Physiology of excitable tissues studies the basic patterns of interaction between the organism, its components and existing environmental factors.

Excitable tissues- nervous tissue, glandular tissue and muscle tissue specially adapted to carry out rapid responses to the action of a stimulus.

Humans and animals live in a world of light, sounds, smells, gravitational forces, mechanical pressure, variable temperature and other signals from the external or internal environment. Everyone knows from their own experience that we are not only able to instantly perceive these signals (also called stimuli), but also respond to them. This perception is carried out by the structures of nervous tissue, and one of the forms of response to perceived signals is motor reactions carried out by muscle tissue. This chapter will examine the physiological basis of the processes and mechanisms that ensure the body’s perception and response to various signals from the external and internal environment.

The most important specialized tissues of the body, which provide the perception of signals and responses to the action of various stimuli, are nervous and muscle tissues, which are traditionally called excitable tissues. However, it is the muscle cells and neurons that are truly excitable in them. Neuroglial cells, of which there are approximately 10 times more in the brain than , do not have excitability.

Excitability- the ability of cells to react in a certain way to the action of a stimulus.

Excitation- an active physiological process, a response of excitable cells, manifested by the generation of an action potential, its conduction and contraction for muscle cells.

Excitability in the evolution of cells developed from the property of irritability inherent in all living cells, and is a special case of irritability.

Irritability- this is a universal property of cells to respond to the action of a stimulus by changing vital processes. For example, neutrophils, having perceived the action of a specific signal - antigen, with their receptors, stop moving in the blood flow, attach to the capillary wall and migrate in the direction of the inflammatory process in the tissue. The epithelium of the oral mucosa reacts to the action of irritating substances by increasing the production and secretion of mucus, and the skin epithelium, when exposed to ultraviolet rays, accumulates a protective pigment.

Excitation is manifested by specific and nonspecific changes recorded in the cell.

Specific manifestation excitation for nerve cells is the generation and conduction of an action potential (nerve impulse) over relatively long distances without reducing its amplitude, and for muscle cells - the generation, conduction of an action potential and contraction. Thus, the key indicator of the occurrence of excitation is the generation of an action potential. A sign of the presence of an action potential is recharging (inversion of the charge sign). In this case, for a short time, the surface of the membrane, instead of the positive one present at rest, acquires a negative charge. In cells that do not have excitability, when exposed to a stimulus, the potential difference on the cell membrane can only change, but this is not accompanied by recharging of the membrane.

To nonspecific manifestations excitations of nerve and muscle cells include changes in the permeability of cell membranes to various substances, acceleration of metabolism and, accordingly, an increase in the absorption of oxygen by cells and the release of carbon dioxide, a decrease in pH, an increase in cell temperature, etc. These manifestations are in many ways similar to the components of the response to the action of a stimulus of non-excitable cells.

Excitation can occur under the influence of signals coming from the external environment, from the cell microenvironment, and spontaneously (automatically) due to changes in the permeability of the cell membrane and metabolic processes in the cell. Such cells are said to have automaticity. Automaticity is inherent in the pacemaker cells of the heart, smooth myocytes of the walls of blood vessels and intestines.

In the experiment, one can observe the development of excitation under the direct influence of stimuli on nervous and muscle tissue. There are irritants (signals) of physical (temperature, electric current, mechanical effects), chemical (neurotransmitters, cytokines, growth factors, flavoring, odorous substances) and physicochemical nature (osmotic pressure, pH).

Based on the biological correspondence of stimuli to the specialization of sensory receptors that perceive the effects of these stimuli in the body, the latter are divided into adequate and inadequate.

Adequate stimuli - irritants, to the perception of which the receptors are adapted and react to a low force of influence. For example, light quanta are adequate for photoreceptors and other cells of the retina, the response to which is registered in the photoreceptors of the retina when only 1-4 quanta are absorbed.

Inappropriate stimuli do not cause excitement even with significant force. Only with excessive forces bordering on damage can they cause excitation. Thus, the sensation of sparks of light may occur when struck in the eye area. In this case, the energy of the mechanical, inadequate stimulus is billions of times greater than the energy of the light stimulus that causes the sensation of light.

Conditions of excitable tissue cells

All living cells have irritability, i.e. the ability to respond to various stimuli and move from a state of physiological rest to a state of activity. This process is accompanied by a change in metabolism, and differentiated tissues (nervous, muscle, glandular) that perform specific functions (conducting a nerve impulse, contraction or secretion) are also accompanied by a change in electrical potential.

Excitable tissue cells can be in three different states(Fig. 1). In this case, cells from a state of physiological rest can move into active states of excitation or inhibition, and vice versa. Cells that are in a state of excitation can move into a state of inhibition, and from a state of inhibition - into a state of excitation. The rate at which different cells or tissues transition from one state to another varies greatly. Thus, motor neurons in the spinal cord can move from a resting state to a state of excitation from 200 to 300 times per second, while interneurons can switch up to 1000 times per second.

Rice. 1. The relationship between the basic physiological states of excitable tissue cells

Physiological rest- a condition characterized by:

• relatively constant level of process exchange;
• lack of functional manifestations of the tissue.

Active state occurs under the influence of a stimulus and is characterized by:

• a pronounced change in the level of metabolic processes;
• manifestations of functional tissue functions.

Excitation- an active physiological process that occurs under the influence of a stimulus, facilitating the transition of tissue from a state of physiological rest to specific activity (generation of a nerve impulse, contraction, secretion). Nonspecific signs of excitement:

• change in membrane charge;
• increased metabolic processes;
• increase in energy costs.

Braking- an active physiological process that occurs under the influence of a certain stimulus and is characterized by inhibition or cessation of the functional activity of the tissue. Nonspecific signs of inhibition:

• change in cell membrane permeability;
• change in the movement of ions through it;
• change in membrane charge;
• decrease in the level of metabolic processes;
• reduction in energy costs.

Basic properties of excitable tissues

Any living tissue has the following properties: excitability, conductivity and lability.

Excitability- the ability of tissue to respond to stimuli by transitioning to an active state. Excitability is characteristic of nervous, muscle and glandular tissues. Excitability is inversely proportional to the strength of the current stimulus: B = 1/S. The greater the strength of the current stimulus, the less excitability, and vice versa. Excitability depends on the state of metabolic processes and the charge of the cell membrane. Inexcitability = refractoriness. Nervous tissue has the greatest excitability, followed by striated skeletal and cardiac muscle tissue, and glandular tissue.

Conductivity- the ability of tissue to conduct excitation in two or one direction. An indicator of conductivity is the speed of excitation (from 0.5 to 120 m/s depending on the tissue and fiber structure). Excitation is transmitted most quickly along the myelinated nerve fiber, then through the unmyelinated fiber, and the synapse has the lowest conductivity.

Functional lability- the ability of tissue to reproduce without distortion the frequency of rhythmically applied impulses. An indicator of functional lability is the number of impulses that a given structure can transmit without distortion per unit of time. For example, a nerve - 500-1000 impulses/s, a muscle - 200-250 impulses/s, a synapse - 100-120 impulses/s.

The role of the force of irritation and the time of its action. Chronaxia - this is a temporary characteristic of excitability. The relationship between the threshold intensity of stimulation and duration is called duration force curve or Goorweg-Weiss curve(Fig. 2). It has the shape of an equilateral hyperbola. Time is plotted on the abscissa axis, and the threshold intensity of stimulation is plotted on the ordinate axis.

Rice. 2. Duration force curve (Goorweg - Weiss)

The abscissa axis represents time (t); along the ordinate - threshold intensity of stimulation (i); 0A - rheobase: 0B - double rheobase: OD - chropaxy; 0J - useful time

From Fig. 2 it can be seen that if the intensity of stimulation is too low (less than OA), the response does not occur at any duration. There is no reaction even if the duration of the stimulus is too short (less than OG). When the intensity of stimulation corresponds to the segment OA, excitation occurs under the condition of a longer duration of action of the irritating impulse. Within the time period determined by the segment OB, there is a relationship between the threshold intensity and the duration of stimulation: a shorter duration of the irritating impulse corresponds to a greater threshold intensity (the segment OD corresponds to OB, and OE corresponds to the segment OB). Beyond this time (TO), changing the duration of the stimulus no longer affects the value of the irritation threshold. The shortest time during which the relationship between the threshold intensity of stimulation and its duration appears is called useful time(coolant segment). Useful time is a temporary measure of arousal. By its value one can judge the functional state of various excitable formations. However, to determine the useful time, it is necessary to find several points on the curve, which requires applying a lot of irritations. Therefore, the definition of another time indicator, which was introduced into the practice of physiological research by L. Lap i k (1907), has become widespread. He proposed the following parameters to characterize the rate of occurrence of the excitation process: rheobase And chronaxia.

Rheobase— this is the threshold intensity of irritation for a long duration of its action (segment OA); chronaxia - the time during which a current equal to double rheobase (RB) must operate to obtain a threshold response (segment RD). During this time, the membrane potential decreases to a value corresponding to the critical level of depolarization. For different excitable formations, the magnitude of chronaxy is not the same. Thus, the chronaxy of the human ulnar nerve is 0.36 ms, the median nerve is 0.26 ms, the common digital flexor is 0.22 ms, and the common extensor is 0.58 ms.

M. Weiss formula

where I is the threshold current; t is the duration of the stimulus (s); a is a constant characterizing the constant time of stimulation from the moment when the curve turns into a straight line running parallel to the ordinate axis; b is a constant corresponding to the strength of stimulation at a constant duration, when the curve crosses a line running parallel to the abscissa axis.

Excitability indicators

To assess the state of excitability in humans and animals, a number of its indicators are studied in an experiment, which indicate, on the one hand, what stimuli the excitable tissue reacts to, and on the other, how it reacts to influences.

The excitability of nerve cells is usually higher than that of muscle cells. The level of excitability depends not only on the type of cell, but also on numerous factors affecting the cell and especially the state of its membrane (permeability, polarization, etc.).

The indicators of excitability include the following.

Stimulus strength threshold- this is the minimum strength of the current stimulus sufficient to initiate excitation. Stimuli whose strength is below the threshold are called subthreshold, and those whose strength is above the threshold are called supra- or superthreshold.

There is an inverse relationship between excitability and the magnitude of the force threshold. The more an excitable cell or tissue reacts to a lesser impact by developing excitation, the higher its excitability.

The excitability of tissue depends on its functional state. With the development of pathological changes in tissues, their excitability can decrease significantly. Thus, measuring the threshold of stimulus strength has diagnostic significance and is used in the electrodiagnosis of diseases of the nervous and muscle tissues. One of its examples can be the electrodiagnosis of dental pulp diseases, called electroodontometry.

Electroodontometry (electroodontodiagnosis) is a method of using electric current for diagnostic purposes to determine the excitability of the nervous tissue of teeth (sensory receptors of the sensitive nerves of the dental pulp). The dental pulp contains a large number of sensitive nerve endings that respond to certain mechanical, temperature and other influences. Electroodontometry determines the threshold for feeling the action of electric current. The electric current threshold for healthy teeth is 2-6 µA. with medium and deep caries - 10-15, acute pulpitis - 20-40, with the death of the coronal pulp - 60, with the death of the entire pulp - 100 μA or more.

The magnitude of the threshold force of irritation of excitable tissue depends on the duration of exposure to the stimulus.

This can be tested experimentally by applying electric current pulses to excitable tissue (nerve or muscle), observing at what values ​​of the strength and duration of the electric current pulse the tissue responds with excitation, and at what values ​​excitation does not develop. If the duration of exposure is very short, then excitation in the tissue may not occur even with superthreshold exposures. If the duration of the stimulus is increased, the tissue will begin to react with excitation to lower-strength impacts. Excitation will occur with the least powerful impact if its duration is infinite. The relationship between the force threshold and the stimulation time threshold sufficient for the development of excitation is described by the force-duration curve (Fig. 3).

Rice. 3. Force-duration curve (the ratio of force and duration of exposure necessary for the occurrence of excitation). Below and to the left of the curve are the ratios of stimulus strength and duration, insufficient for excitation; above and to the right are sufficient

The concept of “rheobase” was introduced specifically to characterize the threshold of electric current, which is widely used as a stimulus in the study of tissue responses. Rheobase- this is the minimum electric current required to initiate excitation, with prolonged exposure to a cell or tissue. Further prolongation of stimulation has virtually no effect on the magnitude of the threshold force.

Irritation time threshold- the minimum time during which a stimulus of threshold strength must act to cause arousal.

There is also an inverse relationship between excitability and the time threshold. The tissue reacts to shorter threshold influences with the development of excitation, the higher the excitability. The threshold time for excitable tissue depends on the strength of the stimulus, as can be seen in Fig. 3.

Chronaxia - the minimum time during which a stimulus with a force equal to two rheobases must act in order to cause excitation (see Fig. 3). This excitability indicator is also used when electric current is used as a stimulus. The chronaxy of nerve cells and skeletal muscle fibers is ten thousandths of a second, and that of smooth muscles is tens of times greater. Chronaxy as an indicator of excitability is used to test the condition and functionality of skeletal muscles and nerve fibers of a healthy person (in particular, in sports medicine). Determining chronaxy is valuable for diagnosing a number of diseases of muscles and nerves, since in this case the excitability of the latter usually decreases and chronaxy increases.

Minimum gradient (steepness) increase in the strength of the stimulus over time. This is the minimum rate of increase in stimulus strength over time sufficient to initiate excitation. If the strength of the stimulus increases very slowly, then the tissue adapts to its action and does not respond with excitation. This adaptation of excitable tissue to a slowly increasing stimulus strength is called accommodation. The greater the minimum gradient, the lower the excitability of the tissue and the more pronounced its ability to accommodate. The practical significance of this indicator lies in the fact that when carrying out various medical manipulations in a person, in some cases it is possible to avoid the development of severe pain and shock conditions by slowly changing the rate of increase in force and the time of exposure.

Lability- functional mobility of excitable tissue. Lability is determined by the rate of elementary physicochemical transformations underlying a single excitation cycle. A measure of lability is the maximum number of cycles (waves) of excitation that a tissue can generate per unit time. Quantitatively, the magnitude of lability is determined by the duration of a single cycle of excitation and the duration of the phase of absolute refractoriness. Thus, interneurons of the spinal cord can reproduce more than 500 cycles of excitation or nerve impulses per second. They have high lability. Motor neurons that control muscle contraction are characterized by lower lability and are capable of generating no more than 100 nerve impulses per second.

Potential difference (ΔE) between the resting potential on the membrane (E 0) and critical level of depolarization membranes (E k). ΔE = (E 0 - E k) is one of the most important indicators of cell excitability. This indicator reflects the physical essence of the stimulus strength threshold. A stimulus is threshold in the case when it is capable of shifting such a level of membrane polarization to E k, upon reaching which an excitation process develops on the membrane. The lower the ΔE value, the higher the excitability of the cell and the weaker influences it will respond with excitation. However, the ΔE indicator is difficult to measure under normal conditions. The physiological significance of this indicator will be considered when studying the nature of membrane potentials.

Laws of response of excitable tissues to irritation

The nature of the response of excitable tissues to the action of stimuli is classically described by the laws of irritation.

Law of force irritation states that when the strength of the suprathreshold stimulus increases to a certain limit, the magnitude of the response also increases. This law is applicable to the contraction response of an integral skeletal muscle and the total electrical response of nerve trunks, which include many fibers with different excitability. Thus, the force of muscle contraction increases with increasing strength of the stimulus acting on it.

For the same excitable structures, the law of stimulation duration and the law of stimulation gradient are applicable. Law of duration of irritation states that the longer the duration of suprathreshold stimulation, the greater the magnitude of the response. Naturally, the answer increases only up to a certain limit. Law of irritation gradient - The greater the gradient of increase in the strength of the stimulus over time, the greater (up to a certain limit) the magnitude of the response.

All or nothing law states that under the action of subthreshold stimuli, excitation does not occur, and under the action of threshold and suprathreshold stimuli, the magnitude of the response due to excitation remains constant. Consequently, already to a threshold stimulus, the excitable structure responds with the maximum possible reaction for a given functional state. A single nerve fiber is subject to this law, on the membrane of which an action potential of equal amplitude and duration is generated in response to the action of threshold and suprathreshold stimuli. The “all or nothing” law governs the reaction of a single skeletal muscle fiber, which responds with action potentials of equal amplitude and duration and the same force of contraction to both threshold and suprathreshold stimuli of different strengths. The nature of contraction of the entire muscle of the ventricles of the heart and atria is also subject to this law.

Law of polar action of electric current (Pfluger) postulates that when excitable cells are exposed to direct electric current at the moment of circuit closure, excitation occurs at the point of application of the cathode, and when opened, at the point of contact with the anode. In itself, the prolonged action of direct current on excitable cells and tissues does not cause excitation in them. The impossibility of initiating excitation by such a current can be considered as a consequence of their accommodation to a stimulus that does not change in time with a zero slope of increase. However, since the cells are polarized and there is an excess of negative charges on their inner surface, and positive charges on the outer surface, then in the area of ​​application of the anode (positively charged electrode) to the tissue under the influence of an electric field, part of the positive charges represented by K+ cations will move inside the cell and their the concentration on the outer surface will become less. This will lead to a decrease in the excitability of cells and the tissue area under the anode. The opposite phenomena will be observed under the cathode.

The effect of electric current on living tissues and recording of bioelectric currents are often used in medical practice for diagnosis and treatment, and especially when conducting experimental physiological studies. This is due to the fact that the values ​​of biocurrents reflect the functional state of tissues. Electric current has a therapeutic effect, it is easily dosed in terms of magnitude and time of exposure, and its effects can be observed at impact forces close to the natural values ​​of biocurrents in the body.

subject

"Excitability and its measurement, lability"

Volgograd – 2018

Content:

Excitability and its measurement, lability.

Properties of biological membranes.

Resting and action membrane potential.

4. Phases of excitability during arousal.

1 Excitability and its measurement, lability

Excitability

The main property of living cells is irritability, i.e. their ability to respond by changing metabolism in response to stimuli.Excitability - the ability of cells to respond to stimulation with excitation. Excitable cells include nerve, muscle and some secretory cells. Excitation is the response of a tissue to its irritation, manifested in a function specific to it (conduction of excitation by nervous tissue, muscle contraction, gland secretion) and nonspecific reactions (generation of an action potential, metabolic changes). One of the important properties of living cells is their electrical excitability, i.e. the ability to be excited in response to an electric current. The high sensitivity of excitable tissues to the action of weak electric current was first demonstrated by Galvani in experiments on a neuromuscular preparation of the hind legs of a frog. If two interconnected plates of different metals, for example copper-zinc, are applied to a neuromuscular preparation of a frog, so that one plate touches the muscle and the other touches the nerve, then the muscle will contract (Galvani’s first experiment). Detailed analysis of the results Galvani's experiments, carried out by A. Volta, allowed us to draw a different conclusion: the electric current does not arise in living cells, but at the point of contact of dissimilar metals with the electrolyte, since tissue fluids are a solution of salts. As a result of his research, A. Volta created a device called the “voltaic column” - a set of successively alternating zinc and silver plates, separated by paper soaked in saline solution. To prove the validity of his point of view, Galvani proposed another experiment: throwing a distal segment of the nerve that innervates this muscle onto a muscle, while the muscle also contracted (Galvani’s second experiment, or experiment without metal). The absence of metal conductors during the experiment allowed Galvani to confirm his point of view and develop ideas about “animal electricity,” i.e., electrical phenomena that arise in living cells. The final proof of the existence of electrical phenomena in living tissues was obtained in the experiment of “secondary tetanus” by Matteucci, in which one neuromuscular preparation was excited by current, and the biocurrents of the contracting muscle were irritated by the nerve of the second neuromuscular preparation. At the end of the 19th century, thanks to the work of L. Herman, E. Dubois-Raymond, Y. Bernstein, it became obvious that the electrical phenomena that arise in excitable tissues are caused by the electrical properties of cellular.

Excitability measurement

Electric current is widely used in experimental physiology when studying the characteristics of excitable tissues, and in clinical practice for diagnostics and therapeutic effects, therefore it is necessary to consider the mechanisms of the effect of electric current on excitable tissues. The reaction of excitable tissue depends on the shape of the current (direct, alternating or pulsed), the duration of the current, and the steepness of the increase (change) in the amplitude of the current.

The impact effect is determined not only by the absolute value of the current, but also by the current density under the stimulating electrode. The current density is determined by the ratio of the current flowing through the circuit to the electrode area, therefore, with monopolar stimulation, the active electrode area is always less than the passive one.

D.C. When a subthreshold direct electric current is briefly passed, the excitability of the tissue under the stimulating electrodes changes. Microelectrode studies have shown that depolarization of the cell membrane occurs under the cathode, and hyperpolarization occurs under the anode. In the first case, the difference between the critical potential and the membrane potential will decrease, i.e., the excitability of the tissue under the cathode increases. Under the anode, the opposite phenomena occur, i.e., excitability decreases. Ifresponds with a passive potential shift, then they talk about electrotonic shifts, or electrotone. With short-term electrotonic shifts, the value of the critical potential does not change.

Since almost all excitable cells have a cell length greater than its diameter, electrotonic potentials are distributed unevenly. At the point of localization of the stimulating electrode, the potential shift occurs very quickly and the time parameters are determined by the value of the membrane capacitance. In remotemembrane, the current not only passes through the membrane, but also overcomes the longitudinal resistance of the internal environment. The electrotonic potential decreases exponentially with increasing length, and the distance at which it decreases by a factor of 1/e (to 37%) is called the length constant (λ).

With a relatively long duration of action of the subthreshold current, not only the membrane potential changes, but also the value of the critical potential. In this case, under the cathode, the level of the critical potential shifts upward, which indicates inactivation of sodium channels. Thus, excitability under the cathode decreases with prolonged exposure to subthreshold current. This phenomenon of decreased excitability during prolonged exposure to a subthreshold stimulus is called accommodation. At the same time, abnormally low-amplitude action potentials arise in the studied cells.

The rate of increase in the intensity of the stimulus is of significant importance in determining the excitable tissue, therefore, rectangular pulses are most often used (a rectangular current pulse has the maximum steepness of increase). Slowing down the rate of change in the amplitude of the stimulus leads to inactivation of sodium channels due to gradual depolarization of the cell membrane, and consequently to a decrease in excitability.

Increasing the stimulus strength to a threshold value leads to the generation of an action potential

Under the anode, under the influence of a strong current, a change in the level of the critical potential occurs, in the opposite direction - downward. In this case, the difference between the critical potential and the membrane potential decreases, i.e., the excitability under the anode increases with prolonged exposure to current.

Obviously, increasing the current value to a threshold value will lead to excitation occurring under the cathode when the circuit is closed. It should be emphasized that this effect can be detected in the case of prolonged exposure to electric current. When exposed to a sufficiently strong current, the shift in the critical potential under the anode can be very significant and reach the initial value of the membrane potential. Turning off the current will cause the hyperpolarization of the membrane to disappear, the membrane potential will return to its original value, and this corresponds to the value of the critical potential, i.e., anode-break excitation occurs.

The change in excitability and the occurrence of excitation under the cathode when closing and the anode when opening is called the law of polar action of current. Experimental confirmation of this dependence was first obtained by Pflueger back in the last century.

As mentioned above, there is a certain relationship between the duration of the stimulus and its amplitude. This dependence in graphical expression is called the “force-duration” curve. Sometimes, after the authors' names, it is called the Goorweg-Weiss-Lapik curve. This curve shows that a decrease in the current value below a certain critical value does not lead to tissue excitation, regardless of the length of time during which this stimulus acts, and the minimum current value that causes excitation is called the irritation threshold, or rheobase. The value of rheobase is determined by the difference between the critical potential and the resting membrane potential.

On the other hand, the stimulus must act for at least a certain time. Reducing the duration of action of the stimulus below a critical value leads to the fact that the stimulus of any intensity has no effect. To characterize the excitability of tissue over time, the concept of a time threshold was introduced - the minimum (useful) time during which a stimulus of threshold strength must act in order to cause excitation.

The time threshold is determined by the capacitive and resistive characteristics of the cell membrane, i.e., the time constant T=RC.

Due to the fact that the value of rheobase can change, especially under natural conditions, and this can lead to a significant error in determining the time threshold, Lapic introduced the concept of chronaxy to characterize the temporal properties of cell membranes. Chronaxy is the time during which a doubled rheobase stimulus must act to cause excitation. The use of this criterion allows you to accurately measure the time characteristics of excitable structures, since the measurement occurs at a sharp bend of the hyperbola

Chronaximetry is used to assess the functional state of the neuromuscular system in humans. With its organic lesions, the value of chronaxy and rheobase of nerves and muscles increases significantly.

Thus, when assessing the degree of excitability of excitable structures, the quantitative characteristics of the stimulus are used - amplitude, duration of action, rate of increase in amplitude. Consequently, a quantitative assessment of the physiological properties of excitable tissue is made indirectly based on the characteristics of the stimulus.

Alternating current. The effectiveness of alternating current is determined not only by the amplitude and duration of exposure, but also by frequency. In this case, low-frequency alternating current, for example, with a frequency of 50 Hz (mains), poses the greatest danger when passing through the heart area. This is primarily due to the fact that at low frequencies the next stimulus may enter theincreased vulnerability of the myocardium and the occurrence of ventricular fibrillation. The effect of current with a frequency above 10 kHz is less dangerous, since the half-cycle duration is 0.05 ms. With such a pulse duration, the cell membrane, due to its capacitive properties, does not have time to depolarize to a critical level. Higher frequency currents usually cause a thermal effect.

Lability

Lability is a relatively high speed of elementary cycles of excitation in nervous, muscle or other excitable tissue. The measure of lability is the largest number of impulses that the tissue is able to reproduce in 1 second while maintaining frequency correspondence with the maximum rhythm of stimulation. Nerve fibers have the greatest lability.

Tissue lability is the ability of tissue to carry out a certain number of completed excitation cycles per second.
Summary: I believe that excitability is one of the most important functions of the body. The concept of “excitability”often used in medical and biological literature to characterize the state of the nerve centers of the brain and spinal cord (for example, respiratory, vasomotor, etc.).

2 Properties of biological membranes

According to modern concepts, biological membranes form the outer shell of all animal cells and form numerous intracellular organelles. The most characteristic structural feature is that membranes always form closed spaces, and this microstructural organization of membranes allows them to perform essential functions.

Structure and functions of cell membranes

1. The barrier function is expressed in the fact that the membrane, using appropriate mechanisms, participates in the creation of concentration gradients, preventing free diffusion. In this case, the membrane takes part in the mechanisms of electrogenesis. These include mechanisms for creating a resting potential, generation of an action potential, mechanisms for the propagation of bioelectric impulses across homogeneous and heterogeneous excitable structures.

2. The regulatory function of the cell membrane is the fine regulation of intracellular contents and intracellular reactions due to the reception of extracellular biologically active substances, which leads to changes in the activity of enzyme systems of the membrane and the launch of mechanisms of secondary “messengers” (“intermediaries”).

3. Conversion of external stimuli of a non-electrical nature into electrical signals (in receptors).

4.Release of neurotransmitters in synaptic endings.

Modern methods of electron microscopy determined the thickness of cell membranes (6-12 nm). Chemical analysis showed that the membranes are mainly composed of lipids and proteins, the amount of which varies among different cell types. The difficulty of studying the molecular mechanisms of the functioning of cell membranes is due to the fact that when isolating and purifying cell membranes, their normal functioning is disrupted. Currently, we can talk about several types of cell membrane models, among which the liquid mosaic model is the most widespread.

According to this model, the membrane is represented by a bilayer of phospholipid molecules, oriented in such a way that the hydrophobic ends of the molecules are located inside the bilayer, and the hydrophilic ends are directed into the aqueous phase. This structure is ideal for the formation of a separation between two phases: extra- and intracellular.

Globular proteins are integrated into the phospholipid bilayer, polarwhich form a hydrophilic surface in the aqueous phase. These integrated proteins perform various functions, including receptor, enzymatic, form ion channels, and areand carriers of ions and molecules.

Some protein molecules diffuse freely in the plane of the lipid layer; in the normal state, parts of protein molecules emerging on different sides of the cell membrane do not change their position. Only a general diagram of the structure of a cell membrane is described here, and significant differences are possible for other types of cell membranes.

Electrical characteristics of membranes. The special morphology of cell membranes determines their electrical characteristics, among which the most important are capacitance and conductivity.

Capacitive properties are mainly determined by the phospholipid bilayer, which is impermeable to hydrated ions and at the same time thin enough (about 5 nm) to allow efficient separation and accumulation of charges and electrostatic interaction of cations and anions. In addition, the capacitive properties of cell membranes are one of the reasons that determine the time characteristics of electrical processes occurring on cell membranes.

Conductivity (g) is the reciprocal of electrical resistance and is equal to the ratio of the total transmembrane current for a given ion to the value that determined its transmembrane potential difference.

Various substances can diffuse through the phospholipid bilayer, and the degree of permeability (P), i.e., the ability of the cell membrane to pass these substances, depends on the difference in concentrations of the diffusing substance on both sides of the membrane, its solubility in lipids and the properties of the cell membrane. The rate of diffusion for charged ions under constant field conditions in a membrane is determined by the mobility of ions, the thickness of the membrane, and the distribution of ions in the membrane. For nonelectrolytes, the permeability of the membrane does not affect its conductivity, since nonelectrolytes do not carry charges, i.e., they cannot carry electric current.

The conductivity of a membrane is a measure of its ionic permeability. An increase in conductivity indicates an increase in the number of ions passing through the membrane.

Structure and functions of ion channels. Na+, K+, Ca2+, Cl- ions penetrate into the cell and exit through special fluid-filled channels. The size of the channels is quite small (diameter 0.5-0.7 nm). Calculations show that the total area of ​​the channels occupies an insignificant part of the surface of the cell membrane.

The function of ion channels is studied in various ways. The most common method is voltage clamp, or “voltage-clamp”. The essence of the method is that, with the help of special electronic systems, the membrane potential is changed and fixed at a certain level during the experiment. In this case, the magnitude of the ionic current flowing through the membrane is measured. If the potential difference is constant, then, in accordance with Ohm's law, the current magnitude is proportional to the conductivity of the ion channels. In response to stepwise depolarization, certain channels open and the corresponding ions enter the cell along an electrochemical gradient, i.e., an ion current arises that depolarizes the cell. This change is detected by a control amplifier and an electric current is passed through the membrane, equal in magnitude but opposite in direction to the membrane ion current. In this case, the transmembrane potential difference does not change. The combined use of voltage clamp and specific ion channel blockers led to the discovery of various types of ion channels in the cell membrane.

Many types of channels for different ions are currently installed. Some of them are very specific, while others, in addition to the main ion, can allow other ions to pass through.

Studying the function of individual channels is possible using the method of local fixation of the “path-clamp” potential. A glass microelectrode (micropipette) is filled with saline solution, pressed against the surface of the membrane and a slight vacuum is created. In this case, part of the membrane is sucked to the microelectrode. If an ion channel appears in the suction zone, then the activity of a single channel is recorded. The system of irritation and recording of channel activity differs little from the voltage recording system.

The current through a single ion channel has a rectangular shape and is the same in amplitude for channels of different types. The duration of the channel's stay in the open state is probabilistic, but depends on the value of the membrane potential. The total ion current is determined by the probability of a certain number of channels being in the open state in each specific period of time.

The outer part of the canal is relatively accessible for study; studying the inner part presents significant difficulties. P. G. Kostyuk developed a method of intracellular dialysis, which allows one to study the function of the input and output structures of ion channels without the use of microelectrodes. It turned out that the part of the ion channel open to the extracellular space differs in its functional properties from the part of the channel facing the intracellular environment.

It is ion channels that provide two important properties of the membrane: selectivity and conductivity.

The selectivity, or selectivity, of the channel is ensured by its special protein structure. Most channels are electrically controlled, that is, their ability to conduct ions depends on the magnitude of the membrane potential. The channel is heterogeneous in its functional characteristics, especially with regard to the protein structures located at the entrance to the channel and at its exit (the so-called gate mechanisms).

Let's consider the principle of operation of ion channels using the sodium channel as an example. It is believed that the sodium channel is closed at rest. When the cell membrane is depolarized to a certain level, the m-activation gate opens (activation) and the flow of Na+ ions into the cell increases. A few milliseconds after the m-gate opens, the p-gate located at the exit of the sodium channels closes (inactivation). Inactivation develops very quickly in the cell membrane and the degree of inactivation depends on the magnitude and time of action of the depolarizing stimulus.

The operation of sodium channels is determined by the value of the membrane potential in accordance with certain laws of probability. It is calculated that the activated sodium channel allows only 6000 ions to pass through in 1 ms. In this case, the very significant sodium current that passes through the membranes during excitation is the sum of thousands of single currents.

When a single action potential is generated in a thick nerve fiber, the change in the concentration of Na+ ions in the internal environment is only 1/100,000 of the internal Na+ ion content of the squid giant axon. However, for thin nerve fibers this change in concentration can be quite significant.

In addition to sodium, other types of channels are installed in cell membranes that are selectively permeable to individual ions: K+, Ca2+, and there are varieties of channels for these ions.

Hodgkin and Huxley formulated the principle of “independence” of channels, according to which the flow of sodium and potassium across the membrane is independent of each other.

The conductivity properties of different channels are not the same. In particular, for potassium channels, the inactivation process does not exist, as for sodium channels. There are special potassium channels that are activated when the intracellular calcium concentration increases and the cell membrane depolarizes. Activation of potassium-calcium-dependent channels accelerates repolarization, thereby restoring the original value of the resting potential.

Calcium channels are of particular interest.

The incoming calcium current is usually not large enough to normally depolarize the cell membrane. Most often, calcium entering the cell acts as a “messenger”, or secondary messenger. Activation of calcium channels is achieved by depolarization of the cell membrane, for example by an incoming sodium current.

The process of inactivation of calcium channels is quite complex. On the one hand, an increase in the intracellular concentration of free calcium leads to inactivation of calcium channels. On the other hand, proteins in the cytoplasm of cells bind calcium, which makes it possible to maintain a stable calcium current for a long time, albeit at a low level; in this case, the sodium current is completely suppressed. Calcium channels play an essential role in heart cells. Electrogenesis of cardiomyocytes is discussed in Chapter 7. The electrophysiological characteristics of cell membranes are studied using special methods.

a. At the leading edge of a moving cell, zones are often observed where the plasma membrane forms numerous wavy projections.b. Cell division is accompanied by deformation of the plasma membrane: it invaginates towards the center of the cell. When a fertilized ctenophore egg divides, the membrane invaginates from only one pole until it reaches the other.c. The membranes are capable of merging with each other. In this photo, the membranes of the egg and sperm are about to merge.Summary: All properties are very beneficial for the body. In my opinion, especially because they bind free radicals and in every possible way interfere with the aging process.

3 Resting and action membrane potential

resting potential

Scheme of the Hodgkin-Huxley experiment. An active electrode was inserted into a squid axon with a diameter of about 1 mm, placed in sea water, and the second electrode (reference electrode) was in sea water. At the moment of insertion of the electrode into the axon, a jump in negative potential was recorded, i.e., the internal environment of the axon was negatively charged relative to the external environment.

The electrical potential of the contents of living cells is usually measured relative to the potential of the external environment, which is usually taken equal to zero. Therefore, concepts such as transmembrane potential difference at rest, resting potential, and membrane potential are considered synonymous. Typically, the resting potential ranges from -70 to -95 mV. According to the concept of Hodgkin and Huxley, the value of the resting potential depends on a number of factors, in particular on the selective permeability of the cellfor various ions; different concentrations of ions in the cell cytoplasm and environmental ions (ion asymmetry); operation of active ion transport mechanisms. All these factors are closely related to each other and their division has a certain convention.

It is known that in an unexcited state, the cell membrane is highly permeable to potassium ions and low permeable to sodium ions. This was shown in experiments using isotopes of sodium and potassium: some time after the introduction of radioactive potassium into the axon, it was detected in the external environment. Thus, there is a passive (along the concentration gradient) release of potassium ions from the axon. The addition of radioactive sodium to the external environment led to a slight increase in its concentration inside the axon. Passive entry of sodium into the axon slightly reduces the magnitude of the resting potential.

It has been established that there is a difference in the concentrations of potassium ions outside and inside the cell, and inside the cell there are approximately 20-50 times more potassium ions than outside the cell

The difference in the concentrations of potassium ions outside and inside the cell and the high permeability of the cell membrane for potassium ions ensure the diffusion current of these ions from the cell to the outside and the accumulation of excess positive K+ ions on the outside of the cell membrane, which counteracts the further exit of K+ ions from the cell. The diffusion current of potassium ions exists until their tendency to move along the concentration gradient is balanced by the potential difference across the membrane. This potential difference is called the potassium equilibrium potential.

Equilibrium potential (for the corresponding ion, Ek) is the potential difference between the internal environment of the cell and the extracellular fluid, at which the input and output of the ion are balanced (the chemical potential difference is equal to the electrical one).

It is important to emphasize the following two points: 1) the state of equilibrium occurs as a result of the diffusion of only a very small number of ions (compared to their total content); The potassium equilibrium potential is always greater (in absolute value) than the real resting potential, since the membrane at rest is not an ideal insulator, in particular there is a small leakage of Na+ ions. A comparison of theoretical calculations using D. Goldman's constant field equations and Nernst's formulas showed good agreement with experimental data when changing the extra- and intracellular concentrations of K+.

The transmembrane diffusion potential difference is calculated using the Nernst formula:

Ek=(RT/ZF)ln(Ko/Ki)

where Ek is the equilibrium potential;

R - gas constant;

T - absolute temperature;

Z - nonone valency;

F - Faraday's constant;

Ko and Ki are the concentrations of K+ ions outside and inside the cell, respectively.

The membrane potential for the concentration of K+ ions at a temperature of +20 °C will be approximately -60 mV. Since the concentration of K+ ions outside the cell is less than inside, Ek will be negative.

At rest, the cell membrane is highly permeable not only to K+ ions. The membrane of muscle fibers is highly permeable to SG ions. In cells with high permeability for Cl- ions, as a rule, both ions (Cl- and K+) participate to almost the same extent in creating the resting potential.

It is known that at any point in the electrolyte the number of anions always corresponds to the number of cations (the principle of electroneutrality), therefore the internal environment of the cell at any point is electrically neutral. Indeed, in the experiments of Hodgkin, Huxley and Katz, moving the electrode inside the axon did not reveal a difference in the transmembrane potential difference.

Since the membranes of living cells are to one degree or another permeable to all ions, it is quite obvious that without special mechanisms it is impossible to maintain a constant difference in ion concentration (ion asymmetry). In cell membranes there are special active transport systems that operate using energy and move ions against a concentration gradient. Experimental evidence of the existence of active transport mechanisms comes from the results of experiments in which ATPase activity was suppressed by various methods, for example, by the cardiac glycoside ouabain. In this case, the concentrations of K+ ions were equalized outside and inside the cell and the membrane potential decreased to zero.

The most important mechanism that maintains a low intracellular concentration of Na+ ions and a high concentration of K+ ions is the sodium-potassium pump. It is known that the cell membrane has a system of transporters, each of which binds to 3 Na+ ions located inside the cell and carries them out. From the outside, the carrier binds to 2 K+ ions located outside the cell, which are transferred into the cytoplasm. The energy supply for the operation of transporter systems is provided by ATP. Operating the pump according to this scheme leads to the following results:

1. A high concentration of K+ ions is maintained inside the cell, which ensures a constant value of the resting potential. Due to the fact that during one cycle of ion exchange one more positive ion is removed from the cell than is introduced, active transport plays a role in creating the resting potential. In this case we talk about an electrogenic pump. However, the contribution of the electrogenic pump to the total resting potential is usually small and amounts to several millivolts.

2. A low concentration of sodium ions inside the cell is maintained, which, on the one hand, ensures the operation of the action potential generation mechanism, and on the other, ensures the preservation of normal osmolarity and cell volume.

3. By maintaining a stable Na+ concentration gradient, the sodium-potassium pump promotes the coupled transport of amino acids and sugars across the cell membrane.

Thus, the occurrence of a transmembrane potential difference (resting potential) is due to the high conductivity of the cell membrane at rest for K+ ions (for muscle cells and Cl- ions), ionic asymmetry of concentrations for K+ ions (for muscle cells and Cl- ions) , the work of active transport systems that create and maintain ion asymmetry.

Action potential

Capacityand the operation of metabolic ion pumps lead to the accumulation of potential electrical energy at the cell membrane in the form of the resting potential. This energy can be released in the form of specific electrical(action potential) characteristic of excitable tissues: nervous, muscle, some receptor and secretory cells. An action potential is a rapid oscillation of the resting potential, usually accompanied by membrane recharging. The shape of the axon action potential and the terminology used to describe the action potential.

To correctly understand the processes occurring during the generation of an action potential, we use an experimental diagram. If short pulses of hyperpolarizing current are applied through the stimulating electrode, an increase in membrane potential proportional to the amplitude of the applied current can be recorded; in this case, the membrane exhibits its capacitive properties - a slow increase and decrease in membrane potential.

The situation will change if short bursts of depolarizing current are applied through the stimulating electrode. At a small (subthreshold) value of the depolarizing current, the membrane will respond with passive depolarization and exhibit capacitive properties. The subthreshold passive behavior of the cell membrane is called electrotonic, or electroton. An increase in depolarizing current will lead to an active reaction of the cell membrane in the form of an increase in sodium conductance (gNa+). In this case, the conductivity of the cell membrane will not obey Ohm's law. Deviation from passive behavior usually appears at 50-80% of the threshold current. Active subthreshold changes in membrane potential are called local responses.

A shift in membrane potential to a critical level leads to the generation of an action potential. The minimum value of current required to achieve the critical potential is called the threshold current. It should be emphasized that there are no absolute values ​​for the threshold current and critical potential level, since these parameters depend on the electrical characteristics of the membrane and the ionic composition of the surrounding environment, as well as on the stimulus parameters.

In the experiments of Hodgkin and Huxley, a surprising effect was discovered at first glance. During the generation of the action potential, the membrane potential did not simply decrease to zero, as would follow from the Nernst equation, but changed its sign to the opposite.

An analysis of the ionic nature of the action potential, initially carried out by Hodgkin, Huxley and Katz, made it possible to establish that the front of the rise of the action potential and the recharging of the membrane (overshoot) are caused by the movement of sodium ions into the cell. As mentioned above, sodium channels turned out to be electrically controlled. The depolarizing current pulse leads to activation of sodium channels and an increase in sodium current. This provides a local response. A shift in the membrane potential to a critical level leads to rapid depolarization of the cell membrane and provides a front for the rise of the action potential. If Na+ ion is removed from the external environment, then the action potential does not arise. A similar effect was achieved by adding TTX (tetrodotoxin), a specific sodium channel blocker, to the perfusion solution. Using the “voltage-clamp” method, it was shown that in response to the action of a depolarizing current, a short-term (1-2 ms) incoming current flows through the membrane, which is replaced after some time by an outgoing current. By replacing sodium ions with other ions and substances, such as choline, it was possible to show that the incoming current is provided by a sodium current, i.e., in response to a depolarizing stimulus, an increase in sodium conductance (gNa+) occurs. Thus, the development of the depolarization phase of the action potential is due to an increase in sodium conductivity.

The critical potential determines the level of maximum activation of sodium channels. If the membrane potential shift reaches a critical potential level, then the process of Na+ ions entering the cell increases like an avalanche. The system begins to work on the principle of positive feedback, i.e., regenerative (self-reinforcing) depolarization occurs.

Membrane recharging, or overshoot, is very common in most excitable cells. The overshoot amplitude characterizes the state of the membrane and depends on the composition of the extra- and intracellular environment. At the overshoot height, the action potential approaches the equilibrium sodium potential, so the sign of the charge on the membrane changes.

It has been experimentally shown that the amplitude of the action potential is practically independent of the strength of the stimulus if it exceeds the threshold value. Therefore, it is customary to say that the action potential obeys the “all or nothing” law.

At the peak of the action potential, the membrane conductance to sodium ions (gNa+) begins to decrease rapidly. This process is called inactivation. The rate and degree of sodium inactivation depend on the magnitude of the membrane potential, i.e. they are voltage-dependent. With a gradual decrease in the membrane potential to -50 mV (for example, with oxygen deficiency, the action of certain drugs), the sodium channel system is completely inactivated and the cell becomes inexcitable.

The potential dependence of activation and inactivation is largely determined by the concentration of calcium ions. As the calcium concentration increases, the value of the threshold potential increases; when it decreases, it decreases and approaches the resting potential. In this case, in the first case, excitability decreases, in the second, it increases.

After reaching the peak of the action potential, repolarization occurs, i.e., the membrane potential returns to the resting control value. Let's look at these processes in more detail. The development of an action potential and recharging of the membrane causes the intracellular potential to become even more positive than the equilibrium potassium potential, and therefore the electrical forces moving potassium ions across the membrane increase. These forces reach their maximum during the peak of the action potential. In addition to the current caused by the passive movement of potassium ions, a delayed outgoing current was discovered, which was also carried by K+ ions, as was shown in experiments using the K+ isotope. This current reaches its maximum 5-8 ms after the onset of action potential generation. The administration of tetraethylammonium (TEA), a potassium channel blocker, slows down the repolarization process. Under normal conditions, a delayed outward potassium current exists for some time after the generation of an action potential and this provides hyperpolarization of the cell membrane, i.e., a positive trace potential. A positive trace potential can also arise as a consequence of the operation of the sodium-electrogenic pump.

Inactivation of the sodium system during the generation of an action potential leads to the fact that the cell cannot be re-excited during this period, i.e., a state of absolute refractoriness is observed.

The gradual restoration of the resting potential during the process of repolarization makes it possible to cause a repeated action potential, but this requires a suprathreshold stimulus, since the cell is in a state of relative refractoriness.

A study of cell excitability during a local response or during a negative trace potential showed that the generation of an action potential is possible when a stimulus is applied below the threshold value. This is a state of supernormality, or exaltation.

The duration of the absolute refractory period limits the maximum frequency of generation of action potentials by a given cell type. For example, with a duration of the absolute refractory period of 4 ms, the maximum frequency is 250 Hz.

N. E. Vvedensky introduced the concept of lability, or functional mobility, of excitable tissues. A measure of lability is the number of action potentials that excitable tissue is capable of generating per unit time. It is obvious that the lability of excitable tissue is primarily determined by the duration of the refractory period. The most labile are the auditory nerve fibers, in which the frequency of generation of action potentials reaches 1000 Hz.

Thus, the generation of an action potential in excitable membranes occurs under the influence of various factors and is accompanied by an increase in the conductivity of the cell membrane for sodium ions, their entry into the cell, which leads to depolarization of the cell membrane and the appearance of a local response. This process can reach a critical level of depolarization, after which the membrane conductivity for sodium increases to a maximum, and the membrane potential approaches the sodium equilibrium potential. After a few milliseconds, sodium channels are inactivated, potassium channels are activated, and the outgoing potassium current increases, which leads to repolarization and restoration of the original resting potential.Membrane potential , electrical potential difference between solutions a and b, separated by a permeable membranem :D a bj = j a-j b. In the particular case when the membrane is permeable only to a certain IN zin (z B- charge number), common for solutions a and b, the membrane potential (sometimes called the Nernst potential) is calculated using the formula:

WhereF - Faraday number,R - gas constant,T - absolute temperature,a B b, a B a- activities . In solutions b and a, D a bj B-standard distribution potential B, equal

Summary: Every cell has a resting membrane potential. Speaking most abstractly, it is needed for the transport of substances - very different - from the cell and into the cell. Without ion transport there is no life.

4) Phases of excitability during excitation.

Changes in cell excitability during the development of excitation

If we take the level of excitability of a cell in a state of physiological rest as the norm, then during the development of the excitation cycle, its fluctuations can be observed. Depending on the level of excitability, the following cell states are distinguished.

Supernormal excitability (exaltation) is a state of a cell in which its excitability is higher than normal. Supernormal excitability is observed during the initial depolarization and during the slow repolarization phase. The increase in cell excitability in these AP phases is due to a decrease in the threshold potential compared to the norm.

Absolute refractoriness is a state of a cell in which its excitability drops to zero. No stimulus, even the strongest, can cause additional stimulation of the cell. During the depolarization phase, the cell is nonexcitable because all its Na+ channels are already in an open state.

Relative refractoriness is a state in which the excitability of the cell is significantly lower than normal; Only very strong stimuli can excite the cell. During the repolarization phase, the channels return to a closed state and cell excitability is gradually restored.

Subnormal excitability is characterized by a slight decrease in cell excitability below normal levels. This decrease in excitability occurs due to an increase in the threshold potential during the hyperpolarization phase.

Comparison of the action potential and myocardial contraction with the phases of changes in excitability. 1 - depolarization phase; 2 - phase of initial rapid repolarization; 3 - slow repolarization phase (plateau phase); 4 - phase of final rapid repolarization; 5 - phase of absolute refractoriness; 6 - phase of relative refractoriness; 7 - phase of supernormal excitability. Myocardial refractoriness practically coincides not only with excitation, but also with the period of contraction.

Summary: I believe thatThe duration and process of each phase depends on the anesthetic substances, and is also associated with a decrease in lability and a violation of the mechanism of excitation along nerve fibers.

Section 1

1. Physiology as a science. The main stages of its development. The significance of the research of V. Harvey, I.M. Sechenova, I.P. Pavlova. Main features of Russian physiology

Physiology – physis – nature, logos – teaching.

Physiology is the science of functions And processes, occurring in the body, as well as the mechanisms of their regulation, ensuring the vital activity of the organism in its interaction with the environment.

Function– specific activity of an organ or system.

For example, one of the functions of the stomach is the secretion of gastric juice.

Process– a sequential change of phenomena or states (or a set of sequential actions) aimed at achieving a certain result.

For example, the process of digestion occurs in the gastrointestinal tract. At the same time, its individual stages (mechanical, chemical processing, absorption) occur in various parts of the digestive tract.

The main stages of the development of physiology:

1) until the 17th century. – the first physiological knowledge based on observation

2) second half of the 17th century. – scientific foundations of physiology: William Harvey laid the foundation for experimental physiology, he was the first to conduct live cutting and acute experience – a short-term physiological experiment with tissue dissection and observation of processes. The experience is accompanied by pain and bleeding, making long-term observation impossible. Harvey studied blood circulation.

3) The modern stage - the second half of the 19th century: chronic experience has been introduced - long-term observation in conditions close to natural, requiring surgical preparation of animals. The work of I.M. Sechenov and I.P. Pavlov in this area was a great merit in physiology and made it possible to study the course of many physiological processes in natural conditions. Sechenov and Pavlov developed the doctrine of the mechanisms of nervous activity. Pavlov can be considered the founder of modern physiology of the whole organism.

The main features of domestic physiology:

1) the development of science was based on dialectical materialism: 1863 – Sechenov wrote the book “Reflexes of the Brain”, in which he argued that “all acts of conscious and unconscious activity are reflexes of the brain”, and that all manifestations of human mental activity end in muscle movements

2) Evolutionary direction: Orbeli - founded evolutionary physiology. Comparative physiology – in organisms at different stages of development. Representative - Ugolev. He developed the theory of functional blocks: as soon as an expedient mechanism arises, its development stops and it moves to other levels of organization (for example, K,Na-ATPase). Arshavsky and Anokhin considered age-related physiology as a special section

3) Systematic approach: P.K. Anokhin developed the doctrine of a functional system - a universal scheme for regulating physiological processes and behavioral reactions of the body. Stimulus [useful result

4) Nervism: Pavlov, Botkin. The nervous system plays the main role in neurohumoral regulation

5) Social orientation: physiology of work, sports, aviation and space, physiology in medical universities

2. The relationship of physiology with other sciences. Social significance of physiology. Its role in the organization of a healthy lifestyle, its significance for clinical medicine, its preventive direction, the formation of medical thinking

Physiological processes are based on the laws of chemistry and physics. Accordingly, these sciences are closely related to each other.

Physiology has given many branches: physiological chemistry, pharmacology, pathological physiology, immunology, molecular biology, etc.

Without knowledge of physiology it is impossible to study the entire complex of medical sciences. There are two main directions in modern medicine: medicinal, dealing with the correction of existing pathology in the human body and preventive, which deals with the prevention of the development of certain diseases in a healthy person. The main science organizing the preventive direction is hygiene.

The importance of physiology in the education of a doctor:

Integration of knowledge about the vital functions of the human body

Pre-medical school of clinical thinking: manifestation and course of body functions, mechanisms of compensation for violations

Formation of the scientific foundations of a healthy lifestyle (healthy lifestyle): rational nutrition, physiology of muscle loads, thermoregulation and the influence of different temperatures

Formation of scientific foundations for diagnosis and treatment: norms of indicators and their integration

Scientific basis of treatment: normalization of physiological processes (for example, blood pressure)

1. Analytical and systematic approach to the study of functions. Functional systems of the body.

A functional system is a dynamic self-regulating organization, all components of which interact and provide a useful result. Anokhin is the founder of the theory of functional systems. Sudakov is a student, a continuator of the theory.

The body secretes functional systems. This concept was formulated by academician P.K. Anokhin (student of I.P. Pavlov). Currently A functional system is understood as a set of physiological systems, individual organs and tissues that interact to obtain a final adaptive result that is beneficial for the body. . As an example, we can cite the final beneficial result in the form of adequate provision of oxygen to the tissues of our body. To achieve this result, the respiratory system, circulatory system and blood system (erythrocyte system) function simultaneously. These three systems form a functional system for supplying the body with oxygen.! There are also other functional systems.

1) apparatus of afferent synthesis: motivational arousal (dominant) - selection of significant signals, situational afferentation, memory, trigger afferentation - unconditioned and conditioned stimuli

2) decision-making stage (frontal lobes)

3) apparatus for accepting the result of an action - in the associative cortex, ring interaction of interneurons

4) stage of efferent synthesis - creation of a program in pyramidal cells of the cortex

5) behavioral act of action aimed at obtaining a result

6) stage of reverse afferentation – assessment of the result. Correction possible

1. Cell physiology. Structure and function of biological membranes. Resting membrane potential and its origin.

Any living cell is distinguished by the presence of metabolism, irritability properties, as well as ionic asymmetry of the internal environment of the cell compared to tissue fluid.

Irritability is the ability of a cell or tissue, in response to the action of a stimulus, to change its metabolism, the permeability of the surface membrane, temperature, shape, motor activity, etc.

At rest, the surface membrane of the cell is polarized, i.e. its inner surface is charged negatively in relation to the outer one. This potential difference is called resting membrane potential (MPP).

The MPP of a cell changes with its age. In a young cell it is minimal in amplitude, increases with age and becomes stable in a mature cell, and decreases again with aging. Secondly, the MPP of a cell can change due to changes in its functional state (energy resources, operation of ion pumps, etc.), due to the effect of environmental factors on it.

The occurrence of MPP is associated with ion asymmetry and different permeability of the surface cell membrane for different ions

Ion asymmetry is the different concentration of different ions on both sides of the cell surface membrane, which is created by the work of ion pumps. Thus, due to the Na/K pump, a high concentration of K + ions and a low concentration of Na + ions is created in the cell compared to the intercellular fluid. The surface membrane has selective (special for different ions) channels. But some channels are closed and through them, even in the presence of a concentration gradient, ions cannot pass from one medium to another, but through open channels the transition of ions can occur. For example, sodium can enter a cell and potassium can leave the cell along a concentration gradient.

The vast majority of membrane sodium channels are closed, but a small proportion are open. Through these channels, sodium slowly enters the cell, causing a slight depolarization of the surface membrane. This is why sodium channels that are open at rest are sometimes called “slow,” while those that are closed are called “fast,” because if they all open, sodium will flow into the cell very quickly.

A small proportion of potassium channels are closed, but the vast majority are open. Therefore, potassium leaves the cell along a concentration gradient. But the release of potassium from the cell is limited by the electric field created by the potassium ions themselves. Thus, the electrochemical gradient between the inner and outer surfaces of the cell membrane at rest is 0.

The main reason for the formation of MPP is the presence of a potassium gradient. Potassium ions found inside the cell are associated with organic anions. When potassium leaves the cell along a concentration gradient, negative ions “tend” to follow it. But their size and charge (the inner walls of ion channels are negatively charged!) do not even allow them to enter the channel. Therefore, the anions remain on the inner surface of the membrane, thus retaining the potassium ions on the outer surface of the membrane. Due to this, a potential difference is formed. Sodium ions enter the cell through slow sodium channels and thereby reduce the amount of MPP created by potassium ions. Chlorine ions also take part in the creation of MPP, which is reflected in the Goldman equation:

PP= RT/F*ln (PKe*CKe+PNae*CNae+PCli*CCli)/(PKi*CKi+PNai*CNai+PCle*PCle)

General properties of excitable tissues. Criteria for assessing tissue excitability. Types of irritants

Excitability– the ability of a tissue, in response to the action of a stimulus of sufficient strength, to transition from a state of rest to a state of excitation.

only have excitability nervous, muscular And glandular fabrics that belong to excitable tissues . These fabrics also have conductivity And lability (functional mobility).

Excitation is an active physiological process that occurs only in excitable tissues and is accompanied by recharging the outer cell membrane , changes in its permeability, cell metabolism, temperature, etc. This process does not stand still, but spreads throughout the entire surface membrane of the cell.

If the stimulus is strong enough, previously closed sodium channels additionally open. Moreover, the stronger the stimulus, the more channels open, which means that the surface membrane of the cell is depolarized to a greater extent.

Irritants vary in strength: threshold, sub-threshold (subthreshold) and suprathreshold . With a single action, only threshold and supra-threshold stimuli cause excitation. A single action of a subthreshold stimulus does not cause an excitation process in tissue that is at rest.

How does the action potential differ when a threshold stimulus is applied to a cell in one case and a supra-threshold stimulus in another? The AP amplitude in both cases is the same (see question 53 - the “All or Nothing” law). But under the action of suprathreshold stimuli, the frequency of occurrence of action potentials will be greater than under the action of a threshold stimulus (see the textbook on normal physiology - “Information Coding”).

Threshold stimulus strength - minimum strength an irritant, under the action of which a process of excitation occurs in the tissue. This quantity is also called irritation threshold or excitation threshold . The last concept is more correct.

The excitation threshold is determined to evaluate tissue excitability. The lower the excitation threshold, the more excitable the tissue. In medicine and physiology, direct current is often used to influence excitable tissue. For such a stimulus, the excitation threshold, expressed in volts, is denoted by the term rheobase .

1. Lability as a property of excitable tissues. The concept of parabiosis (Vvedensky)

Lability, or functional mobility is the ability of a tissue (cell) to reproduce the frequency of stimulation imposed on it from the outside in the form of a sequence of action potentials following each other without distorting the frequency and rhythm of these stimulations. A measure of lability is the maximum frequency of stimulation that is reproduced by the tissue (cell) without distorting their frequency and rhythm.

The ability of a tissue, after responding to one stimulus, to respond to a subsequent one depends on the duration of the refractory period

The longer this period lasts, the less lability the tissue becomes. The duration of the refractory period, in turn, depends on the duration of the action potential, in particular, the depolarization phase, and the duration of the depolarization phase depends on the density of sodium channels on the surface cell membrane. The greater their density, the faster the depolarization phase passes. For example, in the autonomic nervous system the density of sodium channels is much lower than in the somatic nervous system. Therefore, the AP depolarization phase is extended in time, which means that the refractory period lasts longer, which is the reason for the low lability of the structures of the autonomic nervous system

Parabiosis- This is a state borderline between life and death of a cell. He was introduced to the physiology of excitable tissues by Prof. N.E. Vvedensky, studying the work of a neuromuscular drug when exposed to various stimuli

These are a wide variety of damaging effects on an excitable cell (tissue), which, without leading to gross structural changes, to one degree or another disrupt its functional state. Such reasons may be mechanical, thermal, chemical and other irritants.

Under the influence of a damaging agent, a cell (tissue), without losing its structural integrity, completely stops functioning. This condition develops gradually (phasically), as the damaging factor acts (that is, it depends on the duration or strength of the acting stimulus). If the damaging agent is not removed, biological death of the cell (tissue) occurs. If this agent is removed in time, the tissue (also in phases) returns to its normal state.

For a nerve fiber, N.E. Vvedensky identified three phases that sequentially follow each other. These are the equalizing, paradoxical and inhibitory stages. The inhibitory stage is actually parabiosis. Further action of the damaging agent leads to tissue death.

N.E. Vvedensky conducted experiments on a neuromuscular preparation of a frog. In the simplest version, his experiment can be represented as follows. Test stimuli of varying strengths were sequentially applied to the sciatic nerve of the neuromuscular preparation. One irritant was weak(threshold strength), that is, it caused a minimal contraction of the calf muscle. Another irritant was strong(optimal - see optimum stimulus strength), that is, the least of those that cause maximum contraction of the calf muscle.

Then, at point P, a damaging agent was applied to the nerve, and after a few minutes, alternating testing of the neuromuscular preparation with weak and strong stimuli was repeated. At the same time, the following stages developed successively:

1) equalization when in response to a weak stimulus the magnitude of muscle contraction did not change, but in response to a strong stimulus the amplitude of muscle contraction sharply decreased and became the same as in response to a weak stimulus;

2) paradoxical when, in response to a weak stimulus, the magnitude of muscle contraction remained the same, and in response to a strong stimulus, the amplitude of contraction became smaller than in response to a weak stimulus, or the muscle did not contract at all;

3) brake, when the muscle did not respond to both strong and weak stimuli by contracting. It is this state of tissue that is designated as parabiosis.

N.E. Vvedensky’s explanations from the standpoint of modern physiology are as follows. A damaging agent applied at the P point causes functional disturbances in the cell (the opening of sodium channels is difficult due to the phenomenon of sodium inactivation, the operation of the Na/K pump slows down), as a result of which the AP, passing through the P point, is extended in time, which means the duration of the refractory period increases. This, in turn, leads to a decrease in cell lability and makes it difficult to carry out excitation resulting from the action of testing stimuli. Moreover, the conduction of excitation that arises in response to a weak stimulus is not disrupted for a long time, since weak stimuli are transformed in the nerve into a sequence of impulses that follow at a very low frequency. Therefore, after the passage of each of these rare impulses, the tissue has time to completely restore its excitability, which means it perceives and conducts the next impulse

The conduction of excitation that arose in response to a strong testing stimulus (this is a significantly higher frequency of impulses!) quickly leads to disruption of the conduction of excitation through point P, since at a high frequency of impulses the cell does not have time to restore its normal excitability after the previous impulse, and therefore does not can carry out the subsequent one without hindrance.

Parabiosis is not only a laboratory phenomenon, but a phenomenon that, under certain conditions, can develop in a whole organism. For example, parabiotic phenomena develop in the brain during sleep. In the pathophysiology of shock states, you will also encounter the phenomenon of parabiosis. It should be noted that parabiosis as a physiological phenomenon is subject to the general biological law of force, with the difference that as the stimulus increases, the tissue response does not increase, but decreases.

7.Modern idea of ​​the process of excitation. Action potential, its phases. The nature of changes in tissue excitability when it is excited. Local response.

In AP, a depolarization phase, a repolarization phase, and trace potentials are distinguished.

The action of the stimulus leads to a nonspecific cell response in the form of opening of sodium channels, which leads to depolarization of the membrane. This in turn facilitates the opening of more and more sodium channels, which further depolarizes the membrane. Thus, membrane depolarization reaches a certain degree at which All sodium channels open

This degree of depolarization is called critical level of depolarization (CLD). In this case, sodium begins to quickly penetrate into the cell, bringing the potential difference between the inner and outer surfaces of the membrane to 0, and then the membrane is recharged (potential inversion), that is, its inner surface becomes positively charged relative to the outer one. But the flow of sodium ions into the cell is not endless. It is limited by sodium inactivation (the channels cannot be open for a long time!). In addition, sodium ions that have penetrated into the cell create an electric field that prevents further sodium entry

What is the mechanism of the repolarization phase? In response to the entry of sodium ions into the cell, two mechanisms are quickly activated, returning the initial degree of polarization of the membrane. Firstly, those potassium channels that were closed at rest open, and potassium leaves the cell in a much larger volume, which reduces the degree of depolarization of the cell surface membrane. Secondly, the sodium-potassium pump is activated, returning the original ionic asymmetry on both sides of the cell surface membrane. Thus, MPP is restored.

What is the mechanism of trace potentials? Ideally, there should be no trace potentials, since the repolarization phase returns the cell to a resting state with the original MPP and initial excitability. But in reality, the repolarization phase can be extended in time due to insufficiently active Na/K pump and a trace depolarization (negative trace potential) occurs (Fig. 9A). On the contrary, if the work of the Na/K pump is enhanced, then trace hyperpolarization occurs (positive trace potential) (Fig. 9B). Sometimes these potentials follow each other (Fig. 9B).

What is the biological role of resting membrane potential and action potential? These potentials are individual characteristics of excitable cells. In different cells they differ in amplitude, and AP and in duration (in general, as well as its individual phases). Their amplitude changes throughout the life of the cell. In a young cell their amplitude is small, but with age it increases and becomes stable. As the cell ages, their amplitude decreases again. The MPP value indirectly characterizes the excitability of the cell (through the threshold potential). With the help of PD, information is encoded in the nervous system. Through the spatio-temporal set of action potentials, reflex (nervous) regulation of physiological processes is carried out.

How does the resting membrane potential of an excitable cell change when it is exposed to a subthreshold stimulus? The cell does not react at all to subthreshold stimuli that do not exceed 50% of the threshold stimulus in strength. These stimuli are too weak for sodium channels to open additionally on the cell surface membrane in response to them (Fig. 10).

In response to subthreshold stimuli, which are 50% or more in strength of the threshold stimulus, sodium channels in the cell membrane that are closed at rest open additionally. In this case, depolarization of the cell surface membrane occurs, and it will be greater, the stronger the acting subthreshold stimulus. This depolarization is referred to as the “local response.”

Explain the origin of the terms “local” and “gradual” response? The term “local” means that the depolarization that occurs under the influence of a subthreshold stimulus is local in nature and does not spread to neighboring areas. Therefore, the term “local” response is sometimes used. The term “gradual” means that this depolarization is greater the greater the strength of the subthreshold stimulus (“Law of Stimulus Strength”). How does the excitability of a cell change when it is exposed to stimuli? It is impossible to answer this question unambiguously, because... under the influence of stimuli of different strengths, the excitability of the tissue changes differently or does not change at all. To answer this question, you should have an idea of ​​the threshold potential and the reasons that influence its value. What is the threshold potential? This is part of the resting membrane potential (Fig. 11), by the amount of which the surface membrane of the cell must be depolarized in order to achieve a critical level of depolarization (that is, for excitation to occur).

How does the excitability of a cell change when it is exposed to subthreshold stimuli? Under the influence of subthreshold stimuli that are less than 50% of the stimulus threshold, the excitability of the cell does not change (Fig. 12, stimuli 1 and 2), since the threshold potential does not change. The exception is direct current, since the cathode and anode cause passive changes in the MPP and threshold potential

Under the influence of subthreshold stimuli, constituting 50% or more of the value of the stimulation threshold (Fig. 12, stimuli 3, 4, and 5), the excitability of the cell always increases, because the threshold potential decreases. Moreover, the greater the strength of the subthreshold stimulus, the greater the excitability will be.

How will the excitability of a cell change when it is exposed to a threshold and superthreshold stimulus? Changes in excitability will be phasic in nature in accordance with the phases of the action potential that will occur in both cases (Fig. 13). Immediately after the action of the stimulus (until depolarization reaches a critical level), excitability will increase, because the threshold potential will decrease until a critical level of depolarization is reached (Fig. 13A, A). When the CUD is reached, the excitability of the cell will disappear, because all sodium channels will be open, and the cell will have nothing to respond to even a very strong stimulus (Fig. 13A, b). This phase is called absolute refractoriness , that is, the tissue is completely inexcitable at this time. It will accompany the entire depolarization phase and the initial period of the repolarization phase, which is due to the increased release of potassium from the cell. After activation of the Na/K pump, cell excitability begins to recover to initial level. This phase is called relative refractoriness , that is, decreased excitability (Fig. 13A, V). It accompanies the repolarization phase until its end. During this period of time, a sufficiently strong stimulus (superthreshold) can cause a repeated action potential.

During the phase of the negative trace potential, excitability will be increased, since the threshold potential at this time is reduced (Fig. 13B, G). On the contrary, during the phase of the positive trace potential, excitability will be reduced, since the threshold potential at this time becomes greater than in the resting state (Fig. 13B, G).

What is the biological meaning of the complete loss of excitability of a cell when it is excited? Thanks to the absolute refractoriness phase, one AP is separated from another without merging with the previous one. This provides the possibility of encoding information, which is carried out by a nerve cell to implement regulatory influences on other excitable cells. In addition, due to the phase of absolute refractoriness, unilateral conduction of excitation occurs (see answer to question 37).

What is conductivity? The ability of an excitable cell to conduct excitation along the surface cell membrane throughout its entire length and transmit it to other excitable cells. The surface membranes of neurons, muscle and secretory cells are conductive. In all these structures it differs significantly (in the speed of excitation).

What is the reason for the different conductivity in different excitable cells? The rate of excitation depends on the density of sodium channels on the surface membrane of the cell. The larger it is, the higher the speed of excitation. In nerve fibers, the speed of excitation is significantly influenced by its thickness and the degree of myelination. In this regard, fibers of types A, B and C are distinguished. For example, in fibers of type Aα (diameter 12-22 microns, completely covered with the myelin sheath) the conduction speed is the highest - 80-120 m/sec. These fibers conduct excitation from α-motoneurons of the spinal cord to myocytes of skeletal muscles. In type C fibers (diameter is about 1 micron, they do not have a myelin sheath) the excitation conduction speed is the lowest - 0.5-3 m/sec. Such fibers conduct excitation, for example, in postganglionic fibers of the autonomic nervous system (this issue is discussed in more detail in the textbook on normal physiology).

What is the mechanism of excitation? Let's look at it in a diagram explaining the conduction of excitation along an unmyelinated nerve fiber (Fig. 14). At the point A the cell is exposed to a threshold or supra-threshold stimulus (indicated by an arrow), as a result of which the surface membrane in this place is recharged (PD occurs). In the adjacent section of the membrane (let us denote it with a dot V) the membrane still remains polarized. Thus, on the inner and outer surface of the membrane between the points A And V a potential difference arises, which immediately leads to the movement of ions between them, i.e. to the emergence of local currents (Fig. 14A). Let us consider the direction of these local currents in relation to positively charged ions (cations). On the outer surface they move from a point V exactly A, and along the inner surface - vice versa from the point A exactly V. Due to these currents (quite strong) at the point V depolarization of the surface membrane occurs. Moreover, this depolarization reaches a critical level at the point V PD occurs.

At the same time at the point A(Fig. 14B) the nerve fiber is in a state of refractoriness associated with AP. This refractoriness does not allow the excitation to move from the point V back to point A, since local currents cannot cause at a point A critical level of depolarization. At the same time, local currents flowing between points V

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Lability(from Latin labilis - unstable, sliding) - a physiological term denoting functional mobility, the speed with which elementary types of physiological processes progress in the environment of excitable tissue (nervous and muscle).

Lability can be described as the rate of transition to a state of excitation from a state of rest and exit from an excited state. In some tissues and cells such excitation occurs quickly, while in others it occurs slowly.

Lability is defined as the maximum number of impulses that a functional structure or nerve cell is able to transmit without distortion per unit of time. In medicine and biology, this term refers to instability, mobility, variability of mental processes and physiological state - body temperature, pulse, pressure, etc. In psychology, lability is a property of the nervous system, characterizing the rate of appearance and cessation of nervous processes.

The term “lability” was proposed in 1886 by the Russian physiologist N.E. Vvedensky, who considered the measure of lability to be the maximum frequency of tissue stimulation that it reproduces without rhythm transformation. He made an indisputable fact the difference in the amount of response reaction to a stable series of stimuli. He was also able to identify low fatigue of the nerve, which is explained by the low expenditure of its energy on the stimulus. High lability contributes to a reduction in energy costs for the reaction arising from nervous excitement.

Lability itself reflects the time during which excitable tissue restores its performance after each cycle of excitation. The highest lability is inherent in the processes of nerve cells - axons, which are capable of reproducing about 500-1000 impulses per second. Less labile synapses are the peripheral and central contact zones. For example, a motor nerve ending can transmit no more than 100–150 impulses per second to a skeletal muscle. When the vital activity of cells and tissues is suppressed (by drugs, cold, etc.), lability decreases, since the recovery processes slow down and the refractory period increases - the time during which excitability decreases and is restored to the initial level. Lability is a variable value; under the influence of frequent irritations, the refractory period is shortened, which means lability increases.

Lability characterizes the psychological state of a person as changeable and extremely unstable. This feature is inherent in people of creative professions - actors, singers, writers, artists. They experience all feelings very deeply, but the duration of the experiences is not so long.

High lability in psychology characterizes the choleric type temperament, which is characterized by frequent mood swings and increased excitability. There are also advantages to this, since soon not even a trace remains.

Lability is a concept used to describe mobility. The area of ​​application may slightly change the semantic characteristics, indicating both the number of nerve impulses transmitted per unit of time by the cell, and the speed of starting and stopping mental processes.

Lability characterizes the rate of occurrence (from the onset of reaction to inhibition) of elementary processes, and is measured by the highest frequency of impulse reproduction without changes in tissue function and the time of functional recovery. This indicator is not considered a constant value, since it can change from external factors (heat, time of day, force), the effects of chemicals (produced by the body or consumed) and emotional states, so it is only possible to observe the dynamics and predisposition of the body, the prevailing level. It is the change in lability indicators that is key in diagnosing various diseases and norms.

What is lability

In scientific applications, lability is used synonymously with mobility (normally), instability (in pathology) and variability (as a characteristic of the dynamics of a state and processes). To understand the breadth of use of this term, we can consider examples of the fact that there is lability of mood in body temperature, psyche and physiology, and accordingly applies to all processes that have speed, constancy, rhythm, amplitude and other dynamic characteristics in their indicators.

The course of any processes in the body is regulated by the nervous system, therefore, even when talking about indicators of pulse or mood lability, we are still talking about the degree of lability of the nervous system (central or autonomic, depending on the location of the instability). The autonomic nervous system regulates internal organs and systems; accordingly, the general condition of the body depends on its work, the ability to maintain rhythm and stability of processes.

Autonomic lability brings disturbances in the functioning of the heart (manifestations are in the form of arrhythmia, problems with blood pressure and quality), the functioning of the glands (problems with sweating or the production of substances necessary for the quality functioning of the body may begin). Many seemingly psychological problems or those related to the central nervous system are actually solved at the level of reducing autonomic lability, which ensures productive sleep and the absorption of beneficial microelements. At the same time, it is worth remembering that signaling about the level of stress or a critical emotional situation is primarily not the central system, but the autonomic system, by increasing its lability. Mechanisms that activate the work of all organ systems to overcome difficult or extreme situations use the internal reserves of the body, forcing the heart to speed up the rhythm, the lungs to absorb more air, the iron to remove excess adrenaline through sweat, and only then the central nervous system reactions are activated.

Lability of the nervous system or mental lability is characterized by a pathological state of mood disturbance, expressed in its swings and inconstancy. The condition may be the norm for adolescence, but is classified as a spectrum of pathological conditions for adults and requires medical care, as well as the work of a psychologist, even without prescribing medications.

Lability in psychology

Mental lability, considered in psychology, implies its mobility, and in some cases instability, while science itself studies only this aspect of lability, without going into physiology. In most sources, mental lability is considered as a negative quality that requires correction, but it does not give due credit to the fact that this is the main adaptive mechanism of the psyche. It was the speed of reaction and switching between quickly and often unexpectedly changing events in external life that helped humanity survive. The opposite is the psyche, when a person remains constant for a long time, and any changes knock him out of his normal state. Any of these characteristics in its extreme manifestation is negative, but at moderate levels it gives its advantages.

Problems with lability, when a person comes to a psychologist, are associated with frequent changes in mood, while all spectrums are experienced not superficially, but really deeply (i.e., if you feel sad, then you think about opening your veins, and if you are happy, then you want to dance on workplace and give candy to passers-by - and all this within one hour). It is precisely the difficulties in coping with one’s own and the lack of understanding of how this can be corrected that brings many not only mental suffering, but the subsequent changes in health, since the autonomic system, being subordinate to emotional states, also increases the level of its lability.

Such phenomena can be justified by the type of organization of the nervous system, so in people with the speed of reactions is already determined by nature, and accordingly, an increase in lability to a pathological state is more likely. Mood swings can also be triggered by frequent exposure to traumatic situations at an early age. But we should not exclude physiological reasons that affect a person’s psychological state: brain tumors, TBI, vascular diseases.

Correction of such unpleasant conditions begins with diagnosis and exclusion of physiological causes, then, if necessary, correction is possible with mood-stabilizing drugs (antidepressants and tranquilizers), accompanied by a course of psychotherapy. In severe cases, treatment in a hospital may be appropriate; in the mildest cases, you can cope by visiting a psychologist, without interrupting your usual life.

Lability in physiology

In physiology, lability is considered as a property of tissue that characterizes its change during prolonged excitation. Reactions to prolonged excitation can be expressed in three types of response: a response to each impulse, transformation of the original rhythm into a rarer one (for example, a response to every third impulse) or cessation of the response. For each cell of the body, this rhythm is different, and it may differ from the rhythm of the organ consisting of these cells, as well as from the rhythm of the entire organ system. The faster the tissue reacts to irritation, the higher its lability is considered, but there are few indicators of only this time; it is also necessary to take into account the time required for recovery. Thus, the reaction can be quite fast, but due to the long recovery time, the overall lability will be quite low.

Lability increases or decreases depending on the needs of the body (the normal option, without diseases, is considered), and it can increase from the metabolic rate, which forces all systems to speed up the rhythm of work. An increase in lability has been noticed, that when the body is in a working active state, i.e. The lability of your tissues is much higher if you run than if you read while lying down, and the indicators remain at an increased value for some time after the cessation of vigorous activity. Such reactions are associated with the assimilation of a rhythm that meets current environmental conditions and activity needs.

The regulation of physiological lability can also be addressed in cases of disorders of the psychological spectrum, since many conditions have as their root cause not mental disorders or emotional experiences, but physiological disorders. For example, a physiological effect can eliminate sleep problems, which will automatically increase the level of attention and reduce sleep, the treatment of which would be ineffective without taking into account physiological indicators.

Intellectual lability

Intellectual lability is one of the components of the lability of the nervous system and is responsible for the processes of switching between the processes of activation and inhibition. In life, this looks like a fairly high level of mental development and the ability to logically analyze incoming information. Since a critically huge number of information blocks requiring information are received every second, there is a need to sort them as quickly as possible (at a subconscious automatic level) into significant and insignificant.

The presence of a large knowledge base becomes irrelevant and testifies not to knowledge, but to erudition; much more significant is the ability to switch between different sources of information, between different information in meaning, and also to move on to solving the next (albeit opposite) problem in the shortest possible time . At this switching speed, the main thing is to maintain the ability to highlight the main thing for the task at a given time. It is precisely this process of intellectual work that ensures high intellectual lability.

Previously, they did not know about this property, then they talked about it, but rarely, and now, when the pace of life is accelerating, the amount of information consumed is growing at such a pace that a person who lived two hundred years ago would have needed a month to realize that we process within an hour , this becomes a determining factor for success. This gives the ability to respond adequately and as usefully as possible in changing conditions, promotes instant analysis of many factors, which allows minimizing the possibility of error.

In addition, quickly switching between different topics and issues provides innovative thinking, new ways to solve old problems, and rapid assimilation of knowledge and skills, and this happens at a deeper level. For example, historical data on the same event, gleaned from different sources (here one cannot do without using the capabilities of the modern world) provides a more objective and comprehensive understanding than citing the point of view of the author of the textbook. The ability to learn quickly is due to the fact that there is no need to tune in to the arrival of material - ten minutes of reading an article in a minibus, accompanied by listening to new music, or writing a thesis with breaks to watch educational videos becomes a familiar way of functioning, providing new opportunities.

Emotional lability

Mood lability, which is the main reflection of emotional lability, is the variability of the mood pole, often without expressed reasons for this. The nervous system is responsible for our emotional state, and when it is weakened, it becomes hypersensitive, which explains the instant and strong reaction to even minor stimuli. The color can be anything - either happiness or sadness; aggressive affects and apathetic sadness arise with equal ease.

Symptoms may include spontaneity of actions, impulsiveness, lack of ability to predict the consequences of one’s own actions. The occurrence of affective outbursts and uncontrollable states for minor or absent reasons was the reason for including emotional lability in the lists of psychiatric disorders requiring stabilization under medical supervision. It may also not be a separate disease, but a symptom of more dangerous and complex ones (severe tumors, problems with blood pressure, hidden consequences of traumatic brain injuries, etc.). It is difficult to diagnose in childhood, since it has been little studied and is often confused with, therefore, a team of specialists from a psychiatrist, psychologist and neurologist is required for diagnosis.

Emotional instability manifests itself in restlessness, lack of patience and acute reaction to criticism or obstacles, difficulties in establishing logical chains, as well as mood swings. These swings are different from manic-depressive disorder and are characterized by a rapid change of states with the same deep experience of the emotional spectrum.

Any overload of the nervous system contributes to this development of the emotional sphere: emotional stress, psychotraumas or their actualization, hyper- or hypoattention from society, hormonal changes (adolescence and menopause, pregnancy). Physiological reasons: somatic diseases, deficiency of vitamins (especially group B, necessary to maintain the functioning of the nervous system), as well as difficult physical conditions.

If emotional lability is diagnosed, then a psychiatrist should correct it; if the condition is not so dire, then a course of prevention is prescribed by a psychologist. In any case, you should not treat such manifestations with disdain, explaining them as bad character.