Nervous regulation meaning of the nervous system. Physiology of the nervous system

With the evolutionary complexity of multicellular organisms and the functional specialization of cells, the need arose for the regulation and coordination of life processes at the supracellular, tissue, organ, systemic and organismal levels. These new regulatory mechanisms and systems had to appear along with the preservation and complexity of the mechanisms for regulating the functions of individual cells using signaling molecules. Adaptation of multicellular organisms to changes in the environment could be carried out on the condition that new regulatory mechanisms would be able to provide quick, adequate, targeted responses. These mechanisms must be able to remember and retrieve from the memory apparatus information about previous influences on the body, and also have other properties that ensure effective adaptive activity of the body. They became the mechanisms of the nervous system that appeared in complex, highly organized organisms.

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

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

General characteristics of the nervous system

One of the functions of the nervous system is perception various signals (stimulants) of the external and internal environment of the body. Let us remember that any cells can perceive various signals from their environment with the help of specialized cellular receptors. However, they are not adapted to perceive a number of vital signals and cannot instantly transmit information to other cells, which function as regulators of the body’s holistic adequate reactions to the action of stimuli.

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

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

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

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

The nervous system is divided into central (brain and spinal cord) and peripheral - nerve cells and fibers outside the cavity of the skull and spinal canal. The human brain contains more than 100 billion nerve cells (neurons). Clusters of nerve cells that perform or control the same functions form in the central nervous system nerve centers. The structures of the brain, represented by the bodies of neurons, form the gray matter of the central nervous system, and the processes of these cells, uniting into pathways, form the white matter. In addition, the structural part of the central nervous system are glial cells that form neuroglia. The number of glial cells is approximately 10 times the number of neurons, and these cells make up the majority of the mass of the central nervous system.

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

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

Structure of the nervous system

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

Rice. 1. Structure of the nervous system

Rice. 2. Functional division of the nervous system

The meaning of the nervous system:

• unites the organs and systems of the body into a single whole;
• regulates the functioning of all organs and systems of the body;
• communicates the organism with the external environment and adapts it to environmental conditions;
• forms the material basis of mental activity: speech, thinking, social behavior.

Structure of the nervous system

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

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

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

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

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

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

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

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

Functions of the central nervous system

The central nervous system performs several functions.

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

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

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

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

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

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

Reflex regulation of nervous activity

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

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

Reflex translated from Latin means “reflection”. The term “reflex” was first proposed by the Czech researcher I.G. Prokhaska, who developed the doctrine of reflective actions. The further development of reflex theory is associated with the name of I.M. Sechenov. He believed that everything unconscious and conscious occurs as a reflex. But at that time there were no methods for objectively assessing brain activity that could confirm this assumption. Later, an objective method for assessing brain activity was developed by Academician I.P. Pavlov, and it was called the method of conditioned reflexes. Using this method, the scientist proved that the basis of the higher nervous activity of animals and humans are conditioned reflexes, formed on the basis of unconditioned reflexes due to the formation of temporary connections. Academician P.K. Anokhin showed that all the diversity of animal and human activities is carried out on the basis of the concept of functional systems.

The morphological basis of the reflex is , consisting of several nerve structures that ensure the implementation of the reflex.

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

Rice. 4. Scheme of regulation based on the reflex principle. Reflex arc: 1 - receptor; 2 - afferent pathway; 3 - nerve center; 4 - efferent pathway; 5 - working organ (any organ of the body); MN - motor neuron; M - muscle; CN - command neuron; SN - sensory neuron, ModN - modulatory neuron

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

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

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

A receptor is a specialized formation that perceives irritation. The receptor consists of specialized highly sensitive cells.

The afferent link of the arc is a receptor neuron and conducts excitation from the receptor to the nerve center.

The nerve center is formed by a large number of intercalary and motor neurons.

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

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

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

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

Unconditioned reflexes - congenital, hereditary reactions. Unconditioned reflexes are carried out through reflex arcs already formed in the body. Unconditioned reflexes are species specific, i.e. characteristic of all animals of this species. They are constant throughout life and arise in response to adequate stimulation of receptors. Unconditioned reflexes are also classified according to their biological significance: nutritional, defensive, sexual, locomotor, orienting. Based on the location of the receptors, these reflexes are divided into exteroceptive (temperature, tactile, visual, auditory, taste, etc.), interoceptive (vascular, cardiac, gastric, intestinal, etc.) and proprioceptive (muscle, tendon, etc.). Based on the nature of the response - motor, secretory, etc. Based on the location of the nerve centers through which the reflex is carried out - spinal, bulbar, mesencephalic.

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

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

At the heart of modern ideas about the reflex activity of the body is the concept of a useful adaptive result, to achieve which any reflex is performed. Information about the achievement of a useful adaptive result enters the central nervous system via a feedback link in the form of reverse afferentation, which is an obligatory component of reflex activity. The principle of reverse afferentation in reflex activity was developed by P.K. Anokhin and is based on the fact that the structural basis of the reflex is not a reflex arc, but a reflex ring, which includes the following links: receptor, afferent nerve pathway, nerve center, efferent nerve pathway, working organ , reverse afferentation.

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

Properties of nerve centers

Nerve centers have a number of characteristic functional properties.

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

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

A summation of excitations can occur in nerve centers.

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

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

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

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

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

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

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

Coordination activity of the central nervous system and its principles

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

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

Principles of coordination activities

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

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

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

The principle of a common final path follows from the principle of convergence and is close in essence. It is understood as the possibility of carrying out the same reaction, triggered by the final efferent neuron in the hierarchical nerve chain, to which the axons of many other nerve cells converge. An example of a classic terminal pathway is the motor neurons of the anterior horns of the spinal cord or the motor nuclei of the cranial nerves, which directly innervate muscles with their axons. The same motor reaction (for example, bending an arm) can be triggered by the receipt of impulses to these neurons from pyramidal neurons of the primary motor cortex, neurons of a number of motor centers of the brain stem, interneurons of the spinal cord, axons of sensory neurons of the spinal ganglia in response to signals perceived by different sensory organs (light, sound, gravitational, pain or mechanical effects).

Divergence principle is realized in divergent chains of neurons, in which one of the neurons has a branching axon, and each of the branches forms a synapse with another nerve cell. These circuits perform the functions of simultaneously transmitting signals from one neuron to many other neurons. Thanks to divergent connections, signals are widely distributed (irradiated) and many centers located at different levels of the central nervous system are quickly involved in the response.

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

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

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

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

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

The principle of dominance is also implemented based on the peculiarities of interaction between nerve centers. The neurons of the dominant, most active center (focus of excitation) have persistently high activity and suppress excitation in other nerve centers, subordinating them to their influence. Moreover, the neurons of the dominant center attract afferent nerve impulses addressed to other centers and increase their activity due to the receipt of these impulses. The dominant center can remain in a state of excitement for a long time without signs of fatigue.

An example of a state caused by the presence of a dominant focus of excitation in the central nervous system is the state after a person has experienced an important event for him, when all his thoughts and actions in one way or another become associated with this event.

Properties of the dominant

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

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

The main role in regulating the functions of the body and ensuring its integrity belongs to the nervous system. This regulation mechanism is more advanced. Firstly, nervous influences are transmitted much faster than chemical influences, and therefore the body, through the nervous system, carries out rapid responses to the action of stimuli. Due to the significant speed of nerve impulses, interaction between parts of the body is established quickly in accordance with the needs of the body.

Secondly, nerve impulses come to certain organs, and therefore the responses carried out through the nervous system are not only faster, but also more accurate than with humoral regulation of functions.

Reflex is the main form of nervous activity

All activity of the nervous system is carried out by reflex. With the help of reflexes, the interaction of various systems of the whole organism and its adaptation to changing environmental conditions are carried out.

When blood pressure in the aorta rises, the activity of the heart changes reflexively. In response to the temperature influences of the external environment, a person’s skin blood vessels narrow or expand; under the influence of various stimuli, cardiac activity, breathing intensity, etc. reflexively change.

Thanks to reflex activity, the body quickly responds to various influences of the internal and external environment.

Irritations are perceived by special nerve formations - receptors. There are various receptors: some of them are irritated by changes in ambient temperature, others by touch, others by pain stimulation, etc. Thanks to the receptors, the central nervous system receives information about all changes in the environment, as well as changes within the body.

When the receptor is irritated, a nerve impulse arises in it, which spreads along the centripetal nerve fiber and reaches the central nervous system. The central nervous system “learns” about the nature of the irritation by the strength and frequency of nerve impulses. In the central nervous system, a complex process of processing incoming nerve impulses occurs, and through centrifugal nerve fibers, impulses from the central nervous system are sent to the executive organ (effector).

To carry out a reflex act, the integrity of the reflex arc is necessary (Fig. 2).

Experience 2

Immobilize the frog. To do this, wrap the frog in a gauze or linen napkin, leaving only the head exposed. The hind legs should be extended, and the front legs should be tightly pressed to the body. Insert the blunt blade of the scissors into the frog's mouth and cut off the upper jaw with the skull. Don't destroy the spinal cord. A frog in which only the spinal cord is preserved, and the overlying parts of the central nervous system are removed, is called spinal. Secure the frog in the tripod by clamping the lower jaw with a clamp or pinning the lower jaw to a cork secured in the tripod. Leave the frog hanging for a few minutes. Judge the restoration of reflex activity after removal of the brain by the appearance of a response to a pinch. To prevent the skin from drying out, periodically dip the frog into a glass of water. Pour a 0.5% solution of hydrochloric acid into a small glass, lower the frog's hind leg into it and observe the reflexive withdrawal of the leg. Rinse off the acid with water. On the hind leg, in the middle of the lower leg, make a circular cut in the skin and use surgical tweezers to remove it from the bottom of the leg, making sure that the skin is carefully removed from all the toes. Dip the foot into the acid solution. Why doesn't the frog withdraw its limb now? Dip the other frog's leg, from which the skin has not been removed, into the same acid solution. How does the frog react now?

Disrupt the frog's spinal cord by inserting a dissecting needle into the spinal canal. Dip the paw on which the skin is preserved into the acid solution. Why doesn’t the frog withdraw its paw now?

Nerve impulses during any reflex act, arriving in the central nervous system, are able to spread throughout its different parts, involving many neurons in the process of excitation. Therefore, it is more correct to say that the structural basis of reflex reactions is made up of neural chains of centripetal, central and centrifugal neurons.

Feedback principle

There are both direct and feedback connections between the central nervous system and executive organs. When a stimulus acts on the receptors, a motor reaction occurs. As a result of this reaction, receptors are excited in the executive organs (effectors) - muscles, tendons, joint capsules - from which nerve impulses enter the central nervous system. This secondary centripetal impulses, or feedbacks. These impulses constantly signal the nerve centers about the state of the motor system, and in response to these signals, new impulses are sent from the central nervous system to the muscles, including the next phase of movement or changing movement in accordance with the conditions of activity.

Feedback is very important in the coordination mechanisms carried out by the nervous system. In patients whose muscle sensitivity is impaired, movements, especially walking, lose their smoothness and become uncoordinated.

Conditioned and unconditioned reflexes

A person is born with a number of ready-made, innate reflex reactions. This unconditioned reflexes. These include the acts of swallowing, sucking, sneezing, chewing, salivation, secretion of gastric juice, maintaining body temperature, etc. The number of innate unconditioned reflexes is limited, and they cannot ensure the body’s adaptation to constantly changing environmental conditions.

On the basis of innate unconditioned reactions in the process of individual life, conditioned reflexes. These reflexes in higher animals and humans are very numerous and play a huge role in the adaptation of organisms to living conditions. Conditioned reflexes have signaling significance. Thanks to conditioned reflexes, the body is warned in advance that something significant is approaching. By the smell of burning, people and animals learn about approaching trouble, fire; Animals use smell and sounds to find prey or, on the contrary, to escape from attacks by predators. Based on numerous conditional connections formed during an individual’s life, a person acquires life experience that helps him navigate the environment.

In order to make the difference between unconditioned and conditioned reflexes clearer, let's take a (mental) excursion to the maternity hospital.

There are three main rooms in the maternity hospital: the ward where childbirth takes place, the newborn ward and the mothers' room. After the baby is born, he is brought to the newborn ward and given a little rest (usually 6-12 hours), and then taken to the mother to be fed. And as soon as the mother puts the baby to the breast, he grabs her with his mouth and begins to suck. Nobody taught this to a child. Sucking is an example of an unconditioned reflex.

Here is an example of a conditioned reflex. First, as soon as the newborn gets hungry, he starts screaming. However, after two or three days, the following picture is observed in the newborn ward: feeding time approaches, and one after another the children begin to wake up and cry. The nurse takes them in turn and swaddles them, washes them if necessary, and then places them on a special gurney to take them to their mothers. The behavior of the children is very interesting: as soon as they were swaddled, placed on a gurney and taken out into the corridor, they all fell silent, as if on command. A conditioned reflex has developed to the time of feeding, to the environment before feeding.

To develop a conditioned reflex, it is necessary to reinforce the conditioned stimulus with an unconditioned reflex and their repetition. As soon as swaddling, washing and laying on the gurney coincided 5-6 times with subsequent feeding, which here plays the role of an unconditioned reflex, a conditioned reflex was developed: stop screaming, despite the ever-increasing hunger, wait a few minutes until the feeding begins. By the way, if you take children out into the corridor and are late with feeding, then after a few minutes they start screaming.

Reflexes can be simple or complex. All of them are interconnected and form a system of reflexes.

Experience 3

Develop a conditioned blink reflex in a person. It is known that when a stream of air hits the eye, a person closes it. This is a defensive, unconditional reflex reaction. If you now combine blowing air into the eye several times with some indifferent stimulus (the sound of a metronome, for example), then this indifferent stimulus will become a signal for a stream of air to enter the eye.

To blow air into the eye, take a rubber tube connected to an air pump. Place a metronome nearby. Cover the metronome, pear and hands of the experimenter from the subject with a screen. Turn on the metronome and after 3 seconds, press the bulb, blowing a stream of air into the eye. The metronome should continue to work when air is blown into the eye. Turn off the metronome as soon as the blink reflex occurs. After 5-7 minutes, repeat the combination of the metronome sound with blowing air into the eye. Continue the experiment until blinking occurs only with the sound of the metronome, without blowing air. Instead of a metronome, you can use a bell, bell, etc.

How many combinations of a conditioned stimulus with an unconditioned one were needed to form a conditioned blink reflex?

Nervous system regulates the activity of all organs and systems, determining their functional unity, and ensures the connection of the body as a whole with the external environment.

The structural unit of the nervous system is a nerve cell with processes - neuron. The entire nervous system is a collection of neurons that contact each other using special devices - synapses. Based on their structure and function, there are three types of neurons:

• receptor, or sensitive;
• insertion, closing (conductor);
• effector, motor neurons, from which the impulse is sent to the working organs (muscles, glands).

The nervous system is conventionally divided into two large sections - somatic, or animal, nervous system and vegetative, or autonomic nervous system. The somatic nervous system primarily carries out the functions of connecting the body with the external environment, providing sensitivity and movement causing contraction of skeletal muscles. Since the functions of movement and feeling are characteristic of animals and distinguish them from plants, this part of the nervous system is called animal (animal).

The autonomic nervous system influences the processes of so-called plant life, common to animals and plants (metabolism, respiration, excretion, etc.), which is where its name comes from (vegetative - plant). Both systems are closely related to each other, but the autonomic nervous system has a certain degree of independence and does not depend on our will, as a result of which it is also called the autonomic nervous system. It is divided into two parts sympathetic And parasympathetic.

In the nervous system there are central part - brain and spinal cord - central nervous system and peripheral, represented by nerves extending from the brain and spinal cord, is the peripheral nervous system. A cross-section of the brain shows that it consists of gray and white matter.

Gray matter is formed by clusters of nerve cells (with the initial sections of processes extending from their bodies). Individual limited accumulations of gray matter are called cores.

White matter form nerve fibers covered with a myelin sheath (the processes of nerve cells that form the gray matter). Nerve fibers in the brain and spinal cord form pathways.

Peripheral nerves, depending on what fibers (sensory or motor) they consist of, are divided into sensitive, motor And mixed. The bodies of neurons, the processes of which make up the sensory nerves, lie in the nerve ganglia outside the brain. The cell bodies of motor neurons lie in the anterior horns of the spinal cord or motor nuclei of the brain.

I.P. Pavlov showed that the central nervous system can have three types of effects on organs:

• 1) launcher causing or stopping the function of an organ (muscle contraction, gland secretion);
• 2) vasomotor, changing the width of the lumen of blood vessels and thereby regulating the flow of blood to the organ;
• 3) trophic, increasing or decreasing and therefore the consumption of nutrients and oxygen. Thanks to this, the functional state of the organ and its need for nutrients and oxygen are constantly coordinated. When impulses are sent to a working skeletal muscle through motor fibers, causing its contraction, then at the same time impulses are sent through the autonomic nerve fibers, dilating blood vessels and strengthening them. This ensures the energetic ability to perform muscle work.

The central nervous system perceives afferent(sensitive) information that arises when specific receptors are stimulated and, in response to this, forms appropriate efferent impulses that cause changes in the activity of certain organs and systems of the body.

"...if you turn off all the receptors, then a person should fall asleep
dead sleep and never wake up."
THEM. Sechenov

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

The path along which a nerve impulse travels from the receptor to the effector (acting organ) is called reflex arc.

There are five links in the reflex arc:

• receptor;
• sensitive fiber conducting excitation to the centers;
• the nerve center where the switching of excitation from sensory cells to motor cells occurs;
• motor fiber carrying nerve impulses to the periphery;
• the acting organ is a muscle or gland.

Any irritation - mechanical, light, sound, chemical, temperature, perceived by the receptor, is transformed (converted) or, as is now commonly said, encoded by the receptor into a nerve impulse and in this form is sent along sensory fibers to the central nervous system.

With the help of receptors, the body receives information about all changes occurring in the external environment and inside the body.

In the central nervous system, this information is processed, selected and transmitted to motor nerve cells, which send nerve impulses to the working organs - muscles, glands and cause one or another adaptive act - movement or secretion.

The reflex, as an adaptive reaction of the body, ensures a subtle, precise and perfect balancing of the body with the environment, as well as control and regulation of functions within the body. This is its biological significance. A reflex is a functional unit of nervous activity.

All nervous activity, no matter how complex it is, consists of reflexes of varying degrees of complexity, i.e. it is reflected, caused by an external reason, an external push.
From clinical practice: in the clinic of S.P. Botkin observed a patient in whom, of all the receptors in the body, one eye and one ear were functioning. As soon as the patient's eyes were closed and his ear plugged, he fell asleep.

In the experiments of V.S. Galkin's dogs, whose visual, auditory and olfactory receptors were simultaneously turned off by surgery, slept 20-23 hours a day. They awoke only under the influence of internal needs or energetic influence on skin receptors. Consequently, the central nervous system works on the principle of reflex, reflection, and on the stimulus-response principle.

The reflex principle of nervous activity was discovered by the great French philosopher, physicist and mathematician Rene Descartes more than 300 years ago.
The reflex theory was developed in the fundamental works of Russian scientists I.M. Sechenov and I.P. Pavlova.

The time that elapses from the moment the stimulus is applied to the response to it is called the reflex time. It is composed of the time necessary to excite receptors, conduct excitation along sensory fibers, through the central nervous system, through motor fibers, and, finally, the latent (hidden) period of excitation of the working organ. Most of the time is spent on conducting excitation through the nerve centers - central reflex time.

The reflex time depends on the strength of stimulation and the excitability of the central nervous system. With strong irritation it is shorter; with a decrease in excitability, caused, for example, by fatigue, the reflex time increases; with an increase in excitability it decreases significantly.

Each reflex can only be evoked from a specific receptive field. For example, the sucking reflex occurs when the baby's lips are irritated; pupil constriction reflex - in bright light (illumination of the retina), etc.

d.

Each reflex has its own localization(location) in the central nervous system, i.e. that part of it that is necessary for its implementation. For example, the center of pupil dilation is in the upper thoracic segment of the spinal cord. When the corresponding section is destroyed, the reflex is absent.

Only with the integrity of the central nervous system is the perfection of nervous activity preserved. The nerve center is a collection of nerve cells located in various parts of the central nervous system, necessary for the implementation of the reflex and sufficient for its regulation.

Braking

It would seem that the excitation that arises in the central nervous system can spread unhindered in all directions and cover all nerve centers. In reality, this does not happen. In the central nervous system, in addition to the process of excitation, a process of inhibition simultaneously occurs, turning off those nerve centers that could interfere or impede the implementation of any type of activity of the body, for example, bending a leg.

Excitement called a nervous process that either causes the activity of an organ or enhances an existing one.

Under braking understand a nervous process that weakens or stops activity or prevents its occurrence. The interaction of these two active processes underlies neural activity.

The process of inhibition in the central nervous system was discovered in 1862 by I.M. Sechenov. In experiments on frogs, he made transverse sections of the brain at various levels and irritated the nerve centers by placing a crystal of table salt on the section. It was discovered that when the diencephalon is irritated, spinal reflexes are depressed or completely inhibited: the frog's leg, immersed in a weak solution of sulfuric acid, did not withdraw.

Much later, the English physiologist Sherrington discovered that the processes of excitation and inhibition are involved in any reflex act. When a muscle group contracts, the antagonist muscle centers are inhibited. When bending an arm or leg, the centers of the extensor muscles are inhibited. A reflex act is possible only with coupled, so-called reciprocal inhibition of antagonist muscles. When walking, bending the leg is accompanied by relaxation of the extensors and, conversely, when extending, the flexor muscles are inhibited. If this did not happen, then a mechanical struggle of the muscles, convulsions, would arise, and not adaptive motor acts.

When a sensory nerve is irritated,

causing the flexion reflex, impulses are sent to the centers of the flexor muscles and through the Renshaw inhibitory cells to the centers of the extensor muscles. In the first they cause the process of excitation, and in the second - inhibition. In response, a coordinated, coordinated reflex act arises - the flexion reflex.

Dominant

In the central nervous system, under the influence of certain reasons, a focus of increased excitability may arise, which has the property of attracting excitations from other reflex arcs and thereby increasing its activity and inhibiting other nerve centers. This phenomenon is called dominant.

The dominant is one of the main patterns in the activity of the central nervous system. It can arise under the influence of various reasons: hunger, thirst, self-preservation instinct, reproduction. The state of food dominance is well formulated in the Russian proverb: “A hungry godfather has bread on his mind.” In a person, the cause of dominance can be passion for work, love, or parental instinct. If a student is busy preparing for an exam or reading an exciting book, then extraneous noises do not disturb him, but even deepen his concentration and attention.

A very important factor in the coordination of reflexes is the presence in the central nervous system of a certain functional subordination, that is, a certain subordination between its departments that arises in the process of long evolution. The nerve centers and receptors of the head, as the “avant-garde” part of the body, paving the way for the organism in the environment, develop faster. The higher parts of the central nervous system acquire the ability to change the activity and direction of activity of the lower parts.

It is important to note: the higher the level of the animal, the stronger the power of the highest departments of the central nervous system, “the more the highest department is the manager and distributor of the body’s activity” (I.P. Pavlov).

In humans, such a “manager and distributor” is the cerebral cortex. There are no functions in the body that are not subject to the decisive regulatory influence of the cortex.

Scheme 1. Propagation (direction shown by arrows) of nerve impulses along a simple reflex arc

1 - sensitive (afferent) neuron; 2 - intercalary (conductor) neuron; 3 - motor (efferent) neuron; 4 - nerve fibers of the thin and wedge-shaped bundles; 5 - fibers of the corticospinal tract.

Development of a lesson on the topic “Structure and significance of the nervous system. Nervous regulation” introduces students to the structure and classification of the nervous system, determines the relationship between the nervous system and the work of internal organs. Children learn to work independently with the text of the textbook, think logically and formulate the results of logical operations in oral and written form.

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The structure and significance of the nervous system. Nervous regulation.

Goals: understand the structure and classification of the nervous system; structure of nervous tissue, neuron, gray and white matter, nerves, nerve ganglia; the essence of the concepts “reflex”, “reflex arc” and their classification. Form concepts: independently work with the textbook text, extract the necessary information from it; think logically and formulate the results of mental operations in oral and written form.

Tasks: show the leading role of the nervous system in regulating the functioning of organs and ensuring a unified system of the body; form an idea of ​​the structure and functions of the spinal cord; show the connection between the concepts of “reflex” and “spinal cord function”; develop the ability to apply knowledge to explain phenomena.

Equipment: tables: diagram of the structure of the nervous system, “Nerve cells and diagram of the reflex arc”; video "Reflex Arc"

During the classes:

1. Organizing time.
2. Biological dictation.

Students define concepts from the previous lesson.

1. Learning new material.

1. The meaning of the nervous system.

A conversation summarizing the students’ knowledge acquired in different lessons and in different articles of the textbook “Biology: Man.”

The functions of the nervous system are written on the board. Students must support each point with examples and facts from previously studied topics.

1. Anatomical classification of parts of the nervous system.

A story with elements of conversation. Drawing up a diagram of the “Nervous System”

1. Spinal cord

Structure of the spinal cord (teacher explanation)

Spinal cord lies in the spinal canal and in adults is a long (45 cm in men and 41-42 cm in women), somewhat flattened from front to back cylindrical cord, which at the top directly passes into the medulla oblongata, and at the bottom ends with a conical point at the level of the II lumbar vertebra. Knowledge of this fact is of practical importance (in order not to damage the spinal cord during a lumbar puncture for the purpose of taking cerebrospinal fluid or for the purpose of spinal anesthesia, it is necessary to insert a syringe needle between the spinous processes of the III and IV lumbar vertebrae).

Internal structure of the spinal cord.The spinal cord consists of gray matter containing nerve cells and white matter made up of myelinated nerve fibers. Gray matter , lies inside the spinal cord and is surrounded on all sides by white matter. Gray matter forms two vertical columns located in the right and left halves of the spinal cord. In the middle of it is a narrow central canal, the spinal cord, running the entire length of the latter and containing cerebrospinal fluid. White matter consists of nerve processes that make up three systems of nerve fibers:

1. Short bundles of associative fibers connecting parts of the spinal cord at different levels (afferent and interneurons).
2. Long centripetal (sensitive, afferent).
3. Long centrifugal (motor, efferent).

Functions of the spinal cord (Teacher's story, demonstration of the unconditioned knee reflex, image of the reflex arc of the knee reflex)

Reflex - an involuntary act, a quick response of the body to the action of a stimulus, carried out with the participation of the central nervous system and under its control. This is the main form of nervous activity in the body of multicellular animals, including humans.

You know from your zoology course that an organism is born with a large set of ready-made, innate reflexes. Some reflexes are developed during life under certain environmental conditions. What are such reflexes called (unconditioned and conditioned, respectively).

Let us consider the mechanism of the reflex using the example of the knee reflex. All organs of the body have receptors - sensitive nerve endings that convert stimuli into nerve impulses. They are also found in the thigh muscle. If you hit the tendon ligament just below the knee, the muscle is stretched and excitation occurs in its receptors, which is transmitted along the sensory (afferent) nerve to the motor (efferent) nerve, the body of which is located in the spinal cord. Through this neuron, the nerve impulse reaches the same muscle (working organ), and it contracts, extending the leg at the knee joint. Clusters of neurons of the central nervous system that cause a certain reflex action are calledreflex centersthese reflexes. The knee reflex occurs when not one, but many receptors located in one area of ​​the body are stimulated -reflexogenic zone (receptive field).

Thus, the material basis of the reflex isreflex arc- a chain of neurons that forms the path of a nerve impulse during a reflex.

Using this example, fill out the table “Reflex Arc Links” from memory:

Reflex arc links	Functions of links
1. Receptor	Conversion of irritation into nerve impulses
2. Sensitive (afferent, centripetal) neuron	Conduction of impulses to the central nervous system
3. Central nervous system (spinal cord or brain) CNS	Analysis, processing of received signals and their transmission to the motor neuron
4. Executive (efferent, centrifugal) neuron	Conduction of impulses from the central nervous system to the working organ
5. Effector - nerve ending in the executive organ	Response - effect (contraction in a muscle, secretion in a gland)

Watch the video “Reflex Arc”

1. Connection between the spinal cord and the brain(teacher explanation)

1. Consolidation of knowledge.

Frontal written work.

Complete the definitions.

Nerve ganglia are clusters of ______________

Nerves are clusters of ___________________

A reflex is the _____________________ of the body on _____________________, which is carried out with the help of _______________.

1. What is called a reflex?
2. In the dark, entering your room, you accurately locate the switch and turn on the light. Is your movement towards the switch an unconditioned or conditioned reflex? Justify your answer.
3. How many links does the reflex arc include?
4. What anatomical structures are represented by each section of the reflex arc?
5. Is it possible to implement a reflex if one of the links of the reflex arc is disrupted? Why?
6. In some people, the knee reflex is weak. To strengthen it, they suggest clasping your hands in front of your chest and pulling them in different directions. Why does this lead to an increase in the reflex?

HomeworkTextbook by A.G. Dragomilova, R.D. Masha § 46, 49. Workbook No. 2 tasks 150-153, 158, 181.