Inhibition is an independent nervous process that is caused by excitation and manifests itself in the suppression of another excitation.
- Inhibition is an independent nervous process that is caused by excitation and manifests itself in the suppression of another excitation.
- 1862 - discovery by I.M. Sechenov of the effect of central inhibition (chemical stimulation of the visual tubercles of a frog inhibits simple spinal unconditioned reflexes);
- The beginning of the 20th century - Eccles, Renshaw showed the existence of special intercalary inhibitory neurons that have synaptic contacts with motor neurons.
- depending from neural mechanism, distinguish between primary inhibition, carried out with inhibitory neurons And secondary inhibition, carried out without the help of inhibitory neurons.
- Primary braking:
- postsynaptic;
- Presynaptic.
- Secondary braking
- 1. Pessimal;
- 2. Post-activation.
- - the main type of inhibition that develops in the postsynaptic membrane of axosomatic and axodendrial synapses under the influence of activation inhibitory neurons, from the presynaptic endings of which it is released and enters the synaptic cleft inhibitory mediator(glycine, GABA).
- The inhibitory mediator causes an increase in the permeability for K + and Cl- in the postsynaptic membrane, which leads to hyperpolarization in the form of inhibitory postsynaptic potentials (IPSP), the spatiotemporal summation of which increases the level of the membrane potential, reducing the excitability of the membrane of the postsynaptic cell. This leads to the termination of the generation of propagating APs in the axonal colliculus.
- Thus, postsynaptic inhibition is associated with decreased excitability of the postsynaptic membrane.
- Depolarization of the postsynaptic region causes a decrease in the amplitude of AP arriving at the presynaptic terminal of the excitatory neuron (the “barrier” mechanism). It is assumed that the decrease in the excitatory axon excitability during prolonged depolarization is based on the processes of cathodic depression (the critical level of depolarization changes due to the inactivation of Na + channels, which leads to an increase in the depolarization threshold and a decrease in axon excitability at the presynaptic level).
- A decrease in the amplitude of the presynaptic potential leads to a decrease in the amount of the released mediator up to the complete cessation of its release. As a result, the impulse is not transmitted to the postsynaptic membrane of the neuron.
- The advantage of presynaptic inhibition is its selectivity: in this case, individual inputs to the nerve cell are inhibited, while postsynaptic inhibition reduces the excitability of the entire neuron as a whole.
- It develops in axoaxonal synapses, blocking the spread of excitation along the axon. Often found in stem structures, in the spinal cord, in sensory systems.
- Impulses at the presynaptic terminal of the axoaxonal synapse release a neurotransmitter (GABA), which causes prolonged depolarization postsynaptic region by increasing the permeability of their membrane for Cl-.
- It is a type of braking central neurons.
- Occurs with a high frequency of irritation. . It is assumed that the mechanism of inactivation of Na-channels during prolonged depolarization and a change in the properties of the membrane, similar to cathodic depression, underlie. (An example is a frog turned over on its back - a powerful afferent from vestibular receptors - a phenomenon of stupor, hypnosis).
- Does not require special structures. Inhibition is due to pronounced trace hyperpolarization of the postsynaptic membrane in the axonal hillock after prolonged excitation.
- post-activation inhibition
- returnable;
- Reciprocal (conjugated);
- Lateral.
- Inhibition of neuron activity caused by the recurrent collateral of the axon of the nerve cell with the participation of the inhibitory interneuron.
- For example, the motor neuron of the anterior horn of the spinal cord gives rise to a lateral collateral that returns back and ends on inhibitory neurons - Renshaw cells. The axon of the Renshaw cell ends on the same motor neuron, exerting an inhibitory effect on it (feedback principle).
- The coordinated work of antagonistic nerve centers is ensured by the formation of reciprocal relationships between nerve centers due to the presence of special inhibitory neurons - Renshaw cells.
- It is known that flexion and extension of the limbs is carried out due to the coordinated work of two functionally antagonistic muscles: flexors and extensors. The signal from the afferent link through the intermediate neuron causes excitation of the motor neuron innervating the flexor muscle, and through the Renshaw cell it inhibits the motor neuron innervating the extensor muscle (and vice versa).
- During lateral inhibition, excitation transmitted through the collaterals of the axon of the excited nerve cell activates intercalary inhibitory neurons, which inhibit the activity of neighboring neurons in which excitation is absent or weaker.
- As a result, very deep inhibition develops in these neighboring cells. The resulting zone of inhibition is on the side of the excited neuron.
- Lateral inhibition by the neural mechanism of action can take the form of both postsynaptic and presynaptic inhibition. It plays an important role in the selection of a feature in sensory systems, the cerebral cortex.
- Coordination of reflex acts. It directs excitation to certain nerve centers or along a certain path, turning off those neurons and paths whose activity is currently insignificant. The result of such coordination is a certain adaptive reaction.
- Radiation limitation.
- Protective. Protects nerve cells from overexcitation and exhaustion. Especially under the action of superstrong and long-acting stimuli.
- In the implementation of the information and control function of the central nervous system, a significant role belongs to the processes coordination activity of individual nerve cells and nerve centers.
- Coordination- morphofunctional interaction of nerve centers, aimed at the implementation of a certain reflex or regulation of the function.
- Morphological basis of coordination: connection between nerve centers (convergence, divergence, circulation).
- Functional basis: excitation and inhibition.
- Associated (reciprocal) inhibition.
- Feedback. Positive– the signals arriving at the input of the system through the feedback circuit act in the same direction as the main signals, which leads to an increase in the mismatch in the system. negative– signals arriving at the input of the system through the feedback circuit act in the opposite direction and are aimed at eliminating the mismatch, i.e. deviations of parameters from the given program ( PC. Anokhin).
- Common final path (funnel principle) Sherrington). The convergence of nerve signals at the level of the efferent link of the reflex arc determines the physiological mechanism of the "common final path" principle.
- Relief. This is an integrative interaction of nerve centers, in which the total reaction with simultaneous stimulation of the receptive fields of two reflexes is higher than the sum of reactions with isolated stimulation of these receptive fields.
- Occlusion. This is an integrative interaction of nerve centers, in which the total reaction with simultaneous stimulation of the receptive fields of two reflexes is less than the sum of reactions with isolated stimulation of each of the receptive fields.
- Dominant. Dominant called the focus (or dominant center) of increased excitability in the central nervous system temporarily dominant in the nerve centers. By A.A. Ukhtomsky, the dominant focus is characterized by:
- - increased excitability,
- - persistence and inertness of excitation,
- - increased summation of excitation.
- The dominant value of such a focus determines its depressing effect on other adjacent foci of excitation. The dominant principle determines the formation of the dominant excited nerve center in close accordance with the leading motives, the needs of the body at a particular moment in time.
- 7. Subordination. Ascending influences are predominantly excitatory stimulating in nature, descending influences are depressing inhibitory in nature. This scheme is consistent with ideas about the growth in the process of evolution of the role and importance of inhibitory processes in the implementation of complex integrative reflex reactions. Has a regulatory character.
- 1. Name the main inhibitory mediators;
- 2. What type of synapse is involved in presynaptic inhibition?;
- 3. What is the role of inhibition in the coordination activity of the CNS?
- 4. List the properties of the dominant focus in the CNS.
The central nervous system (CNS) is the main part of the nervous system of animals and humans, consisting of neurons and their processes; it is represented in invertebrates by a system of closely interconnected nerve nodes (ganglia), in vertebrates and humans by the spinal cord and brain.
The organism must receive and evaluate information about the state of the external and internal environment and, taking into account urgent needs, build behavior programs. This function is performed by the nervous system, which, according to I.P. Pavlov, is “an inexpressibly complex and subtle instrument of communication, the connection of numerous parts of the body with each other and the body as a most complex system with an infinite number of external influences.”
Thus, the most important functions of the nervous system include: Integrative function 1. Integrative function - control of the work of all organs and systems and ensuring the functional unity of the body. The body responds to any impact as a whole, measuring and subordinating the needs and capabilities of different organs and systems.
Sensory function 2. Sensory function - receiving information about the state of the external and internal environment from special perceiving cells or endings of neurons - receptors. The function of reflection is the function of memory 3. The function of reflection, including mental, and the function of memory is the processing, evaluation, storage, reproduction and forgetting of the information received.
Behavior programming 4. Behavior programming. Based on the incoming and already stored information, the nervous system either builds new programs for interacting with the environment, or chooses the most suitable of the existing programs. In the latter case, species-specific programs can be used that are genetically
The Central Nervous System (CNS) The central nervous system (systema nervosum centrale) is represented by the brain and spinal cord. In their thickness, areas of gray color (gray matter) are clearly defined, clusters of neuron bodies have this appearance, and white matter formed by the processes of nerve cells, through which they establish connections with each other. The number of neurons and the degree of their concentration is much higher in the upper section, which as a result takes on the appearance of a volumetric brain
Central nervous system (CNS) I. Neck nerves. II. Thoracic nerves. III. Lumbar nerves\\\. IV. sacral nerves. V. Coccygeal nerves. -/- 1. Brain. 2. Diencephalon. 3. Midbrain. 4. Bridge. 5. Cerebellum. 6. Medulla oblongata. 7. Spinal cord. 8. Neck thickening. 9. Transverse thickening. 10. "Ponytail"
The main and specific function of the central nervous system is the implementation of simple and complex highly differentiated reflective reactions, called reflexes. In higher animals and humans, the lower and middle sections of the central nervous system - the spinal cord, medulla oblongata, midbrain, diencephalon and cerebellum regulate the activity of individual organs and systems of a highly developed organism, communicate and interact between them, ensure the unity of the organism and the integrity of its activity. The higher department of the central nervous system, the cerebral cortex and the nearest subcortical formations, mainly regulates the connection and relationship of the body as a whole with the environment.
Structural and functional characteristics of the cerebral cortex The cerebral cortex is a multilayer neural tissue with many folds with a total area in both hemispheres of approximately 2200 cm 2, which corresponds to a square with sides of 47 x 47 cm, its volume corresponds to 40% of the mass of the brain, its thickness varies from 1.3 to 4.5 mm, and the total volume is 600 cm 3. The composition of the cerebral cortex includes 10 9 -10 10 neurons and many glial cells, the total number of which is still unknown. There are 6 layers in the bark (I-VI)
Semi-schematic image of the layers of the cerebral cortex (according to K. Brodmann, Vogt; with changes): a - the main types of nerve cells (Golgi stain); b – bodies of neurons (Nissl staining); c – general arrangement of fibers (myelin sheaths). In layers I - IV, the perception and processing of the Signals entering the cortex in the form of nerve impulses takes place. The efferent pathways leaving the cortex are formed predominantly in layers V–VI.
The integrating role of the central nervous system (CNS) is the subordination and integration of tissues and organs into the central-peripheral system, the activity of which is aimed at achieving an adaptive result useful for the body. Such association becomes possible due to the participation of the CNS: in the control of the musculoskeletal system with the help of the somatic nervous system, the regulation of the functions of all tissues and internal organs with the help of the autonomic nervous and endocrine systems, the presence of the most extensive afferent connections of the CNS with all somatic and autonomic effectors.
The main functions of the central nervous system are: 1) regulation of the activity of all tissues and organs and their integration into a single whole; 2) ensuring the adaptation of the organism to environmental conditions (organization of adequate behavior in accordance with the needs of the organism).
Levels of CNS Integration The first level is the neuron. Due to the many excitatory and inhibitory synapses on the neuron, it has evolved into a decisive device in the course of evolution. The interaction of excitatory and inhibitory inputs, subsynaptic neurochemical processes ultimately determine whether a command will be given to another neuron, a working organ or not. The second level is a neuronal ensemble (module), which has qualitatively new properties that are absent in individual neurons, allowing it to be included in more complex types of CNS reactions.
Levels of integration of the central nervous system (continued) The third level is the nerve center. Due to the presence of multiple direct, feedback and reciprocal connections in the CNS, the presence of direct and feedback connections with peripheral organs, nerve centers often act as autonomous command devices that control one process or another on the periphery in the body as a self-regulating, self-healing, self-reproducing system. The fourth level is the highest, uniting all centers of regulation into a single regulatory system, and individual organs and systems into a single physiological system - the body. This is achieved by the interaction of the main systems of the CNS: the limbic, reticular formation, subcortical formations and the neocortex - as the highest department of the CNS, which organizes behavioral reactions and their vegetative support.
An organism is a complex hierarchy (i.e. interconnection and mutual subordination) of systems that make up the levels of its organization: molecular, subcellular, cellular, tissue, organ, systemic and organismic The organism is a self-organizing system. The body itself chooses and maintains the values of a huge number of parameters, changes them depending on the needs, which allows it to provide the most optimal functioning. For example, at low ambient temperatures, the body lowers the body surface temperature (to reduce heat transfer), increases the rate of oxidative processes in internal organs and muscle activity (to increase heat generation). A person insulates the dwelling, changes clothes (to increase the heat-insulating properties), and does this even in advance, proactively reacting to changes in the external environment.
The basis of physiological regulation is the transmission and processing of information. The term "information" should be understood as everything that reflects the facts or events that have occurred, are occurring or may occur. Information processing is carried out by a control system or a regulatory system. It consists of separate elements connected by information channels.
Three levels of structural organization of the regulation system control device (central nervous system); input and output communication channels (nerves, fluids of the internal environment with information molecules of substances); sensors that perceive information at the input of the system (sensor receptors); formations located on the executive organs (cells) and perceiving information from the output channels (cell receptors). The part of the control device that serves to store information is called a storage device or memory device.
The nervous system is one, but conditionally it is divided into parts. There are two classifications: according to the topographic principle, i.e., according to the location of the nervous system in the human body, and according to the functional principle, i.e., according to the areas of its innervation. According to the topographic principle, the nervous system is divided into central and peripheral. The central nervous system includes the brain and spinal cord, and the peripheral nerves extending from the brain (12 pairs of cranial nerves) and nerves extending from the spinal cord (31 pairs of spinal nerves).
According to the functional principle, the nervous system is divided into a somatic part and an autonomous, or vegetative, part. The somatic part of the nervous system innervates the striated muscles of the skeleton and some organs - the tongue, pharynx, larynx, etc., and also provides sensitive innervation of the whole body.
The autonomic part of the nervous system innervates all the smooth muscles of the body, providing motor and secretory innervation of the internal organs, motor innervation of the cardiovascular system and trophic innervation of the striated muscles. The autonomic nervous system, in turn, is divided into two divisions: sympathetic and parasympathetic. The somatic and autonomic parts of the nervous system are closely interconnected, making up one whole.
Feedback Channel Deviation control requires a communication channel between the output of the control system and its central control apparatus, and even between the output and input of the control system. This channel is called feedback. In essence, feedback is the process of influencing the result of an action on the cause and mechanism of this action. It is the feedback that allows the regulation by deviation to work in two modes: compensation and tracking. The compensation mode provides a quick correction of the discrepancy between the real and optimal state of physiological systems in case of sudden environmental influences, i.e. optimizes body reactions. In the tracking mode, regulation is carried out according to predetermined programs, and feedback controls the compliance of the parameters of the activity of the physiological system with a given program. If a deviation occurs, a compensation mode is implemented.
Methods of control in the body launch (initiation) of physiological processes. It is a control process that causes the transition of the organ function from a state of relative rest to an active state or from active activity to a state of rest. For example, under certain conditions, the central nervous system initiates the work of the digestive glands, phase contractions of the skeletal muscles, the processes of urination, defecation, etc. Correction of physiological processes. Allows you to control the activity of an organ that performs a physiological function in automatic mode or initiated by the receipt of control signals. An example is the correction of the work of the heart of the central nervous system through influences transmitted through the vagus and sympathetic nerves. coordination of physiological processes. It provides for the coordination of the work of several organs or systems simultaneously to obtain a useful adaptive result. For example, to carry out the act of upright walking, it is necessary to coordinate the work of the muscles and centers that ensure the movement of the lower limbs in space, the displacement of the center of gravity of the body, and the change in the tone of the skeletal muscles.
The mechanisms of regulation (control) of the vital activity of the body are usually divided into nervous and humoral. The nervous mechanism provides for a change in physiological functions under the influence of control actions transmitted from the central nervous system through nerve fibers to the organs and systems of the body. The nervous mechanism is a later product of evolution compared to the humoral mechanism, it is more complex and more perfect. It is characterized by high propagation speed and accurate transmission of control actions to the control object, high reliability of communication. Nervous regulation provides fast and directed transmission of signals, which in the form of nerve impulses through the corresponding nerve conductors arrive at a specific addressee, the object of regulation.
Humoral mechanisms of regulation use a liquid internal environment to transmit information with the help of chemical molecules. Humoral regulation is carried out with the help of chemical molecules released by cells or specialized tissues and organs. The humoral mechanism of control is the oldest form of interaction between cells, organs and systems, therefore, in the human body and higher animals, one can find various variants of the humoral mechanism of regulation, reflecting to a certain extent its evolution. For example, under the influence of CO 2 formed in the tissues as a result of oxygen utilization, the activity of the respiration center changes and, as a result, the depth and frequency of respiration. Under the influence of adrenaline released into the blood from the adrenal glands, the frequency and strength of heart contractions, the tone of peripheral vessels, a number of functions of the central nervous system, the intensity of metabolic processes in skeletal muscles, and the coagulation properties of blood increase.
Humoral regulation is divided into local, low-specialized self-regulation, and a highly specialized system of hormonal regulation, which provides generalized effects with the help of hormones. Local humoral regulation (tissue self-regulation) is practically not controlled by the nervous system, while the hormonal regulation system is part of a single neurohumoral system.
The interaction of the humoral and nervous mechanisms creates an integrative control option capable of providing an adequate change in functions from the cellular to the organismal levels when the external and internal environment changes. The humoral mechanism uses chemicals, metabolic products, prostaglandins, regulatory peptides, hormones, etc. Thus, the accumulation of lactic acid in the muscles during exercise is a source of information about the lack of oxygen.
The division of the mechanisms of regulation of the vital activity of the body into nervous and humoral is very conditional and can only be used for analytical purposes as a way of studying. In fact, the nervous and humoral mechanisms of regulation are inseparable. information about the state of the external and internal environment is almost always perceived by the elements of the nervous system (receptors); in a humorous way. And the endocrine glands specialized for humoral regulation are controlled by the nervous system. The neurohumoral system of regulation of physiological functions is one.
Neurons The nervous system consists of neurons, or nerve cells, and neuroglia, or neuroglial cells. Neurons are the main structural and functional elements in both the central and peripheral nervous systems. Neurons are excitable cells, meaning they are capable of generating and transmitting electrical impulses (action potentials). Neurons have a different shape and size, form processes of two types: axons and dendrites. A neuron usually has several short branched dendrites, along which impulses follow to the body of the neuron, and one long axon, along which impulses go from the body of the neuron to other cells (neurons, muscle or glandular cells). The transfer of excitation from one neuron to other cells occurs through specialized contacts of synapses. Neurons of neuroglia and action potentials of synapses
Neurons consist of a cell body with a diameter of 3–100 µm, containing a nucleus and organelles, and cytoplasmic processes. Short processes that conduct impulses to the cell body are called dendrites; longer (up to several meters) and thin processes that conduct impulses from the cell body to other cells are called axons. Axons connect with neighboring neurons at synapses
Neuroglia Neuroglia cells are concentrated in the central nervous system, where their number is ten times greater than the number of neurons. They fill the space between neurons, providing them with nutrients. It is possible that neurology cells are involved in storing information in the form of RNA codes. When damaged, neurological cells actively divide, forming a scar at the site of damage; neurolgy cells of a different type turn into phagocytes and protect the body from viruses and bacteria.
Synapses The transmission of information from one neuron to another occurs at synapses. Usually, the axon of one neuron and the dendrites or body of another are connected through synapses. Synapses are also connected to neurons by the endings of muscle fibers. The number of synapses is very high: some brain cells can have up to synapses. At most synapses, the signal is transmitted chemically. Nerve endings are separated from each other by a synaptic cleft about 20 nm wide. Nerve endings have thickenings called synaptic plaques; the cytoplasm of these thickenings contains numerous synaptic vesicles with a diameter of about 50 nm, inside which there is a mediator - a substance with which the nerve signal is transmitted through the synapse. The arrival of a nerve impulse causes the vesicle to merge with the membrane and the neurotransmitter exits the cell. After about 0.5 ms, the mediator molecules enter the membrane of the second nerve cell, where they bind to the receptor molecules and transmit the signal further.
Conducting pathways of the central nervous system, or tracts of the brain and spinal cord, are usually called sets of nerve fibers (systems of fiber bundles) that connect various structures of one or different levels of the hierarchy of structures of the nervous system: structures of the brain, structures of the spinal cord, as well as structures of the brain with structures of the spinal cord. of the central nervous system of the spinal cord of the aggregate of nerve fibers of the system of the structure of the levels of the hierarchy of the nervous system
Conducting paths serve to achieve four main goals: 1. For interconnection with each other sets of neurons (nerve centers) of one or different levels of the nervous system; 2. For the transmission of afferent information to the regulators of the nervous system (to the nerve centers); 3. For the formation of control signals. The name "pathways" does not mean that these paths serve exclusively for the conduction of afferent or efferent information, like the conduction of electric current in the simplest electrical circuits. Chains of neurons - pathways are essentially hierarchically interacting elements of the system regulator. It is in these hierarchical chains, as in the elements of regulators, and not only at the end points of the paths (for example, in the cerebral cortex), that information is processed and control signals are formed for the objects of control of body systems. 4. To transmit control signals from the regulators of the nervous system to control objects - organs and organ systems. Thus, the initially purely anatomical concept of “path”, or the collective “path”, “tract” also has a physiological meaning and is closely related to such physiological concepts as the control system, inputs, regulator, outputs. organism control signals to control objects to organs to organ systems anatomical concept physiological meaning control system inputs regulator outputs
There are three groups of pathways in both the brain and the spinal cord: association pathways composed of associative nerve fibers, commissural pathways composed of commissural nerve fibers, and projection pathways composed of projection nerve fibers. association pathways commissural pathways projection pathways Associative nerve fibers connect areas of gray matter, various nuclei and nerve centers within one half of the brain. Commissural (commissural) nerve fibers connect the nerve centers of the right and left halves of the brain, ensuring their interaction. To connect one hemisphere with another, commissural fibers form adhesions: corpus callosum, fornix commissure, anterior commissure. Projection nerve fibers provide interconnections of the cerebral cortex with the underlying sections: with the basal nuclei, with the nuclei of the brain stem and with the spinal cord. With the help of projection nerve fibers that reach the cerebral cortex, information about the human environment, pictures of the outside world are "projected" onto the cortex, like on a screen. Here, the highest analysis of the information received here is carried out, its assessment with the participation of consciousness.
The blood-brain barrier and its functions Among the homeostatic adaptive mechanisms designed to protect organs and tissues from foreign substances and regulate the constancy of the composition of the intercellular fluid, the blood-brain barrier occupies a leading position. By definition, L. S. Stern, the blood-brain barrier combines a set of physiological mechanisms and corresponding anatomical formations in the central nervous system involved in regulating the composition of cerebrospinal fluid (CSF).
In the ideas about the blood-brain barrier, the following are emphasized as the main provisions: 1) the penetration of substances into the brain is carried out mainly not through the cerebrospinal fluid, but through the circulatory system at the level of the capillary nerve cell; 2) the blood-brain barrier is to a greater extent not an anatomical formation, but a functional concept that characterizes a certain physiological mechanism. Like any physiological mechanism existing in the body, the blood-brain barrier is under the regulatory influence of the nervous and humoral systems; 3) among the factors controlling the blood-brain barrier, the leading factor is the level of activity and metabolism of the nervous tissue
Significance of the BBB The blood-brain barrier regulates the penetration of biologically active substances, metabolites, chemicals from the blood into the brain, affecting the sensitive structures of the brain, prevents foreign substances, microorganisms, and toxins from entering the brain. The main function that characterizes the blood-brain barrier is the permeability of the cell wall. The necessary level of physiological permeability, adequate to the functional state of the body, determines the dynamics of the flow of physiologically active substances into the nerve cells of the brain.
The structure of histohematic barriers (according to Ya. A. Rosin). SC capillary wall; EC endothelium of the blood capillary; BM basement membrane; AC argyrophilic layer; KPO cells of the parenchyma of the organ; TSC transport system of the cell (endoplasmic reticulum); NM nuclear membrane; I am the core; E erythrocyte.
The histohematic barrier has a dual function: regulatory and protective. The regulatory function ensures the relative constancy of the physical and physico-chemical properties, chemical composition, physiological activity of the intercellular environment of the organ, depending on its functional state. The protective function of the histohematic barrier is to protect organs from the ingress of foreign or toxic substances of endo- and exogenous nature.
The leading component of the morphological substrate of the blood-brain barrier, which ensures its functions, is the wall of the brain capillary. There are two mechanisms for the penetration of a substance into brain cells: through the cerebrospinal fluid, which serves as an intermediate link between the blood and the nerve or glial cell, which performs a nutritional function (the so-called liquor pathway) through the capillary wall. In an adult organism, the main route of movement of a substance into nerve cells is hematogenous (through the walls of capillaries); the cerebrospinal fluid path becomes auxiliary, additional.
The permeability of the blood-brain barrier depends on the functional state of the body, the content of mediators, hormones, and ions in the blood. An increase in their concentration in the blood leads to a decrease in the permeability of the blood-brain barrier for these substances.
Functional system of the blood-brain barrier The functional system of the blood-brain barrier seems to be an important component of neurohumoral regulation. In particular, the principle of chemical feedback in the body is realized through the blood-brain barrier. It is in this way that the mechanism of homeostatic regulation of the composition of the internal environment of the body is carried out. The regulation of the functions of the blood-brain barrier is carried out by the higher parts of the central nervous system and humoral factors. A significant role in the regulation is assigned to the hypothalamic-pituitary adrenal system. In the neurohumoral regulation of the blood-brain barrier, metabolic processes are important, in particular in the brain tissue. In various types of cerebral pathology, such as injuries, various inflammatory lesions of the brain tissue, there is a need to artificially reduce the level of permeability of the blood-brain barrier. Pharmacological influences can increase or decrease the penetration into the brain of various substances introduced from the outside or circulating in the blood.
The basis of nervous regulation is the reflex response of the body to changes in the internal and external environment, carried out with the participation of the central nervous system. Under natural conditions, a reflex reaction occurs with a threshold, suprathreshold irritation of the input of the reflex arc of the receptive field of this reflex. A receptive field is a certain area of the perceiving sensitive surface of the body with receptor cells located here, the irritation of which initiates, triggers a reflex reaction. The receptive fields of different reflexes have a certain localization, the receptor cells are appropriately specialized for optimal perception of adequate stimuli (for example, photoreceptors are located in the retina; auditory hair receptors in the spiral (Corti) organ; proprioceptors in muscles, tendons, in articular cavities; taste buds on the surface tongue, olfactory in the mucous membrane of the nasal passages, pain, temperature, tactile receptors in the skin, etc.
The structural basis of the reflex is a reflex arc, a series-connected chain of nerve cells that provides a reaction, or response, to irritation. The reflex arc consists of afferent, central and efferent links interconnected by synaptic connections. The afferent part of the arc begins with receptor formations, the purpose of which is to transform the energy of external stimuli into the energy of a nerve impulse that enters the CNS through the afferent link of the reflex arc
There are various classifications of reflexes: according to the methods of their evoking, the characteristics of the receptors, the central nervous structures of their provision, the biological significance, the complexity of the neural structure of the reflex arc, etc. According to the method of evoking, unconditioned reflexes are distinguished (a category of reflex reactions transmitted by inheritance) conditioned reflexes ( reflex reactions acquired during the individual life of the organism).
Conditioned reflex is a reflex characteristic of an individual. Individuals arise during the life and are not fixed genetically (not inherited). They appear under certain conditions and disappear in their absence. They are formed on the basis of unconditioned reflexes with the participation of higher parts of the brain. Conditioned reflex reactions depend on past experience, on the specific conditions in which a conditioned reflex is formed. The study of conditioned reflexes is associated primarily with the name of IP Pavlov. He showed that a new conditioned stimulus can trigger a reflex response if it is presented for some time along with the unconditioned stimulus. For example, if a dog is allowed to smell meat, then gastric juice is secreted from it (this is an unconditioned reflex). If, however, the bell rings simultaneously with the appearance of meat, then the dog's nervous system associates this sound with food, and gastric juice will be released in response to the bell, even if meat is not presented. And. P. Pavlovastimulus dogmeat gastric juice
Classification of reflexes. There are exteroceptive reflexes - reflex reactions initiated by stimulation of numerous exteroreceptors (pain, temperature, tactile, etc.), interoceptive reflexes (reflex reactions triggered by irritation of interoceptors: chemo-, baro-, osmoreceptors, etc.), proprioceptive reflexes ( reflex reactions carried out in response to irritation of the proprioreceptors of muscles, tendons, articular surfaces, etc.). Depending on the level of activation of the part of the brain, spinal, tabular, mesencephalic, diencephalic, cortical reflex reactions are differentiated. According to their biological purpose, reflexes are divided into food, defensive, sexual, etc.
Types of reflexes Local reflexes are carried out through the ganglia of the autonomic nervous system, which are considered as nerve centers placed on the periphery. Local reflexes control, for example, the motor and secretory functions of the small and large intestines. Central reflexes proceed with the obligatory involvement of various levels of the central nervous system (from the spinal cord to the cerebral cortex). An example of such reflexes is the secretion of saliva when the receptors of the oral cavity are irritated, the lowering of the eyelid when the sclera of the eye is irritated, the withdrawal of the hand when the skin of the fingers is irritated, etc.
Conditioned reflexes underlie acquired behavior. These are the simplest programs. The surrounding world is constantly changing, so only those who quickly and expediently respond to these changes can successfully live in it. As life experience is acquired, a system of conditioned reflex connections is formed in the cerebral cortex. Such a system is called a dynamic stereotype. It underlies many habits and skills. For example, having learned to skate, bike, we subsequently no longer think about how we move so as not to fall.
The feedback principle The notion of a reflex reaction as an expedient response of the body dictates the need to supplement the reflex arc with one more link in the feedback loop, designed to establish a connection between the realized result of the reflex reaction and the nerve center that issues executive commands. Feedback transforms an open reflex arc into a closed one. It can be implemented in different ways: from the executive structure to the nerve center (intermediate or efferent motor neuron), for example, through the recurrent axon collateral of the pyramidal neuron of the cerebral cortex or the motor motor cell of the anterior horn of the spinal cord. Feedback can also be provided by nerve fibers coming to the receptor structures and controlling the sensitivity of the receptor afferent structures of the analyzer. Such a structure of the reflex arc turns it into a self-adjusting neural circuit for the regulation of physiological function, improving the reflex reaction and, in general, optimizing the behavior of the organism.
Reflex. Neuron. Synapse. The mechanism of conduction of excitation through the synapse
Prof. Mukhina I.V.
Lecture No. 6 Medical Faculty
CLASSIFICATION OF THE NERVOUS SYSTEM
Peripheral nervous system
CNS functions:
1). Unification and coordination of all functions of tissues, organs and systems of the body.
2). The connection of the body with the external environment, the regulation of body functions in accordance with its internal needs.
3). The basis of mental activity.
The main activity of the central nervous system is the reflex
Rene Descartes (1596-1650) - for the first time the concept of a reflex as a reflective activity;
Georg Prohasky (1749-1820);
THEM. Sechenov (1863) "Reflexes of the brain", which for the first time proclaimed the thesis that all types of conscious and unconscious human life are reflex reactions.
Reflex (from lat. reflecto - reflection) is the response of the body that occurs to irritation of receptors and is carried out with the participation of the central nervous system.
The reflex theory of Sechenov-Pavlov is based on three principles:
1. Structurality (the structural basis of the reflex is the reflex arc)
2. Determinism (principle causal relationship). Not a single response of the body happens without a reason.
3. Analysis and synthesis (any effect on the body is first analyzed, then summarized).
Morphologically it consists of:
receptor formations, whose purpose is
V transformation of the energy of external stimuli (information)
V nerve impulse energy;
afferent (sensory)) neuron, conducts a nerve impulse to the nerve center;
interneuron (intercalary) neuronor nerve center
representing the central part of the reflex arc;
efferent (motor) neuron, conducting a nerve impulse to the effector;
effector (working body),carrying out relevant activities.
Nerve impulse transmission is carried out by neurotransmitters or neurotransmitters- chemicals released by nerve endings
chemical synapse
STUDY LEVELS OF CNS FUNCTIONING
organism
Structure and function of neurons
Dendrites
Functions of neurons:
1. Integrative;
2. Coordinating
3. Trophic
Purkinje cell |
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Dendrites |
Astrocyte |
(cerebellum) |
pyramidal |
|
Oligodendrocyte |
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cortical neuron |
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"Fundamentals of higher nervous activity" - Internal inhibition. Reflexes. Paradoxical dream. external braking. Insight. Nerve connection. The sequence of elements of the reflex arc. choleric temperament. Formation of a conditioned reflex. Dream. Acquired by the body during life. congenital reflexes. Creation of the doctrine of GNI. Awake. human children. Sanguine temperament. Type of internal braking. True judgments.
"The vegetative part of the nervous system" - Pilomotor reflex. Raynaud's disease. pharmacological tests. Parasympathetic part of the autonomic nervous system. Functions of internal organs. Trial with pilocarpine. solar reflex. limbic system. Bulbar department. Sympathetic part of the autonomic nervous system. Bernard syndrome. Features of autonomic innervation. The defeat of the autonomic ganglia of the face. Sacred department. Cold test. Sympathetic crises.
"Evolution of the nervous system" - Class Mammals. Intermediate brain. The nervous system of vertebrates. Shellfish. Pisces class. oblong (hind) brain. Front section. The evolution of the nervous system. Cerebellum. Bird class. Reflex. Class Amphibians. Neuron. The nervous system is a collection of various structures of the nervous tissue. Evolution of the nervous system of vertebrates. Sections of the brain. Body cells. Nervous tissue is a collection of nerve cells.
"The work of the human nervous system" - Ivan Petrovich Pavlov. Sechenov Ivan Mikhailovich Reflex arc. The reflex principle of the nervous system. Active state of neurons. Comparison of unconditioned and conditioned reflexes. The concept of reflex. M. Gorky. Find a match. knee reflex.
"Physiology of GNI" - Physiology of higher nervous activity. Decreased metabolic activity. cochlear implant. Association of neurons. Patient. global workspace. vegetative state. psychophysiological problem. Module flexibility. Modern neurophysiological theories of consciousness. Formation of a global workspace. Variety of different states of consciousness. The problem of consciousness in cognitive science.
"Features of the higher nervous activity of man" - Unconditional inhibition. Classification of conditioned reflexes. Development of a conditioned reflex. Features of the higher nervous activity of man. Formation of a temporary connection. Types of inhibition of mental activity. The dog eats from a bowl. unconditioned reflexes. Insight. Reflexes. Conditioned reflexes. Saliva is released. Brain functions. Fistula to collect saliva. Types of instincts. The main characteristics of the conditioned reflex.
General physiologycentral nervous
systems
Lecture 2
for 2nd year students
Head cafe Shtanenko N.I.
Lecture plan:
Basic physiological propertiesnerve centers.
Distribution Features
stimulation in the CNS
Braking
V
CNS.
Nature
braking. Types of braking.
The mechanisms of coordination of the reflex
activities
The third level of coordination is carried out in the process of activity of the nerve centers and their interaction
Nerve centers are formedassociation of several local
networks and represent
set of elements capable of
exercise a reflex
or behavioral act.
.–
This
totality
neurons,
necessary for the implementation
certain
reflex
or
regulation of a particular function.
M. Flourance (1842) and N. A. Mislavsky (1885) is a complex structural and functional
Union
nervous
cells,
located at different levels
CNS and providing due to them
integrative activity regulation
holistic adaptive functions
(e.g. respiratory center in the broad sense of the word)
Classification of nerve centers (according to a number of features)
Localizations (cortical, subcortical,spinal);
Functions (respiratory,
vasomotor, heat generation);
Modalities of holistic
biological states (hunger, emotions, drives, etc.) Unilateral conduction of excitation
synaptic delay - slowing down
conducting excitation through the center 1.5-2 ms
Irradiation (divergence)
Convergence (animation)
Circulation (reverb)
The main properties of the nerve centers are determined by the characteristics of their
structure and the presence of interneuronal synaptic connections.
reflex arc
Synaptic delay in the conduction of excitation
the period temporarily required for:1. excitation of receptors (receptor)
for conducting excitation impulses
along afferent fibers to the center;
3.
dissemination
arousal
through
nerve centers;
4.
spreading
arousal
By
efferent fibers to the working body;
2.
5. latent period of the working body.
Reflex time Central reflex time
Reflex time(latent period of the reflex) is
time from the moment of irritation to the final
effect. In a monosynaptic reflex, it reaches 20-25 ms. This
time is spent on excitation of receptors, conduction of excitation along
afferent fibers, transmission of excitation from afferent neurons to
efferent (possibly through several intercalations), conduction of excitation
along efferent fibers and the transfer of excitation from the efferent nerve to
effector.
Central
time
reflex-
This
the time it takes for a nerve impulse to be conducted
by brain structures. In the case of a monosynaptic reflex arc, it
is approximately 1.5-2 ms - this is the time required for the transmission
excitation in one synapse. Thus, the central reflex time
indirectly indicates the number of synaptic transmissions that take place in
this reflex. Central time in polysynaptic reflexes
more than 3 ms. In general, polysynaptic reflexes are very widely
widespread in the human body. Central reflex time
is the main component of the total reflex time.
knee jerk
Examples of reflex arcsknee jerk
Monosynaptic. IN
sharp
sprains
proprioceptors
quadriceps
extension occurs
shins
(- defensive
Reflex time
0.0196-0.0238sec.
alpha motor neurons
proprioceptive
motor
unconditional)
But: even the simplest reflexes do not work separately.
(Here: interaction with the inhibitory chain of the antagonist muscle)
The mechanism of propagation of excitation in the central nervous system
Types of excitation convergence on one neuron
MultitouchMultibiological
Sensory biological
Phenomena of convergence and divergence in the CNS. Principle of “common final path”
REVERBERATION(circulation) inertia
Summation:
sequential (temporary)
spatial
Excitation transformation
(rhythm and frequency)
Posttetanic potentiation
(post-activation)
Time summation
Spatial summation
Summation in the CNS
consistentTemporary
summation
Spatial summation
Transformation of the rhythm of excitation
Rhythm transformation
trigger propertiesaxon colliculus
Threshold 30 mV
Threshold 10 mV
Neuron body
Ek
Eo
axon hillock
Ek
Eo
"At gunshot
neuron responds
machine-gun fire"
Rhythm transformation
50A
50
A
?
50
IN
Phase Relations
incoming impulses
IN
A
100
IN
A
IN
(following
fall into
refractoriness
previous
Features of the spread of excitation in the central nervous system
central relief
A1
At
irritation A
excited
2 neurons (1,2)
2
IN
3
4
5
At
irritated B
excited
2 neurons (5, 6)
6
Cells
peripheral
borders
When irritated A + B
excited 6
neurons (1, 2, 3, 4, 5, 6)
Cells
central
parts
neural pool
Central occlusion
A1
When irritated A
excited 4
neuron (1,2,3,4)
2
3
When irritated B
excited 4
neuron (3, 4, 5, 6)
IN
4
5
6
Cells
central
parts
neural pool
BUT with joint stimulation A + B
4 neurons are excited (1, 2, 5, 6)
The phenomenon of occlusion
3+3=64+4=8
Posttetanic potentiation
Ca2+Ca2+
Reverb scheme
High sensitivity centersto lack of oxygen and glucose
selective sensitivity
to chemicals
Low lability and high fatigue
nerve centers
Tone of nerve centers
Plastic
Synapse plasticity
This is a functional and morphological rearrangementsynapse:
Plasticity increase: facilitation (presynaptic
nature, Ca++), potentiation (postsynaptic nature,
increased sensitivity of postsynaptic receptors Sensitization)
Decrease in plasticity: depression (decrease
neurotransmitter stores in the presynaptic membrane)
- this is a mechanism for the development of habituation - habituation
Long-term forms of plasticity
Long-term potentiation - long-termincreased synaptic transmission
high frequency irritation
last days and months. Characteristic for
all parts of the CNS (hippocampus, glutamatergic
synapses).
long term depression
weakening of synaptic transmission (low
intracellular content of Ca++) active independent
physiological process,
stimulated and
aimed at weakening
termination or prevention
other arousal
T o r m e n t
BrakingInhibition of nerve cells, centers -
functional parity
significance with excitation nervous
process.
But! Braking does not apply
it is “tied” to the synapses on which
inhibition occurs.
Inhibition controls excitation.
Braking functions
Limits the spread of excitation in the central nervous system Radiation, reverberation, animation, etc.Coordinates functions, i.e. directs arousal
along certain pathways to certain nerve
centers
Braking performs a protective or protective
role, protecting nerve cells from excessive
excitation and exhaustion during action
superstrong and prolonged stimuli
Central inhibition was discovered by I.M. Sechenov in 1863
Central inhibition in the CNS (Sechenov)
Sechenov inhibition
Classification of inhibition in the CNS
The electrical state of the membranehyperpolarizing
depolarizing
relation to the synapse
postsynaptic
presynaptic
Neuronal organization
progressive,
returnable,
lateral
Bioelectric activity of a neuron
Brake mediators -
Brake mediators GAMK (gamma-aminobutyric acid)Glycine
Taurine
The occurrence of IPSP in response to afferent stimulation is mandatory
is associated with the inclusion in the inhibitory process of an additional link of the inhibitory interneuron, the axonal endings of which secrete
brake mediator.
Inhibitory postsynaptic potential of IPSP
mv0
4
6
8
ms
- 70
- 74
HYPERPOLARIZATION
K+ Clֿ
TYPES OF BRAKING
P E R V I C N O E:A) POSTSYNAPTIC
B) PRESYNAPTIC
SECONDARY:
A) PESSIMAL according to N. Vvedensky
B) TEXT (with trace hyperpolarization)
(Inhibition followed by excitation)
Ionic nature of postsynaptic inhibition
Post-synaptic inhibition (Latin post behind, after something + Greek sinapsis contact,connection) - a nervous process due to the action on the postsynaptic membrane of specific
inhibitory mediators released by specialized presynaptic nerve endings.
The mediator secreted by them changes the properties of the postsynaptic membrane, which causes suppression
the ability of the cell to generate excitation. This results in a short-term increase
permeability of the postsynaptic membrane to K+ or CI- ions, causing a decrease in its input
electrical resistance and the generation of inhibitory postsynaptic potential (IPSP).
POSTSYNAPTIC INHIBITION
TOCl
GABA
TPSP
Braking mechanisms
Decreased membrane excitabilityresult of hyperpolarization:
1. Release of potassium ions from the cell
2. Entry of chloride ions into the cell
3. Decrease in electrical density
current flowing through the axonal
hillock as a result of activation
chloride channels
Species classification
I.Primary postsynaptic
braking:
a) Central (Sechenov) inhibition.
b) Cortical
c) Reciprocal inhibition
d) Reverse braking
e) Lateral inhibition
Towards:
Direct.
Returnable.
Lateral.
Reciprocal.
MS, MR - flexor and extensor motor neurons.
Scheme of direct postsynapticinhibition in a segment of the spinal cord.
MS, MR - motor neurons
flexor and extensor.
Walking reflex
Examples of reflex arcsWalking reflex
4- release
3
4
1
2
A. continuous
excitation of motor
CNS centers are broken
for successive acts
excitation of the right and
left leg.
(reciprocal + return
th braking)
B. motion control when
help of the postural reflex
(reciprocal inhibition)
Reciprocal inhibition - at the level of segments of the spinal cord
INHIBITION IN THE CNS
BRAKINGReverse braking
by Renshaw
B - arousal
T - braking
In the CNS
Lateral
braking
Reverse (antidromic) inhibition
Reverse postsynaptic inhibition (Greek antidromeo to run in the opposite direction) - the processregulation by nerve cells of the intensity of the signals coming to them according to the principle of negative feedback.
It lies in the fact that the collaterals of the axons of the nerve cell establish synaptic contacts with special
intercalary neurons (Renshaw cells), whose role is to act on neurons that converge on the cell,
sending these axon collaterals. According to this principle, the inhibition of motor neurons is carried out.
Lateral inhibition
Synapses on a neuron
presynaptic inhibition
It is carried out by means of special inhibitory interneurons.Its structural basis is axo-axonal synapses,
formed by axon terminals of inhibitory interneurons and
axonal endings of excitatory neurons. PRESYNAPTIC
BRAKING
1 - axon of an inhibitory neuron
2 - axon of the excitatory neuron
3 - postsynaptic membrane
alpha moto neuron
Cl¯ channel
at the endings of the presynaptic inhibitory
axon releases a neurotransmitter, which
causes depolarization of excitatory
endings
behind
check
increase
their membrane permeability to CI-.
Depolarization
causes
decrease
amplitude of the action potential coming
to the excitatory ending of the axon. IN
As a result, the process is inhibited
release of the neurotransmitter by excitatory
nervous
endings
And
decline
amplitude
exciting
postsynaptic potential.
characteristic feature
presynaptic depolarization is
delayed development and long duration
(several hundred milliseconds), even after
single afferent impulse.
presynaptic inhibition
Presynaptic inhibition primarily blocks weakasynchronous afferent signals and passes stronger,
therefore, it serves as a mechanism for isolating, isolating more
intense afferent impulses from the general stream. It has
great adaptive value for the body, since of all
afferent signals going to the nerve centers, the most
the main ones, the most necessary for this particular time.
Thanks to this, the nerve centers, the nervous system as a whole is freed
from processing less relevant information
Afferent impulses from the flexor muscle, with the help of Renshaw cells, cause presynaptic inhibition on the afferent nerve, which is under
Scheme of presynaptic inhibitionin a segment of the spinal cord.
Afferent
impulses from the muscle
- flexor with
cells
Renshaw call
presynaptic
braking on
afferent nerve
which fits to
motoneuron
extensor.
Examples of inhibitory disorders in the CNS
DISTURBANCE OF POSTSYNAPTIC INHIBITION:STRICHNINE - BLOCKAD OF RECEPTORS OF INDUSTRIAL SYNAPSE
TETANUS TOXIN - RELEASE DISTURBANCE
BRAKE PTO
DISTURBANCE OF PRESYNAPTIC INHIBITION:
PICROTOXIN - BLOCKADA OF PRESYNAPTIC SYNAPSE
Strychnine and tetanus toxin do not affect it.
Postsynaptic reversible inhibition. Blocked by strychnine.
presynaptic inhibition. Blocked by picrotoxin
Species classification
Secondary inhibition is not related toinhibitory structures, is
a consequence of the previous
arousal.
a) Beyond
b) Pessimal inhibition of Vvednsky
c) Parobiotic
d) Inhibition followed by excitation
Induction
By the nature of influence:Positive - observed when braking is changed
increased excitability around you.
Negative - if the focus of excitation is replaced by inhibition
By time:
Simultaneous Positive Simultaneous Induction
observed when braking immediately (simultaneously) creates a state
increased excitability around you.
Sequential When changing the braking process to
excitation - positive series induction
Registration of EPSP and TPSP
PRINCIPLES OF COORDINATION OF REFLEX ACTIVITY
1. RECIPROCITY2. COMMON FINAL PATH
(according to Sherrington)
3. DOMINANTS
4. SUBORDINATIONS OF THE NERVE CENTRAL DOMINANTS
(PO A.A. Ukhtomsky, 1931)
temporarily
dominant
hearth
arousal
V
central
nervous system that determines
current activity of the body
DOMINANT
-DEFINITION OF DOMINANT
(PO A.A. Ukhtomsky, 1931)
temporarily
dominant
reflex
or
behavioral
Act,
which
transformed and directed
for a given time with other
equal conditions work of others
reflex arcs, reflex
apparatus and behavior in general
DOMINANT
-DOMINANT PRINCIPLE
Irritants
Nerve centers
reflexes The main features of the dominant
(according to A.A. Ukhtomsky)
1. Increased excitability of the dominant
center
2. Persistence of excitation in the dominant
center
3. The ability to summarize excitations,
thereby reinforcing their arousal
extraneous impulses
4. Ability to slow down other current
reflexes on a common final path
5. Inertia of the dominant center
6. Ability to disinhibit
Scheme of formation of dominant D - persistent excitation - grasping reflex in a frog (dominant), caused by the application of strychnine. All
DDominant formation scheme
D - persistent excitation grasping reflex
frogs (dominant),
caused by application
strychnine. All annoyances in
points 1,2,3,4 do not give answers,
but only increase the activity
neurons D.
