The pathogenic agent, acting on the body of higher animals and humans, primarily causes irritation of the neuroreceptor devices (extero- or interoreceptors), the sensitivity of which is many times higher than the sensitivity threshold of other tissue elements. Receptor formations are the initial link of reflex arcs, with the help of which the body responds to disease-causing influences emanating from its external or internal environment.

The pathological process may initially manifest itself as tissue damage at the point of application of the stimulus: mechanical, chemical, thermal, infectious, etc. In this case, metabolic disorders and tissue structure arise. But such direct and limited disturbances due to the simultaneous stimulation of neuro-receptor formations that send signals to the central nervous system also lead to a general reaction of the body, which is based on a reflex mechanism. This can be seen, for example, in the burn-inducing experiment. The impact on the body surface of a thermal agent is accompanied by tissue damage and at the same time a reflex increase in blood pressure, changes in blood formation, metabolism, respiratory distress, etc.

As illustrations, one can also cite the participation of the nervous system in the mechanism of occurrence of those phenomena that often accompany the blockage of a blood vessel (embolism), for example, embolism of the vessels of the pulmonary circulation. They consist in a reflex spasm of the pulmonary and coronary arteries, a drop in total blood pressure and a change in breathing. Interruption of reflex pathways with the help of surgical or pharmacological influences weakens these phenomena, which, to a certain extent, depend on local mechanical disturbances of blood flow. Influences on the nervous system can also weaken and restore functions impaired by embolism.

Pathological processes can occur by mechanism Not only unconditional, but also conditional reflexes. With repeated combination of a pathogenic factor with an indifferent stimulus, the latter can also cause this disease, which in this case arises in a conditioned reflex way. For example, in dogs, by the conditioned reflex mechanism, it is possible to reproduce intoxication with morphine, eserine, atropine, bulbocapnin, camphor by the introduction of a physiological solution of sodium chloride. Pathological conditioned reflexes sometimes underlie the occurrence of attacks of bronchial asthma, hay, fever, eczematous skin lesions and other diseases.

In addition to the reflex, there may also be direct effect of pathogenic irritants on the central nervous system, for example, carbon dioxide accumulated in the blood, microbial toxins or toxic metabolic products.

Depending on the etiological factor, the place of its impact and the properties of the organism, the pathogenesis of a particular disease may be associated with a change in the functions of various parts of the nervous system - from the peripheral endings of the centripetal nerves to the cerebral cortex. So, breathing disorders can arise in one case from the initial irritation of the peripheral endings of the pulmonary branches of the vagus nerves, in another - from damage to the medulla oblongata or some parts of the diencephalon, in the third - from dysfunction of the cerebral cortex (for example, shortness of breath during excitement or breakdowns of the higher nervous activity). In the experiment, an increase in blood sugar content can be obtained in several ways: by irritation of the central end of the cut sciatic nerve or by an injection into the medulla oblongata, or by strong emotional arousal. In other words, the emergence of a pathological process can occur in various parts of the body. In this case, the sequence and degree of dysfunction of one or another part of the nervous system have a certain significance in the nature and speed of development of this pathological process. However, due to reflex activity, in the end, other parts of the nervous system are inevitably involved in the pathological process, the parts of which are closely interconnected.

To clarify the participation of the higher parts of the nervous system in the pathogenesis of diseases, it is also important to study its basic laws: typological properties, the ratio of the processes of excitation and inhibition, the phenomena of parabiosis, dominant, trace reactions, etc. (see Chapter IV).

In the pathogenesis of diseases, an important place is occupied by disturbances in the relationship between the central nervous system and the internal environment of the body.

The dependence of the function of internal organs on the activity of the higher parts of the central nervous system has often been noted by clinical medicine. On the one hand, the influence of various experiences and worries on the activity of the heart, breathing and digestion is known, for example, cases of heart paralysis from severe experiences, a change in the rhythm of breathing from sudden fright, indigestion due to a state of mental depression and chronic lack of appetite. On the other hand, there are well-known examples of overcoming bodily ailments in moments of emotional uplift.

On the basis of many years of in-depth studies of the activity of the cerebral hemispheres, IP Pavlov showed that the function of internal organs, regulated by subcortical formations, also has its own "cortical representation". For example, a long-term violation of the motor and secretory activity of the stomach in dogs could be observed as a result of a violation of the functional state of the higher parts of the brain caused by a collision of the processes of excitation and inhibition (collision).

The significance of violations of higher nervous activity in changes in the functions of other internal organs - bile secretion, blood pressure, urine output, and hematopoietic processes - was clarified.

Other studies have shown the possibility of the formation of conditioned reflexes on the activity of internal organs and the importance of interoreception in this process. The possibility of the occurrence of conditioned reflex polyuria (increased urination) and anuria (absence of urination), conditioned reflex bile secretion, spleen contraction, vasoconstriction and dilation, changes in respiration, metabolism, etc. was shown.

These studies served as the basis for the idea of ​​a two-way connection between the activity of the cerebral cortex and the function of internal organs (cortical-visceral relationships according to K.M.Bykov).

When impulses are received from both extero- and interoreceptors, a complex process of analysis and synthesis takes place in the cerebral cortex, the relationships between the processes of excitation and inhibition are created, which determine the nature of its influence on the function of internal organs.

Violations of the normal relationship between the cortex and the subcortical region often underlie a number of diseases, such as peptic ulcer and hypertension, bronchial asthma, and coronary insufficiency.

This influence of the higher parts of the central nervous system is carried out through the lower parts of the nervous system, through the region of the hypothalamus, where centers are located that regulate the processes occurring in the internal environment of the body with the help of efferent neurons. The hypothalamus and the underlying parts of the nervous system themselves may be the initial beginning of the onset of pathological processes, for example, polyuria, obesity, and growth disorders.

A very important link in the regulation of functions is also humoral mechanisms, especially neuro-endocrine and endocrine regulation. In view of the variety of their functions, the endocrine glands often, in close interaction with the nervous system, determine the reaction of a complex organism to the action of an irritant. So, the disorder of urination in the kidneys can be carried out through the subcortical autonomic centers and their connection with the posterior lobe of the pituitary gland, which secretes an antidiuretic hormone that affects the reabsorption function of the kidneys.

With the evolutionary development of organisms, neurohormonal relationships become increasingly important in pathological reactions. In higher animals and humans, a particularly large role belongs to the diencephalo-pituitary ratios and the pituitary-adrenal function closely related to them. When exposed to pathogenic stimuli, the body reflexively produces hormones by the anterior pituitary gland, which affect the hormonal secretion of the adrenal cortex (see the chapter on reactivity). This entire system takes an active part in the adaptability of the organism, in its nonspecific reactions to the action of any pathogenic stimulus.

In addition to the hormones of the endocrine glands, tissue hormones, physiologically active substances, such as active polypeptides and proteins, histamine, acetylcholine, and serotonin, can also participate in the pathogenesis of diseases. They can also be involved in dysregulation of functions, often found during the development of pathological processes, affecting the tissue at the site of their release and formation, or due to their delivery to tissues using the bloodstream.

Thus, the mechanisms of occurrence of pathological processes are defined as properties disease agent and body reaction, its regulatory systems.

Conditioned reflexes and their meaning.

The conditions of the environment in which humans and animals are found are constantly changing. Since unconditioned reflexes are rather conservative, they cannot ensure every time the adaptation of the body's reactions to these changes. In the process of evolution, animals have developed the ability to form reflexes, which are manifested only under certain conditions, called conditioned reflexes by I.P. Pavlov.

Conditioned reflexes unlike unconditional, they are temporary and can fade away with changes in environmental conditions. Coinciding in their action with unconditioned stimuli, conditioned stimuli acquire a signaling, warning meaning. They provide humans and animals with an early response to negative or positive stimuli.

Conditioned reflexes are formed on the basis of unconditioned ones. In the process of development of the organism, they subordinate to themselves the function of the unconditioned, adapting them in accordance with the new requirements of the environment. In the formation of conditioned reflexes, certain rules and conditions should be adhered to. The first and main condition is coincidence in time single or multiple action of a conditioned stimulus (indifferent) with an unconditioned stimulus or actions immediately after it. For example, for the formation of a conditioned salivary reflex in dogs to the sound of a bell, it is necessary that this sound precede feeding several times. After such a combination in time of the conditioned and unconditioned stimuli, saliva is released when only the bell is turned on without being accompanied by food. Consequently, the bell became a conditioned stimulus for salivation. In the same way, conditioned reflexes are formed in humans. For example, consumption of lemon causes salivation. This is an unconditioned reflex reaction. Combining several times drinking lemon with turning on the light, only turning on the light will cause salivation. This is a conditioned reflex reaction.

An important condition for the formation of conditioned reflexes is a certain the sequence of stimuli, due to the fact that under the influence of an unconditioned stimulus in the cerebral cortex in the nerve center of this stimulus, a strong focus of excitation is formed. In this case, the excitability of other parts of the cortex decreases, therefore a weak conditioned stimulus will not cause excitation of the corresponding zone of the cortex. For the formation of conditioned reflexes, it is also necessary that the cerebral cortex be free from other types of activity, and the body is in a normal functional state. The action of constant stimuli, the morbid state of the body significantly complicate the formation of conditioned reflexes. Unlike the brain of animals, the human brain is able to form conditioned reflexes not only in response to specific signals, but also to words, numbers, pictures heard or read, which provides the possibility of abstraction and generalization. The latter form the basis of our thinking and consciousness.

The mechanism of formation of conditioned reflexes. The research of I.P. Pavlov established that the formation of conditioned reflexes is based on the establishment of temporary connections in the cerebral cortex between the nerve centers of the unconditioned and conditioned stimuli. Temporary neural connection is formed as a result of the interaction of the processes of excitation and plowing (paving) the path for its conduction, which simultaneously and repeatedly arise in the cortical centers of unconditioned and conditioned stimuli. The formation of temporary connections is characteristic not only of the cerebral cortex, but also of other parts of the central nervous system. This is evidenced by experiments in which simple conditioned reflexes were developed in animals with the bark removed. Reactions such as conditioned reflexes can be developed in animals without a cortex, and even in invertebrates with very primitive nervous systems, such as annelids.

However, for higher animals and humans, the cerebral cortex plays the main role in the formation of temporary connections, although subcortical structures are also important for the formation of conditioned reflexes.

Thus, conditioned reflexes are formed as a result of the mutually coordinated activity of the cortex and subcortical centers; therefore, the structure of the reflex arc of conditioned reflexes has a rather complex character. The role of the cortex and subcortical structures in the formation of various reflexes is not the same. For example, the cortex and subcortex play the same role in the formation of autonomic conditioned reflexes, while the cortex plays the leading role in complex behavioral reactions. However, in these cases, the subcortical centers and the reticular formation contribute to the formation of conditioned reflexes.

The activity of various parts of the central nervous system during the formation of complex behavioral conditioned reflexes is manifested in the fact that the processes of their formation are accompanied by the appearance of orienting reflex reactions. The increased excitability of the cerebral cortex contributes to the closure of temporary nerve connections.

So, conditioned reflexes enable a person to adapt his behavior in accordance with changes in the environment. Conditioned reflexes are formed on the basis of unconditioned ones. The basis of the mechanism for the formation of conditioned reflexes is the establishment of temporary neural connections in the cerebral cortex between the nerve centers of the unconditioned and conditioned stimuli.

The adaptability of organisms to their environment is the result of evolution.

1) traits of adaptability to the habitat of fish and birds.

2) evidence of the relativity of adaptive traits in the given conditions of existence.

· Body shape. The streamlined body shape helps with movement in water and in the air.

· The shape of the body is similar to the environment.

· Covering coloration similar to the environment.

· Warning coloration, characteristic of poisonous or stinging insects.

· Mimicry. The similarity of defenseless animals to animals with warning coloration.

· Protective formations in the form of needles, thorns, scalding hairs.

· Adaptive behavior that scares off the approach of the enemy.

· Caring for offspring.

Adaptation to the environment is useful only in the conditions in which it was historically formed.

Example: a mole has adaptations to life in the soil, but on the surface it is helpless. Jellyfish are adapted to life in HO, but those washed up on the shore die.

3) What biological consequences can the acquisition of new adaptive traits by populations and species lead to?

The emergence of new species and populations

Complication or simplification of the organization of living organisms

Complete extinction of species and populations

1) reflex- This is the body's response to irritations of the central nervous system caused by the environment.

Conditioned reflexes - these are reflexes that are acquired throughout life and are strictly individual.

Unconditioned reflexes - these are reflexes that are inherited from parents and persist throughout life.

2) reflex principle of the nervous system.

Perception of irritation from the external environment by receptors, the emergence of nerve impulses in them

They are transmitted through sensitive neurons to the spinal cord of the central nervous system

In the nerve center, the signal is switched to the motor neuron associated with the working muscle

The reflex arc is the path along which nerve impulses travel when a reflex is exercised.

Example: a person touches a hot kettle. The nerve impulse is transmitted to the nerve center. There he switches to a motor neuron, as a result of which the person withdraws his hand.

3) the role of reflexes in the life of humans and animals.

Perception and response to environmental stimuli.

The schoolchild learns about conditioned and unconditioned reflexes even in the first lessons of zoology, when a vivid example of “Pavlov's dog” is given, in which salivation begins after giving a certain signal. At the same time, the student gets the first idea about the role of reflexes in human life and about the existence of the so-called "first signal system". However, beyond the scope of the school curriculum, there is such a concept as the "second signaling system", which is of no less importance.

The role of the system of conditioned and unconditioned reflexes in human life

What are the types of reflexes, what is the difference between conditioned and unconditioned reflexes, and what is their meaning?

For example, you burn your finger with a match and pull your hand away, and immediately, without hesitation. Painful irritation of the skin was transmitted by nerve fibers to a group of cells in the central nervous system that are in charge of the motor functions of the muscles of the hands. The excitement that arose in them was immediately transmitted along other nerve fibers to the muscles. They shrank sharply - the hand twitched, the fire no longer burns the finger. This type of human reflex is called unconditioned, there are many such reflexes and they are all innate.

And conditioned reflexes need to be created, developed. Research in this area is associated with the name of our famous physiologist I. P. Pavlov. It was this scientist who substantiated the importance of reflexes in human life and proved that if the system of unconditioned reflexes is repeatedly accompanied by a certain stimulus, then after a while the stimulus will begin to cause this reflex.

Here's an example. You will be injected with a needle and at the same time ringing a bell. After a certain number of repetitions, the sound of the bell becomes a signal to withdraw the hand. The needle did not prick, and the hand twitched involuntarily. The conditioned reflex has been created.

Conditioned and unconditioned reflexes of a person play an important role in life. The child, being burnt by the fire, further withdraws his hand even before the fire again scorches his skin. The forest beast, having become closely acquainted with some danger, behaves more cautiously the next time. Pavlov called this perception of the surrounding reality by the brain of humans and animals the first signal system.

In addition, humans have a second signaling system. In this case, words-images and concepts are the conditioned stimulus. If, say, a person has experienced the strongest fear associated with a fire, then in his presence it is enough to shout “Fire!” To cause the same fear.

Both signaling systems of conditioned reflexes in our body are closely interconnected. They represent the work of our central nervous system. And the latter regulates all the activities of the body. It is known that various emotional experiences (fear, grief, joy, etc.) can cause changes in the work of the heart (faster and slower heart rate, narrowing or dilation of blood vessels, redness or pale skin), can lead to gray hair, and so on. This means that in one way or another we can influence the work of many internal organs, including by word. It is able to noticeably affect the psyche, and therefore the work of the whole organism.

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The formation and significance of conditioned reflexes is an interesting question to consider.

Conditioned Reflex Values

Once the scientist Pavlov divided all reflex reactions into 2 groups - conditioned and unconditioned reflexes.

The formation of conditioned reflexes occurs in the process of combining a conditioned stimulus with an unconditioned reflex. For this to happen, two conditions must be met:

1. The action of the conditioned stimulus must necessarily be somewhat preceded by the action of the unconditioned stimulus.
2. The conditioned stimulus is repeatedly reinforced by the influence of the unconditioned stimulus.

The environment is in constantly changing conditions, therefore, in order to preserve the vital activity of the organism and adaptive behavior, conditioned reflexes are needed, the impact of which is possible due to the participation of the cerebral hemispheres.

It should be noted that conditioned reflexes are not congenital, they are formed throughout life on the basis of unconditioned reflexes under the influence of some environmental factors. Such reflexes are individual, that is, in individuals of the same species, the same reflex may be absent in some, while in others it may be present.

The mechanism for the formation of conditioned reflexes is the process of establishing a temporary connection between 2 sources of excitation in the foci of the brain. They are constantly produced in higher animals, especially in humans. This can be explained by the dynamism of the environment, the constant change of living conditions, to which the nervous system must quickly adapt.

The biological significance of the conditioned reflex huge in the life of animals and humans - they provide adaptive behavior. Thanks to them, it is possible to accurately navigate in time and space, find food, avoid dangers and eliminate harmful effects for the body. The number of conditioned reflexes increases with age. In addition, behavioral experiences are acquired that help adult organisms better adapt to life.