Whatever a person does - walking, running, driving a car, digging the ground, writing - he performs all his actions with the help of skeletal muscles. These muscles are the active part of the musculoskeletal system. They hold the body in an upright position, allow you to take a variety of poses. The abdominal muscles support and protect the internal organs, i.e. perform supporting and protective functions. Muscles are part of the walls of the chest and abdominal cavities, the walls of the pharynx, provide movements of the eyeballs, auditory ossicles, respiratory and swallowing movements. This is only a partial list of skeletal muscle functions.

Therefore, it is not surprising that the mass of skeletal muscles in an adult is 30-35% of body weight. A person has more than 600 skeletal muscles, they are formed by striated muscle tissue.

1 - Scheme of the structure of the muscle fiber:

a - myofibril

2 - Scheme of the structure of myofibrils:

a - shell

b - myosin

g - a bridge between them

d - nerve fiber

Each muscle consists of parallel bundles of striated muscle fibers. Each bundle is dressed in a sheath. And the whole muscle is covered on the outside with a thin connective tissue sheath that protects the delicate muscle tissue. Each muscle fiber also has a thin shell on the outside, and inside it there are numerous thin contractile filaments - myofibrils and a large number of nuclei. Myofibrils, in turn, consist of the thinnest filaments of two types - thick (myosin protein molecules) and thin (actin protein). Because they are educated various types protein, under the microscope, alternating dark and light stripes are visible. Hence the name skeletal muscle tissue- cross-striped. In humans, skeletal muscle consists of two types of fibers - red and white. They differ in the composition and number of myofibrils, and most importantly, in the features of contraction. The so-called white muscle fibers contract quickly, but quickly get tired; red fibers contract more slowly, but may remain contracted for a long time. Depending on the function of the muscles, certain types of fibers predominate in them. Muscles do a lot of work, so they are rich in blood vessels, through which blood supplies them with oxygen, nutrients, and removes metabolic products. Muscles are attached to bones by inextensible tendons that fuse with the periosteum. Usually, the muscles are attached at one end above, and at the other below the joint. With this attachment, muscle contraction sets the bones in motion at the joints.

Depending on the location of the muscles, they can be divided into the following large groups: muscles of the head and neck, muscles of the trunk and muscles of the limbs.

1. Superficial finger flexor.

2. Large pectoral muscle.

3. Deltoid muscle.

4. The biceps of the shoulder.

5. Fibrous plate.

6. Radial flexor of fingers.

7. Serratus anterior.

8. Quadriceps muscle.

9. Sartorius hips.

10. Tibialis anterior.

11. Cruciate muscle.

12. Calf muscle.

13. Biceps muscle.

14. Gluteus maximus.

15. External oblique abdominal muscle.

16. Triceps of the shoulder.

17. Biceps femoris.

18. Deltoid muscle.

19. Trapezius muscle.

20. Infraspinatus muscle.

21. Rhomboid muscle.

22. Biceps muscle of the shoulder.

The muscles of the trunk include the muscles of the back, chest and abdomen. There are superficial muscles of the back (trapezius, latissimus dorsi, etc.) and deep muscles of the back. The superficial muscles of the back provide movement for the limbs and partly for the head and neck; deep muscles are located between the vertebrae and ribs and, when contracted, cause extension and rotation of the spine, maintain the vertical position of the body.

The chest muscles are divided into those attached to the bones of the upper limbs (pectoralis major and minor, serratus anterior, etc.), which move the upper limb, and the chest muscles proper (pectoralis major and minor, serratus anterior, etc.), which change the position of the ribs and thereby providing the act of breathing. This group of muscles also includes the diaphragm, located on the border of the chest and abdominal cavity. Aperture - respiratory muscle. When contracting, it descends, its dome flattens (volume chest increases - inhalation occurs), when relaxed, it rises and takes the form of a dome (the volume of the chest decreases - exhalation occurs). The diaphragm has three openings - for the esophagus, aorta and inferior vena cava.

The muscles of the upper limb are divided into muscles shoulder girdle and free upper limb. The muscles of the shoulder girdle (deltoid, etc.) ensure the movement of the arm in the area of ​​the shoulder joint and the movement of the scapula. The muscles of the free upper limb contain the muscles of the shoulder (the anterior group of flexor muscles in the shoulder and elbow joint- biceps muscle of the shoulder, etc.); the muscles of the forearm are also divided into two groups (anterior - flexors of the hand and fingers, back - extensors); hand muscles provide a variety of finger movements.

The muscles of the lower limb are divided into the muscles of the pelvis and the muscles of the free lower limb (muscles of the thigh, lower leg, foot). The pelvic muscles include the iliopsoas, large, middle and small gluteal, etc. They provide flexion and extension in the hip joint, as well as maintaining the vertical position of the body. There are three muscle groups on the thigh: anterior ( quadriceps hips and others extend the lower leg and flex the thigh), posterior (biceps femoris and others extend the lower leg and flex the thigh) and internal group of muscles that bring the thigh to the midline of the body and flex hip joint. Three groups of muscles are also distinguished on the lower leg: anterior (unbend the fingers and foot), posterior (calf, soleus, etc., flex the foot and fingers), external (bend and abduct the foot).

Among the muscles of the neck, superficial, middle (muscles of the hyoid bone) and deep groups are distinguished. Of the superficial, the largest sternocleidomastoid muscle tilts back and turns the head to the side. The muscles located above the hyoid bone form the lower wall of the oral cavity and lower the lower jaw. The muscles located below the hyoid bone lower the hyoid bone and provide mobility to the cortan cartilage. deep muscles the necks tilt or turn the head and raise the first and second ribs, acting as breathing muscles.

The muscles of the head make up three groups of muscles: chewing, facial and voluntary muscles. internal organs head (soft palate, tongue, eyes, middle ear). Chewing muscles move the lower jaw. Mimic muscles are attached at one end to the skin, the other - to the bone (frontal, buccal, zygomatic, etc.) or only to the skin ( circular muscle mouth). By contracting, they change the expression of the face, participate in the closing and expansion of the openings of the face (eye sockets, mouth, nostrils), provide mobility for the cheeks, lips, nostrils.

Muscles, contracting or tensing, produce work. It can be expressed in the movement of the body or its parts. Such work is done by lifting weights, walking, running. This is dynamic work. When holding parts of the body in a certain position, holding a load, standing, maintaining a pose, static work is performed. The same muscles can perform both dynamic and static work. By contracting, the muscles move the bones, acting on them as levers. The bones begin to move around the fulcrum under the influence of the force applied to them. Movement in any joint is provided by at least two muscles acting in opposite directions. They are called flexor muscles and extensor muscles. For example, when the arm is flexed, the biceps brachii contracts and the triceps relaxes. This is because stimulation of the biceps through the central nervous system causes relaxation of the triceps. Skeletal muscles are attached on both sides of the joint and, when contracted, produce movement in it. Usually, the muscles that perform flexion - flexors - are located in front, and those that produce extension - extensors - are behind the joint. Only in the knee ankle joints the anterior muscles, on the contrary, produce extension, and the posterior muscles produce flexion. The muscles lying outside (laterally) from the joint - abductors - perform the function of abduction, and those lying medially (medially) from it - adductors - adduction. Rotation is produced by muscles located obliquely or transversely with respect to the vertical axis (pronators - rotating inwards, arch supports - outwards). Several muscle groups are usually involved in the implementation of the movement. Muscles that simultaneously produce movement in one direction in a given joint are called synergists (shoulder, biceps shoulder); muscles that perform the opposite function (biceps, triceps muscle of the shoulder) - antagonists. The work of various muscle groups occurs in concert: for example, if the flexor muscles contract, then the extensor muscles relax at this time. "Start up" the muscles in the course of nerve impulses. An average of 20 impulses per second enters one muscle. In each step, for example, up to 300 muscles take part and many impulses coordinate their work. The number of nerve endings in different muscles is not the same. There are relatively few of them in the thigh muscles, and the oculomotor muscles, which make subtle and precise movements all day long, are rich in motor nerve endings. The cerebral cortex is unevenly connected with individual muscle groups. For example, huge areas of the cortex are occupied by motor areas that control the muscles of the face, hand, lips, and foot, and relatively small areas are occupied by the muscles of the shoulder, thigh, and lower leg. The size of individual zones of the motor area of ​​the cortex is proportional not to the mass of muscle tissue, but to the subtlety and complexity of the movements of the corresponding organs. Each muscle has a double nerve subordination. One nerve sends impulses from the brain and spinal cord. They cause muscle contraction. Others, moving away from the nodes that lie on the sides of the spinal cord, regulate their nutrition. The nerve signals that control the movement and nutrition of the muscle are consistent with the nervous regulation of the blood supply to the muscle. It turns out a single triple nervous control.

But, in addition to skeletal muscles, in our body in the connective tissue there are smooth muscles in the form of single cells. In some places they are collected in bunches. Many smooth muscles in the skin, they are located at the base of the hair bag. By contracting, these muscles raise the hair and squeeze out fat from the sebaceous gland. In the eye around the pupil are smooth circular and radial muscles. They work all the time: in bright light, the circular muscles constrict the pupil, and in the dark, the radial muscles contract and the pupil expands. In the walls of all tubular organs - the respiratory tract, blood vessels, digestive tract, urethra, etc. - there is a layer of smooth muscles. Under the influence of nerve impulses, it is reduced. Due to the contraction and relaxation of the smooth cells of the walls of blood vessels, their lumen either narrows or expands, which contributes to the distribution of blood in the body. The smooth muscles of the esophagus, contracting, push a lump of food or a sip of water into the stomach. Complex plexuses of smooth muscle cells are formed in organs with a wide cavity - in the stomach, bladder, uterus. The contraction of these cells causes compression and narrowing of the lumen of the organ. The strength of each cell contraction is negligible, because. they are very small. However, the addition of the forces of entire beams can create a contraction of enormous force. Powerful contractions create a sensation of intense pain. Excitation in smooth muscles spreads relatively slowly, which leads to slow long-term contraction of the muscle and an equally long period of relaxation. Muscles are also capable of spontaneous rhythmic contractions. The stretching of the smooth muscles of the hollow organ when filled with its contents immediately leads to its contraction - this ensures that the contents are pushed further.

Age-related changes in the muscular system

Of course, as we age, our body changes. The musculoskeletal system also changes. In an adult, skeletal muscles make up more than 40% of body weight. With aging, the intensity of muscle mass reduction is more pronounced than the decrease in body weight as a whole. The shape of the muscle changes with age due to its reduction and the corresponding elongation of the tendon. In particular, the length of the Achilles tendon increases from 3.5-4 cm in young people to 6-9 cm in old people. A progressive increase in muscle hypotrophy with age occurs differently in functionally different muscle groups. A similar process develops mainly due to a decrease in the diameter of individual muscle fibers. Yes, muscle fiber diameter chest muscle in young people it is 40-45 microns, at 50 years old - 20-25 microns, at 70 years old - 10-20 microns. Morphological studies different years showed that during aging in skeletal muscles, along with unchanged and compensatory hypertrophied muscle fibers, atrophied myons to varying degrees are found, focal disturbances in the clarity of transverse striation and an increase in the number of nuclei are noted. An electron microscopic examination reveals a violation of the architectonics of the mutual arrangement of mitochondria and elements of the contractile substance. As in other organs, during aging, compensatory-adaptive rearrangements develop in skeletal muscles, manifested by an increase in the area of ​​nuclear membranes, hypertrophy of mitochondria and other organelles. In parallel with changes in muscle fibers, shifts occur in the wall of the blood capillaries that feed them, indicating altered conditions of transcapillary exchange, which, in turn, exacerbates disorders in muscle fibers. The process of regeneration of muscle elements in the old organism begins much later, and replacement with connective tissue earlier than in the young.

For a long time, there was an idea that during contraction, a muscle draws energy from its structure, collapsing. Then these views were supplanted by information about metabolic transformations in the process of muscle activity. At present, it is no longer possible to consider biochemical processes in muscle fibers, regardless of their structure, the metabolic cycle is rigidly tied to the place, and the sequence of transformations in it - to the structural features of the enzyme series.

Depending on the manifestation of the specific function of the muscles, physiological reversible destruction of their ultrastructure occurs in varying degrees of severity - degradation of mitochondria, contractures of individual myofilaments, capillary ruptures, and local violations of the integrity of T-systems. With intensive activity, pronounced damage to individual muscle fibers, microhemorrhages can be noted. It is extremely important to determine the age-related optimum of the contractile function to establish the reversibility limit of these disorders, since some breakdowns are restored without a trace, while others lead to a gradual loss of tissue specificity and subsequent sclerosis. The study of enzymatic activity in muscle tissue during aging showed the presence of very complex rearrangements aimed at maintaining the body's homeostasis.

Fundamentally important is the provision on primary neural age-related shifts during aging of neuro- muscular system, which lead to a deterioration in the connection between the nerve and muscle cells and determine senile changes in skeletal muscles, the least pronounced in the fibers of the diaphragm, which is associated with the primary regulatory influence of neural impulse activity, which is continuously forced during the act of breathing.

With aging, the complex of nervous mechanisms regulating the activity of motoneurons shifts to lower frequencies. The described changes depend on slowly progressive disorders of the neuromuscular contact, a decrease in the size of the senile motor unit, as well as the diameter of muscle fibers. In particular, the decrease in size (but not in the number of motor units) explains why no fibrillation potentials are found in senile muscles. The development of age-related changes in the motor unit, which is accompanied by a deterioration in the contractile properties of muscle fibers, is compensated by reinnervation, so their density in the motor unit increases with aging. Data on changes in the morphological and functional profile of skeletal muscles during aging of the body can to some extent explain the sensitivity of muscles to hypoxia at the later stages of ontogenesis. A kind of adaptation to this factor develops, which is expressed in a lower level of blood flow, which is necessary to maintain stable performance.

Age-related changes in the neuromuscular system are associated with characteristic shifts at all levels: from the muscle fiber to the nerve cells of the highest parts of the central nervous system. They depend on metabolic shifts in the body that increase with aging and are associated with a complex system of restructuring in the regulation of functions. In old age, the ability of the neuromuscular apparatus to adapt under the influence of physical training. Age-related changes in the cardiovascular and nervous systems, the musculoskeletal system lead to various pain sensations, physical weakness, mental fatigue, and slow motor skills. With age, muscles lose strength and atrophy.

Bibliography

1. Vasiliev A.N. The human muscular system. - M., 1998.
2. Shuvalova N.V. The structure of man. - M.: Olma-press, 2000.

In vertebrates and humans, there are three different muscle groups:

• striated muscles of the skeleton;
• striated muscle of the heart;
• smooth muscles of internal organs, blood vessels and skin.

Rice. 1. Types of human muscles

Smooth muscles

Of the two types of muscle tissue (striated and smooth), smooth muscle tissue is at a lower stage of development and is inherent in lower animals.

They form the muscular layer of the walls of the stomach, intestines, ureters, bronchi, blood vessels and other hollow organs. They consist of spindle-shaped muscle fibers and do not have transverse striation, since the myofibrils in them are located less ordered. In smooth muscles, individual cells are interconnected by special sections of the outer membranes - nexuses. These contacts propagate action potentials from one muscle fiber to another. Therefore, the entire muscle is quickly involved in the excitation reaction.

Smooth muscles carry out the movements of internal organs, blood and lymphatic vessels. In the walls of the internal organs, they, as a rule, are located in the form of two layers: the inner annular and the outer longitudinal. In the walls of the artery, they form spiral structures.

A characteristic feature of smooth muscles is their ability to spontaneous automatic activity (muscles of the stomach, intestines, gallbladder, ureters). This property is regulated by nerve endings. Smooth muscles are plastic, i.e. able to maintain the length given by stretching without changing the stress. Skeletal muscle, on the contrary, has low plasticity, and this difference can be easily established in the following experiment: if you stretch both smooth and striated muscles with the help of weights and remove the load, then the skeletal muscle immediately after this is shortened to its original length, and the smooth muscle for a long time may be stretched.

This property of smooth muscle is great importance for the functioning of internal organs. It is the plasticity of smooth muscles that provides only a small change in pressure inside the bladder when it is filled.

Rice. 2. A. Skeletal muscle fiber, cardiac muscle cell, smooth muscle cell. B. Skeletal muscle sarcomere. B. The structure of smooth muscle. D. Mechanogram of skeletal muscle and heart muscle.

Smooth muscles have the same basic properties as striated skeletal muscles, but some special properties:

• automation, i.e. the ability to contract and relax without external stimuli, but due to excitations that arise in themselves;
• high sensitivity to chemical irritants;
• pronounced plasticity;
• contraction in response to rapid stretching.

Contraction and relaxation of smooth muscles occurs slowly. This contributes to the onset of peristaltic and pendulum movements of the organs of the digestive tract, which leads to the movement of the food bolus. Prolonged contraction of smooth muscles is necessary in the sphincters of hollow organs and prevents the release of contents: bile into gallbladder, Urine In The Bladder. The contraction of smooth muscle fibers occurs regardless of our desire, under the influence of internal, not subject to consciousness causes.

striated muscles

striated muscles are located on the bones of the skeleton and by contraction set in motion individual joints and the whole body. form a body, or soma, therefore they are also called somatic, and the system that innervates them - the somatic nervous system.

Thanks to the activity of the skeletal muscles, the movement of the body in space, the various work of the limbs, the expansion of the chest during breathing, the movement of the head and spine, chewing, and facial expressions are carried out. There are over 400 muscles. The total muscle mass is 40% of the weight. Usually the middle part of the muscle consists of muscle tissue and forms the abdomen. The ends of the muscles - tendons are built from dense connective tissue; they are connected to the bones with the help of the periosteum, but can be attached to another muscle, and to the connective layer of the skin. In the muscle, muscle and tendon fibers are combined into bundles with the help of loose connective tissue. Between the bundles are nerves and blood vessels. proportional to the number of fibers that make up the belly of the muscle.

Rice. 3. Functions of muscle tissue

Some muscles pass through only one joint and, when contracted, set it in motion - single-joint muscles. Other muscles pass through two or more joints - multi-joint, they produce movement in several joints.

When the ends of the muscle attached to the bones approach each other, and the size of the muscle (length) decreases. Bones connected by joints act as levers.

By changing the position of the bone levers, the muscles act on the joints. In this case, each muscle affects the joint in only one direction. A uniaxial joint (cylindrical, block-shaped) has two muscles or groups of muscles acting on it that are antagonists: one muscle is a flexor, the other is an extensor. At the same time, as a rule, two or more muscles, which are synergists, act on each joint in one direction (synergism is a joint action).

At a biaxial joint (ellipsoid, condyle, saddle), the muscles are grouped according to its two axes, around which movements are made. To the spherical joint, which has three axes of movement (multiaxial joint), the muscles are adjacent from all sides. So, for example, in shoulder joint there are flexor and extensor muscles (movements around the frontal axis), abductor and adductor (sagittal axis) and rotators around the longitudinal axis, inward and outward. There are three types of muscle work: overcoming, yielding and holding.

If, due to muscle contraction, the position of a body part changes, then the resistance force is overcome, i.e. overcoming work is done. The work, in which the force of the muscle is inferior to the action of gravity and the load held, is called yielding. In this case, the muscle functions, but it does not shorten, but lengthens, for example, when it is impossible to lift or hold a body with a large mass. With a great effort of the muscles, this body has to be lowered onto some surface.

Holding work is performed due to muscle contraction, the body or load is held in a certain position without moving in space, for example, a person holds a load without moving. In this case, the muscles contract without changing the length. The force of muscle contraction balances the mass of the body and the load.

When a muscle, contracting, mixes the body or its parts in space, they perform overcoming or yielding work, which is dynamic. Statistical is holding work, in which there is no movement of the whole body or part of it. The mode in which the muscle can freely shorten is called isotonic(there is no change in muscle tension and only its length changes). The mode in which the muscle cannot shorten is called isometric- only the tension of muscle fibers changes.

Rice. 4. Human muscles

The structure of striated muscles

Skeletal muscles consist of a large number of muscle fibers, which are combined into muscle bundles.

One bundle contains 20-60 fibers. Muscle fibers are cylindrical cells 10-12 cm long and 10-100 microns in diameter.

Each muscle fiber has a sheath (sarcolemma) and cytoplasm (sarcoplasm). In the sarcoplasm are all the components of the animal cell and thin threads are located along the axis of the muscle fiber - myofibrils, Each myofibril is made up of protofibrils, which include filaments of myosin and actin proteins, which are the contractile apparatus of the muscle fiber. Myofibrils are separated by partitions, which are called Z-membranes, into sections - sarcomeres. At both ends of the sarcomeres, thin actin filaments are attached to the Z-membrane, and thick myosin filaments are located in the middle. Actin filaments with their ends partially enter between myosin filaments. In a light microscope, myosin filaments look like a light strip in a dark disk. Under electron microscopy, skeletal muscles appear striated (striated).

Rice. 5. Cross bridges: Ak - actin; Mz - myosin; Gl - head; Ш - neck

On the sides of the myosin filament there are protrusions called cross bridges(Fig. 5), which are located at an angle of 120° with respect to the axis of the myosin filament. Actin filaments look like a double filament twisted into a double helix. In the longitudinal grooves of the actin helix are strands of the tropomyosin protein, to which the troponin protein is attached. At rest, tropomyosin protein molecules are arranged in such a way as to prevent myosin cross-bridges from attaching to actin filaments.

Rice. 6. A - the organization of cylindrical fibers in the skeletal muscle attached to the bones by tendons. B - Structural organization of filaments in a skeletal muscle fiber, creating a pattern of transverse bands.

Rice. 7. The structure of actin and myosin

In many places, the surface membrane deepens in the form of microtubes inside the fiber, perpendicular to its longitudinal axis, forming a system transverse tubules(T-system). Parallel to the myofibrils and perpendicular to the transverse tubes between the myofibrils is a system longitudinal tubules(sarcoplasmic reticulum). The end extensions of these tubes are terminal tanks - come very close to the transverse tubules, forming together with them the so-called triads. The main amount of intracellular calcium is concentrated in the cisterns.

Mechanism of skeletal muscle contraction

Muscle is made up of cells called muscle fibers. Outside, the fiber is surrounded by a sheath - the sarcolemma. The sarcolemma contains cytoplasm (sarcoplasm) containing nuclei and mitochondria. It contains a huge amount of contractile elements called myofibrils. Myofibrils run from one end of a muscle fiber to the other. They exist relatively short term- about 30 days, after which their complete change takes place. In the muscles, there is an intensive protein synthesis necessary for the formation of new myofibrils.

muscle fiber contains a large number of nuclei, which are located directly under the sarcolemma, since the main part of the muscle fiber is occupied by myofibrils. It is the presence of a large number of nuclei that ensures the synthesis of new myofibrils. Such a rapid change of myofibrils ensures high reliability of the physiological functions of muscle tissue.

Rice. 7. A - scheme of organization of the sarcoplasmic reticulum, transverse tubules and myofibrils. B — diagram of the anatomical structure of the transverse tubules and sarcoplasmic reticulum in an individual skeletal muscle fiber. B - the role of the sarcoplasmic reticulum in the mechanism of skeletal muscle contraction

Each myofibril consists of regularly alternating light and dark areas. These areas, having different optical properties, create a transverse striation of the muscle tissue.

In a skeletal muscle, contraction is caused by an impulse sent to it along a nerve. The transmission of a nerve impulse from a nerve to a muscle is carried out through a neuromuscular synapse (contact).

A single nerve impulse, or a single irritation, leads to an elementary contractile act - a single contraction. The beginning of the contraction does not coincide with the moment of application of the irritation, since there is a latent or latent period (the interval between the application of the irritation and the beginning of the muscle contraction). During this period, the development of the action potential, the activation of enzymatic processes and the breakdown of ATP. After that, the contraction begins. The breakdown of ATP in muscle leads to the conversion of chemical energy into mechanical energy. Energy processes are always accompanied by the release of heat, and thermal energy is usually intermediate between chemical and mechanical energies. In the muscle, chemical energy is converted directly into mechanical energy. But heat in the muscle is formed both due to the shortening of the muscle, and during its relaxation. The heat generated in the muscles plays a large role in maintaining body temperature.

Unlike the heart muscle, which has the property of automation, i.e. it is able to contract under the influence of impulses that arise in itself, and unlike smooth muscles, which are also capable of contracting without receiving signals from the outside, the skeletal muscle contracts only when signals from it are received. Signals directly to muscle fibers come through the axons of motor cells located in the anterior horns of the gray matter of the spinal cord (motoneurons).

The reflex nature of muscle activity and coordination of muscle contractions

Skeletal muscles, unlike smooth muscles, are capable of making arbitrary rapid contractions and thereby producing significant work. The working element of a muscle is a muscle fiber. A typical muscle fiber is a structure with several nuclei pushed to the periphery by a mass of contractile myofibrils.

Muscle fibers have three main properties:

• excitability - the ability to respond to the actions of the stimulus by generating an action potential;
• conductivity - the ability to conduct a wave of excitation along the entire fiber in both directions from the point of irritation;
• contractility - the ability to contract or change voltage when excited.

In physiology, there is the concept of a motor unit, which means one motor neuron and all the muscle fibers that this neuron innervates. Motor units vary in volume, from 10 muscle fibers per unit for muscles that perform precise movements, to 1000 or more fibers per motor unit for "strength-oriented" muscles. The nature of the work of skeletal muscles can be different: static work (maintaining a posture, holding a load) and dynamic work (moving a body or load in space). Muscles are also involved in the movement of blood and lymph in the body, the production of heat, the acts of inhalation and exhalation, they are a kind of depot for water and salts, they protect internal organs, such as the muscles of the abdominal wall.

Skeletal muscle has two main modes of contraction - isometric and isotonic.

The isometric mode is manifested in the fact that during its activity tension increases in the muscle (force is generated), but due to the fact that both ends of the muscle are fixed (for example, when trying to lift a very large load), it does not shorten.

The isotonic regime is manifested in the fact that the muscle initially develops tension (force) capable of lifting a given load, and then the muscle shortens - changes its length, maintaining tension equal to the weight of the load being held. It is practically impossible to observe a purely isometric or isotonic contraction, but there are methods of the so-called isometric gymnastics when the athlete tenses the muscles without changing the length. These exercises develop muscle strength to a greater extent than exercises with isotonic elements.

The contractile apparatus of skeletal muscle is represented by myofibrils. Each myofibril with a diameter of 1 micron consists of several thousand protofibrils - thin, elongated polymerized molecules of myosin and actin proteins. Myosin filaments are two times thinner than actin filaments, and at rest of the muscle fiber, actin filaments enter in free rings between myosin filaments.

In the transfer of excitation, calcium ions play an important role, which enter the interfibrillar space and trigger the contraction mechanism: mutual retraction of actin and myosin filaments relative to each other. Thread retraction occurs with the obligatory participation of ATP. In the active centers located at one of the ends of the myosin filaments, ATP is split. The energy released during the breakdown of ATP is converted into motion. In skeletal muscle, the supply of ATP is small - only 10 single contractions. Therefore, a constant resynthesis of ATP is necessary, which goes in three ways: the first is due to the reserves of creatine phosphate, which are limited; the second is the glycolytic pathway during the anaerobic breakdown of glucose, when two ATP molecules are formed per glucose molecule, but lactic acid is simultaneously formed, which inhibits the activity of glycolytic enzymes, and finally the third is the aerobic oxidation of glucose and fatty acids in the Krebs cycle, which occurs in mitochondria and forms 38 ATP molecules per 1 glucose molecule. The last process is the most economical, but very slow. Constant training activates the third oxidation pathway, resulting in increased muscle endurance to prolonged stress.

The muscular system is one of the most important biological subsystems with which the body performs various movements.

It can be represented as a collection of muscle fibers capable of contraction. The fibers are interconnected into bundles that form the muscles as special organs, or they themselves enter the internal organs. much higher than other organs: in some animals it is 50 percent of the total body weight, and in humans - 40 percent. The muscular system converts chemical energy into heat and

muscular musculature

In vertebrates, the muscular musculature is divided into the following groups:

• Somatic, containing the insides and forming the muscles of the limbs. It includes skeletal muscles.
• Visceral (part of the viscera). It is smooth and cardiac muscle.

The human muscular system

Skeletal muscles are random and striated. They are attached to the bones and are cylindrical fibers 1-10 cm long.

Each muscle fiber is an undifferentiated cytoplasm (sarcoplasm) with big amount nuclei located on the periphery. The periphery includes differentiated striated myofibrils. The periphery is surrounded by a transparent membrane (sarcolemma), which includes collagen fibrils. A small group of fibers is surrounded by endomysium; large muscle connections are bundles of fibers enclosed in an internal remysium; each muscle is surrounded by an external peremium. Muscular and connective tissues of each other continue and are interconnected. The entire muscle is enclosed in a sheath called fascia. The muscular system consists of muscles, each of which is connected to and permeated by nerves and blood vessels.

Muscles help maintain the balance of the body, carry out movement in space and the vital movements of all parts of the body.

Smooth muscles located in the walls of blood vessels and internal organs. The length of the muscles of this species is 0.02-0.2 mm. They are devoid of striation, their shape resembles a spindle. Smooth muscle cells have an oval nucleus in the center.

Smooth muscles help transport what is contained in hollow organs (food in the intestines, for example). They are involved in the regulation of pressure, expansion and other movements in the body. The autonomic nervous system is responsible for the contraction of smooth muscles.

The muscular system also includes heart muscle, which is found only in the heart walls. It is continuously reduced throughout life, providing blood circulation through the vessels and nourishing the tissues and organs with the necessary substances.

Musculoskeletal system

The human body contains about 400 striated muscles, which contract under the control of the central nervous system.

Includes muscles, bones, tendons, joints, ligaments and cartilage, which make up almost 75% of a person's weight. This system gives the human body a certain shape, allows it to stand and move. The bone skeleton serves as a framework for organs and tissues, it also reliably protects important organs from damage. Minerals such as phosphorus and calcium accumulate in the bones. The inside of the bones is represented by participating in the formation of all blood cells (erythrocytes, leukocytes and platelets).

In case of injuries and diseases of any part of the musculoskeletal system, the statics and dynamics of the whole organism are disturbed. In addition to the fact that the entire musculoskeletal system suffers, the internal organs also cease to function correctly. For example, when one of the limbs is shortened, the spine is bent, which causes deformation of the chest, as a result, breathing also suffers.

structures of the bones of the skull; 5) connection of bones.

Formulation of the protocol. Draw preparations, put the appropriate labels.

MUSCULAR SYSTEM

The muscular system is the active part of the human musculoskeletal system, and the bones and ligaments make up its passive part. With the help of the muscular system and bones, the position of the human body in space changes, respiratory and swallowing movements are carried out, and facial expressions are formed. Skeletal muscles (Fig. 53) are involved in the formation of the oral, thoracic, abdominal and pelvic cavities; are part of the walls of hollow organs (pharynx, larynx, etc.); cause a change in the position of the eyeball in the orbit; affect the auditory ossicles in the tympanic cavity of the middle ear. Muscular activity not only provides movement, but also affects blood circulation, development and shape of bones. Systematic muscle loads promote growth muscle mass by increasing the structures that make up the muscles.

Rice. 53. Scheme of skeletal muscle:

A - muscle fibers are attached to the tendons; B - a separate fiber, consisting of myofibrils; B - a separate myofibril: alternation of light actin I-disks and dark myosin A-disks; the presence of H-zone and M-line; D- transverse bridges between thick myosin and thin actin filaments

Skeletal muscles in newborns and children make up about 20-25% of body weight, while in adults - up to 40%, and in the elderly and old people - up to 25-30%. More than half of all muscles are located in the head and trunk, and 20% - on the upper limbs. There are about 400 muscles in the human body, which consist of striated muscle tissue and have an arbitrary

reduction.

MUSCLE CONSTRUCTION

Muscle (musculus) as an organ consists of muscle tissue, loose and dense connective tissue, vessels and nerves, has a certain shape and performs a function corresponding to it.

The basis of the muscle is formed by thin bundles of transversely dosal muscle fibers, which are covered from above with a connective tissue sheath - endomysium. Larger bundles are separated from one another by the perimysium, and the entire muscle is surrounded by the epimysium, which then passes into the tendon and is called

peritendinia.

Loose connective tissue forms a soft muscle skeleton, from which muscle fibers originate, and dense tissue forms the tendon ends of the muscle. About 1/3 of the fibers are attached to the bones, and 2/3 are supported by the connective tissue formations of the muscles. Muscle bundles form a fleshy abdomen, which can actively contract, and then, passing into the tendon, is attached to the bones. The initial part of the muscles, especially the long ones, is also called the head, and the end - the tail.

tendons in different muscles unequal in size. They are longest in the muscles of the limbs. The muscles that make up abdominal wall, have a wide flat tendon - aponeurosis.

The digastric muscle has an intermediate tendon, between the two abdomens, or several short tendons that interrupt the course of muscle bundles (for example, in the rectus abdominis muscle). The tendon is much thinner than the muscle, but its strength is very high. So the heel (Achilles) tendon can withstand a load of about 500 kg, and the tendon of the quadriceps femoris muscle - 600 kg.

The blood supply and innervation of the muscle is carried out from the inside of the muscle, where capillaries and nerve fibers that carry motor impulses go to each muscle fiber.

There are sensitive nerve endings in the tendons and muscles.

TO MUSCLE LASSIFICATION

Human muscles are classified according to their shape, position on the body, the direction of the fibers, the function performed, in relation to the joints, etc. (Table 3).

Table 3

The shape of the muscles depending on the location of the muscle fibers to the tendon

	Relative to		Towards		Towards
	to the joints	location in		performed		body parts
		human body
	Single joint	Surface	Circular	Respiratory
Short	Biarticular	deep	Parallel	Chewable
	Polyarticular		ribbon-like	Mimic	Torso:
			Fusiform
	Flexors		jagged
	Extensors
	Diverting				Of course
	Leading
	Arch supports		2) bipinnate;
	Pronators		3) multi-pinnate
	Sphincters
	Extenders

The shape of the muscles can be very diverse, it depends on the location of the muscle fibers to the tendon (Fig. 54).

Rice. 54. Muscle Shape:

A - spindle-shaped; B - biceps muscle; B - digastric muscle; G- muscle with tendon bridges; D - two-pinnate muscle; E - unipennate muscle; 1- belly muscle; 2, 3 - muscle tendons; 4 - tendon jumper; 5 - intermediate tendon

The fusiform muscles are more common. In them, the fiber bundles are oriented parallel to the long axis of the muscle, and the abdomen, gradually narrowing, passes into the tendon. Muscles in which muscle fibers are attached to the tendon on only one side are called unipennate, and on both sides

Two-pinnate. Muscles can have one or more heads, hence the name: biceps, triceps, quadriceps. Some muscle fibers are located circularly and form sphincter muscles that surround the oral and anal openings, etc.

The name of the muscle can reflect its shape (rhomboid, trapezoid, square), size (long, short, large, small), the direction of the muscle bundles or the muscle itself (oblique, transverse), its function (flexion, extension, rotation, lifting).

In relation to the joints, the muscles are located differently, which is determined by their structure and function. If the muscles act on one joint, they are called single-joint, but if they are thrown over two or more joints, they are called bi-articular and multi-articular. Some muscles may originate from bones and attach to bones without being joined by joints (eg, hyoid, maxillohyoid, facial muscles, floor of the mouth, perineal muscles).

IN AUXILIARY DEVICE AND WORK OF MUSCLES

Muscles are equipped with various formations (auxiliary apparatus), which create favorable conditions for their contraction. The auxiliary apparatus includes fascia (ligaments), tendon sheaths, synovial bags and muscle blocks of the sesamoid bone. Fascia is a connective tissue sheath of a muscle that forms a case for it, separates one from the other, reduces muscle friction, and forms a support for the abdomen during contraction. Distinguish fascia proper and superficial. Each area has own fascia(for example, shoulder, forearm), but if the muscles lie in several layers, then they have a deep fascia. superficial fascia is located under the skin and covers the entire muscle group, and the deep one is deeper and surrounds special muscles and muscle groups. Intermuscular partitions usually pass between muscle groups. Muscles that perform a large load have a denser fascia, reinforced with tendon fibers (for example, fascia of the thigh, fascia of the lower leg), and muscles with a small load have a loose, fragile fascia. In some places, thickening of the fascia is observed: tendon arches located above the underlying neurovascular bundles. Fascia in

the area of ​​some compounds (ankle, wrist) has a thickening and forms a fibrous bridge - a muscle retainer, which creates an appropriate direction of movement for the tendons.

tendon sheath creates conditions for unhindered movement of tendons; it has a closed slit-like cavity bounded by two sheets and filled with liquid inside.

In places where the tendons or muscle are thrown over the bone or muscle, there are synovial bags, which perform the same functions as the vagina. The synovial sac is shaped like a flat connective sac with fluid inside. On the one hand, the wall of the bag fuses with a movable organ (muscle), and on the other, with a bone or tendon.

If the synovial bag lies between the tendon and the bone protrusion covered with cartilaginous tissue, then a so-called muscle block is formed, which changes the direction of the tendon, serves as a support for it, and increases the leverage for applying force. The same function is performed by sesamoid bones (patella, pisiform bone).

Contracting under the influence of nerve impulses, the muscles act through the joints on the bones and change their movement. In a uniaxial joint (cylindrical, blocky), movement occurs only around one axis. If the muscles surround the joint from two sides and participate in two directions, flexion and extension or adduction and abduction occur. Muscles that act in opposite directions are called antagonists, and muscles that act in the same direction are called synergists.

Since the muscle is attached to the bones, its ends approach each other during contraction; thus the muscle performs the corresponding work. In this case, the position of the body or its part in space changes, the force of gravity is overcome. In this regard, there are overcoming, holding and yielding muscle work.

Overcoming work performed in the event that the force of muscle contraction changes the position of the body or part of it with overcoming the forces of resistance.

Holding job called the work in which the strength of the muscles holds the body or load in the appropriate position without movement in space.

Yielding work work is considered in which the muscle strength is inferior to the action of the gravity of the body part (limb) and the load holding it.

The bones connected by the joints act as levers when the muscles contract. Depending on the location of the acting forces relative to the fulcrum, two types of levers are distinguished.

The lever of the first kind is two-armed if the fulcrum is in the middle between the points of application of forces, for example, the connection of the spine with the skull (Fig. 55).

Rice. 55. Balance lever:

The lever of the second kind is single-armed. It is of two types. The first type - the lever of force - takes place if the shoulder for applying muscle force is longer than the shoulder for resistance (Fig. 56).

Rice. 56. Lever of Power:

A - fulcrum; B - point of application of force; B - point of resistance

In another type of single-arm lever - the speed lever - the shoulder for applying muscle force is shorter than the resistance shoulder, where the opposing force, gravity, is applied (Fig. 57). Muscle strength depends on anatomical, physiological and other factors.

The muscular system consists of approximately 600 muscles that ensure the movement of the body in space, maintaining posture, the processes of breathing, chewing, swallowing, speech, participating in the work of internal organs, blood circulation, thermoregulation, metabolism, and also playing an important role in a person's perception of the position of the body and its parts in space. The muscle is a holistic organ, consisting of striated muscle tissue, as well as dense and loose connective tissue. The innervation and blood supply of the muscle is provided by the vessels and nerves passing through it.

In the structure of the muscle, the abdomen and tendon are distinguished (Fig. 3.13). The muscle belly serves for contraction and consists of bundles of striated muscle tissue - muscle fibers that run parallel to each other and are interconnected by loose connective tissue. The connective tissue located between the muscle bundles, but at the ends of the muscle abdomen, passes into the tendon - the passive part of the muscle, with which it is attached to the bones. The abdomen of the muscle has a red-brown color, the tendon, consisting of dense connective tissue, has a brilliant light golden color and is located at both ends of the muscle. It is dense, contains few blood vessels and has more low level metabolism. Most of the tendons extend from the head of the muscle in the form of white strands and firmly hold the tendon to the bone, penetrating the periosteum and attaching to the compact layer of the bone. The long tendons of the hand or foot are surrounded by a sheath that contains an oily synovial fluid. It lubricates the tendons, making it easier to glide when the muscles of the forearm or calf pull on the fingers or toes. Flat-shaped tendons that not only connect muscles to bones, but also muscles to each other (for example, joints facial muscles) are called aponeuroses. Some muscles do not have tendons, they start from the bone and are attached to it by the abdomen (such muscles are called sessile).

Rice. 3.13.

The main properties of muscle tissue - contractility, excitability And elasticity - inherent in the muscle as an organ. Muscle contractility is regulated by the nervous system. Muscles contain nerve endings - receptors and effectors. Receptors - sensitive nerve endings that perceive the degree of contraction and stretching of the muscle, speed, acceleration, force of movement. They can be free (in the form of terminal branches of the sensory nerve) or non-free (in the form of a complexly built neuromuscular spindle). From the receptors, information about the state of the muscle and the implementation of the motor program enters the central nervous system. Impulses from the central nervous system travel to the muscles through effectors, making them excited. Nerves that regulate metabolic processes and muscle tone at rest are also suitable for muscles. This relationship allows nervous system regulate the activity of muscles and metabolic processes in them and, ultimately, perform the tasks of adaptation and functioning in the environment.

The degree of muscle development depends on various factors: heredity, gender, physical activity, nutrition, etc. Regular physical activity leads to an increase in weight and muscle volume (the so-called functional hypertrophy).

Muscles are divided into topographic groups: muscles of the head, neck, back, chest, abdomen; muscles of the girdle of the upper limbs, shoulder, forearm, hand; muscles of the pelvis, thigh, lower leg, foot. In these groups, the anterior and posterior muscle groups, superficial and deep, external and internal muscles are distinguished. On fig. 3.14 shows the main muscles of the human body.

Rice. 3.14. :

• 1 – front view :
• 1 – frontal belly of the occipital-frontal muscle; 2 - circular muscle of the mouth; 3 – chin; 4 - sternohyoid; 5 - trapezoidal; 6 – triceps shoulder; 7 – straight abdomen; 8 – external oblique abdomen; 9 – radial flexor of the hand; 10 – stretching the wide fascia of the thigh; 11 – ilio-lumbar; 12 – scallop; 13 – long leading; 14 – tailor; 15 – straight thigh; 16 - tender; 17 – internal wide; 18 – diverting thumb; 19 - tendons of the long muscle, extensor fingers; 20 long muscle, extensor fingers; 21 - soleus; 22 – anterior tibial; 23 – gastrocnemius; 24 - outer wide; 25 – short muscle that extends the thumb; 26 – long muscle that abducts the thumb; 27 – ulnar extensor of the hand; 28 – short radial extensor of the hand; 29 – extensor of fingers; 30 – long radial extensor of the hand; 31 – brachioradial; 32 – triceps shoulder; 33 - anterior gear; 34 – double-headed shoulder; 35 – large chest; 36 – deltoid; 37 – front staircase; 38 – middle staircase; 39 – sternocleidomastoid; 40 – lowering the corner of the mouth; 41 – chewing; 42 – large zygomatic; 43 – temporal;
• 2 – back view :
• 1 – occipital belly of the occipital-frontal muscle; 2 – trapezoidal; 3 – deltoid; 4 – triceps shoulder; 5 - two-headed shoulder; 6 – round pronator; 7 and 23 – brachioradial; 8 – radial flexor of the hand; 9 – long palmar; 10 – ulnar flexor of the hand; 11 – superficial finger flexor; 12 And 16 – semimembranous; 13 – semitendinous; 14 – tender; 15 – biceps thigh; 17 – gastrocnemius; 18 – soleus; 19 – large gluteal; 20 – short muscle that abducts the thumb; 21 – middle gluteal; 22 – external oblique abdomen; 24 – latissimus dorsi; 25 – anterior dentate; 26 – big round; 27 – small round; 28 – infraspinatus; 29 – sternocleidomastoid; 30 – belt head; 31 – chewing; 32 – semi-spinous head; 33 – temporal

The action of skeletal muscles is carried out according to the laws of levers and is aimed at changing the position of a body part in space or in counteracting the forces of gravity while maintaining a static posture. Muscle tendons are attached to different bones, muscle contraction leads to a change in the position of the bone or, conversely, to its retention in a certain position. Any movement is carried out not by one, but by several muscles, the action of which can be unidirectional (muscles -synergists ) or multidirectional (muscles- antagonists). A complex set of muscle contractions leads to a smooth and coordinated movement. The muscles that provide certain movements are called the functional group. For example, a group of muscles that flex a joint works simultaneously with a group of muscles that extend a joint, and the action of any muscle can occur only with simultaneous relaxation of the antagonist muscle. This consistency is called muscle coordination. For example, the coordinated work of paired antagonists of the biceps and triceps of the shoulder allows you to raise and lower your arms, bend and unbend them at the elbow (Fig. 3.15).

Rice. 3.15.

Muscles have an intensive metabolism, so they have a well-developed blood circulation, through which oxygen, nutrients and biologically active substances are delivered to the muscles, metabolic products and carbon dioxide are removed. The blood flow in the muscle is continuous, but its activity depends on the nature and intensity of the work of the muscle. In the absence of muscle load, about a third of all capillaries function; with its increase, their number increases significantly. Determined that large muscles organisms are "helpers" of the heart, acting as a pump in the movement of blood through the vessels. Therefore, the load on the heart muscle during physical activity in people with a well-developed muscular system is less than in untrained people.

In the body, each skeletal muscle is always in a state of a certain tension, readiness for action, which is called muscle tone. In children, muscle tone is lower than in adults, in women it is lower than in men, and in all it largely depends on fitness.

The influence of the load on the human muscular apparatus

The load has a shaping effect on the muscles. Strengthened muscle work contributes to an increase in the mass of muscle tissue, a certain degree of which is called muscle hypertrophy. Depending on the characteristics of physical activity, a significant part of the muscles of the body or their individual groups can become hypertrophied. This phenomenon is based on an increase in the mass of muscle fibers and the number of myofibrils contained in them, which leads to an increase in muscle diameter, activation of metabolic processes, an increase in strength and speed of contraction, and the total muscle mass in trained people can reach 50% of body weight instead of the usual 30– 40%.

The opposite process is muscle atrophy, which develops with prolonged inactivity: with damage to the tendon or nerve, the application of plaster on the limb, a long stay in bed due to illness. The diameter of muscle fibers and the activity of metabolic processes in them decrease during atrophy. After the resumption of muscle activity, atrophy gradually disappears.

Fatigue - a temporary decrease in the efficiency of the body or any organ, which occurs as a result of work and disappears after rest. Muscle fatigue during prolonged exercise is caused by the depletion of energy reserves in the muscle tissue necessary for muscle fiber contraction and the accumulation of "waste" that does not have time to be excreted - metabolic products that inhibit the activity of muscle fibers. In addition, an important role is played by fatigue that occurs in the nerve centers that control the work of this muscle group. In the works of I. M. Sechenov (1903) it was shown that restoration is best achieved not with passive, but with outdoor activities(change of activity).

The fatigue of a child is directly dependent on age and is due to the age-related characteristics of nervous activity, since the muscle itself can contract without fatigue for quite a long time. In infancy, the time of active mobile wakefulness is about 1.5–2 hours, then it increases slightly. It can develop and, if necessary, slow down motor activity for a long time. The restoration of muscle performance during rest occurs most quickly at the age of 7–9 years, during the puberty period (by the age of 13–15) it decreases and again increases by the age of 16–18. Muscle adaptation to physical activity against the background of growing fatigue is called endurance, it also undergoes certain changes in ontogeny: the greatest increase in endurance with muscle load is observed at 7–10 years old, in boys at 17 years old endurance is twice as high as at 7 years old, by the end of puberty adolescents’ endurance reaches 85% of the value of this indicator in adults, the peak of endurance occurs at the age of 20-29 years, then it gradually decreases and by the age of 70 is approximately 25% of the maximum level.