Long thin muscle fibers from which a skeletal muscle was built is giant cells formed during ontogenesis when merging the set of individual cells. In an adult, they can reach 5 cm long! Numerous kernels in such a cell are located directly under the cytoplasmic membrane, and the main part of the cytoplasm consists of eopibrils stretched along the entire cell (1-2 μm thick), with characteristic transverse allocations (Fig. 3). Sarcomers include such a "coloring" of myofibrill, the composition of each of which includes two sets of parallel, partially overlapping filaments: thick alone, which form a dark strip and stretch from one edge to another, and thin actines lying in the region of the light strip and partially setting in Dark strip area (Fig. 4). One sarcomer from another is separated by the Z-disk.
Fig. 3. Scheme of a small segment of a skeletal muscle cell ( muscular fiber)
Fig. 4. A. Electronic micrograph of a longitudinal cut through the cell of the skeletal muscle of the rabbit (with a small magnification). Conducted regular transverse allocations. The cell contains a plurality of parallel myofibrils (see Fig. 3). B. Small plot of the same photo: Showing two adjacent myofibrils and sarcomer details are shown. B. Scheme of the structure of a separate sarcomer, explaining the origin of dark and bright strips, which are visible on electronic micrographs
The cytoplasm provides myofibrils with energy in the form of ATP - many mitochondria are found in the actively functioning muscle. In addition, the cytoplasm contains glycogen, phosphocreatin, glycolytic enzymes.
The skeletal muscle turns the chemical energy accumulated in ATP, into mechanical with very high efficiency - in the form of heat is lost only 30-50%. (For comparison: Automotive engine when burning gasoline usually loses in the form of heat 80-90%.)
With muscular reduction due to the binding of myosine actin, thick and thin threads slide relative to each other (Fig. 5).
Fig. 5. A diagram illustrating the muscular reduction process on the principle of sliding threads: thick and thin philants slide each other without changing your own length
The physiological regulator of muscle contraction is calcium ions. At rest, the system of active transport of calcium ions is working, and they accumulate in a kind of storage, from which they are released under the action of a nervous impulse, providing muscle contraction.
Calcium ion transport system operates due to ATP energy. The amount of ATP, which is available in the muscle, is enough to maintain the work of the contractile apparatus of everything for a split second. How does the muscle work for a longer time? It turns out that the energy is in the form of phosphocreatine, or creatine phosphate, which can carry more high-energy phosphate groups than the universal ATP. Phosphocreatin restores ATP, thereby ensuring the influx of energy for muscle contraction. However, in the working muscle, phosphocreatine reserves are quickly depleted, and this reduces the content of ATP.
With a longer physical load of the muscles are provided by energy due to glycolysis - cleavage of carbohydrates under the action of enzymes with the accumulation of energy in the form of ATP. When the creatine reserves in the muscle are depleted, the energy charge of the muscular contraction is reduced, which leads to glycolysis stimulation, tricarboxylic acid cycle and oxidative phosphorylation in the working muscle.
In the absence of oxygen during the splitting of the carbohydrate molecule, two molecules of lactic acid (or lactate) and two ATP molecules are formed. However, if the muscle glycohylic is used for glycolysis, then two lactate molecules and three ATP molecules occur.
Glycogen is, as you know, the main reserve polysaccharide, inhouses in muscles and liver. With a reduced level of glycogen in the muscles and the liver and the availability of free blood glucose, it is used for the synthesis of glycogen. And, on the contrary, with the needs of the body in the energy source for glycolysis processes, glycogen is successfully used.
Muscular system The most developed compared to other organism systems. To ensure the work of the muscles, it is necessary for a huge amount of energy that a person can be obtained by creatinephosphate (phosphocreatine), carbohydrates in the form of glycogen and glucose and fats. These three types of energy carriers differ in the magnitude of the energy exempted during their use of energy and by how long it can serve as a "fuel" source. So it is a mechanism for ensuring muscle muscles (Table 2, 3). It is well known that with continuous non-intensive work in the flow of oxidative processes, fats or carbohydrates are used, and during operation there are several greater intensity using anaerobic glycolysis mechanisms. With a very intense short load, the work of the muscles is ensured by phosphagenes. Accordingly, each of the energy sources has its own energy value and is used under certain conditions (Table 4).
Working muscles for aerobic oxidation of carbohydrates compared to other organs consume a very large amount of oxygen (Table 5).
Table 2. Energy reserves in human body mass 70 kg
Table 3. Maximum possible power skeletal muscles man when using various substrates and catabolic paths
Table 4. Maximum energy formation rate from various sources during exercise
Source of energy |
Maximum speed Muscles |
The amount in the muscle, mmol / kg of formation of rich in energy phosphate bonds, mmol / s / kg |
Maximum speed of products, kcal / h / kg |
Musimum speed maintenance time |
Creatine phosphate |
||||
Anaerobic glycoliz |
||||
Aerobic oxidation of glucose and glycogen |
||||
Aerobic oxidation |
Not limited |
Not limited |
Table 5. Relative oxygen consumption by various human bodies alone and with severe work *
Tone skeletal muscles. Alive, outside of work, the muscles are never completely relaxed, but retain some tension called tone. Externally, this is expressed in muscle elasticity. The skeletal muscle tone is associated with entering the muscle of the individual following each other with a large interval of nerve pulses, exciting alternately different muscle fibers. These pulses occur in the spinal cord motnelones, the activity of which in turn is maintained by impulses emanating both from the overlying centers and from the periphery from the stretching receptors ("muscle spindle") located in the muscles themselves.
In humans, the muscle tone in known limits can be adjusted arbitrarily: at the request, a person can almost completely relax the muscles or somewhat strain them without making it, however, at the same time.
Work and power of muscles.The size of the reduction (degree of shortening) of the muscle with this force of irritation depends on both its morphological properties and from the physiological state. Long muscles are reduced by a large amount than short. Moderate muscle stretching increases its contractile effect, with a strong tension, the muscle contraction is weakened. If a muscle fatigue develops as a result of long work, the value of its reduction falls.
To measure the muscle force, the maximum load is determined, which it is able to lift. This force can be very large: a dog, for example, the muscles of the jaw can raise the cargo, exceeding its body weight 8.3 times. The strength of the calf muscles of a person is judged by the magnitude of the cargo, laid on his shoulders, with whom he is able to lift on socks.
Fig. 6. Types of structure of various muscles (by A.A. Ukhtomsky).
A - Muscles with parallel stroke fibers; B - spindle-like muscle; B - Celebrate Muscle
The power of the muscle will not depend on its length, but from the cross section: the greater the physiological cross-section of the muscle, i.e. The sum of the transverse sections of all its fibers, the greater the cargo that it is able to raise. The physiological cross-section coincides with the geometric only in muscles with longitudinally located fibers; In muscles with oblique fibers, the amount of cross sections of the fibers can significantly exceed the geometric cross-section of the muscle itself (Fig. 6). For this reason, the power of the muscle with oblique fibers is much larger than the power of the muscles of the same thickness, but with longitudinal fibers. To compare the power of different muscles, the maximum cargo that the muscle is able to lift, divide on its cross-sectional area, calculating the absolute muscular power. For example, absolute force ion muscle The person is 5.9 kg / cm 2, the shoulder flexor - 8.1, the chewing muscle - 10, the two-headed arm muscles - 11.4, the three-headed shoulder muscles - 16.8, smooth muscles - 1 kg / cm 2.
Most mammals and human muscles have a peristry structure. Conduous muscle has a great physiological section, and therefore it has a lot of power.
The work of the muscle is measured by the product of the raised cargo by the magnitude of the shortening of the muscle, i.e. It is expressed in kilogram meters or gramsantimeters.
The content of myoglobin muscle fibers are divided into red, white and intermediate. Red fibers are considered "slow", and white - "fast." Some scientists believe that at the birth of a person's muscles consist only from "slow" fibers and some of them in the process of development turns into "fast". Others are convinced that the location of the muscles, the features of their structure and functions are predetermined by genetically.
Red fibers work mainly in aerobic mode, and white - in conditions of lack of oxygen, i.e. Different metabolic processes proceed in them. Red fibers are usually used to perform mild or moderate work, and white begin to function only after a significant increase in the inflow of exciting pulses during very intensive work. Intermediate type fibers retain properties and red, and white fibers and are called "quick red".
The percentage of those or other fibers predetermines the athlet specialization. As a rule, holders preferably red muscles reach the best results in sports requiring increased endurance (swimming, cycling, Running on medium and long distances etc.). Those who have more white muscle fibers, better perform strength exercises. The latter is also explained by the fact that white fibers are easier hypertrophy (increasing in volume). However, not everything is predetermined only by nature. There are also training factors that some experts prefer in the formation of muscle structure.
As the muscles are "getting used to" to physical exertion.During training in muscles, the mechanisms of stocking and use of energy substrates are formed: creatine phosphate, glycogen and fats (as triacylglycerides). ATP and creatine phosphate, or phosphagene, very little in the muscle. Phosphates are constantly synthesized (the creatine phosphate content in white muscle fibers is approximately 30 μmol per 1 g of crude masses of the muscle), but is rapidly spent with the load ongoing for more than a few seconds. Energy-intensive glycogen and triacylglycerides constitute the bulk of the backup sources of "fuel" for muscles.
Under the influence of high-speed and power training in white muscle fibers, the activity of glycolithic enzymes increases and a large amount of glycogen is formed, which is intensified in the muscles in the form of granules around which the corresponding enzymes are placed. Changes in the buffer systems of muscle cells occur: as soon as inside the cell, the pH changes, it immediately affects the work of enzymes responsible for Glycoliz.
The total amount of operation that anaerobic glycoliz can provide at intensive load depends on the glycogen reserve (with a decay of each of its molecule, 6.2 mol ATP) is formed). The use of glycogen reserves in muscles is launched hormonal and nerve stimuli. One of these hormones is adrenaline - is able to significantly activate the processes of using glycogen for ATP resintez.
Under the influence of training, anaerobic glycoliz in muscles can be repeatedly increased. Thus, according to some data, in trained sprinters, the glycolysis processes in the muscles of the legs are intensified in two thousand times.
However, due to the anaerobic glycolysis, a person is able to perform a load of only 2-3 minutes. After that, the processes of oxidative phosphorylation are inevitably launched.
With long work, red and intermediate muscle fibers become the main actors. The energy for the activities of these muscles is formed in mitochondria (they are much larger in the cells of red muscle fibers than in white) with the help of oxidative enzymes in the presence of sufficient oxygen.
Glycogen, which is actively used in short work, is (along with fats) the main endogenous substrate and during long-term load. Both of these types of "fuel", especially fats, are contained in the form of reserves in red and intermediate fibers. Fats are somewhat inferior to glycogen in the efficiency of energy output per unit of oxygen consumed: 5.6 mol ATP is formed during their oxidation.
In case of oxidative phosphorylation, the muscle can receive energy substrates and from the central depot (glycogen from the liver and fat from adipose tissue) and even use energy sources from the outside during operation, for example, carbohydrate additives in the marathon race - nature has provided additional features for long-term operation.
For representatives sports specieswho train on endurance will be curious the fact that the lengthy and intensive work of the muscles is provided to the energy best with the simultaneous use of carbohydrates and fats. It would seem here a certain paradox. After all, carbohydrates only enough for 20-30 minutes of intensive work, and fats can be used much longer. However, the matter is that the use of alone fats provides twice as long as the energy generation rate than the simultaneous use of fats and carbohydrates. And on this depends the intensity of the work performed. Thus, according to biochemists, glycogen is the best "fuel" to ensure high-intensity long-term work in aerobic conditions. Scientists have even found the dependence of the duration of work to complete exhaustion from the glycogen content in the muscles before starting the load. However, if the load lasts 2-3 hours, the body begins to use to provide muscle contractions and glycogen, and fats. When moving to splitting fats, the capacity of the work is reduced. Initially, triacylglycerides are used, and then free fatty acids that come from blood.
Attrets specializing in strength sports, and bodybuilders, of course, are interested in the issue of working hypertrophy of muscles.
Systematic intensive work of the muscle leads to an increase in the mass of muscle tissue. This phenomenon is called muscle working hypertrophy. The basis of hypertrophy is an increase in the mass of protoplasm of muscle fibers, leading to their thickening. This increases the content of proteins and glycogen, as well as the substances of the energy necessary for muscle contraction - ATP and creatine phosphate. Therefore, the strength and speed of reduction of the hypertrophied muscle is higher than non-refined.
The increase in the mass of muscle tissue in trained people leads to the fact that the muscles of the body can be 50% of the body weight (instead of the usual 35-40%).
Hypertrophy is developing if a person daily for a long time produces muscle work, requiring a large voltage (power load). Muscular work produced without much effort, even if it continues for a very long time, does not lead to muscle hypertrophy.
Muscle hypertrophy is very important for the execution of a short-term "explosive" work. It may be due to the fact that the stocks of creatine phosphate in human muscles do not increase more than a certain amount per unit mass of muscles. Thus, an increase in muscle volume contributes to an increase in the total amount of this energy-intensive substrate in muscles and, accordingly, an increase in the ability to more effectively perform the operation of maximum power.
The opposite working hypertrophy is the phenomenon of muscle atrophy. It develops in all cases when the muscle for some reason loses the ability to perform its normal operation, for example, with a long immobilization of the limb in a gypsum bandage, with a duty of the patient's stay in bed, with the cut of the tendon, as a result of which the muscle ceases to work against the load, and T ..
In atrophy, the diameter of muscle fibers and the content of contracty proteins, glycogen, ATP and other important substances are sharply falling for contractile activities. With the resumption of normal operation, the atrophy muscles gradually disappear.
Muscle fatigue.The temporary decrease in muscle performance, coming as a result of work or training and disappearing after rest is determined by fatigue.
If it is for a long time to annoy rhythmic electric stimuli insulated muscle to which a small cargo is suspended, the amplitude of its abbreviations gradually decreases until it reaches zero. The curve thus obtained is called the fatigue curve.
Along with the change in the amplitude of abbreviations during fatigue, the latent period of reduction increases and excitability decreases. But all these changes occur not immediately after the start of the municipality, there is a certain period during which an increase in the amplitudes of abbreviations and a slight increase in muscle excitability is observed. At the same time, the muscle becomes easily tensile. In such cases, they say that the muscle "is being done", i.e. Adapts to work at a given rhythm and irritation force. With further long irritation, the fatigue of muscle fibers occurs.
This may be due to the accumulation of metabolic products in the muscle (in particular, lactic acid, which is formed during the cleavage of glycogen), which are inactive effect on the performance of muscle fibers. Some of these products, as well as potassium ions diffound from the fibers outside into the near-cellular space and have an inhibitory effect on the ability of an excitable membrane to generate potentials of action.
In addition, the development of fatigue in the muscle affects the gradual exhaustion in it of energy reserves.
Everything described above refers to isolated muscle. After all, when working in the body, the muscle is continuously supplied with blood and, therefore, it receives a certain amount of nutrients (glucose, amino acids) and is released from the exchange products that violate the normal life of muscle fibers. The main difference is that in the body, exciting pulses come to the muscle from the nerve. The neuromuscular compound is tires much earlier than muscle fibers, and therefore blocking the transmission of excitation from the nerve to the muscle protects the latter from the exhaustion caused by long-term operation. In a holistic body, even earlier neuromuscular compounds are tired when nervous centers are tired.
Restoration of the working capacity of the tired muscles of the man's hand after long-term work on the lifting of the cargo can be accelerated if during the rest to produce work with another hand or lower limbs.
To be continued
What is the question of the appearance of calcium in the cytoplasm of skeletal muscle cells? Posted by the author loss The best answer is calcium is a factor that resolving muscle cuts: with an increase in the concentration of calcium ions. in myioflasm there is an accession to the regulatory protein, as a result of which actin becomes able to interact with myosine; Connecting, these two proteins form actomiosis, and the muscle is reduced. In the process of forming actomiosis, ATP cleavage occurs, whose chemical energy ensures the execution of mechanical work and is partially dissipated as heat. The greatest contractual activity of the skeletal muscle is observed at the calcium concentration of 10-6-10 (minus B) -7 mol; When decreasing the concentration of Ca ions (less than 10-7 mol), the muscle fiber loses the ability to shorten and voltage. The effect of Ca on the tissue is manifested in changing their trophic, the intensity of oxidation and reduction processes and in other reactions associated with the formation of energy. Changing the concentration of Ca in the washing of the nervous fluid cell significantly affects the permeability of its membrane for potassium ions and especially for sodium ions, and the decrease in the CA level causes an increase in the permeability of the membrane for sodium ions and increasing the incubibilities of the neuron. Increased CA concentration has a stabilizing effect on the membrane nervous cell. The role of Ca in processes associated with the synthesis and isolating the nerve endings of mediators providing the synaptic transmission of the nerve impulse is established.
The transfer of molecules and ions against an electrochemical gradient (active transport) is associated with significant energy costs. Often gradients reach large quantities. For example, a concentration gradient of hydrogen ions on the plasma membrane of the cells of the stomach mucosa of the stomach is 10v6tes, the gradient of the concentration of calcium ions on the sarcoplasmic reticulum membrane - 10V4 degrees, while the flows of ions against the gradient are significant. As a result, energy costs for transport processes reach, for example, in humans, more than 1/3 of the entire metabolic energy. The plasma membranes of cells of various organs found systems of active transport of sodium ions and potassium - sodium pump. This system pumped sodium from the cell and potassium into the cell (antiport) against their electrochemical gradients. The transfer of ions is carried out by the main component of the sodium pump - Na +, K +-dependent ATP-az due to hydrolysis ATP. Three sodium ions and two potassium ions are transported to each hydrolyzed ATP molecule. There are two types of CA2 + -ATF-AZ. One of them provides the emission of calcium ions from the cell in the intercellular medium, the other is the accumulation of calcium from the cellular content to the intracellular depot. Both systems are capable of creating a significant calcium ion gradient. K +, N + -TF-Aza detected in the mucous membrane of the stomach and intestines. It is able to transport H + through the membrane vesicles of the mucous membrane during hydrolysis of ATP. In the microsomes of the stomach mucosa of the frog, an anionic ATP-Aza was found, capable of hydrolysis of ATP to carry out antiport of bicarbonate and chloride.
Mineral substances are part of all living fabrics. However, the normal functioning of tissues is ensured not only by the presence of certain mineral salts in them, but also strictly determined by their relation. Mineral substances maintain the necessary osmotic pressure in biological fluids and ensure the constancy of acid-alkaline equilibrium in the body. We consider the main minerals.
Potassium is mainly contained in cells, sodium - In the intercellular fluid. For normal vital activity of the body, a strictly defined ratio of sodium and potassium particles is required. The proper ratio of these ions ensures the normal excitability of nervous and muscle tissues. Sodium plays a big role in maintaining the constancy of osmotic pressure. With a reduced potassium content in the myocardium (muscular heart fabric), the contractile function of the heart is disturbed. But with an excess of potassium, the heart activity is also violated. The daily need of an adult: sodium - 4-6 g, potassium - 2-3 g
Calcium It is included in the bones in the form of phosphoric salts. His ions provide normal brain activity and skeletal muscles. The presence of calcium is necessary for blood coagulation. Excess calcium increases the frequency and force of heart abbreviations, and with ultrasound concentrations in the body can cause a heart stop. The daily need of an adult in calcium - 0.7-0.8 g
Phosphorus It is part of all cells and interstitial liquids. It plays a big role in the exchange of proteins, fats, carbohydrates and vitamins. This substance is an indispensable component of rich substances. Salts of phosphoric acids support the constancy of acid-alkaline equilibrium of blood and other tissues. The daily need of an adult in phosphorus - 1.5-2 g.
Chlorine It is contained in the body mainly in the sodium compound and is part of the hydrochloric acid of the gastric juice. Chlorine is necessary for normal vital cells of cells. The daily need of an adult in Chlorine - 2-4
Iron is an part of Hemoglobin and some enzymes. By providing oxygen transport, it takes part in oxidative processes. The daily need for the hardware for men is 10 mg, for women - 18 mg.
Bromine In small quantities is contained in the blood and in other tissues. Intensifying braking in the crust of large hemispheres, it contributes to the normal ratio between the processes of excitation and braking.
Iodine - Mandatory component of the thyroid hormone. The disadvantage of this substance in the body causes a violation of many functions. The daily need for iodine for adult healthy people is 0.15 mg (150 μg).
Sulfur It is part of many proteins. It is contained in some enzymes, hormones, vitamins and other connections that play an important role in metabolism. In addition, sulfuric acid is used by the liver to neutralize some substances.
For the normal life of the body, in addition to these substances, they have magnesium, zinc, etc., some of them (aluminum, cobalt, manganese, etc.) are part of the body in such minor quantities that they are called microelements. A diverse nutrition is usually fully provided by all minerals.
Muscular contraction is a vital function of the body associated with defensive, respiratory, food, sex, excretory and other physiological processes. All types of arbitrary movements are walking, facial expressions, movements of eyeballs, swallowing, breathing, etc. are carried out by skeletal muscles. Incoming movements (except for the reduction of the heart) are the peristalsis of the stomach and intestines, the change in the tone of blood vessels, maintaining the tone of the bladder - is due to the reduction of smooth muscles. The work of the heart is ensured by a reduction in cardiac muscles.
Structural organization of skeletal muscle
Muscle fiber and miofibrilla (Fig. 1).The skeletal muscle consists of a variety of muscle fibers that have points of attachment to the bones and located in parallel to each other. Each muscle fiber (myocyte) includes many subunits - myofibrils that are built from the blocks repetitive in the longitudinal direction (sarcomers). Sarcomer is a functional unit of the cutting apparatus of the skeletal muscle. Myofibrils in muscle fibers lie in such a way that the location of the sarcomers in them coincides. This creates a picture of transverse allocations.
Sarcomer and fillants. Sarcomers in the Miofibrilla are separated from each other Z -plastins, which contain Beta Aktinin protein. In both directions from Z -splastics, thin aktinum fillants. Between them there are thicker mosinovaya fillants.
Aktinova Pillament Externally resembles two beads twisted in a double helix, where every bead is a protein molecule aktin. In the deepening of actin helix at an equal distance, the protein molecules are troponinconnected with filamentous protein molecules tropomyozine.
Myosine fillants are formed by repeating protein molecules mozin. Each molecule of myosin has a head and tail. Myosin head can bind to actin molecule, forming the so-called transverse bridge.
Muscular fiber cell membrane forms invagination ( cross tubes), which perform the function of excitation to the sarcoplasmic reticulum membrane. Sarpoplasmacakes Reticulum (longitudinal tubes) It is an intracellular network of closed tubes and performs the function of depositing Ca ++ ions.
Muscular unit.The functional unit of the skeletal muscle is muscular unit (de). De is a set of muscle fibers that are innervated by one motionerone processes. The excitation and reduction of the fibers that are part of one de, occurs simultaneously (when excited by the corresponding motor mechanone). Separate de can be excited and declined independently of each other.
Molecular cutting mechanismsskeletal muscle
According to slip theory threadsMuscular reduction occurs due to the moving movement of actin and mosine phillaments relative to each other. The thread slip mechanism includes several consecutive events.
• Myosin heads join the centers for binding the actin fillament (Fig. 2, a).
• The interaction of myozin with actin leads to conformational rearrangements of myosin molecule. Heads acquire atpasic activity and rotate 120 °. Due to the rotation of the filament heads, actin and myosin are moving to the "one step" relative to each other (Fig. 2, b).
• The disconnection of actin and alone and the reduction of the sign of the head occurs as a result of attachment to the molecule of the ATP molecules and its hydrolysis in the presence of CA ++ (Fig. 2, B).
• Cycle "Binding - a change in the conformation - disconnection - the restoration of conformation" occurs many times, as a result of which the actin and mosicinal fillants are shifted relative to each other, Z-Discovery of sarcomers come closer and the myofibrill is shortened (Fig. 2, d).
Conjugation of excitation and reductionin skeletal muscle
At resting the slip of the threads in the fibrille does not occur, since the binding centers on the surface of the actin are closed with tropomyosis protein molecules (Fig. 3, a, b). Excitation (depolarization) of myofibrils and the actual muscular reduction are associated with the process of an eletromechanical interface, which includes a number of consecutive events.
• As a result of the operation of the neuromuscular synapse on a postsynaptic membrane, a VSP occurs, which generates the development of the potential of action in the field surrounding the postsynaptic membrane.
• Excitation (action potential) applies to the membrane of myofibrils and due to the system of transverse tubes reaches a sarcoplasmic reticulum. Depolarization of the sarcoplasmic reticulum membrane leads to the discovery of CA ++-channels in it, through which the Ca ++ ions (Fig. 3, B) are extended to the sarcoplasma.
• CA ++ ions are associated with protein troponin. Troponin changes its conformation and shifts the tropomyosis protein molecules, which closed the centers of actin binding (Fig. 3, g).
• Myosin heads are joined to the opened binding centers, and the reduction process begins (Fig. 3, e).
For the development of these processes, a certain period of time is required (10-20 ms). Time from the moment of excitement of muscle fiber (muscles) before its reduction is called latent abbreviation period.
Skeletal muscle relaxation
The relaxation of the muscle is caused by the inverse transfer of CA ++ ions by means of a calcium pump in the channels of sarcoplasmic reticulum. As CA ++ removes from cytoplasm open centers binding is becoming less and in the end, actin and myosine fillants are completely discharged; There is a relaxation of the muscle.
Contracture Call a resistant long-term reduction of the muscle, which persists after the termination of the stimulus. A short-term contracture can develop after a tetanic reduction as a result of the accumulation of a large amount of CA ++ in the sarcoplasm; Long (sometimes irreversible) contracture may occur as a result of poisoning poisons, metabolic disorders.
Phases and reducing modes of skeletal muscle
Muscular contraction phases
When irritating the skeletal muscle with a single pulse of the electrical current of the overall force, a single muscle contraction occurs, in which 3 phases are distinguished (Fig. 4, a):
• Latent (hidden) reduction period (about 10 ms), during which the potential of action is developing and the processes of electromechanical conjugation processes; Muscle excitability during a single reduction varies in accordance with the phases of the potential of action;
• shortening phase (about 50 ms);
• Phase of relaxation (about 50 ms).
 |
Fig. 4. Characteristics of single muscular reduction. The origin of the toothed and smooth Tetanus. B. - phases and periods of Iyshek cuts, Muscle length change shown in blue muscle action potential - red, muscle causity - Violet. |
Muscular cuts
In natural conditions in the body of a single muscular abbreviation, it is not observed, since in the motor nerves, innervating muscles, there are a series of action potentials. Depending on the frequency of the muscle coming to the muscle, the muscle can be reduced in one of the three modes (Fig. 4, b).
• Single muscle contractions occur at a low frequency of electrical pulses. If the next impulse comes into the muscle after the release of the relaxation phase, a series of consecutive single abbreviations occurs.
• At a higher pulse frequency, the next impulse may coincide with the phase of relaxation of the previous reduction cycle. The amplitude of abbreviations will be summed up, will arise toto Tetanus - Long abbreviation, interrupted by period of incomplete muscle relaxation.
• with further increasing pulse frequency, each next pulse will act on the muscle during the shortening phase, resulting in smooth Tetanus - Long reduction, not interrupted relaxation periods.
Optimum and pessimum frequency
The amplitude of the tetanic reduction depends on the frequency of the pulses irritating the muscle. Optimum frequency They call such a frequency of irritating pulses, at which each subsequent pulse coincides with the phase of increased excitability (Fig. 4, a) and accordingly causes the thetanus of the greatest amplitude. Pessimum frequency They call a higher frequency of irritation at which each subsequent current pulse falls into the refractor phase (Fig. 4, a), as a result of which the amplitude of Tetanus is significantly reduced.
Work of skeletal muscle
The reduction force of the skeletal muscle is determined by 2 factors:
• the number of de who participate in the reduction;
• The frequency of reduction of muscle fibers.
The operation of the skeletal muscle is performed due to the agreed change in the tone (voltage) and the length of the muscle during the reduction.
Siele muscle work:
dynamic overcoming work It is performed when the muscle, shrinking, moves the body or its part in space;
static (holding) work It is performed if due to the reduction of the muscles of the body part of the body is saved in a certain position;
dynamic inferior work It is performed if the muscle is functioning, but it is stretched, since it is not enough effort to move or retain the body parts.
During the performance of the muscle, the muscles can shrink:
isotono - the muscle is shortened at constant voltage (external load); Isotonic reduction is reproduced only in the experiment;
isometrics - the muscle tension increases, and its length does not change; The muscle is reduced isometrically when performing static work;
auxotono - the muscle voltage changes as it shortening; Auxotonic reduction is performed with dynamic overcoming work.
Middle load rule - Muscle can make the maximum work at average loads.
Fatigue - the physiological state of the muscle, which develops after committing long work and is manifested by a decrease in the amplitude of abbreviations, the elongation of the latent period of reduction and the relaxation phase. The reasons for fatigue are: the exhaustion of ATP stock, accumulation in the muscle of metabolism products. Muscle fatigue at rhythmic work is less than the fatigue of synapses. Therefore, when a muscular work is performed, fatigue is initially evolving at the level of centapers of the CNS and neuro-muscular synapses.
Structural organization and reductionsmooth muscles
Structural organization. The smooth muscle consists of single cells of the spindle-shaped ( myocyte), which are located in the muscle more or less chaotically. Cutting fillants are located irregularly, as a result of which there is no transverse muscle aperture.
The reduction mechanism is similar to that in the skeletal muscle, but the speed of slipping the phillament and the rate of hydrolysis of ATP is 100-1000 times lower than in skeletal muscles.
Mechanism of mapping of excitation and reduction. When excitation, the CA ++ cell enters the cytoplasm of myocytes not only from sarcoplasmatic reticulum, but also from the intercellular space. CA ++ ions with the participation of squirodulin protein activate the enzyme (mosin kinase), which transfers phosphate group with ATP on myosin. Phosphorylated myosin heads acquire the ability to join Aktin Fillaments.
Reduction and relaxation of smooth muscles. The rate of removal of CA ++ ions from sarcoplasm is significantly less than in a skeletal muscle, as a result of which relaxation occurs very slowly. Smooth muscles perform long-term tonic cuts and slow rhythmic movements. Due to the low intensity of hydrolysis of ATP, smooth muscles are optimally adapted for a long reduction that does not lead to fatigue and large energy consumption.
Physiological properties of muscles
Common physiological properties of skeletal and smooth muscles are excitability and society. The comparative characteristic of skeletal and smooth muscles is shown in Table. 6.1. The physiological properties and features of cardiac muscles are discussed in the "Physiological Mechanisms of Homeostasis".
Table 7.1.Comparative characteristics of skeletal and smooth muscles
Property |
Skeletal muscles |
Smooth muscles |
Depolarization rate |
slow |
|
Refractory period |
short |
long |
Character of abbreviation |
fast Fazic |
slow tonic |
Energy costs |
||
Plastic |
||
Automatia |
||
Conductivity |
||
Innervation |
motioneiron somatic NS. |
postganglyonary neurons of vegetative NA |
Movements carried out |
arbitrary |
involuntary |
Chemicals Sensitivity |
||
The ability to divide and differentiate |
Plastic Smooth muscles manifests itself in the fact that they can maintain a constant tone in both shortened and stretched state.
Conductivity The smooth muscle tissue is manifested in the fact that the excitation extends from one myocyte to another through specialized electrically conductive contacts (Nexus).
Property Automation Smooth muscles manifests itself in the fact that it can be reduced without the participation of the nervous system due to the fact that some myocytes are able to spontaneously generate rhythmically repeated potentials of action.
Mobility is a characteristic feature of all forms of life. The directional movement takes place when the chromosome is discrepanted in the process of cellular division, the active transport of molecules, moving the ribosoma during protein synthesis, reducing and relaxing muscles. Muscular contraction is the most perfect form of biological mobility. At the heart of any movement, including muscular, are common molecular mechanisms.
A person distinguish several types of muscle tissue. Cross-striped muscle Makes up the muscles of the skeleton (skeletal muscles that we can cut arbitrarily). Smooth muscular tissue is part of the muscles of the internal organs: the gastrointestinal tract, bronchi, urinary tract, blood vessels. These muscles are reduced involuntarily, regardless of our consciousness.
In this lecture, we will consider the structure and processes of reduction and relaxation of skeletal muscles, since they are the greatest interest in biochemistry of sports.
Mechanism muscular abbreviation So far, it is not completely disclosed.
The following is reliably.
1. The source of energy for muscle contraction is ATP molecules.
2. Hydrolysis of ATP is catalyzed with muscular reduction by myosin, having enzymatic activity.
3. The launch mechanism of the muscular reduction is to increase the concentration of calcium ions in the sarcoplasm of the myocytes caused by the nervous motor pulse.
4. During muscle contraction between thin and thick threads, Miofibrils arise transverse bridges or spikes.
5. During muscle contraction, there is a slip of thin threads along the thickness, which leads to the shortening of myofibrils and all muscle fibers in general.
Hypotheses explaining muscle reduction mechanism a lot, but the most reasonable is the so-called hypothesis (theory) "sliding threads" or "rowing hypothesis".
In the terrible muscle, thin and thick threads are in a disconnected state.
Under the influence of the nerve pulse, calcium ions extend from the tanks of the sarcoplasmic network and are joined to the protein of thin threads - troponin. This protein changes its configuration and changes the actin configuration. As a result, a transverse bridge is formed between actin of thin yarns and myosine thick threads. This increases the atpaz activity of myosin. Myozin splits the ATP and due to the myosin head distinguished at the same time, like a hinge or the weight of the boat turns, which leads to a slipping of muscle threads towards each other.
Making a turn, bridges between the threads are broken. The atpaz activity of myosin is sharply reduced, the hydrolysis of ATP is stopped. However, with further intake of the nerve pulse, the transverse bridges are re-formed, since the process described above is repeated again.
In each cycle of the reduction, 1 ATP molecule is consumed.
The basis of muscle contraction is two processes:
spiral twisting of contractile proteins;
cyclically repeated formation and dissociation of the complex between the chain of myosin and actin.
Muscular reduction is initiated by the arrival of the potential of the action on the protector plate of the motor nerve, where neurogormon acetylcholine is released, the function of which is the transfer of pulses. First, acetylcholine interacts with acetylcholine receptors, which leads to the spread of the potential of action along the Sarchatim. All this causes an increase in the permeability of the Sarchatomma for Na + cations, which rush inside the muscular fiber, neutralizing a negative charge on internal surface Sarchatimmas. The sarcollama is associated with transverse tubes of sarcoplasmic reticulum, according to which the excitation wave is distributed. From the tubes, the excitation wave is transmitted to the membranes of bubbles and tanks that are powered by myofibrils in areas where the interaction of actin and alone yarns is interacted. When the signal is transmitted to the sarcoplasmic reticulum tanks, the latter begin to free the CA 2+ located in them. The released CA 2+ binds to the TN-C, which causes conformational shifts transmitted to tropomyosis and further to actin. Aktin, as it were, is released from the complex with the components of thin filaments in which it was located. Further, Aktin interacts with myosin, and the result of such an interaction is the formation of spikes, which makes the movement of thin threads along the thick.
The generation of force (shortening) is due to the nature of the interaction between the Mosin and Aktin. On the mosine rod there is a mobile hinge, in whose area there is a turn when binding to the globular head of myozin with a specific area of \u200b\u200bactin. It is such turns that occur simultaneously in numerous areas of interaction of myosin and actin are the cause of attaching actin filaments (thin threads) in the H-zone. Here they are in contact (with maximum shortening) or even overlap with each other, as shown in the figure.
in
Picture. Reduction mechanism: but- rest state; b.- moderate reduction; in- Maximum abbreviation
Energy for this process supplies hydrolysis ATP. When ATP joins the head of the molecule of myosin, where the active center of the mosic atphase is localized, the links between fine and thick threads are not formed. The calcium cation that appears neutralizes the negative ATF charge, contributing to approximately with the active center of the Mosinic ATPase. As a result, myosis phosphorylation occurs, i.e., myosin is charged with energy that is used to form a spike with actin and to advance the fine thread. After a thin thread is moved to one "step", ADP and phosphoric acid are cleaved from the actomyosine complex. Then a new ATP molecule is joined to the mosic head, and the whole process is repeated with the next head of the molecule of myozin.
ATP cost is necessary for muscle relaxation. After stopping the action of the SA 2+ motor pulse, goes into the tanks of sarcoplasmic reticulum. TN-C loses the associated calcium, the consequence of this is the conformations-on-one in the Troponin-Tropomyozin complex, and the TN-I again closes the active acts centers, making them unable to interact with myosin. The concentration of Ca 2+ in the region of contracting proteins becomes below the threshold, and muscle fibers lose the ability to form actomiosis.
Under these conditions, the elastic forces of stroma deformed at the time of abbreviation take the top, and the muscle is relaxing. In this case, thin threads are extracted from the space between the thick threads of the disk A, the zone N and the disk I acquire the initial length, the Z lines are distinguished from each other for the same distance. The muscle becomes thinner and longer.
Hydrolysis speed ATFwith muscular work is huge: up to 10 mK mole per 1 g of muscles for 1 min. General stocks ATFsmall, so to ensure normal muscles ATFshould be recovered at the same speed, which it is spent.
Muscle relaxationcomes after stopping the receipt of a long nerve impulse. At the same time, the permeability of the sarcoplasmic network tank wall decreases, and calcium ions under the action of a calcium pump using ATP energy, go into tanks. The removal of calcium ions into the reticulum tanks after the termination of the motor pulse requires significant energy. Since the removal of calcium ions occurs in the direction of a higher concentration, i.e. Against the osmotic gradient, then two ATP molecules spend on the removal of each calcium ion. The concentration of calcium ions in sarcoplasm is quickly reduced to the initial level. Proteins again acquire the conformation characteristic for the state of rest.