX AS THE MAIN MECHANISM OF NERVOUS ACTIVITY

The main mechanism of nervous activity is the reflex. Reflex- this is the body's reaction to external or internal influences through the central nervous system.

Term "reflex" was introduced into physiology by the French scientist Rene Descartes in the 17th century But to explain mental activity, it was applied only in 1863 by the founder of Russian materialistic physiology M. I. Sechenov. Developing the teachings of I. M. Sechenov, I. P. Pavlov experimentally researched features of the functioning of the reflex.

All reflexes are divided into two groups: conditional £^ and unconditional.

™ " Unconditioned reflexes - these are innate reactions of the body to vital stimuli (food, smell, taste, danger, etc.). They do not require any conditions for their development (for example, the blink reflex, salivation at the sight of food).

Unconditioned reflexes are a natural reserve of ready-made stereotypical reactions of the body. They arose as a result of a long evolutionary development of this species of animals. Unconditioned reflexes are the same in all individuals of the same species, this is the physiological mechanism of instincts. But the behavior of higher animals and humans is characterized not only by innate, i.e. unconditioned, reactions, but also by such reactions that are acquired by a given organism in the process

SYSTEMICITY IN THE WORK OF THE CORK

It is an organized set of cells specialized in conducting electrical signals.

The nervous system is made up of neurons and glial cells. The function of neurons is to coordinate actions using chemical and electrical signals sent from one place to another in the body. Most multicellular animals have nervous systems with similar basic characteristics.

Content:

The nervous system captures stimuli from the environment (external stimuli) or signals from the same organism (internal stimuli), processes the information, and generates different responses depending on the situation. As an example, we can consider an animal that senses the proximity of another living being through cells that are sensitive to light in the retina. This information is transmitted by the optic nerve to the brain, which processes it and emits a nerve signal, and causes certain muscles to contract through the motor nerves to move in the opposite direction of the potential danger.

Functions of the nervous system

The human nervous system controls and regulates most bodily functions, from stimuli through sensory receptors to motor actions.

It consists of two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is made up of the brain and spinal cord.

The PNS is made up of nerves that connect the CNS to every part of the body. The nerves that carry signals from the brain are called motor or efferent nerves, and the nerves that carry information from the body to the CNS are called sensory or afferent.

At the cellular level, the nervous system is defined by the presence of a type of cell called a neuron, also known as a "nerve cell". Neurons have special structures that allow them to quickly and accurately send signals to other cells.

Connections between neurons can form circuits and neural networks that generate the perception of the world and determine behavior. Along with neurons, the nervous system contains other specialized cells called glial cells (or simply glia). They provide structural and metabolic support.

Nervous system malfunction can result from genetic defects, physical damage, injury or toxicity, infection, or simply aging.

Structure of the nervous system

The nervous system (NS) consists of two well-differentiated subsystems, on the one hand the central nervous system, and on the other, the peripheral nervous system.

Video: The human nervous system. Introduction: basic concepts, composition and structure

At a functional level, the peripheral nervous system (PNS) and the somatic nervous system (SNS) differentiate into the peripheral nervous system. The SNS is involved in the automatic regulation of internal organs. The PNS is responsible for capturing sensory information and allowing voluntary movements such as shaking hands or writing.

The peripheral nervous system consists mainly of the following structures: ganglia and cranial nerves.

autonomic nervous system

autonomic nervous system

The autonomic nervous system (ANS) is divided into the sympathetic and parasympathetic systems. The ANS is involved in the automatic regulation of internal organs.

The autonomic nervous system, together with the neuroendocrine system, is responsible for regulating the internal balance of our body, lowering and raising hormone levels, activating internal organs, etc.

To do this, it transmits information from the internal organs to the CNS through afferent pathways and emits information from the CNS to the muscles.

It includes cardiac muscle, smooth skin (which supplies the hair follicles), smoothness of the eyes (which regulates pupil contraction and dilation), smoothness of blood vessels, and smoothness of the walls of internal organs (gastrointestinal system, liver, pancreas, respiratory system, reproductive organs, bladder...).

The efferent fibers are organized into two distinct systems called the sympathetic and parasympathetic systems.

Sympathetic nervous system is mainly responsible for preparing us to act when we feel a significant stimulus by activating one of the automatic responses (such as running away or attacking).

parasympathetic nervous system, in turn, maintains optimal activation of the internal state. Increase or decrease activation as needed.

somatic nervous system

The somatic nervous system is responsible for capturing sensory information. For this purpose, it uses sensory sensors distributed throughout the body, which distribute information to the CNS and thus transfer from the CNS to the muscles and organs.

On the other hand, it is a part of the peripheral nervous system associated with the voluntary control of bodily movements. It consists of afferent or sensory nerves, efferent or motor nerves.

Afferent nerves are responsible for transmitting sensation from the body to the central nervous system (CNS). Efferent nerves are responsible for sending signals from the CNS to the body, stimulating muscle contraction.

The somatic nervous system consists of two parts:

• Spinal nerves: arise from the spinal cord and consist of two branches, a sensory afferent and another efferent motor, so they are mixed nerves.
• Cranial Nerves: Sends sensory information from the neck and head to the central nervous system.

Both are then explained:

cranial nervous system

There are 12 pairs of cranial nerves that arise from the brain and are responsible for transmitting sensory information, controlling certain muscles, and regulating certain glands and internal organs.

I. Olfactory nerve. It receives olfactory sensory information and carries it to the olfactory bulb located in the brain.

II. optic nerve. It receives visual sensory information and transmits it to the vision centers of the brain via the optic nerve, passing through the chiasm.

III. Internal ocular motor nerve. It is responsible for controlling eye movements and regulating pupil dilation and contraction.

IV Intravenous-tricoleic nerve. It is responsible for controlling eye movements.

V. Trigeminal nerve. It receives somatosensory information (eg heat, pain, texture...) from sensory receptors in the face and head and controls the chewing muscles.

VI. External motor nerve of the ophthalmic nerve. Eye movement control.

VII. facial nerve. Receives taste information of the tongue (those located in the middle and previous parts) and somatosensory information about the ears, and controls the muscles necessary to perform facial expressions.

VIII. Vestibulocochlear nerve. Receives auditory information and controls balance.

IX. Glossopharyngeal nerve. Receives taste information from the very back of the tongue, somatosensory information about the tongue, tonsils, pharynx, and controls the muscles needed for swallowing (swallowing).

X. Vagus nerve. Receives sensitive information from the digestive glands and heart rate and sends the information to the organs and muscles.

XI. Dorsal accessory nerve. Controls the muscles of the neck and head that are used for movement.

XII. hypoglossal nerve. Controls the muscles of the tongue.

The spinal nerves connect the organs and muscles of the spinal cord. Nerves are responsible for transmitting information about the sensory and visceral organs to the brain and relaying orders from the bone marrow to the skeletal and smooth muscles and glands.

These connections control the reflex actions that are performed so quickly and unconsciously because the information does not have to be processed by the brain before a response is given, it is directly controlled by the brain.

There are a total of 31 pairs of spinal nerves that emerge bilaterally from the bone marrow through the space between the vertebrae, called the foramen magnum.

central nervous system

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

At the neuroanatomical level, two types of substances can be distinguished in the CNS: white and gray. The white matter is formed by the axons of neurons and structural material, and the gray matter is formed by the neuronal soma, where the genetic material is located.

This difference is one of the reasons behind the myth that we only use 10% of our brain, since the brain is made up of about 90% white matter and only 10% gray matter.

But while gray matter seems to be made up of material that only serves to connect, it is now known that the number and manner in which connections are made have a marked effect on brain function, because if the structures are in perfect condition, but between they don't have connections, they won't work correctly.

The brain is made up of many structures: the cerebral cortex, basal ganglia, limbic system, diencephalon, brainstem, and cerebellum.

Cortex

The cerebral cortex can be divided anatomically into lobes separated by grooves. The most recognized are the frontal, parietal, temporal, and occipital, although some authors state that there is also a limbic lobe.

The cortex is divided into two hemispheres, right and left, so that the halves are present symmetrically in both hemispheres, with right frontal lobes and left lobes, right and left parietal lobes, etc.

The hemispheres of the brain are separated by an interhemispheric fissure, and the lobes are separated by various grooves.

The cerebral cortex can also be attributed to the functions of the sensory cortex, the association cortex, and the frontal lobes.

The sensory cortex receives sensory information from the thalamus, which receives information through sensory receptors, with the exception of the primary olfactory cortex, which receives information directly from sensory receptors.

Somatosensory information reaches the primary somatosensory cortex located in the parietal lobe (in the postcentral gyrus).

Each sensory information reaches a certain point in the cortex, which forms a sensory homunculus.

As can be seen, the areas of the brain corresponding to the organs do not correspond to the same order in which they are located in the body and they do not have a proportional ratio of sizes.

The largest cortical areas, compared to the size of organs, are the hands and lips, since in this area we have a high density of sensory receptors.

Visual information reaches the primary visual cortex located in the occipital lobe (in the groove) and this information has a retinotopic organization.

The primary auditory cortex is located in the temporal lobe (Brodmann's area 41), responsible for receiving auditory information and creating tonotopic organization.

The primary taste cortex is located in the anterior part of the impeller and in the anterior sheath, while the olfactory cortex is located in the piriform cortex.

The association cortex includes primary and secondary. Primary cortical association is located next to the sensory cortex and integrates all the characteristics of the perceived sensory information, such as color, shape, distance, size, etc. of the visual stimulus.

The root of the secondary association is located in the parietal operculum and processes the integrated information to send it to more "advanced" structures such as the frontal lobes. These structures place it in context, give it meaning, and make it conscious.

The frontal lobes, as we have already mentioned, are responsible for processing high-level information and integrating sensory information with motor actions that are performed in such a way that they correspond to the perceived stimulus.

In addition, they perform a number of complex, usually human tasks called executive functions.

Basal ganglia

The basal ganglia (from the Greek ganglion, "conglomerate", "knot", "tumor") or basal ganglia are a group of nuclei or masses of gray matter (clumps of bodies or neuronal cells) that lie at the base of the brain between the ascending and descending white matter tracts and riding on the brainstem.

These structures are connected to each other and together with the cerebral cortex and association through the thalamus, their main function is to control voluntary movements.

The limbic system is formed by subcortical structures, that is, below the cerebral cortex. Among the subcortical structures that do this, the amygdala stands out, and among the cortical structures, the hippocampus.

The amygdala is almond-shaped and consists of a series of nuclei that emit and receive afferents and outputs from different regions.

This structure is associated with several functions such as emotional processing (especially negative emotions) and its influence on learning and memory processes, attention, and some perceptual mechanisms.

The hippocampus, or hypocampal formation, is a seahorse-like cortical region (hence the name hippocampus, from the Greek hypos, horse and monster of the sea) and communicates in two directions with the rest of the cerebral cortex and with the hypothalamus.

Hypothalamus

This structure is especially important for learning because it is responsible for memory consolidation, that is, the transformation of short-term or immediate memory into long-term memory.

diencephalon

diencephalon located in the central part of the brain and consists mainly of the thalamus and hypothalamus.

thalamus consists of several nuclei with differentiated connections, which is very important in the processing of sensory information, since it coordinates and regulates information coming from the spinal cord, brain stem and the brain itself.

Thus, all sensory information passes through the thalamus before reaching the sensory cortex (with the exception of olfactory information).

Hypothalamus consists of several nuclei that are widely interconnected. In addition to other structures, both the central and peripheral nervous systems such as the cortex, spinal cord, retina, and endocrine system.

Its main function is to integrate sensory information with other types of information, such as emotional, motivational, or past experiences.

The brain stem is located between the diencephalon and the spinal cord. It consists of the medulla oblongata, bulge, and mesencephalin.

This structure receives most of the peripheral motor and sensory information, and its main function is to integrate sensory and motor information.

Cerebellum

The cerebellum is located at the back of the skull and is shaped like a small brain, with a cortex on the surface and white matter inside.

It receives and integrates information mainly from the cerebral cortex. Its main functions are coordination and adaptation of movements to situations, as well as maintaining balance.

Spinal cord

The spinal cord passes from the brain to the second lumbar vertebra. Its main function is to link the CNS to the SNS, for example by receiving motor commands from the brain to the nerves that innervate the muscles so that they give a motor response.

In addition, he can initiate automatic responses by receiving some very important sensory information such as a prick or a burn.

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 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 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 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 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 respiratory tract. 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 activity

• 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.

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) 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.

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

Neuron

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

Rice. 1. Structure of a neuron.

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

The structure of the human nervous system

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

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

Nerves leaving the CNS make up the peripheral part of the nervous system. It consists of nerves and nerve nodes.

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

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

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

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

The autonomic nervous system (ANS) regulates:

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

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

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

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

The ANS is divided into 2 subsystems:

• sympathetic;
• parasympathetic.

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

Parasympathetic slow down the work of the organs and turn on during rest and relaxation.

For example, sympathetic nerves dilate the pupil, stimulate salivation. Parasympathetic, on the contrary, narrow the pupil, slow down salivation.

Reflex

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

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

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

Rice. 3. Scheme of the reflex arc.

Sequence: sensory nerve - CNS - motor nerve is called the reflex arc.

Brain

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

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

What have we learned?

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

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The entire nervous system is divided into central and peripheral. The central nervous system includes the brain and spinal cord. Nerve fibers - the peripheral nervous system - diverge from them throughout the body. It connects the brain with the sense organs and with the executive organs - the muscles and glands.

All living organisms have the ability to respond to physical and chemical changes in the environment. Stimuli of the external environment (light, sound, smell, touch, etc.) are converted by special sensitive cells (receptors) into nerve impulses - a series of electrical and chemical changes in the nerve fiber. Nerve impulses are transmitted along sensitive (afferent) nerve fibers to the spinal cord and brain. Here, the corresponding command impulses are generated, which are transmitted along the motor (efferent) nerve fibers to the executive organs (muscles, glands). These executive organs are called effectors. The main function of the nervous system is the integration of external influences with the corresponding adaptive response of the body.

The structural unit of the nervous system is a nerve cell - a neuron. It consists of a cell body, a nucleus, branched processes - dendrites - along them nerve impulses go to the cell body - and one long process - an axon - along it a nerve impulse passes from the cell body to other cells or effectors. The processes of two adjacent neurons are connected by a special formation - a synapse. It plays an essential role in filtering nerve impulses: it passes some impulses and delays others. Neurons are connected to each other and carry out joint activities.

The central nervous system consists of the brain and spinal cord. The brain is divided into the brainstem and the forebrain. The brain stem consists of the medulla oblongata and midbrain. The forebrain is divided into intermediate and final.

All parts of the brain have their own functions. Thus, the diencephalon consists of the hypothalamus - the center of emotions and vital needs (hunger, thirst, libido), the limbic system (in charge of emotional-impulsive behavior) and the thalamus (which performs filtering and primary processing of sensory information).

In humans, the cerebral cortex is especially developed - the organ of higher mental functions. It has a thickness of 3 mm, and its total area is on average 0.25 sq.m. The bark is made up of six layers. The cells of the cerebral cortex are interconnected. There are about 15 billion of them. Different cortical neurons have their own specific function. One group of neurons performs the function of analysis (crushing, dismemberment of a nerve impulse), the other group performs synthesis, combines impulses coming from various sensory organs and parts of the brain (associative neurons). There is a system of neurons that keeps traces of previous influences and compares new influences with existing traces.

According to the features of the microscopic structure, the entire cerebral cortex is divided into several dozen structural units - fields, and according to the location of its parts - into four lobes: occipital, temporal, parietal and frontal. The human cerebral cortex is a holistically working organ, although its individual parts (areas) are functionally specialized (for example, the occipital region of the cortex performs complex visual functions, the frontotemporal region - speech, the temporal - auditory). The largest part of the motor zone of the human cerebral cortex is associated with the regulation of the movement of the labor organ (hand) and speech organs.

All parts of the cerebral cortex are interconnected; they are also connected to the underlying parts of the brain, which carry out the most important vital functions. Subcortical formations, regulating innate unconditional reflex activity, are the area of ​​those processes that are subjectively felt in the form of emotions (they, according to I.P. Pavlov, are “a source of strength for cortical cells”).

The human brain contains all the structures that arose at various stages of the evolution of living organisms. They contain the "experience" accumulated in the process of the entire evolutionary development. This testifies to the common origin of man and animals. As the organization of animals at various stages of evolution becomes more complex, the importance of the cerebral cortex grows more and more.

The main mechanism of nervous activity is the reflex. Reflex - the reaction of the body to external or internal influences through the central nervous system. The term "reflex" was introduced into physiology by the French scientist René Descartes in the 17th century. But to explain mental activity, it was used only in 1863 by the founder of Russian materialistic physiology, M.I. Sechenov. Developing the teachings of I.M. Sechenov, I.P. Pavlov experimentally investigated the features of the functioning of the reflex.

All reflexes are divided into two groups: conditioned and unconditioned.

Unconditioned reflexes are innate reactions of the body to vital stimuli (food, danger, etc.). They do not require any conditions for their development (for example, the blink reflex, salivation at the sight of food). Unconditioned reflexes are a natural reserve of ready-made, stereotyped reactions of the body. They arose as a result of a long evolutionary development of this species of animals. Unconditioned reflexes are the same in all individuals of the same species; it is the physiological mechanism of instincts. But the behavior of higher animals and humans is characterized not only by innate, i.e. unconditional reactions, but also such reactions that are acquired by a given organism in the course of its individual life activity, i.e. conditioned reflexes.

Conditioned reflexes are a physiological mechanism for adapting the body to changing environmental conditions. Conditioned reflexes are such reactions of the body that are not innate, but are developed in various lifetime conditions. They arise under the condition of constant precedence of various phenomena to those that are vital for the animal. If the connection between these phenomena disappears, then the conditioned reflex fades away (for example, the growl of a tiger in a zoo, without being accompanied by its attack, ceases to frighten other animals).

The brain does not go on about only current influences. He plans, anticipates the future, carries out an anticipatory reflection of the future. This is the main feature of his work. The action must achieve a certain future result - the goal. Without preliminary modeling by the brain of this result, regulation of behavior is impossible. So, brain activity is a reflection of external influences as signals for certain adaptive actions. The mechanism of hereditary adaptation is unconditioned reflexes, and the mechanism of individually variable adaptation is conditioned reflexes, complex complexes of functional systems.

Neuron, types of neurons

Neuron (from the Greek nuron - nerve) is a structural and functional unit of the nervous system. This cell has a complex structure, is highly specialized and contains a nucleus, a cell body and processes in structure. There are over one hundred billion neurons in the human body. The complexity and diversity of the functions of the nervous system are determined by the interaction between neurons, which, in turn, is a set of different signals transmitted as part of the interaction of neurons with other neurons or muscles and glands. Signals are emitted and propagated by ions, which generate an electrical charge that travels along the neuron.

Types of neurons.

By localization: central (located in the central nervous system); peripheral (located outside the central nervous system - in the spinal, cranial ganglia, in the autonomic ganglia, in the plexuses and intraorganically).

On a functional basis: receptor (afferent, sensitive) are those nerve cells through which impulses go from receptors to the central nervous system. They are divided into: primary afferent neurons - their bodies are located in the spinal ganglia, they have a direct connection with receptors and secondary afferent neurons - their bodies lie in the visual tubercles, they transmit impulses to the overlying sections, they are not connected with receptors, they receive impulses from others neurons; efferent neurons transmit impulses from the central nervous system to other organs. Motor neurons are located in the anterior horns of the spinal cord (alpha, beta, gamma - motor neurons) - provide a motor response. Neurons of the autonomic nervous system: preganglionic (their bodies lie in the lateral horns of the spinal cord), postganglionic (their bodies are in the autonomic ganglia); intercalary (interneurons) - provide the transmission of impulses from afferent to efferent neurons. They make up the bulk of the gray matter of the brain, are widely represented in the brain and its cortex. Types of intercalary neurons: excitatory and inhibitory neurons.