a set of nervous formations in vertebrates and humans, through which the perception of stimuli acting on the body, the processing of the resulting excitation impulses, and the formation of responses are realized. Thanks to it, the functioning of the body as a whole is ensured:
1) contacts with the outside world;
2) implementation of goals;
3) coordination of the work of internal organs;
4) holistic adaptation of the body.
The neuron is the main structural and functional element of the nervous system. Stand out:
1) the central nervous system - which consists of the brain and spinal cord;
2) the peripheral nervous system - which consists of nerves extending from the brain and spinal cord, from the intervertebral nerve nodes, as well as from the peripheral part of the autonomic nervous system;
3) vegetative nervous system - structures of the nervous system that provide control of the vegetative functions of the body.
NERVOUS SYSTEM
English nervous system) - a set of nervous formations in the human body and vertebrates. Its main functions: 1) providing contacts with the outside world (perceiving information, organizing the body's reactions - from simple responses to stimuli to complex behavioral acts); 2) realization of a person’s goals and intentions; 3) integration of internal organs into systems, coordination and regulation of their activities (see Homeostasis); 4) organization of the holistic functioning and development of the body.
The structural and functional element of N. s. is a neuron - a nerve cell consisting of a body, dendrites (the receptor and integrating apparatus of the neuron) and an axon (its efferent part). At the terminal branches of the axon there are special formations that contact the body and dendrites of other neurons - synapses. There are 2 types of synapses - excitatory and inhibitory; with their help, the transmission or blocking of an impulse message passing through the fiber to the destination neuron occurs, respectively.
The interaction of postsynaptic excitatory and inhibitory effects on one neuron creates a multi-conditional response of the cell, which is the simplest element of integration. Neurons, differentiated by structure and function, are combined into neural modules (neural ensembles) - trace. a stage of integration that ensures high plasticity in the organization of brain functions (see Plasticity n.s.).
N. s. divided into central and peripheral. Ts.n. With. consists of the brain, which is located in the cranial cavity, and the spinal cord, located in the spine. The brain, especially its cortex, is the most important organ of mental activity. The spinal cord carries out g.o. innate forms of behavior. Peripheral N. s. consists of nerves extending from the brain and spinal cord (the so-called cranial and spinal nerves), intervertebral nerve nodes, as well as from the peripheral part of the autonomic N. s. - accumulations of nerve cells (ganglia) with nerves approaching them (preganglionic) and extending from them (postganglionic).
The control of the vegetative functions of the body (digestion, blood circulation, breathing, metabolism, etc.) is carried out by the vegetative nervous system, which is divided into sympathetic and parasympathetic departments: the 1st department mobilizes the functions of the body in a state of increased mental stress, the 2nd - ensures the functioning of internal organs under normal conditions. Si. Brain blocks, Deep brain structures, Cerebral cortex, Neuron detector, Properties of n. With. (N.V. Dubrovinskaya, D.A. Farber.)
NERVOUS SYSTEM
nervous system) - a set of anatomical structures formed by nervous tissue. The nervous system consists of many neurons that transmit information in the form of nerve impulses to various parts of the body and receive it from them to maintain the active functioning of the body. The nervous system is divided into central and peripheral. The brain and spinal cord form the central nervous system; The peripheral includes paired spinal and cranial nerves with their roots, their branches, nerve endings and ganglia. There is another classification, according to which the unified nervous system is also conventionally divided into two parts: somatic (animal) and autonomic (autonomic). The somatic nervous system innervates mainly the organs of the soma (body, striated or skeletal muscles, skin) and some internal organs (tongue, larynx, pharynx), and ensures communication of the body with the external environment. The autonomic (autonomic) nervous system innervates all the internal organs, glands, including endocrine ones, smooth muscle organs and skin, blood vessels and heart, regulates metabolic processes in all organs and tissues. The autonomic nervous system, in turn, is divided into two parts: parasympathetic and sympathetic. In each of them, as in the somatic nervous system, there are central and peripheral sections (ed.). The main structural and functional unit nervous system is a neuron (nerve cell).
Nervous system
Word formation. Comes from the Greek. neuron - vein, nerve and systema - connection.
Specificity. Its work ensures:
Contacts with the outside world;
Realization of goals;
Coordination of the work of internal organs;
Holistic adaptation of the body.
The neuron is the main structural and functional element of the nervous system.
The central nervous system, which consists of the brain and spinal cord,
Peripheral nervous system, consisting of nerves extending from the brain and spinal cord, intervertebral nerve ganglia;
Peripheral division of the autonomic nervous system.
NERVOUS SYSTEM
A collective designation for the complete system of structures and organs consisting of nervous tissue. Depending on what is the focus of attention, different schemes for highlighting parts of the nervous system are used. The most common anatomical division is the central nervous system (brain and spinal cord) and the peripheral nervous system (everything else). Another taxonomy is based on function, dividing the nervous system into the somatic nervous system and the autonomic nervous system, the former for voluntary, conscious sensory and motor functions, and the latter for visceral, automatic, involuntary functions.
Source: Nervous system
A system that ensures the integration of the functions of all organs and tissues, their trophism, communication with the outside world, sensitivity, movement, consciousness, alternation of wakefulness and sleep, the state of emotional and mental processes, including manifestations of higher nervous activity, the development of which determines the characteristics of a person’s personality. S.Sc. is divided primarily into central, represented by brain tissue (brain and spinal cord), and peripheral, which includes all other structures of the nervous system.
With the evolutionary complexity of multicellular organisms and 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 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 cranial cavity 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 at different 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. 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. 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 transport 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.
According to their 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: the functions of various organs and systems of the body 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 conditions environment. 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 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 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 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 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 effects of various chemical substances.
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. With frequent use of synapses, the synthesis of receptors and transmitters is accelerated.
Along with excitation, inhibition processes occur in the nerve center.
Coordination activity of the central nervous system 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 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 food or liquid from entering the respiratory tract. The coordination function of the central nervous system is fundamentally important for the implementation 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 sensory 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 at different levels of the central nervous system are quickly involved in the response.
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 change. As a result, it is formed closed loop regulation, in which the role of a feedback channel is played by afferent fibers that transmit 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.
The nervous system is the center of nerve communications and the body's most important regulatory system: it organizes and coordinates vital actions. But it has only two main functions: stimulating muscles for movement and regulating the functioning of the body, as well as the endocrine system.
The nervous system is divided into the central nervous system and the peripheral nervous system.
From a functional point of view, the nervous system can be divided into somatic (controlling voluntary actions) and autonomic or autonomic (coordinating involuntary actions) systems.
central nervous system
Includes the spinal cord and brain. Here the cognitive and emotional functions of a person are coordinated. From here all movements are controlled and the weight of feeling is developed.
Brain
In an adult, the brain is one of the heaviest organs in the body, weighing approximately 1300 g.
It is the center of interaction of the nervous system, and its main function is to transmit and respond to received nerve impulses. In its various areas it acts as a mediator of respiratory processes, solving specific problems and hunger.
The brain is divided structurally and functionally into several main parts:
Spinal cord
It is located in the spinal canal and is surrounded by meninges that protect it from injury. In an adult, the length of the spinal cord reaches 42-45 cm and extends from the elongated brain (or the inner part of the brain stem) to the second lumbar vertebra and has a different diameter in different parts of the spine.
31 pairs of peripheral spinal nerves depart from the spinal cord, which connect it to the entire body. Its most important function is to connect various parts of the body to the brain.
Both the brain and spinal cord are protected by three layers of connective tissue. Between the most superficial and middle layers there is a cavity where fluid circulates, which, in addition to protection, also nourishes and cleanses nerve tissue.
Peripheral nervous system
Consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves. It constitutes an intricate network that forms nervous tissue that is not part of the central nervous system and is represented mainly by peripheral nerves responsible for muscles and internal organs.
Cranial nerves
12 pairs of cranial nerves arise from the brain and pass through the openings of the skull.
All cranial nerves are found in the head and neck, with the exception of the tenth nerve (vagus), which also involves various structures of the chest and stomach.
Spinal nerves
Each of the 31 pairs of nerves originate in the dorsal M03IC and then pass through the intervertebral foramina. Their names are associated with the place where they originate: 8 cervical, 12 thoracic, 5 lumbar, 5 cruciate and 1 coccygeal. After passing through the intervertebral foramen, each branch is divided into 2 branches: the anterior, large one, which stretches into the distance to cover the muscles and skin on the front and sides and the skin of the extremities, and the posterior, smaller one, which covers the muscles and skin of the back. The thoracic spinal nerves also communicate with the sympathetic part of the autonomic nervous system. At the top of the neck, the roots of these nerves are very short and located horizontally.
Nervous system(sustema nervosum) is a complex of anatomical structures that ensure the individual adaptation of the body to the external environment and the regulation of the activity of individual organs and tissues.
Only a biological system can exist that is capable of acting in accordance with external conditions in close connection with the capabilities of the organism itself. It is this single goal - the establishment of behavior and state of the organism that is adequate to the environment - that the functions of individual systems and organs at each moment of time are subordinated to. In this regard, the biological system acts as a single whole.
The nervous system, together with the endocrine glands, is the main integrating and coordinating apparatus, which, on the one hand, ensures the integrity of the body, and on the other, its behavior adequate to the external environment.
The nervous system includes the brain and spinal cord, as well as nerves, ganglia, plexuses, etc. All these formations are predominantly built from nervous tissue, which:
- capable get excited under the influence of irritation from the environment internal or external to the body and
- excite in the form of a nerve impulse to various nerve centers for analysis, and then
- transmit the “order” developed at the center executive bodies
to perform a response of the body in the form of movement (movement in space) or changes in the function of internal organs.
Brain- part of the central system located inside the skull. Consists of a number of organs: the cerebrum, cerebellum, brainstem and medulla oblongata.
Spinal cord– forms the distribution network of the central nervous system. Lies inside spinal column, and all the nerves that form the peripheral nervous system depart from it.
Peripheral nerves- are bundles or groups of fibers that transmit nerve impulses. They can be ascending, if they transmit sensations from the whole body to the central nervous system, and descending, or motor, if they convey commands from the nerve centers to all parts of the body.
The human nervous system is classified
According to the conditions of formation and type of management as:
- Lower nervous activity
- Higher nervous activity
According to the method of transmitting information as:
- Neurohumoral regulation
- Reflex regulation
By area of localization as:
- Central nervous system
- Peripheral nervous system
By functional affiliation as:
- Autonomic nervous system
- Somatic nervous system
- Sympathetic nervous system
- Parasympathetic nervous system
central nervous system(CNS) includes those parts of the nervous system that lie within the skull or spinal column. The brain is a part of the central nervous system enclosed in the cranial cavity.
The second major section of the central nervous system is the spinal cord. Nerves enter and exit the central nervous system. If these nerves lie outside the skull or spine, they become part of peripheral nervous system. Some components of the peripheral system have very distant connections with the central nervous system; many scientists even believe that they can function with very limited control from the central nervous system. These components, which appear to operate independently, constitute an autonomous, or autonomic nervous system, which will be discussed in subsequent chapters. Now it is enough for us to know that the autonomic system is mainly responsible for regulating the internal environment: it controls the functioning of the heart, lungs, blood vessels and other internal organs. The digestive tract has its own internal autonomic system, consisting of diffuse nerve networks.
The anatomical and functional unit of the nervous system is the nerve cell - neuron. Neurons have processes with which they connect with each other and with innervated formations (muscle fibers, blood vessels, glands). The processes of a nerve cell are functionally unequal: some of them conduct stimulation to the neuron body - this is dendrites, and only one shoot - axon- from the nerve cell body to other neurons or organs.
The processes of neurons are surrounded by membranes and combined into bundles, which form nerves. The membranes isolate the processes of different neurons from each other and contribute to the conduction of excitation. The sheathed processes of nerve cells are called nerve fibers. The number of nerve fibers in different nerves ranges from 102 to 105. Most nerves contain processes of both sensory and motor neurons. Interneurons are predominantly located in the spinal cord and brain, their processes form the pathways of the central nervous system.
Most nerves in the human body are mixed, meaning they contain both sensory and motor nerve fibers. That is why, when nerves are damaged, sensory disorders are almost always combined with motor disorders.
Irritation is perceived by the nervous system through the sense organs (eye, ear, organs of smell and taste) and special sensitive nerve endings - receptors located in the skin, internal organs, blood vessels, skeletal muscles and joints.
The nervous system consists of the spinal cord, brain, sensory organs, and all the nerve cells that connect these organs to the rest of the body. Together, these organs are responsible for controlling the body and communicating between its parts. The brain and spinal cord form a control center known as the central nervous system (CNS), where information is evaluated and decisions are made. The sensory nerves and sensory organs of the peripheral nervous system (PNS) monitor... [Read below]
[Start at the top] ... conditions inside and outside the body and send this information to the central nervous system. Efferent nerves in the PNS carry signals from the control center to muscles, glands, and organs to regulate their functions.
Nervous tissue
Most tissues of the nervous system are composed of two classes of cells: neurons and neuroglia.
Neurons, also known as nerve cells, communicate in the body through the transmission of electrochemical signals. Neurons are quite different from other cells in the body due to the many complex cellular processes that occur in their central body. The cell body is the roughly circular part of the neuron that contains the nucleus, mitochondria, and most of the cell's organelles. Small tree-like structures called dendrites extend from the cell body to receive stimuli from the environment, these are called receptors. Transmitting nerve cells are called axons, they extend from the cell body to send signals forward to other neurons or effector cells in the body.
There are 3 main classes of neurons: afferent neurons, efferent neurons and interneurons.
Afferent neurons. Also known as sensory neurons, they transmit afferent sensory signals to the central nervous system from receptors in the body.
Efferent neurons. Also known as motor neurons, efferent neurons carry signals from the central nervous system to effectors in the body such as muscles and glands.
Interneurons. Interneurons form complex networks in the central nervous system to integrate information received from afferent neurons and direct body function through efferent neurons.
Neuroglia. Neuroglia, also known as glial cells, act as the “messenger” of cells in the nervous system. Each neuron in the body is surrounded by anywhere from 6 to 60 neuroglia, which protect, nourish and insulate the neuron. Because neurons are extremely specialized cells that are essential to the body's functioning and almost never reproduce, neuroglia are vital to maintaining a functional nervous system.
Brain
The brain, a soft, wrinkled organ that weighs about 1.2 kg, is located inside the cranial cavity, where the bones of the skull surround and protect it. Approximately 100 billion neurons in the brain form main center body control. The brain and spinal cord together form the central nervous system (CNS), where information is processed and responses are generated. The brain is the seat of higher mental functions such as consciousness, memory, planning and voluntary action, and it also controls lower body functions such as maintaining breathing, heart rate, blood pressure and digestion.
Spinal cord
It is a long, thin mass of grouped neurons that carry information, located in the spinal cavity. Beginning in the medulla oblongata at its upper end and continuing downward in the lumbar region of the spine. In the lumbar region, the spinal cord divides into a bundle of individual nerves called the cauda equina (due to its resemblance to a horse's tail), which continues down to the sacrum and coccyx. The white matter of the spinal cord acts as the main conduit for nerve signals from the brain to the body. The gray matter of the spinal cord integrates reflexes to stimuli.
Nerves
Nerves are bundles of axons in the peripheral nervous system (PNS) that act as information conduits for transmitting signals between the brain and spinal cord, as well as the rest of the body. Each axon wrapped in a sheath of connective tissue is called an endoneuritis. Individual axons, grouped into groups of axons, the so-called fascicles, are wrapped in a sheath of connective tissue and are called perineurium. Finally, many fascicles are packed together into another layer of connective tissue called the epineurium to form the entire nerve. The covering of connective tissue that wraps nerves helps protect axons and increase the speed at which they are transmitted within the body.
Afferent, efferent and mixed nerves.
Some of the nerves in the body are specialized to carry information in only one direction, similar to a one-way street. Nerves that carry information from sensory receptors only to the central nervous system are called afferent neurons. Other neurons, known as efferent neurons, carry signals only from the central nervous system to effectors such as muscles and glands. Finally, some nerves - mixed type, which contain both afferent and efferent axons. Mixed nerve functions are like 2 one-way streets, where afferent axons act as a lane to the central nervous system, and efferent axons act as a lane away from the central nervous system.
Cranial nerves.
Extend from bottom side brain has 12 pairs of cranial nerves. Each pair of cranial nerves is identified by a Roman numeral from 1 to 12, based on its location along the anterior-posterior axis of the brain. Each nerve also has a descriptive name (eg, olfactory, optic, etc.) that identifies its function or location. Cranial nerves provide direct connections to the brain for special sensory organs, muscles of the head, neck and shoulders, heart and gastrointestinal tract.
Spinal nerves.
There are 31 pairs of spinal nerves located on the left and right sides of the spinal cord. Spinal nerves are mixed nerves that carry both sensory and motor signals between the spinal cord and specific areas of the body. The 31 pairs of nerves in the spinal cord are divided into 5 groups, named after the 5 regions of the spinal column. Thus, there are 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves and 1 pair of coccygeal nerves. A separate spinal nerve exits the spinal cord through the intervertebral foramina between a pair of vertebrae or between the C1 vertebra and the occipital bone of the skull.
Meninges
The meninges are the protective covering of the central nervous system (CNS). It consists of three layers: the dura mater, the arachnoid mater and the pia mater.
Hard shell.
This is the thickest, toughest and most superficial layer of the shell. Made from dense, irregular connective tissue, it contains many tough collagen fibers and blood vessels. The dura mater protects the central nervous system from external damage, contains cerebrospinal fluid, which surrounds the central nervous system and supplies blood to the nervous tissue of the central nervous system.
Cobweb matter.
Much thinner than the dura mater. It lines the dura mater inside and contains many thin fibers that connect it to the main pia mater. These fibers traverse a fluid-filled space called the subarachnoid space between the arachnoid membrane and the pia mater.
The proper functioning of the nervous system is affected by both physical and psychological stress, so it is important to periodically relieve tension arising from stressful situations. One way to unload is to change from a bad to a good mood, for example, when viewing entertainment sites.
Pia materia.
The pia mater is a thin and very thin layer of tissue that lies on the outside of the brain and spinal cord. Contains many blood vessels that nourish the nervous tissue of the central nervous system. The pia mater penetrates into the valleys of the sulci and fissures of the brain, as it covers the entire surface of the central nervous system.
Cerebrospinal fluid
The space surrounding the organs of the central nervous system is filled with a clear fluid known as cerebrospinal fluid (CSF). It is formed from blood plasma with the help of special structures called the choroid plexus. The choroid plexus contains many capillaries lined with epithelial tissue that filters blood plasma and allows filtered fluid to enter the space around the brain.
The newly created CSF flows through the inside of the brain in hollow spaces called ventricles and through a small cavity in the middle of the spinal cord called the central canal. It also flows through the subarachnoid space around outside brain and spinal cord. CSF is continually produced in the choroid plexus and is reabsorbed into the blood in structures called arachnoid villi.
Cerebrospinal fluid provides several vital functions of the central nervous system:
It absorbs shock between the brain and skull, and between the spinal cord and vertebrae. This shock absorption protects the central nervous system from shocks or sudden changes in speed, such as during a car accident.
CSF reduces the mass of the brain and spinal cord due to buoyancy. The brain is a very large but soft organ that requires a large volume of blood to function effectively. The reduced weight in the cerebrospinal fluid allows the brain's blood vessels to remain open and helps protect nerve tissue from the fate of being crushed under its own weight.
It also helps maintain chemical homeostasis in the central nervous system. Since it contains ions, nutrients, oxygen and albumin, which maintain the chemical and osmotic balance of nervous tissue. CSF also removes waste products that are formed as by-products of cellular metabolism within nerve tissue.
Sense organs
All sense organs are components of the nervous system. Special sensory organs, taste, smell, hearing and balance are known, and specialized organs such as eyes, taste buds and olfactory epithelium have been discovered. Sensory receptors for common senses like touch, temperature and pain are found throughout most of the body. All sensory receptors in the body are connected to afferent neurons, which carry their sensory information to the central nervous system to be processed and integrated.
Functions of the nervous system
It has three main functions: sensory, connective (conductive) and motor.
Sensory.
The sensory function of the nervous system involves collecting information from sensory receptors that control the internal and external conditions of the body. These signals are then transmitted to the central nervous system (CNS) for further processing by afferent neurons (and nerves).
Integration.
Integration is the processing of multiple sensory signals that are transmitted to the central nervous system at any given time. These signals are processed, compared, used to make decisions, discarded, or stored in memory as deemed appropriate. Integration occurs in the gray matter of the brain and spinal cord and is carried out by interneurons. Many interneurons work together to form complex networks that provide this processing power.
Motor function. After networks of interneurons in the CNS evaluate sensory information and decide on action, they stimulate efferent neurons. Efferent neurons (also called motor neurons) carry signals from the gray matter of the central nervous system through the nerves of the peripheral nervous system to effector cells. The effector may be cardiac or skeletal muscle tissue or glandular tissue. The effector then releases a hormone or moves a body part to respond to the stimulus.
Divisions of the nervous system
CNS - central
The spinal cord and brain together form the central nervous system, or CNS. The CNS acts as the body's control center, providing its processing, memory and regulatory systems. The central nervous system is involved in all conscious and subconscious collection of sensory information from the body's sensory receptors in order to remain aware of the body's internal and external conditions. Using this sensory information, it makes decisions about what conscious and subconscious actions to take to maintain the body's homeostasis and ensure its survival. The CNS is also responsible for higher nervous system functions such as language, creativity, expression, emotion, and personality. The brain is the seat of consciousness and determines who we are as people.
Peripheral nervous system
It (PNS) includes all parts of the nervous system outside the brain and spinal cord. These parts include all the cranial and spinal nerves, ganglia and sensory receptors.
Somatic nervous system
The SNS is a division of the PNS that includes all free efferent neurons. The SNS is the only consciously controlled part of the PNS and is responsible for stimulating the skeletal muscles in the body.
Autonomic nervous system
The ANS is a division of the PNS that includes all involuntary efferent neurons. It controls subconscious effectors such as visceral muscle tissue, cardiac muscle tissue and glandular tissue.
There are 2 divisions of the autonomic nervous system in the body: the sympathetic and parasympathetic divisions.
Sympathetic.
The sympathetic division forms the body's "fight or flight" response to stress, danger, excitement, physical exercise, emotions and embarrassment. The sympathetic division increases breathing and heart rate, releases adrenaline and other stress hormones, and decreases digestion to cope with these situations.
Parasympathetic.
The parasympathetic region produces a rest response when the body is relaxed or at rest. The parasympathetic division works to override the sympathetic division after a stressful situation. Other functions of the parasympathetic division include decreasing breathing and heart rate, increasing digestion, and allowing the elimination of waste.
Enteric nervous system
The ENS is a division of the ANS that is responsible for regulating digestion and the functions of the digestive organs.
The ENS receives signals from the central nervous system through the sympathetic and parasympathetic divisions of the ANS system to help regulate its functions. However, the ENS generally operates independently of the central nervous system and continues to function without any external influence. For this reason, the ENS is often called the "second brain." The ENS is a huge system; there are almost as many neurons in the ENS as there are in the spinal cord.
Action potentials
Neurons function through the generation and propagation of electrochemical signals known as action potentials (APs). The hotspot is created by the movement of sodium and potassium ions across the neuronal membrane.
Resting potential.
At rest, neurons maintain the concentration of sodium ions regardless of the concentration of potassium ions inside the cell. This concentration is maintained by the cell membrane's sodium-potassium pump, which forces 3 sodium ions out of the cell for every 2 potassium ions entering the chamber. The ion concentration results in a residual electrical potential of 70 millivolts (mV), which means that there is a negative charge inside the cell compared to the surrounding environment.
Threshold potential.
If the signal allows enough positive ions to accumulate to enter the cell region and cause it to reach -55 mV, then the cell region will allow sodium ions to diffuse into the cell. - 55 MV threshold potential for neurons, as this is the “trigger” voltage they must reach to cross the threshold in forming an action potential.
Depolarization.
Sodium carries a positive charge, which causes the cell to depolarize from its normal negative charge. The voltage to depolarize all neurons is +30 mV. Depolarization of the cell is the access point that is transmitted along the neuron as a nerve signal. Positive ions spread to neighboring regions of the cell, initiating a new hotspot in those regions where they reach -55 mV. The impulse continues to travel down the neuron's cell membrane until it reaches the end of the axon.
Repolarization.
Once the depolarization voltage of +30 mV is reached, voltage-gated potassium ion channels become open, allowing positive potassium ions to diffuse out of the cell. The loss of potassium along with the pumping of sodium ions back out of the chamber through the sodium-potassium pump restores the cell to a resting potential of -55 mV. At this point, the neuron is ready to begin a new action potential.
Synapse
A synapse is a node between a neuron and another cell. Synapses can form between 2 neurons or between a neuron and an effector cell. There are two types of synapses found in the body: chemical synapses and electrical synapses.
Chemical synapses.
At the end of the neuron is an area known as the axon. The axon is separated from the next cell by a small gap known as the synaptic cleft. When the signal reaches the axon, it opens voltage-gated calcium ion channels. Calcium ions cause vesicles containing chemicals known as neurotransmitters to release their contents by exocytosis into the synaptic cleft. NT molecules cross the synaptic cleft and bind to receptor molecules on the cell, forming synapses with the neuron. These receptor molecules open ion channels that can either stimulate the cell receptor to form a new action potential or can inhibit the cell from forming an action potential when stimulated by another neuron.
Electrical synapses.
Electrical synapses form when 2 neurons are connected by small holes called gap junctions. The gap in the connection allows electric current move from one neuron to another, so that the signal from one chamber is transmitted directly to another cell through the synapse.
Myelination
The axons of many neurons are covered with a coating known as myelin to increase the speed of nerve conduction throughout the body. Myelin is formed by 2 types of glial cells: Schwann cells in the PNS and oligodendrocytes in the central nervous system. In both cases, glial cells are wrapped in their plasma membrane around the axon many times to form a thick coating of lipids. The development of these myelin sheaths is known as myelination.
Myelination speeds up the movement of impulses in axons. The process of myelination begins with the acceleration of nerve conduction during fetal development and continues into early adulthood. Myelinated axons turn white due to the presence of lipids. They form the white matter of the brain, internal and external spinal cord. White matter is specialized for carrying information quickly through the brain and spinal cord. The gray matter of the brain and spinal cord are unmyelinated integration centers where information is processed.
Reflexes
Reflexes are quick, involuntary reactions in response to stimuli. The most well-known reflex is the patellar reflex, which is tested when a doctor taps a patient's knee during a physical examination. Reflexes are integrated in the gray matter of the spinal cord or brain stem. Reflexes allow the body to respond to stimuli very quickly, sending responses to effectors before nerve signals reach the conscious part of the brain. This explains why people often pull their hands away from a hot object before they realize they are in danger.
Functions of cranial nerves
Each of the 12 cranial nerves has a specific function within the nervous system.
The olfactory nerve (I) carries odor information to the brain from the olfactory epithelium in the roof of the nasal cavity.
The optic nerve (II) transmits visual information from the eyes to the brain.
The oculomotor, trochlear, and abducens nerves (III, IV, and VI) all work together to allow the brain to control eye movement and focusing. The trigeminal nerve (V) carries sensations from the face and innervates the muscles of mastication.
The facial nerve (VII) innervates the facial muscles to make facial expressions and carries taste information from the anterior 2/3 of the tongue.
The vestibulocochlear nerve (VIII) carries auditory information from the ears to the brain.
The glossopharyngeal nerve (IX) carries taste information from the posterior 1/3 of the tongue and aids in swallowing.
The vagus nerve (X), called the vagus nerve because it supplies many different areas, travels through the head, neck, and torso. It carries information about the state of vital organs in the brain, provides motor signals for speech control, and provides parasympathetic signals to many organs.
The accessory nerve (XI) controls movements of the shoulders and neck.
The hypoglossal nerve (XII) moves the tongue for speech and swallowing.
Sensory physiology
All sensory receptors can be classified according to their structure and the type of stimulation they detect. Structurally, there are 3 classes of sensory receptors: free, encapsulated nerve endings, and specialized cells.
Free nerve endings are simply free dendrites at the end of a neuron that extend into the tissue. Pain, heat and cold are all felt through free nerve endings. Encapsulated is free nerve endings, wrapped in round capsules of connective tissue. When the capsule is deformed by touch or pressure, the neuron is excited to send signals to the central nervous system. Specialized cells detect stimuli from 5 special senses: vision, hearing, balance, smell and taste. Each of the special senses has its own unique sensory cells, such as the rods and cones in the retina for detecting light in the organs of vision.
Functionally, there are 6 main classes of receptors: mechanoreceptors, nociceptors, photoreceptors, chemoreceptors, osmoreceptors and thermoreceptors.
Mechanoreceptors.
Mechanoreceptors are sensitive to mechanical stimuli such as touch, pressure, vibration, and blood pressure.
Nociceptors.
Nociceptors respond to stimuli such as extreme heat, cold, or tissue damage by sending pain signals to the central nervous system.
Photoreceptors.
The photoreceptors in the retina are designed to detect light to provide the sense of vision.
Chemoreceptors.
Chemoreceptors are receptors for detecting chemicals in the blood and provide the senses of taste and smell.
Osmoreceptors.
Osmoreceptors are capable of monitoring blood osmolarity to determine the body's hydration level.
Thermoreceptors.
Thermoreceptors are receptors for detecting temperature inside and around the body.