Types and modes of muscle contractions. Muscle work and strength. Types of nerve fibers. Modes of muscle activity Mechanism of muscle contraction
To understand the essence of the isometric gymnastics method, I suggest you plunge into the interesting world of the physiology of muscle contraction, that is, find out how the muscles of our body work. Carry out a simple experiment: expose your shoulder so that your biceps is visible, and place your other hand on it. Begin to slowly bend your bare arm at the elbow - you will feel a contraction of the biceps. The weight of the arm remains the same, so the muscle tenses more or less evenly during movement.
This muscle contraction is called isotonic(Greek isos – equal).
This mode of operation leads to movement - in fact, what the muscle is intended for. But note that not only the muscle moves, but also the bones and joints. They are the weak link that wears out the fastest. Joint cartilage is one of the most vulnerable tissues of the body. There are no blood vessels in it, so the cartilage is nourished very slowly due to diffusion - “impregnation” of nutrients from neighboring bones, and, unfortunately, for this reason it is practically not restored.
Active movements, and even with a load, seriously load the articular cartilage. Excessive work overloads the joints, and the cartilage layer becomes thinner, “erased,” causing the bones to literally creak. Arthrosis is the name of a joint disease associated with the aging of articular cartilage. Every movement in such a joint can cause pain, so movement is limited, and you have to say goodbye to gymnastics.
Let's try to continue our simple physiological experiments. Try to tighten your biceps brachii so that your forearm and shoulder remain motionless. Do you feel muscle tension? Of course, but at the same time the hand is motionless, there is no movement in the joint. This mode of operation is called isometric. A regime that protects your joints and trains muscle fibers, leaving you with the joy of movement for many years!
Each movement, like a shadow, is followed by exhaustion and fatigue, and the desire for relaxation and rest invariably leads to the cessation of exercise. So after our experiments, relax your shoulder and let your arm hang freely down like a tree branch - feel the degree of muscle relaxation and remember this feeling. Let's move on to the last experiment.
Start bending the elbow joint of one arm, and try to keep it from moving with the other - this is the isometric biceps tension you already know. Hold this position for twenty seconds. Now quickly walk with your back to the wall, place the palm of your working hand on the wall, fingers down, and slowly squat down, keeping your arm straight. Do you feel a stretch in your biceps? Yes, this is a strong and even slightly painful, but pleasant feeling.
Stretch your arm for no more than 10 seconds. Now relax and lower your hand down. I am sure that now you feel the relaxation of your biceps much more than after regular curls. This condition received a special name - post-isometric relaxation, which you just learned how to do on your own. I think it becomes clear to you that stretching and relaxing muscles after isometric tension is much more effective than regular stretching.
So, isometric gymnastics is based on muscle tension WITHOUT MOVEMENT. It preserves joints, prevents wear and tear of articular cartilage and the progression of arthrosis. In many exercises, the isometric contraction phase is followed by a stretch phase. This is an effective technique that relaxes the muscle, relieves muscle spasm and has a pronounced analgesic effect. Remember how pleasant it is to stretch after a long sitting - isometric gymnastics will both train and relax the target muscle - the one that needs to be loaded specifically for your pathology or problem.
Conclusions:
Isometric contraction of a muscle is its tension without movement in the joint.
Isometric gymnastics, strengthening muscles, spares joints and cartilage.
Stretching the muscle after isometric tension (post-isometric relaxation) is an effective technique for muscle relaxation and pain relief.
Muscle contraction is a vital function of the body associated with defensive, respiratory, nutritional, sexual, excretory and other physiological processes. All types of voluntary movements - walking, facial expressions, movements of the eyeballs, swallowing, breathing, etc. are carried out by skeletal muscles. Involuntary movements (except for heart contraction) - peristalsis of the stomach and intestines, changes in the tone of blood vessels, maintenance of bladder tone - are caused by contraction of smooth muscles. The work of the heart is ensured by the contraction of the cardiac muscles.
Structural organization of skeletal muscle
Muscle fiber and myofibril (Fig. 1). Skeletal muscle consists of many muscle fibers that have points of attachment to bones and are located parallel to each other. Each muscle fiber (myocyte) includes many subunits - myofibrils, which are built from blocks (sarcomeres) repeating in the longitudinal direction. The sarcomere is the functional unit of the contractile apparatus of skeletal muscle. The myofibrils in the muscle fiber lie in such a way that the location of the sarcomeres in them coincides. This creates a pattern of cross striations.
Sarcomere and filaments. Sarcomeres in the myofibril are separated from each other by Z-plates, which contain the protein beta-actinin. In both directions, thin actin filaments. In the spaces between them there are thicker myosin filaments.
Actin filament externally resembles two strings of beads twisted into a double helix, where each bead is a protein molecule actin. Protein molecules lie in the recesses of actin helices at equal distances from each other. troponin, connected to thread-like protein molecules tropomyosin.
Myosin filaments are formed by repeating protein molecules myosin. Each myosin molecule has a head and tail. The myosin head can bind to an actin molecule, forming a so-called cross bridge.
The cell membrane of the muscle fiber forms invaginations ( transverse tubules), which perform the function of conducting excitation to the membrane of the sarcoplasmic reticulum. Sarcoplasmic reticulum (longitudinal tubules) It is an intracellular network of closed tubes and performs the function of depositing Ca++ ions.
Motor unit. The functional unit of skeletal muscle is motor unit (MU). MU is a set of muscle fibers that are innervated by the processes of one motor neuron. Excitation and contraction of the fibers that make up one motor unit occur simultaneously (when the corresponding motor neuron is excited). Individual motor units can be excited and contracted independently of each other.
Molecular mechanisms of contractionskeletal muscle
According to thread sliding theories, muscle contraction occurs due to the sliding movement of actin and myosin filaments relative to each other. The thread sliding mechanism involves several sequential events.
Myosin heads attach to actin filament binding centers (Fig. 2, A).
The interaction of myosin with actin leads to conformational rearrangements of the myosin molecule. The heads acquire ATPase activity and rotate 120°. Due to the rotation of the heads, the actin and myosin filaments move “one step” relative to each other (Fig. 2, B).
Disconnection of actin and myosin and restoration of the head conformation occurs as a result of the attachment of an ATP molecule to the myosin head and its hydrolysis in the presence of Ca++ (Fig. 2, B).
The cycle “binding – change in conformation – disconnection – restoration of conformation” occurs many times, as a result of which actin and myosin filaments are displaced relative to each other, the Z-disks of sarcomeres come closer and the myofibril is shortened (Fig. 2, D).
Pairing of excitation and contractionin skeletal muscle
In the resting state, thread sliding in the myofibril does not occur, since the binding centers on the actin surface are closed by tropomyosin protein molecules (Fig. 3, A, B). Excitation (depolarization) of the myofibril and muscle contraction itself are associated with the process of electromechanical coupling, which includes a series of sequential events.
As a result of the activation of a neuromuscular synapse on the postsynaptic membrane, an EPSP arises, which generates the development of an action potential in the area surrounding the postsynaptic membrane.
Excitation (action potential) spreads along the myofibril membrane and, through a system of transverse tubules, reaches the sarcoplasmic reticulum. Depolarization of the sarcoplasmic reticulum membrane leads to the opening of Ca++ channels in it, through which Ca++ ions enter the sarcoplasm (Fig. 3, B).
Ca++ ions bind to the protein troponin. Troponin changes its conformation and displaces the tropomyosin protein molecules that covered the actin binding centers (Fig. 3, D).
Myosin heads attach to the opened binding centers, and the contraction process begins (Fig. 3, E).
The development of these processes requires a certain period of time (10–20 ms). The time from the moment of excitation of a muscle fiber (muscle) to the beginning of its contraction is called latent period of contraction.
Skeletal muscle relaxation
Muscle relaxation is caused by the reverse transfer of Ca++ ions through the calcium pump into the channels of the sarcoplasmic reticulum. As Ca++ is removed from the cytoplasm, there are fewer and fewer open binding sites, and eventually the actin and myosin filaments are completely disconnected; muscle relaxation occurs.
Contracture called a persistent, long-term contraction of a muscle that persists after the cessation of the stimulus. Short-term contracture can develop after tetanic contraction as a result of the accumulation of large amounts of Ca++ in the sarcoplasm; long-term (sometimes irreversible) contracture can occur as a result of poisoning and metabolic disorders.
Phases and modes of skeletal muscle contraction
Phases of muscle contraction
When skeletal muscle is irritated by a single pulse of electric current of suprathreshold strength, a single muscle contraction occurs, in which 3 phases are distinguished (Fig. 4, A):
latent (hidden) period of contraction (about 10 ms), during which the action potential develops and electromechanical coupling processes occur; muscle excitability during a single contraction changes in accordance with the phases of the action potential;
shortening phase (about 50 ms);
relaxation phase (about 50 ms).
 |
Rice. 4. Characteristics of a single muscle contraction. Origin of serrated and smooth tetanus. B– phases and periods of muscle contraction, Change in muscle length shown in blue, muscle action potential- red, muscle excitability- purple. |
Modes of muscle contraction
Under natural conditions, a single muscle contraction is not observed in the body, since a series of action potentials occur along the motor nerves innervating the muscle. Depending on the frequency of nerve impulses coming to the muscle, the muscle can contract in one of three modes (Fig. 4, B).
Single muscle contractions occur at a low frequency of electrical impulses. If the next impulse enters the muscle after the completion of the relaxation phase, a series of successive single contractions occurs.
At a higher impulse frequency, the next impulse may coincide with the relaxation phase of the previous contraction cycle. The amplitude of contractions will be summed up, and there will be serrated tetanus- prolonged contraction, interrupted by periods of incomplete muscle relaxation.
With a further increase in the pulse frequency, each subsequent pulse will act on the muscle during the shortening phase, resulting in smooth tetanus- prolonged contraction, not interrupted by periods of relaxation.
Optimum and pessimum frequency
The amplitude of tetanic contraction depends on the frequency of impulses irritating the muscle. Optimum frequency they call the frequency of irritating impulses at which each subsequent impulse coincides with the phase of increased excitability (Fig. 4, A) and, accordingly, causes tetanus of the greatest amplitude. Pessimum frequency called a higher frequency of stimulation, at which each subsequent current pulse falls into the refractory phase (Fig. 4, A), as a result of which the amplitude of the tetanus decreases significantly.
Skeletal muscle work
The strength of skeletal muscle contraction is determined by 2 factors:
- the number of units involved in the reduction;
frequency of contraction of muscle fibers.
The work of skeletal muscle is accomplished through a coordinated change in tone (tension) and length of the muscle during contraction.
Types of skeletal muscle work:
dynamic overcoming work occurs when a muscle, contracting, moves the body or its parts in space;
static (holding) work performed if, due to muscle contraction, parts of the body are maintained in a certain position;
dynamic yielding operation occurs when a muscle functions but is stretched because the force it makes is not enough to move or hold parts of the body.
During work, the muscle can contract:
isotonic– the muscle shortens under constant tension (external load); isotonic contraction is reproduced only in experiment;
isometrics– muscle tension increases, but its length does not change; the muscle contracts isometrically when performing static work;
auxotonic– muscle tension changes as it shortens; auxotonic contraction is performed during dynamic overcoming work.
Rule of average loads– the muscle can perform maximum work under moderate loads.
Fatigue– a physiological state of a muscle that develops after prolonged work and is manifested by a decrease in the amplitude of contractions, an extension of the latent period of contraction and the relaxation phase. The causes of fatigue are: depletion of ATP reserves, accumulation of metabolic products in the muscle. Muscle fatigue during rhythmic work is less than synapse fatigue. Therefore, when the body performs muscular work, fatigue initially develops at the level of the synapses of the central nervous system and neuromuscular synapses.
Structural organization and reductionsmooth muscles
Structural organization. Smooth muscle consists of single spindle-shaped cells ( myocytes), which are located in the muscle more or less chaotically. Contractile filaments are arranged irregularly, as a result of which there is no transverse striation of the muscle.
The mechanism of contraction is similar to that of skeletal muscle, but the rate of filament sliding and the rate of ATP hydrolysis are 100–1000 times lower than in skeletal muscle.
The mechanism of coupling of excitation and contraction. When the cell is excited, Ca++ enters the cytoplasm of the myocyte not only from the sarcoplasmic reticulum, but also from the intercellular space. Ca++ ions, with the participation of the calmodulin protein, activate the enzyme (myosin kinase), which transfers the phosphate group from ATP to myosin. Phosphorylated myosin heads acquire the ability to attach to actin filaments.
Contraction and relaxation of smooth muscles. The rate of removal of Ca++ ions from the sarcoplasm is much less than in skeletal muscle, as a result of which relaxation occurs very slowly. Smooth muscles perform long tonic contractions and slow rhythmic movements. Due to the low intensity of ATP hydrolysis, smooth muscles are optimally adapted for long-term contraction, which does not lead to fatigue and high energy consumption.
Physiological properties of muscles
The general physiological properties of skeletal and smooth muscles are excitability And contractility. Comparative characteristics of skeletal and smooth muscles are given in table. 6.1. The physiological properties and characteristics of the cardiac muscle are discussed in the section “Physiological mechanisms of homeostasis”.
Table 7.1.Comparative characteristics of skeletal and smooth muscles
Property |
Skeletal muscles |
Smooth muscle |
Depolarization rate |
slow |
|
Refractory period |
short |
long |
Nature of contraction |
fast phasic |
slow tonic |
Energy costs |
||
Plastic |
||
Automatic |
||
Conductivity |
||
Innervation |
motor neurons of the somatic NS |
postganglionic neurons of the autonomic nervous system |
Performed movements |
arbitrary |
involuntary |
Chemical sensitivity |
||
Ability to divide and differentiate |
Plastic smooth muscles is manifested in the fact that they can maintain constant tone both in a shortened and in an extended state.
Conductivity smooth muscle tissue is manifested in the fact that excitation spreads from one myocyte to another through specialized electrically conductive contacts (nexuses).
Property automation smooth muscle is manifested in the fact that it can contract without the participation of the nervous system, due to the fact that some myocytes are able to spontaneously generate rhythmically repeating action potentials.
The contraction is isotonic, in which the muscle fibers are shortened and thickened, and their tension remains virtually unchanged.
Large medical dictionary. 2000 .
See what “isotonic contraction” is in other dictionaries:
Contraction of a muscle under constant tension, expressed in a decrease in its length and an increase in cross-section. In the body I. m.s. is not observed in its pure form. To purely I. m.s. movement of the unloaded limb is approaching; at… …
isotonic contraction- izotoninis raumens susitraukimas statusas T sritis Kūno kultūra ir sportas apibrėžtis Raumens susitraukimas, kurio metu raumeninės skaidulos keičia savo ilgį (patrumpėja ir pastorėja), o įtampa beveik nekinta, pvz., tolygiai, vi enodu greičiu… …Sporto terminų žodynas
isotonic- (isos equal + tonos tension) – contraction of muscle fiber, manifested by shortening and thickening; the voltage remains virtually unchanged...
Isotonic contraction- muscles (from isos equal, tonus tension) – when a muscle contracts during irritation, its length changes, but its tone does not change... Glossary of terms on the physiology of farm animals
Contraction of a muscle, expressed in increasing its tension while maintaining a constant length (for example, contraction of a muscle of a limb, both ends of which are fixed motionless). In the body to I. m.s. the tension developed by the muscle when attempting... is approaching. Great Soviet Encyclopedia
Shortening or tension of muscles in response to irritation caused by motor discharge. neurons. The M. s model has been adopted, according to which, when the surface of the muscle fiber membrane is excited, the action potential first spreads through the system... ... Biological encyclopedic dictionary
MUSCLE CONTRACTION- the main function of muscle tissue is the shortening or tension of muscles in response to irritation caused by the discharge of motor neurons. M. s. underlies all movements of the human body. There are M. s. isometric, when the muscle develops force... ... Psychomotorics: dictionary-reference book
HEART- HEART. Contents: I. Comparative anatomy........... 162 II. Anatomy and histology........... 167 III. Comparative Physiology......... 183 IV. Physiology................... 188 V. Pathophysiology................ 207 VI. Physiology, pat.... ... Great Medical Encyclopedia
A motor unit (MU) is the functional unit of skeletal muscle. The ME includes a group of muscle fibers and the motor neuron that innervates them. The number of muscle fibers that make up one IU varies in different muscles. For example, where... ... Wikipedia
ISOTONIC- Literally – equal tension. Therefore, an isotonic contraction is one in which there is equal tension in the muscle during movement, as occurs when simply raising the arm: an isotonic solution is one in which... ... Explanatory dictionary of psychology
Kharkov State Academy of Physical Culture
Department of Hygiene and Human Physiology
Essay
in the discipline: "Human Physiology"
On the topic: “Forms and types of muscle contractions. Regulation of tension, strength and muscle fatigue."
Completed by: student of group 43 of the correspondence department
Prosin I. V.
Kharkov – 2015
1. Introduction
2) Forms and types of muscle contractions.
3) Strength and muscle function.
4) Muscle fatigue
5) Conclusion
6) List of references used
Introduction
In the human body, according to their structure and physiological properties, there are 3 types of muscle tissue:
1. Skeletal.
2. Smooth.
3. Cardiac.
All muscle types have certain properties:
1. Excitability.
2. Conductivity.
3. Contractility - change in length or tension
4. The ability to relax.
Under natural conditions, muscle activity is reflexive in nature. The electrical activity of a muscle can be recorded using an electromyograph. Electromyography is used in sports medicine.
Reduction skeletal muscles occurs in response to nerve impulses coming from special nerve cells - motor neurons. During contraction, muscle fibers develop voltage. The tension developed during contraction is realized by the muscles in different ways, which determines the different forms and types of muscle contraction.
Forms and types of muscle contractions.
The muscle is capable of contracting both at rest and in a shortened or stretched state. At rest length, the muscle can develop very high tension.
Firstly, because the optimal degree of contact between actin and myosin filaments makes it possible to create the maximum number of bridging connections and thereby actively and strongly develop the tension of the contractile component.
Secondly, because the elastic component of the muscle is already pre-stretched like a spring, additional tension has already been created. The actively developed tension of the contractile component is summed up with the elastic tension accumulated in the elastic component and is realized into one high, resulting muscle tension.
Subsequent pre-stretching of the muscle, which significantly exceeds the state at rest length, leads to insufficient contact between actin and myosin filaments. At the same time, the conditions for the development of significant and active sarcomere tension noticeably worsen.
However, with a large pre-stretch of the involved muscles, for example, with a wide swing in the javelin throw, athletes achieve better results than without a swing. This phenomenon is explained by the fact that the increase in pre-tension of the elastic component exceeds the decrease in the active development of tension in the contractile component. There are different forms and types of muscle contraction.
With a dynamic form, the muscle changes its length; static – tension (but does not change length); auxotonic – length and tension.
There are these types of contractions: isometric, isokinetic and mixed.
Due to targeted strength training (the method of repeated submaximal load), the cross-section and number of both contractile elements (myofibrils) and other connective tissue elements of the muscle fiber (mitochondria, phosphate and glycogen depots, etc.) increase.
True, this process leads to a direct increase in the contractile force of muscle fibers, and not to an immediate increase in their cross-section. Only after this development has reached a certain level can continued strength training help to increase the thickness of the muscle fibers and thereby increase the cross-section of the muscle (hypertrophy).
Thus, the increase in the cross-section of the muscle occurs due to thickening of the fibers (increase in sarcomeres in the cross-section of the muscle), and not due to an increase in the number of muscle fibers, as is often mistakenly assumed.
The number of fibers in each individual muscle is determined genetically, and, as scientific research shows, this number cannot be changed through strength training. Interestingly, people differ significantly in the number of muscle fibers per muscle.
An athlete whose biceps contains a large number of fibers has a better chance of increasing the cross-section of that muscle by training to thicken the fibers than an athlete whose biceps contains a relatively small number of fibers. In the most capable representatives of sports that require maximum and high-speed strength, with systematic and persistent training, the proportion of muscles to total body weight increases to 60% or more.
The strength of skeletal muscle, as already noted, depends mainly on its cross-section, i.e., on the number and thickness of myofibrils located parallel in the fibers, and the number of possible bridging connections between myosin and actin filaments made up of this number.
Thus, if an athlete increases the diameter of muscle fibers, then he increases his strength. However, strength and muscle mass do not increase at the same rate. If muscle mass doubles, strength increases approximately threefold. In women, the force is 60-100 N/cm2 (6-10 kg/cm2, and in men - 70-120 N/cm2. The large spread of these indicators (force output per 1 cm2 of cross-sectional area) is explained by various factors, both dependent and and independent of training, such as intramuscular and intermuscular coordination, energy reserves, and fiber structure.
When muscles are excited, thin filaments of actin move on both sides between thick filaments of myosin. The muscle contracts and its length decreases. Since each myofibril consists of a larger number (n) of successively located sarcomeres, the magnitude and rate of change in muscle length is n times greater than that of one sarcomere.
The traction force developed by a myofibril consisting of n successively located sarcomeres is equal to the traction force of one sarcomere. These same n sarcomeres connected in parallel (corresponding to a large number of myofibrils) give an n-fold increase in traction force, but the rate of change in muscle length is the same as the rate of contraction of one sarcomere.
Therefore, an increase in the physiological diameter of a muscle leads to an increase in its strength, but does not change the speed of its shortening, and vice versa, an increase in the length of a muscle leads to an increase in the speed of contraction, but does not affect its strength. We say: short muscles are strong, long muscles are fast.
Strength and muscle function.
Muscle strength is determined by the maximum tension it can develop under conditions of isometric contraction or when lifting a maximum load. To measure muscle strength, determine the maximum load that it is able to lift.
The strength of a muscle, other things being equal, depends not on its length, but on its cross-section. To be able to compare the strength of different muscles, the maximum load that a muscle is able to lift is divided by the number of square centimeters of its cross section. Absolute muscle strength is expressed in kg per 1 cm2.
When lifting a load, the muscle performs mechanical work, which is measured by the product of the mass of the load and the height of its lifting and is expressed in kilograms. The muscle does the most work at medium loads.
A temporary decrease in muscle performance that occurs as a result of work and disappears after rest is called fatigue. The latter is a complex physiological process associated primarily with fatigue of the nerve centers. A certain role in the development of fatigue is played by the accumulation of metabolic products (lactic acid, etc.) in the working muscle and the gradual depletion of energy reserves.
At rest, outside of work, the muscles are not completely relaxed, but retain some tension, called tone. The external expression of tone is a certain degree of muscle elasticity. Muscle tone is caused by continuously incoming nerve impulses from the motor neurons of the spinal cord. Skeletal muscle tone plays an important role in maintaining a certain body position in space, maintaining balance and muscle elasticity.
There are three modes of muscle contraction:
Isotonic;
Isometric;
Mixed (auxometric).
The isotonic mode of muscle contraction is characterized by a predominant change in the length of the muscle fiber, without a significant change in tension. This mode of muscle contraction is observed, for example, when lifting light and medium weight loads.
The isometric mode of muscle contraction is characterized by a predominant change in muscle tension, without a significant change in length. An example is changes in the state of the muscles when a person tries to move a large object (for example, when trying to move a wall in a room).
Mixed (auxometric) type of muscle contraction, the most realistic, most common option. Contains components of the first and second options in different proportions depending on actual environmental conditions.
Types of muscle contraction
There are three types of muscle contraction:
Single muscle contraction;
Tetanic muscle contraction (tetanus);
Tonic muscle contraction.
In addition, tetanic muscle contraction is divided into serrated and smooth tetanus.
A single muscle contraction occurs under conditions of action on the muscle of threshold or suprathreshold electrical stimuli, the interpulse interval of which is equal to or greater than the duration of a single muscle contraction. In a single muscle contraction, three time periods are distinguished: latent period, shortening phase and relaxation phase (see Fig. 3).
Rice. 3 Single muscle contraction and its characteristics.
LP – latent period, FU – shortening phase, FR – relaxation phase
Tetanic muscle contraction (tetanus) occurs under conditions of action on the skeletal muscle of a threshold or suprathreshold electrical stimulus, the interpulse interval of which is less than the duration of a single muscle contraction. Depending on the duration of the interstimulus intervals of the electrical stimulus, either jagged or smooth tetanus may occur when exposed to it. If the interpulse interval of the electrical stimulus is less than the duration of a single muscle contraction, but greater than or equal to the sum of the latent period and the shortening phase, serrated tetanus occurs. This condition is met when the frequency of the pulsed electrical stimulus increases in a certain range.
If the duration of the interpulse interval of the electrical stimulus is less than the sum of the latent period and the shortening phase, smooth tetanus occurs. In this case, the amplitude of smooth tetanus is greater than the amplitude of both single muscle contraction and serrated tetanic contraction. With a further decrease in the interpulse interval of the electrical stimulus, and therefore with an increase in frequency, the amplitude of tetanic contractions increases (see Fig. 4).
Rice. 4 Dependence of the shape and amplitude of tetanic contractions on the frequency of the stimulus. – the beginning of the action of the stimulus, - the end of the action of the stimulus.
However, this pattern is not absolute: at a certain frequency value, instead of the expected increase in the amplitude of smooth thetatnus, the phenomenon of its decrease is observed (see Fig. 5). This phenomenon was first discovered by the Russian scientist N.E. Vvedensky and was called pessimum. According to N.E. Vvedensky, the basis of pessimal phenomena is the mechanism of inhibition.
Rice. 5. Dependence of the amplitude of smooth tetanus on the frequency of the stimulus. The designations are the same as in Figure 5.
