Home Fertilizers From what the nervous system is formed. Nervous system. As you know, the nervous system first appears in lower multicellular invertebrates. Diseases of the nervous system

Fertilizers

From what the nervous system is formed. Nervous system. As you know, the nervous system first appears in lower multicellular invertebrates. Diseases of the nervous system

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

Nervous system Is a set of special structures that unites and coordinates the 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 subdivided into the hindbrain (and pons 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 (stimuli) of the external and internal environment of the body. Let's remember that any cells can perceive various signals from the environment of existence with the help of specialized cellular receptors. However, they are not adapted to the perception of a number of vital signals and cannot instantly transmit information to other cells, which function as regulators of the body's integral adequate responses to stimuli.

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

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

Signals and the results of their analysis are used by the nervous system to organizing responses on changes in the external or internal environment, regulation and coordination functions of cells and supercellular structures of the body. Such responses are carried out by the effector organs. The most frequent variants of responses to stimuli are motor (motor) reactions of skeletal or smooth muscles, changes in the secretion of epithelial (exocrine, endocrine) cells, initiated by the nervous system. Taking a direct part in the formation of responses to changes in the environment of existence, the nervous system performs the functions regulation of homeostasis, securing functional interaction organs and tissues and their integration into a single whole organism.

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

The nervous system is divided into central (brain and spinal cord) and peripheral - nerve cells and fibers outside the cranial cavity and spinal canal. The human brain contains over 100 billion nerve cells (neurons). 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, combining into pathways, form the white matter. In addition, the structural part of the central nervous system is glial cells that form neuroglia. The number of glial cells is about 10 times the number of neurons, and these cells make up the majority of the mass of the central nervous system.

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

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

The structure of the nervous system

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

Rice. 1. The structure of the nervous system

Rice. 2. Functional division of the nervous system

The importance of the nervous system:

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

The 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 perception of information by the neuron. The axon starts from the cell body as an axon mound, 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 neurotransmitters or neuromodulators. Therefore, the process of mediator release by presynaptic endings can be influenced by other neurons. Also, the membrane of the terminals contains a large number of 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 IF Ivanov): a - the structure of the neuron: 7 - body (perikarion); 2 - core; 3 - dendrites; 4.6 - neurites; 5.8 - myelin sheath; 7- collateral; 9 - interception of the node; 10 - the nucleus of the lemmocyte; 11 - nerve endings; b - types of nerve cells: I - unipolar; II - multipolar; III - bipolar; 1 - neuritis; 2 -dendrite

Usually, in neurons, an action potential arises in the area of the membrane of the axonal hillock, the excitability of which is 2 times higher than the excitability of other areas. From here, the excitement spreads along the axon and the cell body.

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

Each neuron in the central nervous system performs three physiological roles: perceives 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); insert (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 - lemmocytes (Schwann cells). Neurons and glial cells are separated by intercellular gaps, which communicate with each other and form a fluid-filled intercellular space of neurons and glia. Through this space, an exchange of substances occurs between nerve and glial cells.

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.

Central nervous system functions

The central nervous system has 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 various components of the body into a single whole (integration), their coordinated functioning is provided by the central nervous system.

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

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

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

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

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

Reflex regulation of nervous activity

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

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

Reflex translated from Latin means "reflection". The term "reflex" was first proposed by the Czech researcher I.G. Prokhaskaya, who developed the doctrine of reflective actions. The further development of the reflex theory is associated with the name of I.M. Sechenov. He believed that everything unconscious and conscious is done according to the type of reflex. But then there were no methods of objective assessment of brain activity that could confirm this assumption. Later, an objective method for assessing brain activity was developed by academician I.P. Pavlov, and he received the name of the conditioned reflex method. Using this method, the scientist proved that conditioned reflexes, which are formed on the basis of unconditioned reflexes due to the formation of temporary connections, are the basis of the higher nervous activity of animals and humans. 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, which provides the implementation of the reflex.

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

Rice. 4. Scheme of regulation according to the principle of reflex. 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; KN - command neuron; CH - sensory neuron, ModN - modulatory neuron

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

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

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

A receptor is a specialized entity that perceives irritation. The receptor is composed 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 intercalated and motor neurons.

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

A special link of reverse afferentation perceives the parameters of the action performed by the working organ and transmits this information to the nerve center. The nerve center is an acceptor of the action of the link of reverse afferentation and receives information from the working organ about the perfect 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 subdivided into unconditioned and conditioned.

Unconditioned reflexes - congenital, hereditarily transmitted reactions. Unconditioned reflexes are carried out through the 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 the receptors. Unconditioned reflexes are also classified according to their biological significance: food, defensive, sexual, locomotor, orienting. According to the location of the receptors, these reflexes are subdivided into exteroceptive (temperature, tactile, visual, auditory, gustatory, etc.), interoceptive (vascular, cardiac, gastric, intestinal, etc.) and proprioceptive (muscle, tendon, etc.). By the nature of the response - to motor, secretory, etc. By finding the nerve centers through which the reflex is carried out - to spinal, bulbar, mesencephalic.

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

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

At the heart of modern ideas about the reflex activity of the body is the concept of a useful adaptive result, for the achievement of which any reflex is performed. Information about the achievement of a useful adaptive result enters the central nervous system through the feedback link in the form of reverse afferentation, which is an obligatory component of reflex activity. The principle of back afferentation in reflex activity was developed by P.K. , reverse afferentation.

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

Properties of nerve centers

Nerve centers have a number of characteristic functional properties.

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

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

Summation of excitations can occur in the nerve centers.

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

The transformation of the excitation rhythm occurs in them, i.e. a decrease or increase in the number of excitation impulses leaving the nerve center in comparison with the number of impulses coming to it.

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

Nerve centers, unlike nerve fibers, are capable of rapid fatigue. Synaptic fatigue 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 flow of a certain number of impulses from the receptors.

Nerve centers are characterized by plasticity - the ability to increase their functionality. This property may be due to synaptic relief - improved conduction in synapses after a short stimulation of the afferent pathways. With the frequent use of synapses, the synthesis of receptors and a transmitter 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 Central nervous system. It is understood as the regulation of the distribution of excitation and inhibition in neural structures, as well as the interaction between nerve centers, which ensure the effective implementation of reflex and voluntary reactions.

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

Coordination principles

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

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

Convergence principle is realized in convergent circuits of neurons, in which axons of a number of others converge or converge to one of them (usually an efferent). Convergence provides signals from different nerve centers or receptors of different modalities (different sensory organs) to the same neuron. On the basis of convergence, a variety of stimuli can cause the same type of response. For example, a sentry reflex (turning the eyes and head - alertness) can be triggered by light, sound, and tactile stimuli.

The principle of a common final path follows from the principle of convergence and is close in nature. It is understood as the possibility of carrying out one and 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 final pathway is the motor neurons of the anterior horns of the spinal cord or the motor nuclei of the cranial nerves, which directly innervate the muscles with their axons. One and the same motor reaction (for example, arm flexion) 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 the action of signals received by different sense organs (to light, sound, gravitational, painful or mechanical effects).

Divergence principle is realized in the divergent circuits 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 function of simultaneously transmitting signals from one neuron to many other neurons. Due to divergent connections, signals are widely distributed (irradiated) and many centers located at different levels of the central nervous system are quickly involved in the response.

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

The participation of feedback can be considered on the example of the implementation of the flexion reflex caused by mechanical action on the skin receptors (Fig. 5). With reflex contraction of the flexor muscle, the activity of proprioceptors and the frequency of sending nerve impulses along afferent fibers to the a-motor neurons of the spinal cord, which innervate this muscle, change. As a result, a closed control loop is formed, 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 motoneurons) receives information about the change in the state of the muscle caused by the transmission of impulses along the motor fibers. Thanks to the feedback, a kind of regulatory nerve ring is formed. Therefore, some authors prefer to use the term “reflex ring” instead of the term “reflex arc”.

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

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

The principle of reciprocal relations it is realized in the interaction between antagonist nerve centers. For example, between a group of motor neurons that control arm flexion and a group of motor neurons that control arm extension. Due to reciprocal relationships, 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 carried out 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.

Dominant principle it is also implemented based on the characteristics of the interaction between the nerve centers. The neurons of the dominant, most active center (focus of excitation) have persistent high activity and suppress excitation in other nerve centers, subjecting them to their influence. Moreover, the neurons of the dominant center attract to themselves afferent nerve impulses addressed to other centers, and increase their activity due to the receipt of these impulses. The dominant center can be in a state of 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 a state after a person has experienced an event that is important for him, when all his thoughts and actions in one way or another become associated with this event.

Dominant properties

Increased excitability
Persistence of arousal
Inertia of arousal
Ability to suppress subdominant lesions
Ability to add 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.

In evolution, the nervous system has undergone several stages of development, which have become turning points in the qualitative organization of its activity. These stages differ in the number and types of neuronal formations, synapses, signs of their functional specialization, in the formation of groups of neurons interconnected by a common function. There are three main stages of the structural organization of the nervous system: diffuse, nodular, tubular.

Diffuse the nervous system is the most ancient; it is found in coelenterates (hydra) animals. Such a nervous system is characterized by a multiplicity of connections between neighboring elements, which allows excitation to spread freely along the nervous network in all directions.

This type of nervous system provides wide interchangeability and thus greater reliability of functioning, however, these reactions are imprecise, vague in nature.

Nodal the type of nervous system is typical for worms, molluscs, crustaceans.

It is characterized by the fact that the connections of nerve cells are organized in a certain way, the excitation passes along strictly defined paths. This organization of the nervous system is more vulnerable. Damage to one node causes disruption of the functions of the whole organism as a whole, but in its qualities it is faster and more accurate.

Tubular the nervous system is characteristic of chordates, it includes features of the diffuse and nodal types. The nervous system of higher animals took all the best: high reliability of the diffuse type, accuracy, locality, and the speed of organizing nodal type reactions.

The leading role of the nervous system

At the first stage of the development of the world of living beings, the interaction between the simplest organisms was carried out through the aquatic environment of the primitive ocean, into which the chemicals released by them entered. The first ancient form of interaction between the cells of a multicellular organism is chemical interaction through metabolic products entering the body fluids. Such metabolic products, or metabolites, are the breakdown products of proteins, carbon dioxide, etc. these are the humoral transmission of influences, the humoral correlation mechanism, or communication between organs.

The humoral connection is characterized by the following features:

the lack of an exact address to which the chemical is directed to enter the blood or other body fluids;
the chemical spreads slowly;
the chemical acts in negligible amounts and is usually rapidly degraded or excreted from the body.

Humoral connections are common to both the animal world and the plant world. At a certain stage in the development of the animal world, in connection with the appearance of the nervous system, a new, nervous form of connections and regulation is formed, which qualitatively distinguishes the animal world from the plant world. The higher in its development the organism of an animal, the more important is the interaction of organs through the nervous system, which is designated as reflex. In higher living organisms, the nervous system regulates humoral connections. In contrast to the humoral connection, the nerve connection has a precise orientation towards a specific organ and even a group of cells; communication takes place hundreds of times faster than the rate at which chemicals spread. The transition from a humoral connection to a nervous one was accompanied not by the destruction of the humoral connection between the cells of the body, but by submission to the nervous connections and the emergence of neuro-humoral connections.

At the next stage in the development of living things, special organs appear - glands, in which hormones are produced, which are formed from the nutrients entering the body. The main function of the nervous system is both in the regulation of the activity of individual organs among themselves, and in the interaction of the organism as a whole with its surrounding external environment. Any impact of the external environment on the body is primarily on the receptors (sense organs) and is carried out through changes caused by the external environment and the nervous system. As the nervous system develops, its higher section - the cerebral hemispheres - becomes "the manager and distributor of all the body's activities."

The structure of the nervous system

The nervous system is formed by nervous tissue, which consists of a huge amount neurons- a nerve cell with processes.

The nervous system is conventionally divided into central and peripheral.

central nervous system includes the brain and spinal cord, and peripheral nervous system- nerves extending from them.

The brain and spinal cord are a collection of neurons. On a transverse section of the brain, white and gray matter are distinguished. The gray matter consists of nerve cells, and the white matter consists of nerve fibers, which are processes of nerve cells. In different parts of the central nervous system, the location of the white and gray matter is not the same. In the spinal cord, the gray matter is inside, and the white matter is outside, in the brain (cerebral hemispheres, cerebellum), on the contrary, the gray matter is outside, white is inside. In different parts of the brain, there are separate clusters of nerve cells (gray matter) located inside the white matter - kernels... Clusters of nerve cells are also found outside the central nervous system. They're called knots and belong to the peripheral nervous system.

Reflex activity of the nervous system

The main form of activity of the nervous system is the reflex. Reflex- the reaction of the body to a change in the internal or external environment, carried out with the participation of the central nervous system in response to stimulation of the receptors.

With any irritation, excitation from the receptors is transmitted along the centripetal nerve fibers to the central nervous system, from where, through the intercalary neuron along the centrifugal fibers, it goes to the periphery to one or another organ, the activity of which changes. This entire path through the central nervous system to the working organ is called reflex arc usually formed by three neurons: sensory, intercalary and motor. A reflex is a complex act, in the implementation of which a much larger number of neurons are involved. Excitation, getting into the central nervous system, spreads to many parts of the spinal cord and reaches the brain. As a result of the interaction of many neurons, the body responds to stimulation.

Spinal cord

Spinal cord- a strand about 45 cm long, 1 cm in diameter, located in the canal of the spine, covered with three meninges: hard, arachnoid and soft (vascular).

Spinal cord is located in the spinal canal and is a strand that passes into the medulla oblongata at the top, and ends at the bottom at the level of the second lumbar vertebra. The spinal cord consists of gray matter, which contains nerve cells, and white matter, which contains nerve fibers. The gray matter is located inside the spinal cord and is surrounded on all sides by white matter.

In cross-section, the gray matter resembles the letter H. In it, anterior and posterior horns are distinguished, as well as a connecting bar, in the center of which is a narrow canal of the spinal cord containing cerebrospinal fluid. In the thoracic region, lateral horns are distinguished. They contain the bodies of neurons that innervate the internal organs. The white matter of the spinal cord is formed by nerve processes. Short processes connect parts of the spinal cord, and long ones make up the conductive apparatus of bilateral connections with the brain.

The spinal cord has two thickenings - the cervical and lumbar, from which nerves extend to the upper and lower extremities. 31 pairs of spinal nerves depart from the spinal cord. Each nerve starts from the spinal cord with two roots - anterior and posterior. Back roots - sensitive consist of processes of centripetal neurons. Their bodies are located in the spinal nodes. Front roots - motor- are the processes of centrifugal neurons located in the gray matter of the spinal cord. As a result of the fusion of the anterior and posterior roots, a mixed spinal nerve is formed. The spinal cord contains centers that regulate the simplest reflex acts. The main functions of the spinal cord are reflex activity and conduction of arousal.

The human spinal cord contains the reflex centers of the muscles of the upper and lower extremities, perspiration and urination. The function of arousal is that impulses pass through the spinal cord from the brain to all areas of the body and vice versa. Along the ascending pathways, centripetal impulses from organs (skin, muscles) are transmitted to the brain. In descending paths, centrifugal impulses are transmitted from the brain to the spinal cord, then to the periphery, to the organs. If the pathways are damaged, there is a loss of sensitivity in various parts of the body, a violation of voluntary muscle contractions and the ability to move.

Evolution of the vertebrate brain

The formation of the central nervous system in the form of a neural tube first appears in chordates. Have lower chordates the neural tube persists throughout life, in higher- vertebrates - in the embryonic stage, a neural plate is laid on the dorsal side, which is immersed under the skin and coiled into a tube. In the embryonic stage of development, the neural tube forms three swellings in the anterior part - three cerebral vesicles, from which the parts of the brain develop: the anterior vesicle gives the forebrain and diencephalon, the middle bladder turns into the midbrain, the posterior bladder forms the cerebellum and medulla oblongata... These five brain regions are characteristic of all vertebrates.

For lower vertebrates- fish and amphibians - the predominance of the midbrain over the rest of the sections is characteristic. Have amphibians the forebrain slightly increases and a thin layer of nerve cells forms in the roof of the hemispheres - the primary cerebral vault, the ancient cortex. Have reptiles the forebrain is significantly enlarged due to the accumulation of nerve cells. Most of the roof of the hemispheres is occupied by the ancient crust. For the first time, the rudiment of a new bark appears in reptiles. The forebrain hemispheres creep into other parts, as a result of which a bend is formed in the diencephalon. Since the ancient reptiles, the cerebral hemispheres have become the largest section of the brain.

In the structure of the brain birds and reptiles much in common. On the roof of the brain is the primary cortex, the midbrain is well developed. However, in birds, compared to reptiles, the total brain mass and the relative size of the forebrain increase. The cerebellum is large and has a folded structure. Have mammals the forebrain reaches its greatest size and complexity. Most of the brain matter is the new cortex, which serves as the center of higher nervous activity. The intermediate and middle regions of the brain in mammals are small. The expanding hemispheres of the forebrain cover them and crush them under themselves. Some mammals have a smooth brain without grooves and convolutions, but most mammals have grooves and convolutions in the cerebral cortex. The appearance of grooves and convolutions occurs due to the growth of the brain with a limited size of the skull. Further growth of the cortex leads to the appearance of folding in the form of grooves and convolutions.

Brain

If the spinal cord in all vertebrates is more or less developed in the same way, then the brain will differ significantly in size and complexity of structure in different animals. The forebrain undergoes especially drastic changes in the course of evolution. In lower vertebrates, the forebrain is poorly developed. In fish, it is represented by the olfactory lobes and nuclei of gray matter in the thickness of the brain. The intensive development of the forebrain is associated with the emergence of animals on land. It differentiates into the diencephalon and into two symmetrical hemispheres, which are called terminal brain... The gray matter on the surface of the forebrain (cortex) first appears in reptiles, further developing in birds and especially in mammals. Only birds and mammals become truly large hemispheres of the forebrain. In the latter, they cover almost all other parts of the brain.

The brain is located in the cranial cavity. It includes the trunk and the telencephalon (cerebral cortex).

Brain stem consists of the medulla oblongata, pons varoli, midbrain and diencephalon.

Medulla is a direct continuation of the spinal cord and expanding, passes into the hindbrain. It basically retains the shape and structure of the spinal cord. In the thickness of the medulla oblongata, there are accumulations of gray matter - the nuclei of the cranial nerves. The rear axle includes cerebellum and pons... The cerebellum is located above the medulla oblongata and has a complex structure. On the surface of the cerebellar hemispheres, the gray matter forms the cortex, and inside the cerebellum - its nucleus. Like the spinal cord, it performs two functions: reflex and conduction. However, the reflexes of the medulla oblongata are more complex. This is expressed in an important meaning in the regulation of cardiac activity, the state of blood vessels, respiration, and sweating. The centers of all these functions are located in the medulla oblongata. There are also centers for chewing, sucking, swallowing, saliva and gastric juice. Despite its small size (2.5–3 cm), the medulla oblongata is a vital part of the central nervous system. Damage to it can cause death due to cessation of breathing and heart activity. The conductive function of the medulla oblongata and the pons varoli is to transmit impulses from the spinal cord to the brain and vice versa.

V midbrain the primary (subcortical) centers of vision and hearing are located, which carry out reflex orientational reactions to light and sound stimuli. These reactions are expressed in various movements of the trunk, head and eyes towards stimuli. The midbrain consists of the legs of the brain and the quadruple. The midbrain regulates and distributes the tone (tension) of the skeletal muscles.

Diencephalon consists of two departments - thalamus and hypothalamus, each of which consists of a large number of nuclei of the optic hillocks and the sub-hillock area. Through the visual hillocks, centripetal impulses are transmitted to the cerebral cortex from all receptors in the body. Not a single centripetal impulse, wherever it comes from, can pass to the cortex, bypassing the visual hillocks. Thus, through the diencephalon, all receptors communicate with the cerebral cortex. In the sub-tuberous area, there are centers that affect metabolism, thermoregulation and endocrine glands.

Cerebellum located behind the medulla oblongata. It is composed of gray and white matter. However, unlike the spinal cord and the trunk, the gray matter - the cortex - is located on the surface of the cerebellum, and the white matter is located inside, under the cortex. The cerebellum coordinates movements, makes them clear and smooth, plays an important role in maintaining the balance of the body in space, and also affects muscle tone. With damage to the cerebellum, a person experiences a drop in muscle tone, movement disorder and a change in gait, speech slows down, etc. However, after a while, movements and muscle tone are restored due to the fact that the intact parts of the central nervous system take over the functions of the cerebellum.

Large hemispheres- the largest and most developed part of the brain. In humans, they form the bulk of the brain and are covered with bark over their entire surface. The gray matter covers the outside of the hemispheres and forms the cerebral cortex. The cortex of the human hemispheres has a thickness of 2 to 4 mm and is composed of 6-8 layers formed by 14-16 billion cells, different in shape, size and functions. There is a white matter under the bark. It consists of nerve fibers that connect the cortex with the lower parts of the central nervous system and individual lobes of the hemispheres among themselves.

The cerebral cortex has convolutions, separated by grooves, which significantly increase its surface. The three deepest grooves divide the hemispheres into lobes. There are four lobes in each hemisphere: frontal, parietal, temporal, occipital... Excitation of different receptors goes to the corresponding perceiving areas of the cortex, called zones, and from here they are transmitted to a specific organ, prompting it to action. The following zones are distinguished in the bark. Auditory zone located in the temporal lobe, receives impulses from the auditory receptors.

Visual zone lies in the occipital region. Impulses from eye receptors come here.

Olfactory zone is located on the inner surface of the temporal lobe and is associated with receptors in the nasal cavity.

Sensitive motor the zone is located in the frontal and parietal lobes. This zone contains the main centers of movement of the legs, trunk, arms, neck, tongue and lips. The center of speech also lies here.

The cerebral hemispheres are the highest part of the central nervous system that controls the functioning of all organs in mammals. The significance of the cerebral hemispheres in humans also lies in the fact that they represent the material basis of mental activity. I.P. Pavlov showed that mental activity is based on physiological processes in the cerebral cortex. Thinking is associated with the activity of the entire cerebral cortex, and not only with the function of its individual areas.

Department of the brain	Functions
Medulla	Conductor	The connection of the spinal cord and overlying parts of the brain.
Medulla	Reflex	Regulation of the respiratory, cardiovascular, digestive systems: food reflexes, reflexes of salivation, swallowing; protective reflexes: sneezing, blinking, coughing, vomiting.
Pons	Conductor	It connects the cerebellar hemispheres to each other and to the cerebral cortex.
Cerebellum	The coordinating	Coordination of voluntary movements and maintaining the position of the body in space. Regulation of muscle tone and balance
Midbrain	Conductor	Orientation reflexes to visual, sound stimuli ( turns of the head and torso).
Midbrain	Reflex	Regulation of muscle tone and body posture; coordination of complex motor acts ( finger and hand movements) etc.
Diencephalon	thalamus collection and evaluation of incoming information from the sense organs, transmission of the most important information to the cerebral cortex; regulation of emotional behavior, pain. hypothalamus controls the work of the endocrine glands, cardiovascular system, metabolism ( thirst, hunger), body temperature, sleep and wakefulness; gives the behavior an emotional coloring ( fear, rage, pleasure, discontent)

Cerebral cortex

Surface cerebral cortex in humans, it is about 1500 cm 2, which is many times larger than the inner surface of the skull. Such a large surface of the cortex was formed due to the development of a large number of grooves and convolutions, as a result of which most of the cortex (about 70%) is concentrated in the grooves. The largest grooves of the cerebral hemispheres - central that runs across both hemispheres, and temporal separating the temporal lobe from the rest. The cerebral cortex, despite its small thickness (1.5–3 mm), has a very complex structure. It has six main layers, which differ in the structure, shape and size of neurons and connections. In the cortex are the centers of all sensitive (receptor) systems, representations of all organs and parts of the body. In this regard, centripetal nerve impulses from all internal organs or parts of the body approach the cortex, and it can control their work. Through the cerebral cortex, a closure of conditioned reflexes occurs, through which the body constantly, throughout its life, very accurately adapts to the changing conditions of existence, to the environment.

3. DEVELOPMENT OF THE NERVOUS SYSTEM IN PHILOGENESIS

Polygenesis of invertebrate nerve cells is the basis for a variety of mediator mechanisms in their nervous system.

coelenterates. Cavities are two-layer animals. Their body is a hollow sac, the inner cavity of which is the digestive cavity. The nervous system of the coelenterates belongs to the diffuse type. Each nerve cell in it is connected by long processes to several neighboring ones, forming a nervous network. The nerve cells of the coelenterates do not have specialized polarized processes. Their processes conduct excitation in any direction and do not form long pathways. Contacts between nerve cells of the diffuse nervous system are of several types. Exists plasma contactsanastomoses). Appear and slotted contacts between the processes of nerve cells, like synapses. Moreover, among them there are contacts in which synaptic vesicles are located on both sides of the contact - the so-called symmetrical synapses, and there is asymmetrical synapses:

1 - mouth opening; 2 - tentacle; 3 - outsole

1 - nerve node; 2 - pharynx; 3 - abdominal longitudinal trunk; 4 - lateral nerve trunk

The next stage in the development of invertebrates is the appearance of three-layer animals - flatworms. Like coelenterates, they have an intestinal cavity communicating with the external environment through the oral opening. However, they have a third germinal layer - the mesoderm and a bilateral type of symmetry. The nervous system of the lower flatworms belongs to the diffuse type. However, several nerve trunks are already separating from the diffuse network (Fig. 9 , 3 , 4 ).

4 , 5 6 orthogon.

3 ). The cells of the cerebral

1 - tentacular outgrowth; 2 - nerve innervating the outgrowth; 3 - cerebral ganglion; 4 - lateral longitudinal nerve trunk; 5 - abdominal longitudinal nerve trunk; 6 - commissure

ganglion, long processes appear, going into the longitudinal trunks of the orthogon (Fig. 10, 4 , 5 ).

The next stage in the development of invertebrates is the emergence of segmented animals - annelids. ganglion - neuropil - interlacing of nerve cell processes and glial cells. The ganglion is located on the ventral side of the segment under the intestinal tube. It sends its sensory and motor fibers to its own segment and to two adjacent ones. Thus, each ganglion has three pairs of lateral nerves, each of which is mixed and innervates its own segment. Sensory fibers coming from the periphery enter the ganglion through the ventral nerve roots. Motor fibers leave the ganglion along the dorsal nerve roots. Accordingly, sensory neurons are located in the ventral part of the ganglion, and motor neurons are located in the dorsal part. In addition, in the ganglion there are small cells that innervate the internal organs (vegetative elements), they are located laterally - between sensory and motor neurons. No grouping of elements was found among the neurons of the sensory, motor, or associative zones of annelid ganglia; the neurons are diffusely distributed, i.e. do not form centers.

The ganglia of annelids are linked together in a chain. Each subsequent ganglion is connected to the previous one using

1 - supraopharyngeal nerve ganglion;

2 - subopharyngeal nerve ganglion;

3 - complex merged ganglion of the thoracic segment; 4 - abdominal ganglion; 5 - peripheral nerve; 6 - connector

nerve trunks, which are called connectors.

arthropods, i.e. built like the abdominal nerve chain, but can reach a high level of development (Fig. 11). It includes a significantly developed supraopharyngeal ganglion, which performs the function

1 - mushroom body; 2 - protocerebrum; 3 - visual blade; 4 - deutocerebrum; 5 - tritocerebrum

tion of the brain, the suboesophageal ganglion, which controls the organs of the oral apparatus, and the segmental ganglia of the abdominal nerve chain. The ganglia of the abdominal nerve chain can merge with each other, forming complex ganglion masses.

Brain arthropods consists of three sections: anterior - protocerebrum, middle - deutocerebrum and rear - tritocerebrum.

neurosecretory cells.

In the process of evolution, initially diffusely located bipolar neurosecretory cells perceived signals either by processes or by the entire cell surface, then neurosecretory centers, neurosecretory tracts and neurosecretory contact areas were formed. Subsequently, the specialization of nerve centers took place, the degree of reliability in the relationship between the two main regulatory systems (nervous and humoral) increased, and a fundamentally new stage of regulation was formed - subordination to the neurosecretory centers of the peripheral endocrine glands.

1 - cerebral commissure; 2 - cerebral ganglia; 3 - pedal ganglia; 4 - connector; 5 - visceral ganglia

Nervous system shellfish also has ganglionic structure(fig. 13). In the simplest representatives of the type, it consists of several pairs of ganglia. Each pair of ganglia controls a specific group of organs: leg, visceral organs, lungs, etc. - and is located next to the innervated organs or inside them. Ganglia of the same name are connected in pairs by commissures. In addition, each ganglion is connected by long connectives to the cerebral ganglion complex.

In more highly organized mollusks (cephalopods), the nervous system is transformed (Fig. 14). Her ganglia merge and form a common periopharyngeal mass - brain.

Evolution of the nervous system.

3.1. The origin and function of the nervous system.

The nervous system in all animals is of ectodermal origin. It performs the following functions:

The body's relationship with the environment (perception, transmission of irritation and response to irritation);

The connection of all organs and organ systems into a single whole;

The nervous system underlies the formation of higher nervous activity.

3.2. Evolution of the nervous system in a series of invertebrates.

For the first time, the nervous system appeared in coelenterates and had diffuse or mesh type nervous system, i.e. the nervous system is a network of nerve cells distributed throughout the body and interconnected by thin processes. It has a typical structure in hydra, but already in jellyfish and polyps, clusters of nerve cells appear in certain places (near the mouth, along the edges of the umbrella), these clusters of nerve cells are the precursors of the sense organs.

Further, the evolution of the nervous system follows the path of concentration of nerve cells in certain places of the body, i.e. along the path of the formation of nerve nodes (ganglia). These nodes primarily arise where there are cells that perceive irritation from the environment. So with radial symmetry, a radial type of the nervous system arises, and with bilateral symmetry, the concentration of nerve nodes occurs at the anterior end of the body. Paired nerve trunks running along the body extend from the head nodes. This type of nervous system is called the ganglion stem.

This type of nervous system has a typical structure in flatworms, i.e. at the front end of the body there are paired ganglia, from which nerve fibers and sensory organs extend forward, and nerve trunks running along the body.

In roundworms, the cephalic ganglia merge into the periopharyngeal nerve ring, from which nerve trunks also run along the body.

In annelids, a nerve chain is formed, i.e. in each segment, independent paired nerve nodes are formed. All of them are connected by both longitudinal and transverse strands. As a result, the nervous system acquires a staircase-like structure. Often, both chains approach each other, connecting along the middle part of the body into an unpaired abdominal nerve chain.

Arthropods have the same type of nervous systems, but the number of nerve nodes decreases, and their size increases, especially in the head or cephalothoracic region, i.e. there is a process of cephalization.

In molluscs, the nervous system is represented by nodes in different parts of the body, connected by cords and nerves extending from the nodes. Gastropods have pedal, cerebral, and pleural-visceral nodes; in bivalves - pedal and pleural-visceral; in cephalopods - pleural-visceral and cerebral nerve nodes. An accumulation of nervous tissue is observed around the pharynx in cephalopods.

3.3. Evolution of the nervous system in chordates.

The nervous system in chordates is represented by a neural tube., which differentiates into the brain and spinal cord.

In the lower chordates, the neural tube looks like a hollow tube (neurocoel) with nerves extending from the tube. In the lancelet, a small expansion is formed in the head region - the anlage of the brain. This expansion is called the ventricle.

In the higher chordates, three swellings are formed at the anterior end of the neural tube: the anterior, middle, and posterior vesicles. From the first cerebral bladder, the anterior and diencephalon is subsequently formed, from the middle - the middle, from the posterior - the cerebellum and the medulla oblongata, passing into the spinal cord.

In all classes of vertebrates, the brain consists of 5 sections (anterior, intermediate, middle, posterior, and oblong), but the degree of their development is not the same in animals of different classes.

So in cyclostomes, all parts of the brain are located one after another in a horizontal plane. The medulla oblongata passes directly into the spinal cord with the central canal in the nutria.

In fish, the brain is more differentiated in comparison with cyclostomes. The volume of the forebrain is increased, especially in lung-breathing fish, but the forebrain is not yet divided into hemispheres and functionally serves as the higher olfactory center. The roof of the forebrain is thin; it consists only of epithelial cells and does not contain nerve tissue. In the diencephalon, with which the pineal gland and the pituitary gland are connected, the hypothalamus is located, which is the center of the endocrine system. The midbrain is the most developed in fish. The visual lobes are well expressed in it. In the midbrain region, there is a bend characteristic of all higher vertebrates. In addition, the midbrain is an analyzing center. The cerebellum, which is part of the hindbrain, is well developed due to the complexity of movement in fish. It is the center of coordination of movement, its size varies depending on the activity of movement of different species of fish. The medulla oblongata provides a connection between the higher parts of the brain and the spinal cord and contains the centers of respiration and blood circulation.

10 pairs of cranial nerves leave the fish brain.

This type of brain, in which the midbrain is the highest center of integration, is called ichthyopside.

In amphibians, the nervous system is similar in structure to the nervous system of lung-breathing fish, but it is distinguished by a significant development and complete separation of paired elongated hemispheres, as well as a weak development of the cerebellum, which is due to the low mobility of amphibians and the uniformity of their movements. But amphibians have a forebrain roof called the primary cerebral vault - the archipallium. The number of cranial nerves, like in fish, is ten. And the type of brain is the same, i.e. ichthyopside.

Thus, all anamnias (cyclostomes, fish and amphibians) have an ichthyopid type of the brain.

In the structure of the brain of reptiles belonging to the higher vertebrates, i.e. to amniotes, the features of a progressive organization are clearly expressed. The forebrain hemispheres gain a significant predominance over other parts of the brain. At their base there are large clusters of nerve cells - striated bodies. On the lateral and medial sides of each hemisphere, islands of the old cortex appear - the archicortex. The size of the midbrain is reduced, and it loses its importance as a leading center. The bottom of the forebrain becomes the analyzing center, i.e. striped bodies. This type of brain is called sauropsid or striatal.... The cerebellum is increased in size due to the variety of movements of reptiles. The medulla oblongata forms a sharp bend, characteristic of all amniotes. 12 pairs of cranial nerves leave the brain.

The same type of brain is typical for birds, but with some peculiarities. The forebrain hemispheres are relatively large. the olfactory lobes in birds are poorly developed, which indicates the role of smell in the life of birds. In contrast, the midbrain is represented by large visual lobes. The cerebellum is well developed, 12 pairs of nerves leave the brain.

The mammalian brain reaches its maximum development. The hemispheres are so large that they cover the midbrain and cerebellum. The cerebral cortex is especially developed, its area is increased due to convolutions and grooves. The bark has a very complex structure and is called the new cortex - the neocortex. A secondary cerebral vault appears - neopallium. Large olfactory lobes are located in front of the hemispheres. The diencephalon, like other classes, includes the pineal gland, pituitary gland, and hypothalamus. The midbrain is relatively small, it consists of four cusps - four-hillocks. The anterior cortex is associated with the visual analyzer, the posterior cortex with the auditory one. Along with the forebrain, the cerebellum progresses strongly. 12 pairs of cranial nerves leave the brain. The analyzing center is the cerebral cortex. This type of brain is called mammary..

3.4. Anomalies and malformations of the nervous system in humans.

1. Acephaly- absence of the brain, vault, skull and facial skeleton; this disorder is associated with underdevelopment of the anterior neural tube and is combined with defects in the spinal cord, bones and internal organs.

2. Anencephaly- the absence of the cerebral hemispheres and the roof of the skull with underdevelopment of the brain stem and is combined with other malformations. This pathology is caused by non-closure (dysraphia) of the head of the neural tube. In this case, the bones of the roof of the skull do not develop, and the bones of the base of the skull show various anomalies. Anencephaly is incompatible with life, the average frequency is 1/1500, and more often in female fetuses.

3. Atelencephaly- arrest of development (heterochrony) of the anterior part of the neural tube at the stage of three bubbles. As a result, the cerebral hemispheres and subcortical nuclei are not formed.

4. Prosencephaly- the telencephalon is divided by a longitudinal groove, but in depth both hemispheres remain connected to each other.

5. Holoprosencephaly- the terminal brain is not divided into hemispheres and looks like a hemisphere with a single cavity (ventricle).

6. Alobaric proencephaly- division of the telencephalon only in the posterior part, and the frontal lobes remain undivided.

7. Aplasia or hypoplasia of the corpus callosum- complete or partial absence of complex brain commissure, i.e. corpus callosum.

8. Hydroencephaly- atrophy of the cerebral hemispheres in combination with hydrocephalus.

9. Agiriya- complete absence of grooves and convolutions (smooth brain) of the cerebral hemispheres.

10. Microgyria- reduction in the number and volume of furrows.

11. Congenital hydrocephalus- obstruction of a part of the ventricular system of the brain and its outlets, it is caused by a primary violation of the development of the nervous system.

12. Spina bifida- defect of closure and separation from the cutaneous ectoderm of the spinal neural tube. Sometimes this anomaly is accompanied by diplomielia, in which the spinal cord is split over a certain length into two parts, each with its own central pocket.

13. Iniencephaly- a rare anomaly incompatible with life, occurs more often in female fetuses. This is a gross anomaly of the occiput and brain. The heads are turned so that the face is turned up. Dorsally, the scalp continues into the skin of the lumbodorsal or sacral area.

Nervous system

The nervous system perceives external and internal stimuli, analyzes and processes incoming information, stores traces of past activity (memory traces) and accordingly regulates and coordinates the functions of the body.

The activity of the nervous system is based on a reflex associated with the propagation of excitation along reflex arcs and the process of inhibition. The nervous system is formed mainly by nervous tissue, the main structural and functional unit of which is the neuron. In the course of the evolution of animals, a gradual complication of the nervous system took place and, at the same time, their behavior became more complex.

Several stages are noted in the development of the nervous system.

Protozoa do not have a nervous system, but some ciliates have an intracellular fibrillar excitable apparatus. As multicellular organisms develop, a specialized tissue is formed that is capable of reproducing active reactions, that is, excitation. The reticular, or diffuse, nervous system first appears in coelenterates (hydroid polyps). It is formed by outgrowths of neurons, diffusely distributed throughout the body in the form of a network. The diffuse nervous system quickly conducts excitation from the point of irritation in all directions, which gives it integrative properties.

The diffuse nervous system is also characterized by minor signs of centralization (in the hydra, the compaction of nerve elements in the region of the sole and oral pole). The complication of the nervous system proceeded in parallel with the development of the organs of movement and was expressed primarily in the isolation of neurons from the diffuse network, their immersion deep into the body and the formation of clusters there. So, in free-living coelenterates (jellyfish), neurons accumulate in the ganglion, forming a diffuse-nodular nervous system. The formation of this type of nervous system is associated, first of all, with the development of special receptors on the surface of the body, capable of selectively reacting to mechanical, chemical and light influences. Along with this, the number of neurons and the variety of their types progressively increase, and neuroglia are formed. Bipolar neurons appear with dendrites and axons. Conducting arousal becomes directional. Nerve structures are also differentiated, in which the corresponding signals are transmitted to other cells that control the body's responses. Thus, some cells specialize in reception, others in conduction, and still others in contraction. Further evolutionary complication of the nervous system is associated with the centralization and development of a nodal type of organization (arthropods, annelids, molluscs). Neurons are concentrated in nerve nodes (ganglia), connected by nerve fibers with each other, as well as with receptors and executive organs (muscles, glands).

Differentiation of the digestive, reproductive, circulatory and other organ systems was accompanied by the improvement of the interaction between them with the help of the nervous system. There is a significant complication and the emergence of many central nervous formations, which are dependent on each other. The parathyroid ganglia and nerves that control feeding and burrowing movements develop in phylogenetically higher forms into receptors that perceive light, sound, and smell; the senses appear. Since the main receptor organs are located at the head end of the body, the corresponding ganglia in the head part of the body develop more strongly, subjugate the activities of the rest and form the brain. Arthropods and annelids have a well-developed nerve chain. The formation of the adaptive behavior of the organism manifests itself most clearly at the highest level of evolution - in vertebrates - and is associated with the complication of the structure of the nervous system and the improvement of the interaction of the organism with the external environment. Some parts of the nervous system show a tendency of increased growth in phylogeny, while others remain underdeveloped. In fish, the forebrain is poorly differentiated, but the hindbrain, midbrain, and cerebellum are well developed. In amphibians and reptiles, the diencephalon and two hemispheres with the primary cerebral cortex are separated from the anterior cerebral bladder.

The nervous system reaches its highest development in mammals, especially in humans, mainly due to the increase and complication of the structure of the cerebral cortex. The development and differentiation of the structures of the nervous system in higher animals determined its division into central and peripheral.

Nervous system

Stages of development of the nervous system

The diffuse nervous system is the most ancient; it is found in coelenterates (hydra) animals. Such a nervous system is characterized by a multiplicity of connections between neighboring elements, which allows excitation to spread freely along the nervous network in all directions.

This type of nervous system provides wide interchangeability and thus greater reliability of functioning, however, these reactions are imprecise, vague in nature.

The nodular type of the nervous system is typical for worms, molluscs, crustaceans.

The tubular nervous system is characteristic of chordates, it includes features of the diffuse and nodal types. The nervous system of higher animals took all the best: high reliability of the diffuse type, accuracy, locality, and the speed of organizing nodal type reactions.

The leading role of the nervous system

The humoral connection is characterized by the following features:

the lack of an exact address to which the chemical is directed to enter the blood or other body fluids;
the chemical spreads slowly;
the chemical acts in negligible amounts and is usually rapidly degraded or excreted from the body.

The structure of the nervous system

The nervous system is formed by nervous tissue, which consists of a huge number of neurons - a nerve cell with processes.

The nervous system is conventionally divided into central and peripheral.

The central nervous system includes the brain and spinal cord, and the peripheral nervous system includes the nerves that branch out from them.

The brain and spinal cord are a collection of neurons. On a transverse section of the brain, white and gray matter are distinguished. The gray matter consists of nerve cells, and the white matter consists of nerve fibers, which are processes of nerve cells. In different parts of the central nervous system, the location of the white and gray matter is not the same. In the spinal cord, the gray matter is inside, and the white matter is outside, in the brain (cerebral hemispheres, cerebellum), on the contrary, the gray matter is outside, white is inside. In different parts of the brain, there are separate clusters of nerve cells (gray matter) located inside the white matter - the nucleus. Clusters of nerve cells are also found outside the central nervous system. These are called nodes and refer to the peripheral nervous system.

Reflex activity of the nervous system

The main form of activity of the nervous system is the reflex. Reflex - the body's response to a change in the internal or external environment, carried out with the participation of the central nervous system in response to stimulation of receptors.

With any irritation, excitation from the receptors is transmitted along the centripetal nerve fibers to the central nervous system, from where, through the intercalary neuron along the centrifugal fibers, it goes to the periphery to one or another organ, the activity of which changes. This entire path through the central nervous system to the working organ, called a reflex arc, is usually formed by three neurons: sensory, intercalary and motor. A reflex is a complex act, in the implementation of which a much larger number of neurons are involved. Excitation, getting into the central nervous system, spreads to many parts of the spinal cord and reaches the brain. As a result of the interaction of many neurons, the body responds to stimulation.

Spinal cord

The spinal cord is a cord about 45 cm long, 1 cm in diameter, located in the canal of the spine, covered with three meninges: hard, arachnoid and soft (vascular).

The spinal cord is located in the spinal canal and is a cord that passes into the medulla oblongata at the top, and ends at the bottom at the level of the second lumbar vertebra. The spinal cord consists of gray matter, which contains nerve cells, and white matter, which contains nerve fibers. The gray matter is located inside the spinal cord and is surrounded on all sides by white matter.

The spinal cord has two thickenings - the cervical and lumbar, from which nerves extend to the upper and lower extremities. 31 pairs of spinal nerves depart from the spinal cord. Each nerve starts from the spinal cord with two roots - anterior and posterior. Dorsal roots - sensitive, consist of processes of centripetal neurons. Their bodies are located in the spinal nodes. The anterior roots - motor - are the processes of centrifugal neurons located in the gray matter of the spinal cord. As a result of the fusion of the anterior and posterior roots, a mixed spinal nerve is formed. The spinal cord contains centers that regulate the simplest reflex acts. The main functions of the spinal cord are reflex activity and conduction of arousal.

Evolution of the vertebrate brain

The formation of the central nervous system in the form of a neural tube first appears in chordates. In the lower chordates, the neural tube remains throughout life, in the higher vertebrates, in the embryonic stage, a neural plate is laid on the dorsal side, which plunges under the skin and folds into a tube. In the embryonic stage of development, the neural tube forms three swellings in the anterior part - three cerebral vesicles, from which the parts of the brain develop: the anterior vesicle gives the forebrain and diencephalon, the middle bladder turns into the midbrain, the posterior bladder forms the cerebellum and the medulla oblongata. These five brain regions are characteristic of all vertebrates.

For the lower vertebrates - fish and amphibians - the predominance of the midbrain over the rest of the sections is characteristic. In amphibians, the forebrain slightly increases and a thin layer of nerve cells forms in the roof of the hemispheres - the primary cerebral vault, the ancient cortex. In reptiles, the forebrain is significantly enlarged due to the accumulation of nerve cells. Most of the roof of the hemispheres is occupied by the ancient crust. For the first time, the rudiment of a new bark appears in reptiles. The forebrain hemispheres creep into other parts, as a result of which a bend is formed in the diencephalon. Since the ancient reptiles, the cerebral hemispheres have become the largest section of the brain.

The structure of the brain of birds and reptiles has much in common. On the roof of the brain is the primary cortex, the midbrain is well developed. However, in birds, compared to reptiles, the total brain mass and the relative size of the forebrain increase. The cerebellum is large and has a folded structure. In mammals, the forebrain reaches its greatest size and complexity. Most of the brain matter is the new cortex, which serves as the center of higher nervous activity. The intermediate and middle regions of the brain in mammals are small. The expanding hemispheres of the forebrain cover them and crush them under themselves. Some mammals have a smooth brain without grooves and convolutions, but most mammals have grooves and convolutions in the cerebral cortex. The appearance of grooves and convolutions occurs due to the growth of the brain with a limited size of the skull. Further growth of the cortex leads to the appearance of folding in the form of grooves and convolutions.

Brain

If the spinal cord in all vertebrates is more or less developed in the same way, then the brain will differ significantly in size and complexity of structure in different animals. The forebrain undergoes especially drastic changes in the course of evolution. In lower vertebrates, the forebrain is poorly developed. In fish, it is represented by the olfactory lobes and nuclei of gray matter in the thickness of the brain. The intensive development of the forebrain is associated with the emergence of animals on land. It differentiates into the diencephalon and two symmetrical hemispheres called the telencephalon. The gray matter on the surface of the forebrain (cortex) first appears in reptiles, further developing in birds and especially in mammals. Only birds and mammals become truly large hemispheres of the forebrain. In the latter, they cover almost all other parts of the brain.

The brain is located in the cranial cavity. It includes the trunk and the telencephalon (cerebral cortex).

The brain stem consists of the medulla oblongata, pons varoli, midbrain and diencephalon.

The medulla oblongata is a direct continuation of the spinal cord and, expanding, passes into the hindbrain. It basically retains the shape and structure of the spinal cord. In the thickness of the medulla oblongata, there are accumulations of gray matter - the nuclei of the cranial nerves. The posterior bridge includes the cerebellum and the pons varoli. The cerebellum is located above the medulla oblongata and has a complex structure. On the surface of the cerebellar hemispheres, the gray matter forms the cortex, and inside the cerebellum - its nucleus. Like the spinal cord, it performs two functions: reflex and conduction. However, the reflexes of the medulla oblongata are more complex. This is expressed in an important meaning in the regulation of cardiac activity, the state of blood vessels, respiration, and sweating. The centers of all these functions are located in the medulla oblongata. There are also centers for chewing, sucking, swallowing, saliva and gastric juice. Despite its small size (2.5–3 cm), the medulla oblongata is a vital part of the central nervous system. Damage to it can cause death due to cessation of breathing and heart activity. The conductive function of the medulla oblongata and the pons varoli is to transmit impulses from the spinal cord to the brain and vice versa.

In the midbrain, there are primary (subcortical) centers of vision and hearing, which carry out reflex orientational reactions to light and sound stimuli. These reactions are expressed in various movements of the trunk, head and eyes towards stimuli. The midbrain consists of the legs of the brain and the quadruple. The midbrain regulates and distributes the tone (tension) of the skeletal muscles.

The diencephalon consists of two sections - the thalamus and the hypothalamus, each of which consists of a large number of nuclei of the optic hillocks and the hypothalamus region. Through the visual hillocks, centripetal impulses are transmitted to the cerebral cortex from all receptors in the body. Not a single centripetal impulse, wherever it comes from, can pass to the cortex, bypassing the visual hillocks. Thus, through the diencephalon, all receptors communicate with the cerebral cortex. In the sub-tuberous area, there are centers that affect metabolism, thermoregulation and endocrine glands.

The cerebellum is located behind the medulla oblongata. It is composed of gray and white matter. However, unlike the spinal cord and the trunk, the gray matter - the cortex - is located on the surface of the cerebellum, and the white matter is located inside, under the cortex. The cerebellum coordinates movements, makes them clear and smooth, plays an important role in maintaining the balance of the body in space, and also affects muscle tone. With damage to the cerebellum, a person experiences a drop in muscle tone, movement disorder and a change in gait, speech slows down, etc. However, after a while, movements and muscle tone are restored due to the fact that the intact parts of the central nervous system take over the functions of the cerebellum.

The cerebral hemispheres are the largest and most developed part of the brain. In humans, they form the bulk of the brain and are covered with bark over their entire surface. The gray matter covers the outside of the hemispheres and forms the cerebral cortex. The cortex of the human hemispheres has a thickness of 2 to 4 mm and is composed of 6-8 layers formed by 14-16 billion cells, different in shape, size and functions. There is a white matter under the bark. It consists of nerve fibers that connect the cortex with the lower parts of the central nervous system and individual lobes of the hemispheres among themselves.

The cerebral cortex has convolutions, separated by grooves, which significantly increase its surface. The three deepest grooves divide the hemispheres into lobes. In each hemisphere, four lobes are distinguished: frontal, parietal, temporal, occipital. Excitation of various receptors enter the corresponding perceiving areas of the cortex, called zones, and from there are transmitted to a specific organ, prompting it to act. The following zones are distinguished in the bark. The auditory zone is located in the temporal lobe and receives impulses from the auditory receptors.

The visual area lies in the occipital region. Impulses from eye receptors come here.

The olfactory zone is located on the inner surface of the temporal lobe and is associated with receptors in the nasal cavity.

The sensory-motor zone is located in the frontal and parietal lobes. This zone contains the main centers of movement of the legs, trunk, arms, neck, tongue and lips. The center of speech also lies here.

Nervous system. As you know, the nervous system first appears in lower multicellular invertebrates;

As you know, the nervous system first appears in lower multicellular invertebrates. The emergence of the nervous system is the most important milestone in the evolution of the animal world, and in this respect even primitive multicellular invertebrates are qualitatively different from the simplest. An important point here is already a sharp acceleration of the conduction of excitation in the nervous tissue: in the protoplasm, the rate of conduction of excitation does not exceed 1-2 microns per second, but even in the most primitive nervous system, consisting of nerve cells, it is 0.5 meters per second!

The nervous system exists in lower multicellular organisms in very diverse forms: reticular (for example, in hydra), annular (jellyfish), radial (starfish) and bilateral. The bilateral form is presented in lower (intestinal) flatworms and primitive mollusks (chiton) only by a net located near the surface of the body, but several longitudinal strands are distinguished by a more powerful development. With its progressive development, the nervous system sinks under the muscle tissue, the longitudinal cords become more pronounced, especially on the abdominal side of the body. At the same time, the anterior end of the body becomes more and more important, the head appears (the process of cephalization), and with it the brain - the accumulation and compaction of nerve elements at the anterior end. Finally, in higher worms, the central nervous system already fully acquires the typical structure of the "nervous ladder", in which the brain is located above the digestive tract and is connected by two symmetrical commissures ("periopharyngeal ring") with the subpharyngeal ganglia located on the abdominal side and further with paired abdominal nerves trunks. The essential elements here are the ganglia, therefore they also speak of the ganglionic nervous system, or the "ganglionic ladder". In some representatives of this group of animals (for example, leeches), the nerve trunks converge so much that a "neural chain" is obtained.

From the ganglia there are powerful conducting fibers that make up the nerve trunks. In giant fibers, nerve impulses are carried out much faster due to their large diameter and small number of synaptic connections (places of contact of the axons of some nerve cells with dendrites and cell bodies of other cells). As for the head ganglia, i.e. brain, they are more developed in more mobile animals, which also have the most developed receptor systems.

The origin and evolution of the nervous system is due to the need to coordinate different-quality functional units of a multicellular organism, to coordinate the processes occurring in different parts of it when interacting with the external environment, to ensure the activity of a complex organism as a single integral system. Only a coordinating and organizing center, which is the central nervous system, can provide flexibility and variability of the body's response under conditions of multicellular organization.

The process of cephalisapia, i.e. isolation of the head end of the body and the appearance of the brain associated with it. Only in the presence of a brain is it possible to truly centralized "coding" of signals coming from the periphery and the formation of integral "programs" of innate behavior, not to mention a high degree of coordination of all external activity of the animal.

Of course, the level of mental development depends not only on the structure of the nervous system. For example, rotifers close to annelids also possess, like those, a bilateral nervous system and a brain, as well as specialized sensory and motor nerves. However, differing little from ciliates in size, appearance and lifestyle, rotifers very much resemble the latter in behavior and do not show higher mental abilities than ciliates. This again shows that the leading for the development of mental activity is not the general structure, but the specific conditions of the animal's life, the nature of its relationships and interactions with the environment. At the same time, this example once again demonstrates with what caution it is necessary to approach the assessment of "higher" and "lower" characters when comparing organisms occupying different phylogenetic positions, in particular when comparing protozoa and multicellular invertebrates.

The nervous system of invertebrates

Invertebrates are characterized by the presence of several sources of origin of nerve cells. In the same type of animal, nerve cells can simultaneously and independently originate from three different germ layers. Polygenesis of invertebrate nerve cells is the basis for a variety of mediator mechanisms in their nervous system.

The nervous system first appears in coelenterates. Cavities are two-layer animals. Their body is a hollow sac, the inner cavity of which is the digestive cavity. The nervous system of the coelenterates belongs to the diffuse type. Each nerve cell in it is connected by long processes to several neighboring ones, forming a nervous network. The nerve cells of the coelenterates do not have specialized polarized processes. Their processes conduct excitation in any direction and do not form long pathways. Contacts between nerve cells of the diffuse nervous system are of several types. Exists plasma contacts ensuring the continuity of the network ( anastomoses). Appear and slotted contacts between the processes of nerve cells, like synapses. Moreover, among them there are contacts in which synaptic vesicles are located on both sides of the contact - the so-called symmetrical synapses, and there is asymmetrical synapses: in them, the vesicles are located only on one side of the slit.

The nerve cells of a typical coelenterate animal hydra are evenly distributed over the surface of the body, forming some clusters in the region of the mouth and sole (Fig. 8). The diffuse neural network conducts excitation in all directions. In this case, the wave of propagating excitement is accompanied by a wave of muscle contraction.

Rice. 8. Diagram of the structure of the diffuse nervous system of a coelenterate animal:

1 - mouth opening; 2 - tentacle; 3 - outsole

Rice. 9. Diagram of the structure of the diffuse-stem nervous system of turbellaria:

1 - nerve node; 2 - pharynx; 3 - abdominal longitudinal trunk; 4 - lateral nerve trunk

In free-living flatworms, the nervous apparatus acquires features of centralization. Nerve elements are collected in several longitudinal trunks (Fig. 10, 4 , 5 ) (the most highly organized animals are characterized by the presence of two trunks), which are interconnected by transverse fibers (commissures) (Fig. 10, 6 ). The nervous system ordered in this way is called orthogon. The trunks of the orthogon are a collection of nerve cells and their processes (Fig. 10).

Along with bilateral symmetry in flatworms, the anterior end of the body is formed, on which the sense organs are concentrated (statocysts, "eyes", olfactory pits, tentacles). Following this, an accumulation of nervous tissue appears at the anterior end of the body, from which the cerebral or cerebral ganglion is formed (Fig. 10, 3 ). In the cells of the cerebral ganglion, long processes appear that extend into the longitudinal trunks of the orthogon (Fig. 10, 4 , 5 ).

Rice. 10. Diagram of the structure of the orthogonal nervous system of the ciliary worm (front end):

1 - tentacular outgrowth; 2 - nerve innervating the outgrowth; 3 - cerebral ganglion; 4 - lateral longitudinal nerve trunk; 5 - abdominal longitudinal nerve trunk; 6 - commissure

Thus, the orthogon represents the first step towards the centralization of the nervous apparatus and its cephalization (the appearance of the brain). Centralization and cephalization are the result of the development of sensory (sensory) structures.

The next stage in the development of invertebrates is the emergence of segmented animals - annelids. Their body is metameric, i.e. consists of segments. The structural basis of the nervous system of annelids is ganglion - a paired accumulation of nerve cells, located one in each segment. Nerve cells in the ganglion are located on the periphery. Its central part is occupied by neuropil - interlacing of nerve cell processes and glial cells. The ganglion is located on the ventral side of the segment under the intestinal tube. It sends its sensory and motor fibers to its own segment and to two adjacent ones. Thus, each ganglion has three pairs of lateral nerves, each of which is mixed and innervates its own segment. Sensory fibers coming from the periphery enter the ganglion through the ventral nerve roots. Motor fibers leave the ganglion along the dorsal nerve roots. Accordingly, sensory neurons are located in the ventral part of the ganglion, and motor neurons are located in the dorsal part. In addition, in the ganglion there are small cells that innervate the internal organs (vegetative elements), they are located laterally - between sensory and motor neurons. No grouping of elements was found among the neurons of the sensory, motor, or associative zones of annelid ganglia; the neurons are diffusely distributed, i.e. do not form centers.

The ganglia of annelids are linked together in a chain. Each subsequent ganglion is connected to the previous one with the help of nerve trunks, which are called connectors. At the anterior end of the body of annelids, two fused ganglia form a large subopharyngeal nerve node. Connections from the suboesophageal ganglion, bypassing the pharynx, flow into the supraesophageal ganglion, which is the most rostral (anterior) part of the nervous system. The epopharyngeal nerve ganglion includes only sensory and associative neurons. No propulsion elements were found there. Thus, the supraesophageal ganglion of annelids is the highest associative center, it exercises control over the suboesophageal ganglion. The subopharyngeal ganglion controls the underlying nodes, it has connections with two or three subsequent ganglia, while the rest of the ganglia of the abdominal nerve chain do not form connections longer than to the neighboring ganglion.

In the phylogenetic series of annelids, there are groups with well-developed sense organs (polychaete worms). In these animals, three sections are distinguished in the supraopharyngeal ganglion. The anterior part innervates the tentacles, the middle part innervates the eyes and antennae. Finally, the hindquarters develop in connection with the improvement of the chemical senses.

The nervous system has a similar structure. arthropods, i.e. built like the abdominal nerve chain, but can reach a high level of development (Fig. 11). It includes the significantly developed supraesophageal ganglion, which performs the function of the brain, the suboesophageal ganglion, which controls the organs of the oral apparatus, and the segmental ganglia of the abdominal nerve chain. The ganglia of the abdominal nerve chain can merge with each other, forming complex ganglion masses.

Rice. 12. Diagram of the structure of the brain of an insect (bee). The left half is its section:

1 - mushroom body; 2 - protocerebrum; 3 - visual blade; 4 - deutocerebrum; 5 - tritocerebrum

Brain arthropod consists of three sections: anterior - protocerebrum, middle - deutocerebrum and rear - tritocerebrum. The insect brain is distinguished by a complex structure. Mushroom bodies located on the surface of the protocerebrum are especially important associative centers of insects, and the more complex the behavior of a species, the more developed its mushroom bodies. Therefore, mushroom bodies are most developed in social insects (Fig. 12).

In almost all parts of the nervous system of arthropods, there are neurosecretory cells. Neurosecretaries play an important regulatory role in the hormonal processes of arthropods.

Rice. 13. Diagram of the structure of the ganglionic nervous system of the lamellar mollusk (toothless):

1 - cerebral commissure; 2 - cerebral ganglia; 3 - pedal ganglia; 4 - connector; 5 - visceral ganglia

In more highly organized mollusks (cephalopods), the nervous system is transformed (Fig. 14). Her ganglia merge and form a common periopharyngeal mass - brain. Two large mantle nerves branch off from the posterior part of the brain and form two large stellate ganglia. Thus, a high degree of cephalization is observed in cephalopods.

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

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

Content:

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

Nervous system functions

The human nervous system controls and regulates most of the body's functions, from stimuli through sensory receptors to motor actions.

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

The PNS is formed by nerves that connect the CNS to every part of the body. Nerves that transmit signals from the brain are called motor or efferent nerves, and nerves that transmit information from the body to the central nervous system are called sensory or afferent nerves.

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

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

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

The structure of the nervous system

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

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

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

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

Autonomic nervous system

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

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

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

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

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

Sympathetic nervous system mainly responsible for preparing us for action when we feel a significant stimulus, activating one of the automatic responses (for example, run away or attack).

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

Somatic nervous system

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

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

The afferent nerves are responsible for transmitting sensations in the body to the central nervous system (CNS). Efferent nerves are responsible for sending signals from the central nervous system to the body, stimulating muscle contraction.

The somatic nervous system consists of two parts:

Spinal nerves: They originate from the spinal cord and are made up of two branches: a sensory afferent and another efferent motor, therefore they are mixed nerves.
Cranial Nerves: Sends sensory information from the neck and head to the central nervous system.

Then both are explained:

Cranial nervous system

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

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

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

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

IV Intravenous trilevoid nerve. He is responsible for controlling eye movements.

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

Vi. External motor nerve of the optic nerve. Control of eye movements.

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

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

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

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

XI. Dorsal accessory nerve. Controls the muscles in the neck and head, which are used for movement.

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

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

These connections drive reflex actions, which are performed so quickly and unconsciously, because information does not have to be processed by the brain before it responds, it is directly controlled by the brain.

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

central nervous system

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

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

This difference is one of the reasons on which the myth is based in which we only use 10% of our brain, since the brain is composed of approximately 90% white matter and only 10% gray matter.

But although gray matter appears to be made of material that only serves to connect, it is known today that the number and way by which the connections are made have a marked effect on brain function, since if the structures are in perfect condition, but between they are not connected, they will not work correctly.

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

Cortex

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

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

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

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

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

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

Each sensory information reaches a specific point in the cortex that forms a sensory homunculus.

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

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

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

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

The primary gustatory cortex is located in the front of the impeller and in the anterior envelope, and the olfactory cortex is located in the cortex of piriformis.

The association bark includes primary and secondary. The primary cortical association is adjacent to the sensory cortex and brings together all the characteristics of perceived sensory information such as color, shape, distance, size, and so on of a visual stimulus.

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

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

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

Basal ganglia

Basal ganglia (from the Greek ganglion, "conglomerate", "node", "tumor") or basal nuclei are a group of nuclei or masses of gray matter (clusters of bodies or neuronal cells) that are located at the base of the brain between the ascending and descending paths of the white matter and riding on the brainstem.

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

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

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

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

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

Hypothalamus

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

Diencephalon

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

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

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

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

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

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

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

Cerebellum

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

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

Spinal cord

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

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

The nervous system in a living organism is represented by a network of communications that ensure its connection with the outside world and its own processes. Its basic element is a neuron - a cell with processes (axons and dendrites) that transmits information electrically and chemically.

Appointment of nervous regulation

For the first time, the nervous system appeared in living organisms when it was necessary to interact more effectively with the environment. The development of the simplest network for transmitting impulses helped not only to perceive signals from the outside. Thanks to her, it became possible to organize your own life processes for more successful functioning.

During evolution, the structure of the nervous system became more complicated: its task was not only to form an adequate response to external influences, but also to organize its own behavior. I.P. Pavlov called this way of functioning

Interaction with the environment of unicellular organisms

The nervous system first appeared in organisms consisting of more than one cell, as it transmits signals between neurons that form a network. But already in protozoa, one can observe the ability to respond to external stimuli provided by intracellular processes.

The nervous system of multicellular organisms is qualitatively different from the analogous formation in protozoa. The latter are located within the entire system of connections within the metabolism of a single cell. The ciliate "learns" about the various processes that take place outside or inside due to changes in the composition of protoplasm and the activity of some other structures. Multicellular living things have a system built of functional units, each of which is endowed with its own metabolic processes.

Thus, for the first time, the nervous system appears in someone who has not one, but several cells, that is, for the prototype, the conduction of impulses in protozoa serves. At their level of vital activity, the production of structures by protoplasm with impulse conductivity is revealed. Similarly, in more complex living beings, this function is performed by individual

Features of the nervous system of coelenterates

Multicellular animals living in colonies do not share functions among themselves, and they do not yet have a nervous network. It occurs at the stage when various functions in the multicellular organism are differentiated.

For the first time, the nervous system appears in hydra and other coelenterates. It is a network that conducts non-targeted signals. The structure is not yet formed, it is diffusely distributed throughout the body of the coelenterate. Ganglion cells and their Nisslevian substance are not fully formed. This is the simplest version of the nervous system.

The type of motor activity of an animal is determined by the diffuse reticular nervous system. Hydra performs peristaltic movements, since it does not have special body parts for movement and other movements. For motor activity, it needs an uninterrupted connection of the contracting elements, while it is required that the bulk of the conducting cells be located in the contractile part. In which animal for the first time the nervous system appears in the form of a diffuse network? Those who are the founders of the human regulation system. This is evidenced by the fact that gastrulation is present in the development of animal embryos.

Features of the nervous system of helminths

The subsequent improvement of nervous regulation was associated with the development of bilateral symmetry instead of radial and the formation of clusters of neurons in various parts of the body.

For the first time, the nervous system appears in the form of cords in 1 At this stage, it is represented by paired head fibers and formed fibers extending from them. In comparison with coelenterates, such a system is much more complicated. In helminths, groups of nerve cells are found in the form of nodes and ganglia. The prototype of the brain is a ganglion in the front of the body that performs regulatory functions. It is called the cerebral ganglion. From it, along the entire body, there are two nerve trunks, connected by jumpers.

All components of the system are not located outside, but immersed in the parenchyma and thus protected from injury. For the first time, the nervous system appears in flatworms along with the simplest sense organs: touch, vision and a sense of balance.

Features of the nervous system of nematodes

The next stage of development is the formation of an annular formation near the pharynx and several long fibers extending from it. With such characteristics, for the first time, the nervous system appears in the periopharyngeal ring, which is a single circular ganglion and performs the functions of the basic organ of perception. Associated with it is the ventral cord and the dorsal nerve.

The nerve trunks in nematodes are located intraepithelially, that is, in the hypodermal ridges. Sensilla - bristles, papillae, supplementary organs, amphids and phasmids - act as the organs of perception. They all have mixed sensitivities.

The most complex sensory organs of nematodes are amphids. They are paired, can be different in shape and are located in the front. Their main task is to recognize chemical agents located far from the body. Some roundworms also have receptors that perceive internal and external mechanical influences. They are called methanems.

Features of the nervous system of ringlets

The formation of ganglia in the nervous system further develops in annelids. In most of them, ganglionization of the abdominal trunks occurs in such a way that each segment of the worm has a pair of nerve nodes that are connected by fibers with adjacent segments. have an abdominal nerve chain formed by the cerebral ganglion and a pair of cords extending from it. They stretch along the abdominal plane. The perceiving elements are located in front and are represented by the simplest eyes, olfactory cells, ciliary fossa and locators. With paired nodes, the nervous system first appeared in annelids, but later it develops in arthropods. They have an increase in ganglia in the head and overlapping of nodes in the body.

Elements of a diffuse network in the human nervous system

The pinnacle of the evolutionary development of the nervous system is the appearance of the brain and spinal cord in humans. However, even in the presence of such complex structures, the original diffuse organization remains. This network entangles every cell of the body: skin, blood vessels, etc. But with such characteristics, for the first time a nervous system appears in someone who did not even have the ability to differentiate the environment.

Thanks to these "residual" structural units, a person has the opportunity to feel various influences even on microscopic areas. The body can react to the appearance of the smallest foreign agent by developing protective reactions. The presence of a diffuse network in the human nervous system is confirmed by laboratory research methods based on the introduction of a dye.

The general line of development of the nervous system during evolution

The evolutionary processes of the nervous system took place in three stages:

diffuse network;
ganglia;
spinal cord and brain.

The structure and function of the central nervous system is very different from earlier types. In its sympathetic section, ganglion and reticular elements are represented. In its phylogenetic development, the nervous system became more and more fragmented and differentiated. The ganglion stage of development differed from the network stage by the presence of neurons still located above the conduction system.

Any living organism is essentially a monolith, consisting of various organs and their systems, which constantly and continuously interact with each other and with the external environment. For the first time, the nervous system appeared in coelenterates; it was a diffuse network that provided an elementary conduction of impulses.

General characteristics of the nervous system

The structure of the nervous system

The structure of the nervous system

Central nervous system functions

Reflex regulation of nervous activity

Properties of nerve centers

Coordination activity of the central nervous system and its principles

Coordination principles

The leading role of the nervous system

The structure of the nervous system

Reflex activity of the nervous system

Spinal cord

Evolution of the vertebrate brain

Brain

Cerebral cortex

Evolution of the nervous system.

Nervous system

Nervous system

Stages of development of the nervous system

The leading role of the nervous system

The structure of the nervous system

Reflex activity of the nervous system

Spinal cord

Evolution of the vertebrate brain

Brain

Nervous system. As you know, the nervous system first appears in lower multicellular invertebrates;

The nervous system of invertebrates

Nervous system functions

The structure of the nervous system

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

Autonomic nervous system

Somatic nervous system

Cranial nervous system

central nervous system

Cortex

Basal ganglia

Diencephalon

Cerebellum

Spinal cord

Appointment of nervous regulation

Interaction with the environment of unicellular organisms

Features of the nervous system of coelenterates

Features of the nervous system of helminths

Features of the nervous system of nematodes

Features of the nervous system of ringlets

Elements of a diffuse network in the human nervous system

The general line of development of the nervous system during evolution

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