Structure and functions of the human nervous system. General structure of the nervous system

GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM

Centers of the nervous system

Inhibition processes in the central nervous system

Reflex and reflex arc. Types of reflex

Functions and parts of the nervous system

The body is a complex, highly organized system consisting of functionally interconnected cells, tissues, organs and their systems. Management of their functions, as well as their integration (interconnection), ensures nervous system. The NS also communicates the body with external environment, by analyzing and synthesizing the various information received from receptors. It provides movement and functions as a regulator of behavior necessary in specific conditions of existence. This ensures adequate adaptation to the surrounding world. In addition, the processes underlying mental activity person (attention, memory, emotions, thinking, etc.).

Thus, nervous system functions:

Regulates all processes occurring in the body;

Carries out the relationship (integration) of cells, tissues, organs and systems;

Performs analysis and synthesis of information entering the body;

Regulates behavior;

Provides processes underlying human mental activity.

According to morphological principle central(brain and spinal cord) and peripheral(paired spinal and cranial nerves, their roots, branches, nerve endings, plexuses and ganglia lying in all parts of the human body).

By functional principle the nervous system is divided into somatic And vegetative. The somatic nervous system provides innervation mainly to the organs of the body (soma) - skeletal muscles, skin, etc. This part of the nervous system connects the body with the external environment through the senses and provides movement. The autonomic nervous system innervates internal organs, vessels, glands, including endocrine, smooth muscles, regulates metabolic processes in all organs and tissues. The autonomic nervous system includes sympathetic, parasympathetic And metasympathetic departments.

2. Structural and functional elements of the NS

Main structural- functional unit NS is neuron with its branches. Their functions are to perceive information from the periphery or from other neurons, process it and transmit it to neighboring neurons or executive organs. In a neuron there are body (soma) And shoots (dendrites And axon). Dendrites are numerous highly branched protoplasmic projections near the soma, through which excitation is conducted to the body of the neuron. Their initial segments have a larger diameter and lack spines (cytoplasmic outgrowths). An axon is the only axial-cylindrical process of a neuron, having a length from several microns to 1 m, the diameter of which is relatively constant throughout its entire length. The terminal sections of the axon are divided into terminal branches, through which excitation is transmitted from the neuron body to another neuron or working organ.

The integration of neurons into the nervous system occurs through interneuronal synapses.

Neuron functions:

1. Perception of information (dendrites and neuron body).

2. Integration, storage and reproduction of information (neuron body). Integrative activity of a neuron consists in the intracellular transformation of many heterogeneous excitations coming to the neuron and the formation of a single response.

3. Synthesis of biologically active substances (neuron body and synaptic endings).

4. Generation of electrical impulses (axon hillock - axon base).

5. Axonal transport and conduction of excitation (axon).

6. Transmission of excitations (synaptic endings).

There are several neuron classifications.

According to morphological classification neurons are distinguished by the shape of the soma. There are granular neurons, pyramidal neurons, stellate neurons, etc. Based on the number of neurons extending from the body, processes are divided into unipolar neurons (one process), pseudounipolar neurons (T-shaped branching process), bipolar neurons (two processes), multipolar neurons (one axon and many dendrites).

Biochemical classification neurons is carried out taking into account the nature of the produced mediator. Based on this, they distinguish cholinergic(mediator acetylcholine), monoaminergic(adrenaline, norepinephrine, serotonin, dopamine), GABAergic(gamma-aminobutyric acid), peptidergic(substance P, enkephalins, endorphins, other neuropeptides), etc. Based on this classification, there are four main diffuse modulating systems:

1. Serotonergic the system originates in the raphe nuclei and secretes the neurotransmitter serotonin. Serotonin is a precursor to melatonin, produced in the pineal gland; may take part in the formation of endogenous opiates. Serotonin plays a major role in regulating mood. The development of mental disorders, manifested by depression and anxiety, and suicidal behavior, is associated with dysfunction of the serotonergic system. Excess serotonin usually causes panic. Antidepressants are based on the mechanisms of blocking the reuptake of serotonin from the synaptic cleft latest generation. Serotonergic neurons in the raphe nuclei are central to the control of the sleep-wake cycle and initiate REM sleep. The serotonergic system of the brain is involved in the regulation of sexual behavior: an increase in the level of serotonin in the brain is accompanied by inhibition of sexual activity, and a decrease in its content leads to its increase.

2. Noradrenergic the system originates in the locus coeruleus of the pons and functions as an "alarm center" that becomes most active when new environmental stimuli occur. Noradrenergic neurons are widely distributed throughout the central nervous system and provide an increase in the overall level of excitation and initiate autonomic manifestations of the stress response.

3. Dopaminergic neurons are widely distributed in the central nervous system. Dopaminergic neurons play an important role in the brain's need satisfaction system (pleasure system). This system underlies addiction to drugs (including cocaine, amphetamines, ecstasy, alcohol, nicotine and cocaine). The development of Parkinson's disease is based on the progressive degeneration of dopamine-containing pigment neurons in the substantia nigra and locus coeruleus. It is assumed that in schizophrenia there is an increase in the activity of the dopamine system of the brain with an increase in the release of dopamine; dopamine agonists such as amphetamine can cause psychoses that are similar to paranoid schizophrenia. Psychomotor processes (exploratory behavior, motor skills) are closely related to dopamine metabolism.

4. Cholinergic neurons are widely distributed in the central nervous system, especially in the basal ganglia and brainstem. Cholinergic neurons are involved in mechanisms of selective attention to specific task and are important for learning and memory. Cholinergic neurons are involved in the pathogenesis of Alzheimer's disease.

One of components CNS is neuroglia(glial cells). It makes up almost 90% of NS cells and consists of two types: macroglia, represented by astrocytes, oligodendrocytes and ependymocytes, and microglia. Astrocytes– large stellate cells perform supporting and trophic (nutritional) functions. Astrocytes ensure the constancy of the ionic composition of the environment. Oligodendrocytes form the myelin sheath of the axons of the central nervous system. Oligodendrocytes outside the central nervous system are called Schwann cells, they take part in axon regeneration. Ependymocytes line the ventricles of the brain and the spinal canal (these are cavities filled with brain fluid, which is secreted by epidemiocytes). Cells microglia can transform into mobile forms, migrate throughout the central nervous system to the site of damage to nervous tissue and phagocytose decay products. Unlike neurons, Glial cells do not generate action potentials, but can influence excitation processes.

According to the histological principle in the structures of the NS it is possible to distinguish white And Gray matter. Gray matter- these are the cerebral cortex and cerebellum, various nuclei of the brain and spinal cord, peripheral (i.e. located outside the central nervous system) ganglia. Gray matter is formed by clusters of neuron cell bodies and their dendrites. It follows that it is responsible for reflex functions: perception and processing of incoming signals, as well as the formation of a response. The remaining structures of the nervous system are formed by white matter. White matter formed by myelinated axons (hence the color and name), the function of which is carrying out nerve impulses.

3. Features of the spread of excitation in the central nervous system

Excitation in the central nervous system is not only transmitted from one nerve cell to another, but is also characterized by a number of features. These are the convergence and divergence of neural pathways, the phenomena of irradiation, spatial and temporal facilitation and occlusion.

Divergence pathways are the contact of one neuron with many neurons of higher orders.

Thus, in vertebrates, there is a division of the axon of the sensitive neuron entering the spinal cord into many branches (collaterals), which are directed to different segments of the spinal cord and to different parts of the brain. Signal divergence is also observed in the output nerve cells. Thus, in humans, one motor neuron excites dozens muscle fibers(in the eye muscles) and even thousands of them (in the muscles of the limbs).

Numerous synaptic contacts of one axon of a nerve cell with a large number of dendrites of several neurons are the structural basis of the phenomenon irradiation excitation (expanding the scope of the signal). Irradiation happens directed, when excitation covers a certain group of neurons, and diffuse. An example of the latter is an increase in the excitability of one receptor site (for example, the right leg of a frog) upon irritation of another (painful effect on the left leg).

Convergence- this is the convergence of many nerve pathways to the same neurons. The most common in the central nervous system is multisensory convergence, which is characterized by the interaction on individual neurons of several afferent excitations of different sensory modalities (visual, auditory, tactile, temperature, etc.).

The convergence of many neural pathways to a single neuron makes that neuron integrator of the corresponding signals. If we're talking about O motor neuron, i.e. final link neural pathway to muscles, talk about common final path. The presence of convergence of multiple paths, i.e. nerve circuits, on one group of motor neurons underlies the phenomena of spatial facilitation and occlusion.

Spatial and temporal relief– this is the excess of the effect of the simultaneous action of several relatively weak (subthreshold) excitations over the sum of their separate effects. The phenomenon is explained by spatial and temporal summation.

Occlusion– this is the opposite phenomenon of spatial relief. Here, two strong (suprathreshold) excitations together cause an excitation of such strength that is less than the arithmetic sum of these excitations separately.

The reason for the occlusion is that these afferent inputs, due to convergence, partly excite the same structures and therefore each can create in them almost the same suprathreshold excitation as together.

Centers of the nervous system

A functionally connected set of neurons located in one or more structures of the central nervous system and providing the regulation of a particular function or the implementation of an integral reaction of the body is called center of the nervous system. Physiological concept of the nerve center differs from the anatomical concept of the nucleus, where closely located neurons are united by common morphological features.

Nerve endings are located everywhere human body. They have a vital function and are an integral part of the entire system. The structure of the human nervous system is a complex branched structure that runs through the entire body.

The physiology of the nervous system is a complex composite structure.

The neuron is considered the basic structural and functional unit of the nervous system. Its processes form fibers that are excited when exposed and transmit impulses. The impulses reach the centers where they are analyzed. Having analyzed the received signal, the brain transmits the necessary reaction to the stimulus to the appropriate organs or parts of the body. Nervous system a person is briefly described by the following functions:

providing reflexes;
regulation of internal organs;
ensuring the interaction of the body with the external environment, by adapting the body to changing external conditions and stimuli;
interaction of all organs.

The importance of the nervous system lies in ensuring the vital functions of all parts of the body, as well as the interaction of a person with the outside world. The structure and functions of the nervous system are studied by neurology.

Structure of the central nervous system

The anatomy of the central nervous system (CNS) is a collection of neuronal cells and neural processes of the spinal cord and brain. A neuron is a unit of the nervous system.

The function of the central nervous system is to ensure reflex activity and process impulses coming from the PNS.

Features of the structure of the PNS

Thanks to the PNS, the activity of the entire human body is regulated. The PNS consists of cranial and spinal neurons and fibers that form ganglia.

Its structure and functions are very complex, so any slightest damage, for example damage to blood vessels in the legs, can cause serious disruption to its functioning. Thanks to the PNS, all parts of the body are controlled and the vital functions of all organs are ensured. The importance of this nervous system for the body cannot be overestimated.

The PNS is divided into two divisions - the somatic and autonomic PNS systems.

Performs double work– collection of information from the senses, and further transmission of this data to the central nervous system, as well as providing motor activity body, by transmitting impulses from the central nervous system to the muscles. Thus, it is the somatic nervous system that is the instrument of human interaction with the outside world, as it processes signals received from the organs of vision, hearing and taste buds.

Ensures the performance of the functions of all organs. It controls the heartbeat, blood flow, respiratory activity. It contains only motor nerves that regulate muscle contraction.

To ensure the heartbeat and blood supply, the efforts of the person himself are not required - this is controlled by the vegetative part PNS. The principles of the structure and function of the PNS are studied in neurology.

Departments of the PNS

The PNS also consists of the afferent nervous system and the efferent division.

The afferent region is a collection of sensory fibers that process information from receptors and transmit it to the brain. The work of this department begins when the receptor is irritated due to any impact.

The efferent system differs in that it processes impulses transmitted from the brain to effectors, that is, muscles and glands.

One of the important parts vegetative department The PNS is the enteric nervous system. The enteric nervous system is formed from fibers located in the gastrointestinal tract and urinary tract. The enteric nervous system controls the motility of the small and large intestine. This section also regulates the secretions released in the gastrointestinal tract and provides local blood supply.

The importance of the nervous system is to ensure the functioning of internal organs, intellectual function, motor skills, sensitivity and reflex activity. The child’s central nervous system develops not only during the prenatal period, but also during the first year of life. The ontogeny of the nervous system begins from the first week after conception.

The basis for brain development is formed already in the third week after conception. The main functional nodes are identified by the third month of pregnancy. By this time, the hemispheres, trunk and spinal cord have already been formed. By the sixth month, the higher parts of the brain are already better developed than the spinal part.

By the time a baby is born, the brain is the most developed. The size of the brain in a newborn is approximately an eighth of the child’s weight and ranges from 400 g.

The activity of the central nervous system and PNS is greatly reduced in the first few days after birth. This may include an abundance of new irritating factors for the baby. This is how the plasticity of the nervous system manifests itself, that is, the ability of this structure to be rebuilt. As a rule, the increase in excitability occurs gradually, starting from the first seven days of life. The plasticity of the nervous system deteriorates with age.

Types of CNS

In the centers located in the cerebral cortex, two processes simultaneously interact - inhibition and excitation. The rate at which these states change determines the types of nervous system. While one part of the central nervous system is excited, another is slowed down. This determines the features intellectual activity, such as attention, memory, concentration.

Types of the nervous system describe the differences between the speed of inhibition and excitation of the central nervous system in different people.

People may differ in character and temperament, depending on the characteristics of the processes in the central nervous system. Its features include the speed of switching neurons from the process of inhibition to the process of excitation, and vice versa.

The types of nervous system are divided into four types.

The weak type, or melancholic, is considered the most predisposed to the occurrence of neurological and psycho-emotional disorders. It is characterized by slow processes of excitation and inhibition. The strong and unbalanced type is choleric. This type is distinguished by the predominance of excitation processes over inhibition processes.
Strong and agile - this is a type of sanguine person. All processes occurring in the cerebral cortex are strong and active. A strong but inert, or phlegmatic type, is characterized by a low speed of switching nervous processes.

The types of the nervous system are interconnected with temperaments, but these concepts should be distinguished, because temperament characterizes a set of psycho-emotional qualities, and the type of the central nervous system describes physiological characteristics processes occurring in the central nervous system.

CNS protection

The anatomy of the nervous system is very complex. The central nervous system and PNS suffer due to the effects of stress, overexertion and lack of nutrition. For the normal functioning of the central nervous system, vitamins, amino acids and minerals are necessary. Amino acids take part in brain function and are building material for neurons. Having figured out why and what vitamins and amino acids are needed for, it becomes clear how important it is to provide the body required quantity these substances. Glutamic acid, glycine and tyrosine are especially important for humans. The regimen for taking vitamin-mineral complexes for the prevention of diseases of the central nervous system and PNS is selected individually by the attending physician.

Damage to the bundles, congenital pathologies and abnormalities of brain development, as well as the action of infections and viruses - all this leads to disruption of the central nervous system and PNS and the development of various pathological conditions. Such pathologies can cause a number of very dangerous diseases - immobility, paresis, muscle atrophy, encephalitis and much more.

Malignant neoplasms in the brain or spinal cord lead to a number of neurological disorders. If you suspect cancer The central nervous system is prescribed an analysis - histology of the affected parts, that is, an examination of the composition of the tissue. A neuron, as part of a cell, can also mutate. Such mutations can be identified by histology. Histological analysis is carried out according to the doctor’s indications and consists of collecting the affected tissue and its further study. For benign formations, histology is also performed.

The human body contains many nerve endings, damage to which can cause a number of problems. Damage often leads to impaired mobility of a body part. For example, an injury to the hand can lead to pain in the fingers and impaired movement. Osteochondrosis of the spine can cause pain in the foot due to the fact that an irritated or compressed nerve sends pain impulses to receptors. If a foot hurts, people often look for the cause in long walking or injury, but pain syndrome may be caused by damage to the spine.

If you suspect damage to the PNS, as well as any related problems, you should be examined by a specialist.

As evolutionary complexity increases multicellular organisms, 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 had to appear along with the preservation and complexity of the mechanisms for regulating the functions of individual cells using signaling molecules. Adaptation of multicellular organisms to changes in the environment could be carried out on the condition that new regulatory mechanisms would be able to provide quick, adequate, targeted responses. These mechanisms must be able to remember and retrieve from the memory apparatus information about previous influences on the body, and also have other properties that ensure effective adaptive activity of the body. They became 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 activities of all organs and systems of the body in constant interaction with the external environment.

The central nervous system includes the brain and spinal cord. The brain is divided into the hindbrain (and pons), reticular formation, subcortical nuclei, . The bodies form the gray matter of the central nervous system, 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 (stimulants) of the external and internal environment of the body. Let us remember that any cells can perceive various signals from their environment with the help of specialized cellular receptors. However, they are not adapted to perceive a number of vital signals and cannot instantly transmit information to other cells, which function as regulators of the body’s holistic adequate reactions 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 changes, vibration, acceleration, compression, stretching), as well as signals of a complex nature (color, complex sounds, words).

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

Signals and the results of their analysis are used by the nervous system to organizing responses 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 responses to impacts 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, the nervous system performs the functions regulation of homeostasis, provision functional interaction organs and tissues and their integration into a single integral organism.

Thanks to the nervous system, adequate interaction of the body with the environment is carried out not only through the organization of responses by effector systems, but also through its own mental reactions - emotions, motivation, 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 cavity of the skull and spinal canal. The human brain contains more than 100 billion nerve cells (neurons). Clusters 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 central nervous system, and the processes of these cells, uniting into pathways, form the white matter. In addition, the structural part of the central nervous system are glial cells that form neuroglia. The number of glial cells is approximately 10 times the number of neurons, and these cells make up the majority of the mass of the central nervous system.

The nervous system, according to the characteristics of its functions and structure, is divided into somatic and autonomic (vegetative). The somatic includes the structures of the nervous system, which provide the perception of sensory signals mainly from the external environment through the sensory organs, and control the functioning of the striated (skeletal) muscles. The autonomic (autonomic) nervous system includes structures that ensure the perception of signals primarily from the internal environment of the body, regulate the functioning 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 on various levels, which are characterized by specific functions and roles in the regulation of life processes. Among them are the basal ganglia, brainstem structures, spinal cord, and peripheral nervous system.

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 that extend from the central nervous system to various organs.

Rice. 1. Structure of the nervous system

Rice. 2. Functional division of the nervous system

The meaning of the nervous system:

unites the organs and systems of the body into a single whole;
regulates the functioning of all organs and systems of the body;
communicates the organism with the external environment and adapts it 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 are highly branched and form many synapses with other cells, which determines their leading role in the neuron’s perception of information. The axon starts from the cell body with an axon hillock, which is a generator of a nerve impulse, which is then carried along the axon to other cells. The axon membrane at the synapse contains specific receptors that can respond to various mediators or neuromodulators. Therefore, the process of transmitter release by presynaptic endings can be influenced by other neurons. The terminal membrane also contains big number calcium channels through which calcium ions enter the terminal when it is excited and activate the release of the mediator.

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

Typically, 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 cell body.

Axons, in addition to their 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 axonal transport.

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

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

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

Neuroglial cells perform many functions: supporting, protective and trophic roles 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 ensured by the central nervous system.

Coordinating: functions various organs and body systems must proceed in harmony, since only with this method of life is it possible to maintain the constancy of the internal environment, as well as to successfully adapt to changing environmental conditions. The central nervous system coordinates the activities of the elements that make up the body.

Regulating: The central nervous system regulates all 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 and the intensity of metabolic processes in the tissues of the body, which underlies the formation of reactions adequate to the changes occurring in the internal and external environment.

Adaptive: The central nervous system communicates the body with the external environment by analyzing and synthesizing various information received from sensory systems. This makes it possible to restructure the activities of various organs and systems in accordance with changes in the environment. It functions as 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 the body, its systems, organs, tissues to changing environmental conditions is called regulation. Regulation provided jointly by the nervous and hormonal systems is called neurohormonal regulation. Thanks to the nervous system, the body carries out its activities according to the principle of reflex.

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

Reflex translated from Latin language means "reflection". The term “reflex” was first proposed by the Czech researcher I.G. Prokhaska, who developed the doctrine of reflective actions. The further development of reflex theory is associated with the name of I.M. Sechenov. He believed that everything unconscious and conscious occurs as a reflex. But at that time there were no methods for objectively assessing brain activity that could confirm this assumption. Later, an objective method for assessing brain activity was developed by Academician I.P. Pavlov, and it was called 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, formed on the basis of unconditioned reflexes due to the formation of temporary connections. Academician P.K. Anokhin showed that all the diversity 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 that ensure 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 based on the reflex principle. Reflex arc: 1 - receptor; 2 - afferent pathway; 3 - nerve center; 4 - efferent pathway; 5 - working organ (any organ of the body); MN - motor neuron; M - muscle; CN - command neuron; SN - sensory neuron, ModN - modulatory neuron

The dendrite of the receptor neuron contacts the receptor, its axon goes to the central nervous system and interacts with the interneuron. From the interneuron, the axon goes to the effector neuron, and its axon goes to the periphery to the executive organ. This is how a reflex arc is formed.

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

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

A 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 various parts of the central nervous system. The nerve center receives impulses from receptors along the afferent pathway, analyzes and synthesizes this information, then transmits the formed program of actions along the efferent fibers to the peripheral executive organ. And the working organ carries out its characteristic activity (the muscle contracts, the gland secretes secretions, 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 an acceptor of the action of the reverse afferentation 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 the 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. characteristic of all animals of this species. They are constant throughout life and arise in response to adequate stimulation of receptors. Unconditioned reflexes are classified according to biological significance: nutritional, defensive, sexual, locomotor, orientation. Based on the location of the receptors, these reflexes are divided into exteroceptive (temperature, tactile, visual, auditory, taste, etc.), interoceptive (vascular, cardiac, gastric, intestinal, etc.) and proprioceptive (muscle, tendon, etc.). Based on the nature of the response - motor, secretory, etc. Based on the location of the nerve centers through which the reflex is carried out - spinal, bulbar, mesencephalic.

Conditioned reflexes - reflexes acquired by an organism during 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 core modern ideas About the reflex activity of the body there 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 via a feedback link in the form of reverse afferentation, which is an obligatory component of reflex activity. The principle of reverse afferentation in reflex activity was developed by P.K. Anokhin and is based on the fact that the structural basis of the reflex is not a reflex arc, but a reflex ring, which includes the following links: receptor, afferent nerve pathway, nerve center, efferent nerve pathway, working organ , reverse afferentation.

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

Properties of nerve centers

Nerve centers have a number of characteristic functional properties.

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

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

A summation of excitations can occur in nerve centers.

There are two main methods of summation: temporal and spatial. At temporal summation several excitation impulses arrive at a neuron through one synapse, are summed up and generate an action potential in it, and spatial summation manifests itself when impulses arrive to one neuron through different synapses.

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

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

Nerve centers, unlike nerve fibers, are capable of rapid fatigue. Synaptic fatigue with 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 receipt 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 at synapses after brief stimulation of afferent pathways. At frequent use synapses, the synthesis of receptors and mediators is accelerated.

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

Coordination activity of the central nervous system and its principles

One of important functions The central nervous system is a coordination function, also called coordination activities CNS. It is understood as the regulation of the distribution of excitation and inhibition in neural structures, as well as the interaction between nerve centers that 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 breathing and swallowing, when during swallowing the breathing center is inhibited, the epiglottis closes the entrance to the larynx and prevents entry into Airways food or liquid. The coordination function of the central nervous system is fundamentally important for the implementation of complex movements carried out with the participation of many muscles. Examples of such movements include articulation of speech, the act of swallowing, and gymnastic movements that require the coordinated contraction and relaxation of many muscles.

Principles of coordination activities

Reciprocity - mutual inhibition of antagonistic groups of neurons (flexor and extensor motor neurons)
Final neuron - activation of an efferent neuron from various receptive fields and competition between various afferent impulses for a given motor neuron
Switching is the process of transferring activity from one nerve center to the antagonist nerve center
Induction - change from excitation to 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 a function
A dominant is 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.

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

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 carrying out the same reaction, triggered by the final efferent neuron in the hierarchical nerve chain, to which the axons of many other nerve cells converge. An example of a classic terminal pathway is the motor neurons of the anterior horns of the spinal cord or the motor nuclei of the cranial nerves, which directly innervate muscles with their axons. The same motor reaction (for example, bending an arm) can be triggered by the receipt of impulses to these neurons from 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 signals perceived by different sensory organs (light, sound, gravitational, pain or mechanical effects).

Divergence principle 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. Thanks to divergent connections, signals are widely distributed (irradiated) and many centers located on the same surface are quickly involved in the response. different levels CNS.

The principle of feedback (reverse afferentation) lies in the possibility of transmitting information about the reaction being performed (for example, about movement from muscle proprioceptors) via afferent fibers back to the nerve center that triggered it. Thanks to feedback, a closed neural chain (circuit) is formed, through which you can control the progress of the reaction, regulate the strength, duration and other parameters of the reaction, if they were not implemented.

The participation of feedback can be considered using the example of the implementation of the flexion reflex caused by mechanical action on skin receptors (Fig. 5). With a reflex contraction of the flexor muscle, the activity of proprioceptors and the frequency of sending nerve impulses along afferent fibers to the a-motoneurons of the spinal cord innervating this muscle changes. As a result, a closed regulatory loop is formed, in which the role of a feedback channel is played by afferent fibers, transmitting information about contraction to the nerve centers from muscle receptors, and the role of a direct communication channel is played by efferent fibers of motor neurons going to the muscles. Thus, the nerve center (its motor neurons) receives information about changes in the state of the muscle caused by the transmission of impulses along motor fibers. Thanks to 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 has 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 circuit in the neural circuits of the simplest reflexes

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

The principle of dominance is also implemented based on the peculiarities of interaction between nerve centers. The neurons of the dominant, most active center (focus of excitation) have persistently high activity and suppress excitation in other nerve centers, subordinating 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 remain in a state of excitement 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 a person has experienced an important event for him, when all his thoughts and actions in one way or another become associated with this event.

Properties of the dominant

Increased excitability
Excitation persistence
Excitation inertia
Ability to suppress subdominant lesions
Ability to sum up excitations

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

Ministry of Education of Ukraine

KhSPU im. G.S. Frying pan

Institute of Economics and Law

Correspondence Faculty "Legal Studies"

ABSTRACT

Subject: Nervous system .

Vikonav: student

Having verified:

Kharkiv 1999 r_k

STRUCTURE OF THE NERVOUS SYSTEM

The importance of the nervous system

The nervous system plays a critical role in regulating body functions. It ensures the coordinated functioning of cells, tissues, organs and their systems. In this case, the body functions as a single whole. Thanks to the nervous system, the body communicates with the external environment.

The activity of the nervous system underlies feelings, learning, memory, speech and thinking - mental processes, with the help of which a person not only learns environment, but can also actively change it.

Nervous tissue

The nervous system is formed by nervous tissue, which consists of neurons and small satellite cells.

Neurons – the main cells of the nervous tissue: they provide the functions of the nervous system.

Satellite cells surround neurons, providing nutrition, support and protective functions. There are approximately 10 times more satellite cells than neurons.

A neuron consists of a body and processes. There are two types of processes: dendrites And axons . The shoots can be long or short.

Most dendrites are short, highly branched processes. One neuron can have several of them. Nerve impulses travel along dendrites to the body of the nerve cell.

Axon - a long, most often slightly branched process along which impulses travel from the cell body. Each nerve cell has only 1 axon, the length of which can reach several tens of centimeters. Along the long processes of nerve cells, impulses in the body can be transmitted over long distances.

Long shoots are often covered with a sheath of fat-like substance white. Their accumulations in the central nervous system form white matter . Short processes and cell bodies of neurons do not have such a membrane. Their clusters form Gray matter .

Neurons vary in shape and function. Just neurons sensitive , transmit impulses from the sensory organs to the spinal cord and brain. The bodies of sensory neurons lie on the way to the central nervous system in the nerve ganglia. Nerve nodes are clusters of nerve cell bodies outside the central nervous system. Other neurons motor , transmit impulses from the spinal cord and brain to the muscles and internal organs. Communication between sensory and motor neurons occurs in the spinal cord and brain interneurons , whose bodies and processes do not extend beyond the brain. The spinal cord and brain are connected to all organs by nerves.

Nerves - accumulations of long processes of nerve cells covered with a membrane. Nerves made up of motor neuron axons are called motor nerves . Sensory nerves consist of dendrites of sensory neurons. Most nerves contain both axons and debris. Such nerves are called mixed. Through them, impulses travel in two directions - to the central nervous system and from it to the organs.

Divisions of the nervous system.

The nervous system consists of central and peripheral sections. Central department represented by the brain and spinal cord, protected by membranes made of connective tissue. TO peripheral department include nerves and ganglia.

The part of the nervous system that regulates the work of skeletal muscles is called somatic. Through the somatic nervous system, a person can control movements, voluntarily induce or stop them. The part of the nervous system that regulates the activity of internal organs is called autonomic. The work of the autonomic nervous system is not subject to human will. It is impossible, for example, to stop the heart at will, speed up the digestion process, or delay sweating.

The autonomic nervous system has two divisions: sympathetic and parasympathetic. Most internal organs are supplied by the nerves of these two sections. As a rule, they have opposite effects on organs. For example, sympathetic nerve strengthens and speeds up the work of the heart, and parasympathetic slows down and weakens it.

Reflex .

Reflex arc. The response to irritation of the body, carried out and controlled by the central nervous system, is called a reflex. The path along which nerve impulses are carried out during a reflex is called a reflex arc. The reflex arc consists of five parts: the receptor, the sensory pathway, the central nervous system region, the motor pathway and the working organ.

The reflex arc begins with a receptor. Each receptor perceives a specific stimulus: light, sound, touch, smell, temperature, etc. Receptors convert these stimuli into nerve impulses - signals from the nervous system. Nerve impulses are electrical in nature, spread along the membranes of the long processes of neurons and are the same in animals and humans. From the receptor, nerve impulses are transmitted along a sensitive pathway to the central nervous system. This path is formed by a sensory neuron. From the central nervous system, impulses travel along the motor pathway to the working organ. Most reflex arcs also include interneurons, which are located both in the spinal cord and in the brain.

Human reflexes are varied. Some of them are very simple. For example, withdrawing a hand in response to an injection or burn of the skin, sneezing when foreign particles enter the nasal cavity. During a reflex response, receptors in the working organs transmit signals to the central nervous system, which controls how effective the response is.

Thus, the principle of operation of the nervous system is reflex.

Structure of the spinal cord.

The spinal cord is located in the bony spinal canal. It looks like a long white cord with a diameter of about 1 cm. In the center of the spinal cord there is a narrow spinal canal filled cerebrospinal fluid. There are two deep longitudinal grooves on the anterior and posterior surfaces of the spinal cord. They divide it into right and left halves.

The central part of the spinal cord is formed by gray matter, which consists of interneurons and motor neurons. Surrounding the gray matter is white matter, formed by long processes of neurons. They run up or down along the spinal cord, forming ascending and descending pathways.

31 pairs of mixed spinal neurons depart from the spinal cord, each of which begins with two roots: anterior and posterior.

The dorsal roots are the axons of sensory neurons. The clusters of cell bodies of these neurons form the spinal ganglia. The anterior roots are the axons of motor neurons.

Functions of the spinal cord. The spinal cord performs 2 main functions: reflex and conduction.

The reflex function of the spinal cord provides movement. Reflex arcs pass through the spinal cord, which are associated with contraction of the skeletal muscles of the body (except for the muscles of the head).

The spinal cord, together with the brain, regulates the functioning of internal organs: heart, stomach, Bladder, genitals.

The white matter of the spinal cord provides communication and coordinated work of all parts of the central nervous system, performing a conductive function. Nerve impulses entering the spinal cord from receptors are transmitted along ascending pathways to the underlying parts of the spinal cord and from there to the organs.

The brain regulates the functioning of the spinal cord. There are cases when, as a result of an injury or fracture of the spine, the connection between the spinal cord and the brain is interrupted. The brain of such people functions normally. But most spinal reflexes, the centers of which are located below the site of injury, disappear. Such people can turn their heads, make chewing movements, change the direction of their gaze, and sometimes their hands work. In the same time Bottom part their bodies are devoid of sensitivity and motionless.

Brain.

The brain is located in the cranial cavity. It includes the following sections: medulla oblongata, pons, cerebellum, midbrain, diencephalon and cerebral hemispheres. The brain, like the spinal cord, contains white and gray matter. White matter forms pathways. They connect the brain with the spinal cord, as well as parts of the brain with each other. Thanks to the pathways, the entire central nervous system functions as a single whole. Gray matter in the form of separate clusters - nuclei - is located inside the white matter. In addition, the gray matter, covering the cerebral hemispheres and cerebellum, forms the cortex. Functions of parts of the brain. Medulla and the bridge are a continuation of the spinal cord and perform reflex and conductor functions. The nuclei of the medulla oblongata and pons regulate digestion, respiration, cardiac activity and other processes, so damage to the medulla oblongata and pons is life-threatening. These parts of the brain are associated with the regulation of chewing, swallowing, sucking, and defensive reflexes: vomiting, sneezing, coughing.

The cerebellum is located directly above the medulla oblongata. Its surface is formed by gray matter - the cortex, under which the white matter contains nuclei. The cerebellum is connected to many parts of the central nervous system. The cerebellum regulates motor acts. When the normal activity of the cerebellum is disrupted, people lose the ability to make precise coordinated movements and maintain body balance. Such people cannot, for example, thread a thread through a needle, their gait is unsteady and resembles the gait of a drunk, the movements of their arms and legs when walking are awkward, sometimes sharp, and sweeping.

In the midbrain there are nuclei that constantly send nerve impulses to the skeletal muscles, maintaining their tension - tone. In the midbrain there are reflex arcs of orienting reflexes to visual and sound stimuli. Indicative reflexes manifest themselves in turning the head and body in the direction of irritation.

The medulla oblongata, pons, and midbrain form the brainstem. 12 pairs of cranial nerves depart from it. Nerves connect the brain with the sensory organs, muscles and glands located on the head. One pair of nerves nervus vagus– connects the brain with internal organs: heart, lungs, stomach, intestines, etc.

Through the diencephalon, impulses arrive to the cerebral cortex from all receptors. Most of complex motor reflexes, such as walking, running, swimming, are associated with the diencephalon. The diencephalon regulates metabolism, food and water consumption, maintenance constant temperature bodies. Neurons of some diencephalon nuclei produce biological substances, carrying out humoral regulation.

The structure of the cerebral hemispheres. In humans, the highly developed cerebral hemispheres (right and left) cover the midbrain and diencephalon. The surface of the cerebral hemispheres is formed by gray matter - the cortex. Under the cortex there is white matter, in the thickness of which the subcortical nuclei are located. The surface of the hemispheres is folded. The grooves and convolutions increase the surface area of the cortex to an average of 2000 - 5000 cm. More than 2/3 of the surface area of the cortex is hidden in the grooves. There are about 14 billion neurons in the cerebral cortex. Each hemisphere is divided by grooves into the frontal, parietal, temporal and occipital lobes. The deepest grooves are the central one, separating frontal lobe from the parietal, and lateral, delimiting the temporal lobe.

The significance of the cerebral cortex. The cerebral cortex is divided into sensory and motor areas. Sensitive areas receive impulses from sensory organs, skin, internal organs, muscles, tendons. When neurons are excited sensitive areas sensations arise. The visual area is located in the occipital lobe cortex. Normal vision is possible when this area of the cortex is intact. The auditory zone is located in the temporal zone. When it is damaged, a person ceases to distinguish sounds. In the area of the cortex behind the central sulcus there is a zone of musculocutaneous sensitivity. In addition, zones of taste and olfactory sensitivity are distinguished in the cerebral cortex. In front of the central sulcus is the motor cortex. Excitation of neurons in this zone ensures voluntary human movements. The cortex functions as a single whole and is the material basis of human mental activity. Specific mental functions such as memory, speech, thinking and behavior regulation are associated with the cerebral cortex.

GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM

Functions of the nervous system

Centers of the nervous system

Inhibition processes in the central nervous system

Reflex and reflex arc. Types of reflex

Functions and parts of the nervous system

The body is a complex, highly organized system consisting of functionally interconnected cells, tissues, organs and their systems. Management of their functions, as well as their integration (interconnection), ensures nervous system. The NS also communicates the body with the external environment by analyzing and synthesizing various information received from receptors. It provides movement and functions as a regulator of behavior necessary in specific conditions of existence. This ensures adequate adaptation to the surrounding world. In addition, the processes underlying human mental activity (attention, memory, emotions, thinking, etc.) are associated with the functions of the central nervous system.

Thus, nervous system functions:

Regulates all processes occurring in the body;

Carries out the relationship (integration) of cells, tissues, organs and systems;

Performs analysis and synthesis of information entering the body;

Regulates behavior;

Provides processes underlying human mental activity.

By functional principle the nervous system is divided into somatic And vegetative. The somatic nervous system provides innervation mainly to the organs of the body (soma) - skeletal muscles, skin, etc. This part of the nervous system connects the body with the external environment through the senses and provides movement. The autonomic nervous system innervates internal organs, blood vessels, glands, including endocrine glands, smooth muscles, and regulates metabolic processes in all organs and tissues. The autonomic nervous system includes sympathetic, parasympathetic And metasympathetic departments.

2. Structural and functional elements of the NS

The main structural and functional unit of the NS is neuron with its branches. Their functions are to perceive information from the periphery or from other neurons, process it and transmit it to neighboring neurons or executive organs. In a neuron there are body (soma) And shoots (dendrites And axon). Dendrites are numerous highly branched protoplasmic projections near the soma, through which excitation is conducted to the body of the neuron. Their initial segments have a larger diameter and lack spines (cytoplasmic outgrowths). An axon is the only axial-cylindrical process of a neuron, having a length from several microns to 1 m, the diameter of which is relatively constant throughout its entire length. The terminal sections of the axon are divided into terminal branches, through which excitation is transmitted from the neuron body to another neuron or working organ.

The integration of neurons into the nervous system occurs through interneuronal synapses.

Neuron functions:

1. Perception of information (dendrites and neuron body).

3. Synthesis of biologically active substances (neuron body and synaptic endings).

4. Generation of electrical impulses (axon hillock - axon base).

5. Axonal transport and conduction of excitation (axon).

6. Transmission of excitations (synaptic endings).

There are several neuron classifications. According to morphological classification neurons are distinguished by the shape of the soma. There are granular neurons, pyramidal neurons, stellate neurons, etc. Based on the number of neurons extending from the body, processes are divided into unipolar neurons (one process), pseudounipolar neurons (T-shaped branching process), bipolar neurons (two processes), multipolar neurons (one axon and many dendrites).

Functional classification neurons is based on the nature of the function they perform. Highlight afferent (sensitive, receptor) neurons (pseudounipolar), efferent (motor neurons, motor) neurons (multipolar) and associative (insertion, interneurons) neurons (mostly multipolar). Biochemical classification of neurons is carried out taking into account the nature of the produced mediator. Based on this, they distinguish cholinergic(mediator acetylcholine), monoaminergic(adrenaline, norepinephrine, serotonin, dopamine), GABAergic(gamma-aminobutyric acid), peptidergic(substance P, enkephalins, endorphins, other neuropeptides), etc.

One of the components of the central nervous system is neuroglia(glial cells). It makes up almost 90% of NS cells and consists of two types: macroglia, represented by astrocytes, oligodendrocytes and ependymocytes, and microglia. Astrocytes– large stellate cells perform supporting and trophic (nutritional) functions. Astrocytes ensure the constancy of the ionic composition of the environment. Oligodendrocytes form the myelin sheath of the axons of the central nervous system. Oligodendrocytes outside the central nervous system are called Schwann cells, they take part in axon regeneration. Ependymocytes line the ventricles of the brain and the spinal canal (these are cavities filled with brain fluid, which is secreted by epidemiocytes). Cells microglia can transform into mobile forms, migrate throughout the central nervous system to the site of damage to nervous tissue and phagocytose decay products. Unlike neurons, Glial cells do not generate action potentials, but can influence excitation processes.

According to the histological principle in the structures of the NS it is possible to distinguish white And Gray matter. Gray matter– these are the cerebral cortex and cerebellum, various nuclei of the brain and spinal cord, peripheral (i.e. located outside the central nervous system) ganglia. Gray matter is formed by clusters of neuron cell bodies and their dendrites. It follows that it is responsible for reflex functions: perception and processing of incoming signals, as well as the formation of a response. The remaining structures of the nervous system are formed by white matter. White matter formed by myelinated axons (hence the color and name), the function of which is carrying out nerve impulses.

3. Features of the spread of excitation in the central nervous system

Divergence pathways are the contact of one neuron with many neurons of higher orders.

Thus, in vertebrates, there is a division of the axon of the sensitive neuron entering the spinal cord into many branches (collaterals), which are directed to different segments of the spinal cord and to different parts of the brain. Signal divergence is also observed in the output nerve cells. Thus, in humans, one motor neuron excites dozens of muscle fibers (in the eye muscles) and even thousands of them (in the muscles of the limbs).

The convergence of many neural pathways to a single neuron makes that neuron integrator of the corresponding signals. If we are talking about motor neuron, i.e. the final link of the nervous path to the muscles, they speak of common final path. The presence of convergence of multiple paths, i.e. nerve circuits, on one group of motor neurons underlies the phenomena of spatial facilitation and occlusion.

Centers of the nervous system

Structure and functions of the human nervous system. General structure of the nervous system

Structure of the central nervous system

Features of the structure of the PNS

Departments of the PNS

Types of CNS

CNS protection

General characteristics of the nervous system

Structure of the nervous system

Structure of the nervous system

Functions of the central nervous system

Reflex regulation of nervous activity

Properties of nerve centers

Coordination activity of the central nervous system and its principles

Principles of coordination activities

ABSTRACT

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