The principle of the functioning of the human nervous system. Basic principles of the functioning of the nervous system What is the principle underlying nervous activity

3-1. What is the principle behind the activity nervous system? Draw a diagram of its implementation.

3-2. List the protective reflexes that occur when irritating the mucous membrane of the eyes, nasal cavity, mouth, pharynx and esophagus.

3-3. Perform the gag reflex on all classification signs.

3-4. Why does the reflex time depend on the number of interneurons?

3-5. Is it possible to register the action potential of nerve A if nerve B is stimulated under the experimental conditions shown in the diagram (at point 1)? What if you irritate nerve A at point 2?

3-6. Will the neuron be excited if subthreshold stimuli are simultaneously applied to it along several axons? Why?

3-7. What should be the frequency of irritating stimuli in order to cause excitation of a neuron by subthreshold stimuli? Give a general answer.

3-8. Neuron A receives stimuli with a frequency of 50 g along two axons approaching it. With what frequency can neuron A send impulses throughout the axon?

3-9. What happens to the spinal cord motor neuron when the Renshaw cell is excited?

3-10. Check if the table is correct:

3-11. Let us assume that the excitation of the center depicted below is sufficient for two neurotransmitter quanta to be released for each neuron. How will the excitation of the center and the function of the apparatus it regulate change if instead of one axon, axons A and B are simultaneously stimulated? What is this phenomenon called?

3-12. To excite the neurons of a given center, two quanta of the transmitter are sufficient. List which neurons of the nerve center will be excited if stimulation is applied to axons A and B, B and C, A, B and C? What is this phenomenon called?

3-13. What are the main advantages of neural regulation of functions over humoral regulation?

3-14. By prolonged irritation of the somatic nerve, the muscle is brought to fatigue. What happens to the muscle if we now connect the stimulation of the sympathetic nerve to this muscle? What is this phenomenon called?

3-15. The figure shows the kimograms of the cat's knee reflex. What structures of the midbrain are irritated by the reflex changes depicted on kymograms 1 and 2?

3-16. Irritation of what structure of the midbrain causes the reaction depicted in the given electroencephalogram? What is the name of this reaction?

Alpha rhythm Beta rhythm

3-17. At what level is it necessary to transect the brainstem in order to obtain the changes in muscle tone shown in the figure? What is this phenomenon called?

3-18. How will the tone of the front and hind limbs change in a bulbar animal when its head is thrown back?

3-19. How will the muscle tone of the fore and hind limbs of a bulbar animal change when its head is tilted forward?

3-20. Mark alpha, beta, theta and delta waves on the EEG and give their frequency and amplitude characteristics.

3-21. When measuring the excitability of the soma, dendrites and axonal hillock of the neuron, the following figures were obtained: the rheobase of different parts of the cell turned out to be equal to 100 mV, 30 mV, 10 mV. Tell me, which sections of the cell correspond to each of the parameters?

3-22. A muscle weighing 150 g consumed 20 ml in 5 minutes. oxygen. How much oxygen per minute is consumed in these conditions 150 g. nervous tissue?

3-23. What happens in the nerve center if impulses arrive at its neurons with a frequency at which acetylcholine does not have time to be completely destroyed by cholinesterase and accumulates in large quantities on the postsynaptic membrane?

3-24. Why, when strychnine is injected, does a frog experience convulsions in response to any, even the slightest, irritation?

3-25. How will the contraction of the neuromuscular drug change if cholinesterase or amine oxidase is added to the perfused fluid?

3-26. The dog's cerebellum was removed two months ago. What symptoms of impaired motor function can you find in this animal?

3-27. What happens to the alpha rhythm on the EEG in humans when the eyes are exposed to light stimulation and why?

3-28. Which of the presented curves correspond to the action potential (AP), excitatory postsynaptic potential (EPSP) and inhibitory postsynaptic potential (EPSP)?

3-29. The patient has a complete rupture of the spinal cord between the thoracic and lumbar regions. Will he have disorders of the act of defecation and urination, and if so, how will they manifest themselves at different times after the injury?

3-30. After a gunshot wound to the buttocks, a person developed a non-healing ulcer on the lower leg. How can you explain its appearance?

3-31. The reticular formation of the brainstem is destroyed in the animal. Can the phenomenon of Sechenov's inhibition manifest itself under these conditions?

3-32. When the cerebral cortex is irritated, the dog makes movements with its front paws. What area of ​​the brain do you think is irritated?

3-33. The animal was injected with a large dose of chlorpromazine, which blocks the ascending activating system of the reticular formation of the brain stem. How does the behavior of the animal change, and why?

3-34. It is known that during a narcotic sleep during an operation, the narcotizer constantly monitors the reaction of the patient's pupils to light. For what purpose does he do this and what may be the reason for the absence of this reaction?

3-35. Sick left-handed, suffering motor aphasia... What area of ​​the cerebral cortex is affected?

3-36. The sick right-hander does not remember the names of objects, but gives a correct description of their purpose. What area of ​​this person's brain is affected?

3-37. Muscle fiber usually has one end plate, and each end plate potential exceeds a threshold level. On the central neurons, there are hundreds and thousands of synapses and EPSPs of individual synapses do not reach the threshold level. What is the physiological meaning of these differences?

3-38. Two students decided to prove in an experiment that skeletal muscle tone is maintained reflexively. Two spinal frogs were hung on a hook. Their lower legs were slightly tucked in, which indicates the presence of tone. Then the first student cut the anterior roots of the spinal cord, and the second - the posterior ones. Both frogs' legs dangled like whips. Which student delivered the experience correctly?

3-39. Why can the duration of the period of clinical death be prolonged by cooling the brain?

3-40. Why, when a person is fatigued, the accuracy of movements is first disturbed, and then the strength of contractions?

3-41. When the knee reflex in the patient is poorly expressed, to enhance it, it is sometimes suggested that the patient clasp his hands in front of the chest and pull them in different directions. Why does this lead to increased reflex?

3-42. When one axon is stimulated, 3 neurons are excited. When the other is irritated - 6. With joint stimulation, 15 neurons are excited. On how many neurons do these axons converge?

3-43. Learning to write, the child "helps" himself with his head and tongue. What is the mechanism of this phenomenon?

3-44. A flexion reflex was triggered in the frog. In this case, the flexor centers are excited and the extensor centers are reciprocally inhibited. During the experiment, the postsynaptic potentials of the motor neurons are recorded. Which of the responses (flexor EPSP or extensor EPSP) is recorded later?

3-45. With presynaptic inhibition, membrane depolarization occurs, and with postsynaptic inhibition, hyperpolarization occurs. Why do these opposite reactions produce the same inhibitory effect?

3-46. When a person gets up, gravity begins to act on him. Why don't the legs bend at the same time?

3-47. Does the animal retain any reflexes, except for the spinal cord, after cutting the spinal cord under the medulla oblongata? Breathing is supported artificially.

3-48. How can descending influences from the central nervous system change motor activity without affecting the motor neurons of the spinal cord?

3-49. The animal underwent successively two complete sections of the spinal cord under the oblong cord - at the level of C-2 and C-4 segments. How will the blood pressure change after the first and second cut?

3-50. Two patients had a cerebral hemorrhage - one of them in the cerebral cortex. in the other - in the medulla oblongata. Which patient has a more unfavorable prognosis?

3-51. What will happen to a cat that is in a state of decerebrational rigidity after cutting the brainstem below the red nucleus if the dorsal roots of the spinal cord are now severed?

3-52. The skater requires particularly precise footwork when running around the bends of the stadium track. Does it matter in this situation what position the athlete's head is in?

3-53. Motion sickness (motion sickness) occurs when the vestibular apparatus is irritated, which affects the redistribution of muscle tone. What explains the appearance of symptoms of nausea and dizziness with motion sickness?

3-54. In an experiment on a dog, the area of ​​the ventromedial nucleus of the hypothalamus was heated to 50 ° C, then the animal was kept under normal conditions. How has changed appearance dogs after a while?

3-55. When the cerebral cortex is turned off, a person loses consciousness. Is such an effect possible with absolutely intact bark and normal blood supply?

3-56. The patient is found to have gastrointestinal disorders. The doctor in the clinic sent him to a neurological clinic for treatment, not a therapeutic one. How could such a decision be dictated?

3-57. One of the main criteria for brain death is the absence of electrical activity in it. Is it possible by analogy to talk about the death of a skeletal muscle if at rest it is not possible to register an electromyogram from it?

(Problems No. 3-58 - 3-75 from the Collection of Problems edited by G. I. Kositsky [1])

3-58. Can an unconditioned reflex be carried out with the participation of only one part of the central nervous system? Is the spinal reflex carried out in the whole organism with the participation of only one ("own") segment of the spinal cord? Do the reflexes of a spinal animal differ, and if so, how do they differ from the spinal reflexes carried out with the participation of the higher located parts of the central nervous system?

3-59. At what level, I or II, should the brain incision be made and how should Sechenov's experiment be performed in order to prove the presence of intracentral inhibition?

Frog brain diagram

3-60. Indicate in the picture the structures that perceive changes in the state of skeletal muscles and name their afferent and efferent innervation. What are called gamma-efferent fibers and what role do they play in proprioception? Using the diagram, describe the physiological role of the muscle spindle

3-61. What types of braking can be carried out in the structures shown in Figures 1 and 2?

Schemes different forms inhibition in the central nervous system

3-62. Name the structures indicated in the diagram by the numbers 1, 2, 3. What process occurs in the terminal branches of axon 1 if an impulse comes to it along path 1? What process will occur under the action of impulses from neuron 2 in nerve endings 1?

Location of inhibitory synapses on presynaptic axon ramifications

3-63. Where can the electrical activity shown in the figure be recorded and what is it called? In which nervous process type 1 electrical activity is recorded and in which type 2 bioelectrical reflections of the functional state of synapses.

3-64. What is the name of the state in which the cat shown in Figure 2 is located? On which line I, II, III or IV should the incision be made in order for the cat to develop a condition similar to that shown in the figure? Which nuclei and which part of the central nervous system are separated from the lower ones during this cut? 1. Diagram of brain transections at different levels. 2. Cat after brain stem transection.

3-65. What structural feature of the autonomic nervous system is shown in the diagram? What features of the innervation of organs are associated with such a structure of synaptic connections in the ganglion?

3-66. Having considered the presented schemes of reflex arcs, determine:

1) Is it possible to register the action potential on the 2nd sensitive root during stimulation of the 1st in experiment A?

2) Is it possible to register the action potential on the motor root 2 upon stimulation of the motor root 1 in experiment B?

3) What physiological phenomenon is evidenced by the facts obtained in these experiments?

3-67. In what case will there be summation, in what case - occlusion? What type of summation in the central nervous system is shown in the diagram?

3-68. The diagram of which department of the autonomic nervous system is shown in the figure? What organs and systems of the body are inverted by this section of the autonomic nervous system?

3-69. The diagram of which part of the autonomic nervous system is shown in the figure? Name the segments of the spinal cord in which its centers are located. What organs and systems of the body are innervated by this department?

3-70. Explain why there is no primary response to the second "stimulus" (when the time of application of the first (conditioning) and second (testing) stimuli is very close) Primary responses arising in specific projection zones of the cortex during two consecutive stimulation of the sensitive nerve trunks. The letters a, b, c, d, e, etc. indicate the order of the experiment. The numbers indicate the time in ms, between stimuli

3-71. Why does the reaction of the cerebral cortex in animals with afferent stimulation and with stimulation of the reticular formation have the same manifestations on the EEG? What is this reaction called?

Electroencephalogram changes in afferent stimulation (A)

and with irritation of the reticular formation (B).

3-72. Consider both figures and explain why, when nonspecific nuclei of the thalamus are stimulated, EEG changes are recorded in different parts of the cerebral cortex? What is the name of such a reaction of the cerebral cortex? Figure A schematically shows the electrical response of various areas of the cerebral cortex to stimulation of the rhythmic current of nonspecific thalamic nuclei in a cat. Figure B shows a record of EEG changes in zones 1, 2, 3. At the bottom - a mark of irritation.

3-73. What reaction to the sound of the metronome is recorded in the EEG of a cat in a calm state? What is the difference between the EEG in Figure A and the EEG in Figure B? What is the reason for such changes in the EEG when the cat reacts to the appearance of the mouse?

Electroencephalographic reactions of a cat to the sound of a metronome in various motivational states (A and B).

3-74. When irritating what structures of the brain can a defensive reaction be obtained? When stimulating what structures of the brain can a self-stimulation reaction be obtained in animals?

Behavioral reactions of rats upon stimulation of hypothalamic structures

3-75. Which reflex is shown in the figure? Please explain. How will muscle tone change if the posterior root of the spinal cord is damaged?

(Problems No. 3-76 - 3-82 from the CD-appendix in the Textbook on Physiology, edited by K.V. Sudakov [3])

3-76. Two motor somatic reflexes were caused by stimuli of the same strength in the experimental animal. The afferent and efferent parts of the reflex arc in the first reflex are much longer than in the reflex arc of the second reflex. However, the reflex reaction time is shorter in the first case. How can one explain the high reaction rate in the presence of more extended afferent and efferent pathways? What type are the nerve fibers that provide the conduction of excitation along the afferent and efferent parts of the somatic reflex arc?

3-77. The introduction of the drug to the experimental animal leads to the cessation of somatic reflexes. What areas of the reflex arc need to be subjected to electrical stimulation in order to determine whether this drug blocks the conduction of excitation in the synapses of the central nervous system, neuromuscular synapse, or disrupts the contractile activity of the skeletal muscle itself.

3-78. Alternating stimulation of two excitatory nerve fibers converging to one neuron does not cause its excitation. When only one of the fibers is stimulated with a doubled frequency, the neuron is excited. Can excitation of a neuron occur with simultaneous stimulation of fibers converging to it?

3-79. Nerve fibers A, B and C converge to one neuron. The arrival of excitation along fiber A causes depolarization of the neuron membrane and the emergence of an action potential (AP). With the simultaneous arrival of excitation along fibers A and B, PD does not arise and hyperpolarization of the neuron membrane is observed. With the simultaneous arrival of excitation along fibers A and C, AP also does not occur, but hyperpolarization of the neuron membrane does not occur. Which of the fibers are excitatory and which are inhibitory? What mediators are inhibitory in the central nervous system? In which case is inhibition most likely to occur by the postsynaptic mechanism, in which case - by the presynaptic one?

3-80. A person injured in a car accident ruptured the spinal cord, resulting in paralyzed lower limbs? At what level did the spinal cord rupture occur?

3-81. The regulation of physiological functions is provided by nerve centers - sets of structures of the central nervous system, which can be located at different levels of the brain, and contribute to the maintenance of vital processes. From this point of view, which lesion, other things being equal, is more unfavorable for the patient's survival - a hemorrhage in the medulla oblongata or cerebral hemispheres?

3-82. The pharmacological drug reduces the increased excitability of the cerebral cortex. In experiments on animals, it was shown that the drug has no direct effect on the neurons of the cortex. What structures of the brain can this drug affect to cause a decrease in the increased excitability of the cerebral cortex?

What is the principle behind the work of the nervous system? What is called a reflex? Name the links of the reflex arc, their position and function.

The work of the nervous system is based on the reflex principle.

Reflex - the body's response to stimulation of receptors, carried out with the participation of the central nervous system (CNS). The path along which the reflex is carried out is called the reflex arc. The reflex arc consists of the following components:

A receptor that perceives irritation;

Sensitive (centripetal) nerve pathway through which excitation is transmitted from the receptor to the central nervous system;

Nervous center - a group of intercalary neurons located in the central nervous system and transmitting nerve impulses from sensitive nerve cells to motor cells;

The motor (centrifugal) nerve pathway, which transmits excitation from the central nervous system to the executive organ (muscle, etc.), the activity of which changes as a result of a reflex.

The simplest reflex arcs are formed by two neurons (knee reflex) and contain sensory and motor neurons. The reflex arcs of most reflexes include not two, but a larger number of neurons: sensory, one or more intercalated, and motor. By means of intercalary neurons, communication with the overlying parts of the central nervous system is carried out and information is transmitted about the adequacy of the response of the executive (working) organ to the received stimulus.

1. Dominant principle was formulated by A.A. Ukhtomsky as the basic principle of the work of nerve centers. According to this principle, the activity of the nervous system is characterized by the presence in the central nervous system of dominant (dominant) foci of excitation in a given period of time, in the nerve centers, which determine the direction and nature of the body's functions during this period. The dominant focus of arousal is characterized by the following properties:

* increased excitability;

* persistence of excitement (inertia), since it is difficult to suppress other excitement;

* the ability to summarize subdominant excitations;

* the ability to inhibit subdominant foci of excitation in functionally different nerve centers.

2. The principle of spatial relief. It manifests itself in the fact that the total response of the organism under the simultaneous action of two relatively weak stimuli will be greater than the sum of the responses received under their separate action. The reason for the relief is associated with the fact that the axon of an afferent neuron in the CNS synapses with a group of nerve cells, in which the central (threshold) zone and the peripheral (subthreshold) "border" are distinguished. The neurons located in the central zone receive from each afferent neuron a sufficient number of synaptic endings (for example, 2 each) (Fig. 13) to form an action potential. The neuron of the subthreshold zone receives from the same neurons a smaller number of endings (1 each), so their afferent impulses will be insufficient to cause the generation of action potentials in the neurons of the "border", and only subthreshold excitation arises. As a result, with separate stimulation of afferent neurons 1 and 2, reflex reactions occur, the total severity of which is determined only by the neurons of the central zone (3). But with simultaneous stimulation of afferent neurons, action potentials are also generated by neurons in the subthreshold zone. Therefore, the severity of such a total reflex response will be greater. This phenomenon is called the central relief. It is more often observed when weak stimuli act on the body.

3. The occlusion principle... This principle is the opposite of spatial relief and it consists in the fact that two afferent inputs jointly excite a smaller group of motor neurons compared to the effects when they are separately activated, the reason for occlusion is that afferent inputs due to convergence are partly addressed to the same motor neurons, which are inhibited when both inputs are activated simultaneously (Fig. 13). The phenomenon of occlusion is manifested in cases of the use of strong afferent stimuli.

4. Feedback principle... The processes of self-regulation in the body are similar to the technical ones, which involve automatic regulation of the process using feedback. The presence of feedback allows us to correlate the severity of changes in the parameters of the system with its operation as a whole. The connection of the output of the system with its input with a positive gain is called positive feedback, and with a negative gain, it is called negative feedback. In biological systems, positive feedback is realized mainly in pathological situations. Negative feedback improves the stability of the system, that is, its ability to return to its original state after the cessation of the influence of disturbing factors.

Feedbacks can be classified according to various criteria. For example, according to the speed of action - fast (nervous) and slow (humoral), etc.

There are many examples of the manifestation of feedback effects. For example, in the nervous system, this is how the activity of motor neurons is regulated. The essence of the process is that excitation impulses propagating along the axons of motor neurons reach not only muscles, but also specialized intermediate neurons (Renshaw cells), the excitation of which inhibits the activity of motor neurons. This effect is known as the return braking process.

An example of positive feedback is the process of the emergence of an action potential. Thus, during the formation of the ascending part of the PD, the depolarization of the membrane increases its sodium permeability, which in turn increases the depolarization of the membrane.

Feedback mechanisms are of great importance in maintaining homeostasis. For example, maintaining a constant level is carried out by changing the impulse activity of the baroreceptors of the vascular reflexogenic zones, which alter the tone of the vasomotor sympathetic nerves and thus normalize blood pressure.

5. The principle of reciprocity (combination, conjugation, mutual exclusion). It reflects the nature of the relationship between the centers responsible for the implementation of opposite functions (inhalation and exhalation, flexion and extension of the limb, etc.). For example, the activation of the proprioceptors of the flexor muscle simultaneously excites the motor neurons of the flexor muscle and inhibits the motor neurons of the extensor muscle through the intercalary inhibitory neurons (Fig. 18). Reciprocal inhibition plays an important role in the automatic coordination of motor acts,

The principle of a common final path. The effector neurons of the central nervous system (primarily the motor neurons of the spinal cord), being the final in the chain consisting of afferent, intermediate and effector neurons, can be involved in the implementation of various reactions of the body by excitations coming to them from a large number of afferent and intermediate neurons, for which they are the final path (from the central nervous system to the effector). For example, on the motor neurons of the anterior horns of the spinal cord, which innervate the muscles of the limb, the fibers of the afferent neurons, neurons of the pyramidal tract and the extrapyramidal system (cerebellar nuclei, reticular formation and many other structures) end. Therefore, these motoneurons, which provide reflex activity of the limb, are considered as the final path for the general realization of many neural influences on the limb.

33. BRAKING PROCESSES IN THE CENTRAL NERVOUS SYSTEM.

In the central nervous system, two main, interrelated processes are constantly functioning - excitation and inhibition.

Braking is active biological process, aimed at weakening, stopping or preventing the onset of the excitation process. The phenomenon of central inhibition, that is, inhibition in the central nervous system, was discovered by IM Sechenov in 1862 in an experiment called the "experiment of Sechenov's inhibition." The essence of the experiment: a crystal was applied to the cut of the visual hillocks in the frog table salt, which led to an increase in the time of motor reflexes, i.e., to their inhibition. Reflex time is the time from the onset of irritation to the onset of the response.

Inhibition in the central nervous system has two main functions. First, it coordinates functions, that is, it directs excitation along certain paths to certain nerve centers, while turning off those paths and neurons whose activity is not currently needed to obtain a specific adaptive result. The importance of this function of the inhibition process for the functioning of the organism can be observed in an experiment with the introduction of strychnine to an animal. Strychnine blocks inhibitory synapses in the central nervous system (mainly glycinergic) and thereby removes the basis for the formation of the inhibition process. Under these conditions, irritation of the animal causes an uncoordinated reaction, which is based on diffuse (generalized) irradiation of excitation. In this case, adaptive activity becomes impossible. Secondly, inhibition performs a protective or protective function, protecting nerve cells from overexcitation and exhaustion under the action of super-strong and prolonged stimuli.

BRAKING THEORY. N. Ye. Vvedensky (1886) showed that very frequent irritations of the nerve of a neuromuscular preparation cause muscle contractions in the form of smooth tetanus, the amplitude of which is small. N. Ye. Vvedensky believed that in a neuromuscular preparation with frequent irritation, a process of pessimal inhibition occurs, that is, inhibition is, as it were, a consequence of overexcitation. It has now been established that its mechanism consists in prolonged, stagnant depolarization of the membrane caused by an excess of a mediator (acetylcholine) released during frequent stimulation of the nerve. The membrane completely loses its excitability due to inactivation of sodium channels and is unable to respond to the arrival of new excitations by releasing new portions of the transmitter. Thus, excitement turns into the opposite process - inhibition. Consequently, excitation and inhibition are, as it were, the same process, arise in the same structures, with the participation of the same mediator. This theory of inhibition is called unitary-chemical or monistic.

Mediators on the postsynaptic membrane can cause not only depolarization (EPSP), but also hyperpolarization (EPSP). These mediators increase the permeability of the subsynaptic membrane for potassium and chlorine ions, as a result of which the postsynaptic membrane hyperpolarizes and TPSP appears. This theory of inhibition is called binary-chemical, according to which inhibition and excitation develop "according to different mechanisms, with the participation of inhibitory and excitatory mediators, respectively.

CENTRAL BRAKING CLASSIFICATION.

Inhibition in the central nervous system can be classified according to various criteria:

* according to the electrical state of the membrane - depolarizing and hyperpolarizing;

* in relation to the synapse - presynaptic and postsynaptic;

* on neuronal organization - translational, lateral (lateral), return, reciprocal.

Postsynaptic inhibition develops in conditions when the mediator released by the nerve ending changes the properties of the postsynaptic membrane in such a way that the ability of the nerve cell to generate excitation processes is suppressed. Postsynaptic inhibition can be depolarizing, if it is based on the process of prolonged depolarization, and hyperpolarizing, if it is hyperpolarization.

Presynaptic inhibition due to the presence of intercalary inhibitory neurons that form axo-axonal synapses on afferent terminals that are presynaptic in relation to, for example, a motor neuron. In any case of activation of an inhibitory interneuron, it causes depolarization of the membrane of afferent terminals, which worsens the conditions for conducting AP through them, which thus reduces the amount of mediator released by them, and, consequently, the efficiency of synaptic transmission of excitation to the motor neuron, which reduces its activity (Fig. 14) ... The mediator in such axo-axonal synapses is, apparently, GABA, which causes an increase in the permeability of the membrane for chlorine ions, which leave the terminal and partially, but for a long time, depolarize it.

Translational braking due to the inclusion of inhibitory neurons along the path of excitation (Fig. 15).

Reverse braking carried out by intercalary inhibitory neurons (Renshaw cells). Impulses from motor neurons, through collaterals extending from its axon, activate the Renshaw cell, which in turn causes inhibition of the discharges of this motor neuron (Fig. 16). This inhibition is realized due to inhibitory synapses formed by the Renshaw cell on the body of the motor neuron that activates it. Thus, a circuit with negative feedback is formed from two neurons, which makes it possible to stabilize the discharge frequency of the motor neuron and suppress its excessive activity.

Lateral (lateral) inhibition... Intercalated cells form inhibitory synapses on neighboring neurons, blocking lateral pathways for the propagation of excitation (Fig. 17). In such cases, excitement is directed only along a strictly defined path. It is lateral inhibition that provides, in the main, systemic (directed) irradiation of excitation in the central nervous system.

Reciprocal inhibition. An example of reciprocal inhibition is inhibition of antagonist muscle centers. The essence of this type of inhibition is that the excitation of the proprioceptors of the flexor muscles simultaneously activates the motoneurons of these muscles and intercalary inhibitory neurons (Fig. 18). Excitation of interneurons leads to postsynaptic inhibition of motor neurons of the extensor muscles.

The main and specific manifestation of the activity of the nervous system is the reflex principle. This is the body's ability to respond to external or internal stimuli with a motor or secretory response. The foundations of the doctrine of the reflex activity of the body were laid by the French scientist Rene Descartes (1596-1650). Highest value had his ideas about the reflex mechanism of the relationship of the organism with the environment. The term "reflex" itself was introduced much later - mainly after the publication of the works of the outstanding Czech anatomist and physiologist G. Prohaski (1749-1820).

A reflex is a natural reaction of the body in response to stimulation of receptors, which is carried out by a reflex arc with the participation of the central nervous system. This is an adaptive reaction of the body in response to a change in internal or environment... Reflex reactions ensure the integrity of the organism and the constancy of its internal environment, the reflex arc is the main unit of integrative reflex activity.

A significant contribution to the development of reflex theory was made by I.M. Sechenov (1829-1905). He was the first to use the reflex principle to study the physiological mechanisms of mental processes. In the work "Reflexes of the Brain" (1863) I.M. Sechenov argued that the mental activity of humans and animals is carried out by the mechanism of reflex reactions that occur in the brain, including the most complex of them - the formation of behavior and thinking. On the basis of his research, he concluded that all acts of conscious and unconscious life are reflexive. Reflex theory of I.M. Sechenov was the basis on which the teachings of I.P. Pavlova (1849-1936) on higher nervous activity. The method of conditioned reflexes developed by him expanded the scientific understanding of the role of the cerebral cortex as a material substrate of the psyche. I.P. Pavlov formulated a reflex theory of the brain, which is based on three principles: causality, structure, the unity of analysis and synthesis. PK Anokhin (1898-1974) proved the importance of feedback in the reflex activity of the organism. Its essence lies in the fact that during the implementation of any reflex act, the process is not limited only by the effector, but is accompanied by the excitation of the receptors of the working organ, from which information about the consequences of the action comes by afferent pathways to the central nervous system. There were ideas about the "reflex ring", "feedback".

Reflex mechanisms play an essential role in the behavior of living organisms, ensuring their adequate response to environmental signals. For animals, reality is signaled almost exclusively by irritations. This is the first signaling system of reality, common to humans and animals. I.P. Pavlov proved that for humans, unlike animals, the object of display is not only the environment, but also social factors. Therefore, for him, the second signaling system acquires decisive importance - the word as the signal of the first signals.

The conditioned reflex underlies the higher nervous activity of humans and animals. It is always included as an essential component in the most difficult manifestations of behavior. However, not all forms of behavior of a living organism can be explained from the point of view of the reflex theory, which reveals only the mechanisms of action. The reflex principle does not answer the question of the expediency of human and animal behavior, does not take into account the result of the action.

Therefore, over the past decades, on the basis of reflex ideas, the concept of the leading role of needs as the driving force of human and animal behavior has been formed. The presence of needs is a necessary prerequisite for any activity. The activity of the body acquires a certain direction only if there is a goal that meets the given need. Each behavioral act is preceded by needs that arose in the process of phylogenetic development under the influence of environmental conditions. That is why the behavior of a living organism is determined not so much by a reaction to external influences as by the need to implement the planned program, a plan aimed at satisfying a particular need of a person or animal.

PC. Anokhin (1955) developed the theory of functional systems, which provides for a systematic approach to the study of the mechanisms of the brain, in particular, the development of problems of the structural and functional basis of behavior, physiology of motivations and emotions. The essence of the concept is that the brain can not only adequately respond to external stimuli, but also foresee the future, actively make plans for its behavior and implement them. The theory of functional systems does not exclude the method of conditioned reflexes from the sphere of higher nervous activity and does not replace it with something else. It makes it possible to delve deeper into the physiological essence of the reflex. Instead of the physiology of individual organs or structures of the brain, the systems approach considers the activity of the organism as a whole. For any behavioral act of a person or animal, such an organization of all brain structures is needed that will provide the desired end result. So, in the theory of functional systems, the useful result of an action occupies a central place. Actually, the factors that are the basis for achieving the goal are formed according to the type of versatile reflex processes.

One of the important mechanisms of the activity of the central nervous system is the principle of integration. Due to the integration of somatic and autonomic functions, which is carried out by the cerebral cortex through the structures of the limbic-reticular complex, a variety of adaptive reactions and behavioral acts are realized. The highest level of integration of functions in humans is the frontal cortex.

An important role in mental activity the principle of dominant, developed by O. O. Ukhtomsky (1875-1942), plays a role in humans and animals. Dominant (from Latin dominari to dominate) is an excitation that is superior in the central nervous system, which is formed under the influence of stimuli from the surrounding or internal environment and at a certain moment subjugates the activity of other centers.

The brain with its higher section, the cerebral cortex, is a complex self-regulatory system based on the interaction of excitatory and inhibitory processes. The principle of self-regulation is carried out at different levels of the analytic systems - from the cortical regions to the level of receptors with the constant subordination of the lower parts of the nervous system to the higher ones.

Studying the principles of the functioning of the nervous system, not without reason, the brain is compared with an electronic computer. As you know, the basis for the operation of cybernetic equipment is the reception, transmission, processing and storage of information (memory) with its further reproduction. Information must be encoded for transmission, and decoded for playback. Using cybernetic concepts, we can assume that the analyzer receives, transmits, processes and, possibly, stores information. Its decoding is carried out in the cortical regions. This is probably enough to make an attempt to compare the brain to a computer possible. At the same time, one cannot equate the work of the brain with a computer: “... the brain is the most capricious machine in the world. Let us be modest and careful with conclusions ”(IM Sechenov, 1863). A computer is a machine and nothing else. All cybernetic devices work on the principle of electrical or electronic interaction, and complex biochemical and bioelectric processes also take place in the brain, which was created through evolutionary development. They can only be carried out in living tissue. The brain, unlike electronic systems, does not function according to the "all or nothing" principle, but takes into account a great variety of gradations between these two extremes. These gradations are caused not by electronic, but by biochemical processes. This is the essential difference between the physical and biological. The brain has qualities that go beyond those of a computer. It should be added that the behavioral reactions of the body are largely determined by intercellular interactions in the central nervous system. One neuron, as a rule, is approached by processes from hundreds or thousands of other neurons, and it, in turn, branches off into hundreds or thousands of other neurons. No one can say how many synapses are in the brain, but the number 10 14 (one hundred trillion) does not seem incredible (D. Hubel, 1982). The computer can hold significantly fewer items. The functioning of the brain and the vital functions of the organism are carried out in specific environmental conditions. Therefore, the satisfaction of certain needs can be achieved provided that this activity is adequate to the existing external environment conditions.

For the convenience of studying the basic laws of functioning, the brain is divided into three main blocks, each of which performs its own specific functions.

The first block is the phylogenetically most ancient structures of the limbic-reticular complex, which are located in the brainstem and deep regions of the brain. They include the cingulate gyrus, seahorse (hippocampus), papillary body, anterior thalamic nuclei, hypothalamus, reticular formation. They provide the regulation of vital functions - respiration, blood circulation, metabolism, as well as general tone. With regard to behavioral acts, these formations take part in the regulation of functions aimed at ensuring food and sexual behavior, the processes of preserving the species, in the regulation of systems that ensure sleep and wakefulness, emotional activity, and memory processes.

The second block is a set of formations located behind the central sulcus: somatosensory, visual and auditory zones of the cerebral cortex. Their main functions are: reception, processing and storage of information.

The neurons of the system, which are located mainly in front of the central sulcus and are associated with effector functions, the implementation of motor programs, constitute the third block.

However, it should be recognized that no clear boundaries can be drawn between the sensory and motor structures of the brain. The postcentral gyrus, which is a sensitive projection zone, is closely interconnected with the precentral motor zone, forming a single sensorimotor field. Therefore, it is necessary to clearly understand that this or that human activity requires the simultaneous participation of all parts of the nervous system. Moreover, the system as a whole performs functions that go beyond the functions inherent in each of these blocks.

The functioning of the nervous system is based on reflex activity. Reflex (from Lat. Reflexio - reflect) is the body's response to external or internal irritation with the obligatory participation of the nervous system.

Reflex principle of functioning of the nervous system

A reflex is the body's response to external or internal stimulation. Reflexes are divided into:

1. unconditioned reflexes: innate reactions of the body to irritations carried out with the participation of the spinal cord or brain stem;
2. conditioned reflexes: acquired on the basis of unconditioned reflexes temporary reactions of the body, carried out with the obligatory participation of the cerebral cortex, which form the basis of higher nervous activity.

The morphological basis of the reflex is the reflex arc, represented by a chain of neurons that provide the perception of irritation, the transformation of irritation energy into a nerve impulse, conduction of a nerve impulse to the nerve centers, processing of incoming information and the implementation of a response.

Reflex activity presupposes the presence of a mechanism consisting of three main elements, connected in series with each other:

1. Receptors that perceive irritation and transform it into a nervous impulse; usually receptors are represented by various sensitive nerve endings in organs;

2. Effectors, which result in the effect of stimulating the receptors in the form of a specific reaction; the effectors include all internal organs, blood vessels and muscles;

3. Chains consistently related neurons, which, by directionally transmitting excitation in the form of nerve impulses, ensure the coordination of the activity of the effectors depending on the stimulation of the receptors.

A chain of neurons connected in series forms reflex arc, which constitutes the material substrate of the reflex.

Functionally, neurons forming a reflex arc can be divided into:

1. afferent (sensory) neurons that perceive irritation and transmit it to other neurons. Sensory neurons are always located outside the central nervous system in the sensory ganglia of the spinal and cranial nerves. Their dendrites form sensitive nerve endings in the organs.

2. efferent (motor, motor) neurons, or motor neurons, transmit excitation to effectors (for example, muscles or blood vessels);

3. interneurons (interneurons) connect afferent and efferent neurons with each other and thereby close the reflex connection.

The simplest reflex arc consists of two neurons - afferent and efferent. In a more complex reflex arc, three neurons are involved: afferent, efferent and intercalary. The maximum number of neurons involved in the reflex response of the nervous system is limited, especially in cases when various parts of the brain and spinal cord are involved in the reflex act. Currently, the basis of reflex activity is taken reflex ring. The classical reflex arc is supplemented by the fourth link - the reverse afferentation from the effectors. All neurons involved in reflex activity are strictly localized in the nervous system.

Nerve center

Anatomically, the center of the nervous system is a group of adjacent neurons that are closely interconnected structurally and functionally and perform a common function in reflex regulation. In the nerve center, there is a perception, analysis of incoming information and its transmission to other nerve centers or effectors. Therefore, each nerve center has its own system of afferent fibers, through which it is brought into an active state, and a system of efferent connections that conduct nervous excitation to other nerve centers or effectors. Distinguish peripheral nerve centers represented by nodes ( ganglia ): sensitive and vegetative. In the central nervous system, there are nuclear centers (nuclei)- local clusters of neurons, and cortical centers - extensive dispersal of neurons over the surface of the brain.

Blood supply to the brain and spinal cord

I. Blood supply to the brain carried out by the branches of the left and right internal carotid arteries and branches of the vertebral arteries.

Internal carotid artery having entered the cranial cavity, it is divided into the ophthalmic artery and the anterior and middle cerebral arteries. Anterior cerebral artery feeds mainly the frontal lobe of the brain, middle cerebral artery - parietal and temporal lobes, and ocular artery supplies blood to the eyeball. The anterior cerebral arteries (right and left) are connected by a transverse anastomosis - the anterior communicating artery.

Vertebral arteries (right and left) in the region of the brain stem they connect and form an unpaired basilar artery, feeding the cerebellum and other parts of the trunk, and two posterior cerebral arteries, supplying blood to the occipital lobes of the brain. Each of the posterior cerebral arteries is connected to the middle cerebral artery of its side using the posterior communicating artery.

Thus, at the base of the brain, the arterial circle of the large brain is formed.

Smaller branching of blood vessels in the pia mater

reach the brain, penetrate into its substance, where they are divided into numerous capillaries. From the capillaries, blood is collected in small, and then large venous vessels. Blood from the brain flows into the sinuses of the dura mater. From the sinuses, blood flows through the jugular openings at the base of the skull into the internal jugular veins.

2. Blood supply to the spinal cord is carried out through the anterior and posterior spinal arteries. The outflow of venous blood goes through the veins of the same name into the internal vertebral plexus, located throughout the spinal canal outside of the hard shell of the spinal cord. From the internal vertebral plexus, blood flows into the veins along the spinal column, and from them into the inferior and superior vena cava.

Cerebrospinal fluid system

Inside the bone cavities, the brain and spinal cord are in suspension and are washed from all sides by cerebrospinal fluid - liquor... CSF protects the brain from mechanical influences, ensures the constancy of intracranial pressure, and is directly involved in the transport of nutrients from the blood to the brain tissues. Cerebrospinal fluid is produced by the choroid plexuses of the ventricles of the brain. The circulation of cerebrospinal fluid through the ventricles is carried out according to the following scheme: from the lateral ventricles, fluid enters through the Monroe opening into the third ventricle, and then through the sylvian aqueduct into the fourth ventricle. From it, the cerebrospinal fluid passes through the holes of Magendie and Lyushka into the subarachnoid space. The outflow of cerebrospinal fluid into the venous sinuses occurs through the granulation of the arachnoid membrane - pachyon granulation.

There is a barrier between neurons and blood in the brain and spinal cord called hematoencephalic, which ensures the selective flow of substances from the blood to the nerve cells. This barrier performs a protective function, as it ensures the constancy of the physicochemical properties of the cerebrospinal fluid.

Mediators

Neurotransmitters (neurotransmitters, mediators) - biologically active chemical substances, through which the transmission of an electrical impulse from a nerve cell through the synaptic space between neurons is carried out. A nerve impulse entering the presynaptic terminal causes the release of a neurotransmitter into the synaptic cleft. Mediator molecules react with specific receptor proteins of the cell membrane, initiating a chain of biochemical reactions that cause a change in the transmembrane ion current, which leads to membrane depolarization and the emergence of an action potential.

Until the 1950s, mediators included two groups of low molecular weight compounds: amines (acetylcholine, adrenaline, norepinephrine, serotonin, dopamine) and amino acids (gamma-aminobutyric acid, glutamate, aspartate, glycine). Later, it was shown that a specific group of mediators is made up of neuropeptides, which can also act as neuromodulators (substances that change the magnitude of the response of a neuron to a stimulus). It is now known that a neuron can synthesize and release several neurotransmitters.

In addition, there are special nerve cells in the nervous system - neurosecretory, which provide a connection between the central nervous system and the endocrine system. These cells have a structural and functional organization typical of a neuron. They are distinguished from a neuron by a specific function - neurosecretory, which is associated with the secretion of biologically active substances. The axons of neurosecretory cells have numerous extensions (Hering's bodies), in which neurosecretory is temporarily accumulated. Within the brain, these axons are usually devoid of the myelin sheath. One of the main functions of neurosecretory cells is the synthesis of proteins and polypeptides and their further secretion. In this regard, in these cells, the protein-synthesizing apparatus is extremely developed - the granular endoplasmic reticulum, the Golgi complex, the lysosomal apparatus. By the number of neurosecretory granules in a cell, one can judge its activity.