Internal organs, skin, blood vessels.

Skeletal muscles together with the skeleton they form the musculoskeletal system of the body, which ensures the maintenance of posture and movement of the body in space. In addition, they perform a protective function, protecting internal organs from damage.

Skeletal muscles are an active part of the musculoskeletal system, which also includes bones and their joints, ligaments, and tendons. Muscle mass can reach 50% of total body weight.

From a functional point of view, the motor system also includes motor neurons that send nerve impulses to muscle fibers. The bodies of motor neurons that innervate skeletal muscles with axons are located in the anterior horns of the spinal cord, and those innervating the muscles of the maxillofacial region are located in the motor nuclei of the brain stem. The axon of a motor neuron branches at the entrance to the skeletal muscle, and each branch participates in the formation of the neuromuscular synapse on a separate muscle fiber (Fig. 1).

Rice. 1. Branching of the motor neuron axon into axon terminals. Electron diffraction pattern

Rice. The structure of human skeletal muscle

Skeletal muscles are made up of muscle fibers that are organized into muscle bundles. The set of muscle fibers innervated by the axon branches of one motor neuron is called a motor (or motor) unit. In the eye muscles, 1 motor unit can contain 3-5 muscle fibers, in the trunk muscles - hundreds of fibers, in the soleus muscle - 1500-2500 fibers. The muscle fibers of the 1st motor unit have the same morphofunctional properties.

Functions of skeletal muscles are:

• movement of the body in space;
• movement of body parts relative to each other, including the implementation of respiratory movements that provide ventilation of the lungs;
• maintaining body position and posture.

Skeletal muscles, together with the skeleton, make up the musculoskeletal system of the body, which ensures the maintenance of posture and movement of the body in space. Along with this, skeletal muscles and the skeleton perform a protective function, protecting internal organs from damage.

In addition, striated muscles are important in the production of heat, which maintains temperature homeostasis, and in the storage of certain nutrients.

Rice. 2. Functions of skeletal muscles

Physiological properties of skeletal muscles

Skeletal muscles have the following physiological properties.

Excitability. Provided by property plasma membrane(sarcolemma) respond with excitement to the arrival of a nerve impulse. Due to the greater difference in the resting potential of the membrane of striated muscle fibers (E 0 about 90 mV), their excitability is lower than that of nerve fibers (E 0 about 70 mV). Their action potential amplitude is greater (about 120 mV) than that of other excitable cells.

This makes it possible in practice to quite easily record the bioelectrical activity of skeletal mice. The duration of the action potential is 3-5 ms, which determines the short duration of the absolute refractoriness phase of the excited muscle fiber membrane.

Conductivity. It is ensured by the property of the plasma membrane to form local circular currents, generate and conduct action potentials. As a result, the action potential propagates along the membrane along the muscle fiber and inward along the transverse tubes formed by the membrane. The speed of action potential is 3-5 m/s.

Contractility. It is a specific property of muscle fibers to change their length and tension following the excitation of the membrane. Contractility is provided by specialized contractile proteins of the muscle fiber.

Skeletal muscle also has viscoelastic properties that are important for muscle relaxation.

Rice. Human skeletal muscles

Physical properties of skeletal muscles

Skeletal muscles are characterized by extensibility, elasticity, strength and the ability to perform work.

Extensibility - the ability of a muscle to change length under the influence of a tensile force.

Elasticity - the ability of a muscle to restore its original shape after the cessation of tensile or deforming force.

- the ability of a muscle to lift a load. To compare the strength of different muscles, their specific strength is determined by dividing the maximum mass by the number of square centimeters of its physiological cross-section. Skeletal muscle strength depends on many factors. For example, on the number of motor units excited in this moment time. It also depends on the synchronicity of the motor units. The strength of the muscle also depends on the initial length. There is a certain average length at which a muscle develops maximum contraction.

The strength of smooth muscles also depends on the initial length, the synchronicity of excitation of the muscle complex, as well as on the concentration of calcium ions inside the cell.

Muscle ability do work. Muscle work is determined by the product of the mass of the lifted load and the height of the lift.

Muscle work increases by increasing the mass of the load being lifted, but up to a certain limit, after which an increase in load leads to a decrease in work, i.e. the lift height decreases. Maximum work is performed by the muscle at medium loads. This is called the law of average loads. The amount of muscle work depends on the number of muscle fibers. The thicker the muscle, the more load it can lift. Prolonged muscle tension leads to fatigue. This is due to the depletion of energy reserves in the muscle (ATP, glycogen, glucose), the accumulation of lactic acid and other metabolites.

Auxiliary properties of skeletal muscles

Extensibility is the ability of a muscle to change its length under the influence of a tensile force. Elasticity is the ability of a muscle to return to its original length after the cessation of the tensile or deforming force. Living muscle has small but perfect elasticity: even a small force can cause a relatively large lengthening of the muscle, and its return to its original size is complete. This property is very important for the normal functions of skeletal muscles.

The strength of a muscle is determined by the maximum load that the muscle is able to lift. To compare the strength of different muscles, their specific strength is determined, i.e. the maximum load that a muscle is able to lift is divided by the number of square centimeters of its physiological cross-section.

The ability of a muscle to do work. The work of a muscle is determined by the product of the magnitude of the lifted load and the height of the lift. The work of the muscle gradually increases with increasing load, but up to a certain limit, after which an increase in load leads to a decrease in work, since the height of lifting the load decreases. Hence, maximum work muscle is produced at average loads.

Muscle fatigue. Muscles cannot work continuously. Long-term work leads to a decrease in their performance. A temporary decrease in muscle performance that occurs during prolonged work and disappears after rest is called muscle fatigue. It is customary to distinguish between two types of muscle fatigue: false and true. With false fatigue, it is not the muscle that becomes tired, but a special mechanism for transmitting impulses from nerve to muscle, called a synapse. The reserves of mediators in the synapse are depleted. With true fatigue, the following processes occur in the muscle: accumulation of under-oxidized breakdown products of nutrients due to insufficient oxygen supply, depletion of energy sources necessary for muscle contraction. Fatigue is manifested by a decrease in the force of muscle contraction and the degree of muscle relaxation. If the muscle stops working for a while and is at rest, then the work of the synapse is restored, and metabolic products are removed with the blood and nutrients are delivered. Thus, the muscle regains the ability to contract and produce work.

Single cut

Stimulation of a muscle or the motor nerve innervating it with a single stimulus causes a single contraction of the muscle. There are three main phases of such a contraction: the latent phase, the shortening phase and the relaxation phase.

The amplitude of a single contraction of an isolated muscle fiber does not depend on the strength of stimulation, i.e. obeys the “all or nothing” law. However, the contraction of an entire muscle, consisting of many fibers, when directly stimulated depends on the strength of the stimulation. At threshold current, only a small number of fibers are involved in the reaction, so the muscle contraction is barely noticeable. With increasing strength of irritation, the number of fibers covered by excitation increases; the contraction increases until all fibers are contracted (“maximal contraction”)—this effect is called Bowditch’s ladder. Further intensification of the irritating current does not affect muscle contraction.

Rice. 3. Single muscle contraction: A - moment of muscle irritation; a-6 - latent period; 6-в - reduction (shortening); v-g - relaxation; d-d - successive elastic vibrations.

Tetanus muscle

Under natural conditions, the skeletal muscle receives from the central nervous system not single excitation impulses, which serve as adequate stimuli for it, but a series of impulses, to which the muscle responds with a prolonged contraction. Prolonged muscle contraction that occurs in response to rhythmic stimulation is called tetanic contraction, or tetanus. There are two types of tetanus: serrated and smooth (Fig. 4).

Smooth tetanus occurs when each subsequent excitation impulse enters the shortening phase, and toothed - into the relaxation phase.

The amplitude of the tetanic contraction exceeds the amplitude of a single contraction. Academician N.E. Vvedensky substantiated the variability of the tetanus amplitude by the unequal value of muscle excitability and introduced the concepts of optimum and pessimum of stimulation frequency into physiology.

Optimal This is the frequency of stimulation at which each subsequent stimulation enters the phase of increased excitability of the muscle. In this case, tetanus of maximum magnitude (optimal) develops.

Pessimal This is the frequency of stimulation at which each subsequent stimulation occurs in a phase of reduced excitability of the muscle. The magnitude of tetanus will be minimal (pessimal).

Rice. 4. Contraction of skeletal muscle at different frequencies of stimulation: I - muscle contraction; II — mark of irritation frequency; a - single contractions; b- serrated tetanus; c - smooth tetanus

Muscle contraction modes

Skeletal muscles are characterized by isotonic, isometric and mixed modes of contraction.

At isotonic When a muscle contracts, its length changes, but the tension remains constant. This contraction occurs when the muscle does not overcome resistance (for example, does not move a load). Under natural conditions, contractions of the tongue muscles are close to the isotonic type.

At isometric contraction in the muscle during its activity, tension increases, but due to the fact that both ends of the muscle are fixed (for example, the muscle is trying to lift a large load), it does not shorten. The length of the muscle fibers remains constant, only the degree of their tension changes.

They are reduced by similar mechanisms.

In the body, muscle contractions are never purely isotonic or isometric. They always have a mixed character, i.e. There is a simultaneous change in both the length and tension of the muscle. This reduction mode is called auxotonic, if muscle tension predominates, or auxometric, if shortening predominates.

Muscle structure:

A - appearance bipennate muscle; B - diagram of a longitudinal section of the multipennate muscle; B - cross section of the muscle; D - diagram of the structure of muscle as an organ; 1, 1" - muscle tendon; 2 - anatomical diameter of the muscle belly; 3 - gate of the muscle with neurovascular bundle (a - artery, c - vein, p - nerve); 4 - physiological diameter (total); 5 - subtendinous bursa; 6-6" - bones; 7 - external perimysium; 8 - internal perimysium; 9 - endomysium; 9"-muscular fibers; 10, 10", 10" - sensitive nerve fibers (carry impulses from muscles, tendons, blood vessels); 11, 11" - motor nerve fibers (carry impulses to muscles, blood vessels)

STRUCTURE OF SKELETAL MUSCLE AS AN ORGAN

Skeletal muscles - musculus skeleti - are active organs of the movement apparatus. Depending on the functional needs of the body, they can change the relationship between bone levers (dynamic function) or strengthen them in a certain position (static function). Skeletal muscles, performing a contractile function, transform a significant part of the chemical energy received from food into thermal energy (up to 70%) and into to a lesser extent into mechanical work (about 30%). Therefore, when contracting, a muscle not only performs mechanical work, but also serves as the main source of heat in the body. Together with the cardiovascular system, skeletal muscles are actively involved in metabolic processes and use of the body's energy resources. The presence of a large number of receptors in the muscles contributes to the perception of the muscular-articular sense, which, together with the organs of balance and organs of vision, ensures the execution of precise muscle movements. Skeletal muscles, together with subcutaneous tissue, contain up to 58% water, thereby fulfilling the important role of the main water depots in the body.

Skeletal (somatic) muscles are represented big amount muscles. Each muscle has a supporting part - the connective tissue stroma and a working part - the muscle parenchyma. The more static load a muscle performs, the more developed its stroma is.

On the outside, the muscle is covered with a connective tissue sheath called the external perimysium.

Perimysium. It has different thicknesses on different muscles. Connective tissue septa extend inward from the external perimysium - the internal perimysium, surrounding muscle bundles of various sizes. The greater the static function of a muscle, the more powerful the connective tissue partitions are located in it, the more of them there are. On the internal partitions in the muscles, muscle fibers can be attached, vessels and nerves pass through. Between the muscle fibers there are very delicate and thin connective tissue layers called endomysium - endomysium.

In the stroma of the muscle, represented by the external and internal perimysium and endomysium, muscle tissue (muscle fibers forming muscle bundles) is packed, forming various shapes and size of the muscle belly. The muscle stroma at the ends of the muscle belly forms continuous tendons, the shape of which depends on the shape of the muscles. If the tendon is cord-shaped, it is simply called a tendon - tendo. If the tendon is flat and comes from a flat muscular belly, then it is called an aponeurosis - aponeurosis.

The tendon is also distinguished between outer and inner sheaths (mesotendineum). The tendons are very dense, compact, form strong cords that have high tensile strength. Collagen fibers and bundles in them are located strictly longitudinally, due to which the tendons become a less fatigued part of the muscle. Tendons are attached to the bones, penetrating the fibers into the thickness of the bone tissue (the connection with the bone is so strong that the tendon is more likely to rupture than it comes off the bone). Tendons can move to the surface of the muscle and cover them at a greater or lesser distance, forming a shiny sheath called the tendon mirror.

In certain areas, the muscle includes vessels that supply it with blood and nerves that innervate it. The place where they enter is called the organ gate. Inside the muscle, vessels and nerves branch along the internal perimysium and reach its working units - muscle fibers, on which the vessels form networks of capillaries, and the nerves branch into:

1) sensory fibers - come from the sensitive nerve endings of the proprioceptors, located in all parts of the muscles and tendons, and carry out an impulse sent through the spinal ganglion cell to the brain;

2) motor nerve fibers that carry impulses from the brain:

a) to muscle fibers, ending on each muscle fiber with a special motor plaque,

b) to the muscle vessels - sympathetic fibers carrying impulses from the brain through the sympathetic ganglion cell to the smooth muscles of the blood vessels,

c) trophic fibers ending on the connective tissue base of the muscle. Since the working unit of muscles is the muscle fiber, it is their number that determines

muscle strength; The strength of the muscle depends not on the length of the muscle fibers, but on the number of them in the muscle. The more muscle fibers there are in a muscle, the stronger it is. When contracting, the muscle shortens by half its length. To count the number of muscle fibers, a cut is made perpendicular to their longitudinal axis; the resulting area of ​​transversely cut fibers is the physiological diameter. The area of ​​the cut of the entire muscle perpendicular to its longitudinal axis is called the anatomical diameter. In the same muscle there can be one anatomical and several physiological diameters, formed if the muscle fibers in the muscle are short and have different directions. Since muscle strength depends on the number of muscle fibers in them, it is expressed by the ratio of the anatomical diameter to the physiological one. There is only one anatomical diameter in the muscle belly, but physiological ones can have different numbers (1:2, 1:3, ..., 1:10, etc.). A large number of physiological diameters indicates muscle strength.

Muscles are light and dark. Their color depends on their function, structure and blood supply. Dark muscles are rich in myoglobin (myohematin) and sarcoplasm, they are more resilient. Light muscles are poorer in these elements; they are stronger, but less resilient. In different animals, at different ages and even in different parts of the body, the color of the muscles can be different: in horses the muscles are darker than in other species of animals; young animals are lighter than adults; darker on the limbs than on the body.

CLASSIFICATION OF MUSCLES

Each muscle is an independent organ and has a specific shape, size, structure, function, origin and position in the body. Depending on this, all skeletal muscles are divided into groups.

Internal structure of the muscle.

Skeletal muscles, according to the relationship of muscle bundles with intramuscular connective tissue formations, can have very different structures, which, in turn, determines their functional differences. Muscle strength is usually judged by the number of muscle bundles, which determine the size of the physiological diameter of the muscle. The ratio of the physiological diameter to the anatomical one, i.e. The ratio of the cross-sectional area of ​​the muscle bundles to the largest cross-sectional area of ​​the muscle belly makes it possible to judge the degree of expression of its dynamic and static properties. Differences in these ratios make it possible to subdivide skeletal muscles into dynamic, dynamostatic, statodynamic and static.

The simplest ones are constructed dynamic muscles. They have a delicate perimysium, the muscle fibers are long, run along the longitudinal axis of the muscle or at a certain angle to it, and therefore the anatomical diameter coincides with the physiological 1:1. These muscles are usually associated more with dynamic loading. Possessing a large amplitude: they provide a large range of movement, but their strength is small - these muscles are fast, dexterous, but also quickly tire.

Statodynamic muscles have a more strongly developed perimysium (both internal and external) and shorter muscle fibers running in the muscles in different directions, i.e. forming already

Classification of muscles: 1 – single-joint, 2 – double-joint, 3 – multi-joint, 4 – muscles-ligaments.

Types of structure of statodynamic muscles: a - single-pinnate, b - bipinnate, c - multi-pinnate, 1 - muscle tendons, 2 - bundles of muscle fibers, 3 - tendon layers, 4 - anatomical diameter, 5 - physiological diameter.

many physiological diameters. In relation to one general anatomical diameter, a muscle may have 2, 3, or 10 physiological diameters (1:2, 1:3, 1:10), which gives grounds to say that static-dynamic muscles are stronger than dynamic ones.

Statodynamic muscles perform a largely static function during support, holding the joints straight when the animal is standing, when under the influence of body weight the joints of the limbs tend to bend. The entire muscle can be penetrated by a tendon cord, which makes it possible, during static work, to act as a ligament, relieving the load on the muscle fibers and becoming a muscle fixator (biceps muscle in horses). These muscles are characterized by great strength and significant endurance.

Static muscles can develop as a result of a large static load falling on them. Muscles that have undergone deep restructuring and have almost completely lost muscle fibers actually turn into ligaments that are capable of performing only a static function. The lower the muscles are located on the body, the more static they are in structure. They perform a lot of static work when standing and supporting the limb on the ground during movement, securing the joints in a certain position.

Characteristics of muscles by action.

According to its function, each muscle necessarily has two points of attachment on bone levers - the head and the tendon ending - the tail, or aponeurosis. In work, one of these points will be a fixed point of support - punctum fixum, the second - a moving point - punctum mobile. For most muscles, especially the limbs, these points vary depending on the function performed and the location of the fulcrum. A muscle attached to two points (the head and the shoulder) can move its head when its fixed point of support is on the shoulder, and, conversely, will move the shoulder if during the movement the punctum fixum of this muscle is on the head.

Muscles can act on only one or two joints, but more often they are multi-joint. Each axis of movement on the limbs necessarily has two muscle groups with opposite actions.

When moving along one axis, there will definitely be flexor muscles and extensor muscles, extensors; in some joints, adduction-adduction, abduction-abduction, or rotation-rotation are possible, with rotation to the medial side called pronation, and rotation outward to the lateral side called supination.

There are also muscles that stand out - the tensors of the fascia - tensors. But at the same time, it is imperative to remember that depending on the nature of the load, the same

a multi-joint muscle can act as a flexor of one joint or as an extensor of another joint. An example is the biceps brachii muscle, which can act on two joints - the shoulder and the elbow (it is attached to the shoulder blade, throws over the top of the shoulder joint, passes inside the angle of the elbow joint and is attached to the radius). With a hanging limb, the punctum fixum of the biceps brachii muscle will be in the area of ​​the scapula, in this case the muscle pulls forward, bends the radius and elbow joint. When the limb is supported on the ground, the punctum fixum is located in the area of ​​the terminal tendon on the radius; the muscle already works as an extensor of the shoulder joint (holds shoulder joint in an extended state).

If muscles have the opposite effect on a joint, they are called antagonists. If their action is carried out in the same direction, they are called “companions” - synergists. All muscles that flex the same joint will be synergists; the extensors of this joint will be antagonists in relation to the flexors.

Around the natural openings there are obturator muscles - sphincters, which are characterized by a circular direction of muscle fibers; constrictors, or constrictors, which are also

belong to the type of round muscles, but have a different shape; dilators, or dilators, open natural openings when contracting.

According to anatomical structure muscles are divided depending on the number of intramuscular tendon layers and the direction of the muscle layers:

single-pinnate - they are characterized by the absence of tendon layers and muscle fibers are attached to the tendon of one side;

bipinnate - they are characterized by the presence of one tendon layer and muscle fibers are attached to the tendon on both sides;

multipinnate - they are characterized by the presence of two or more tendon layers, as a result of which the muscle bundles are intricately intertwined and approach the tendon from several sides.

Classification of muscles by shape

Among the huge variety of muscles in shape, the following main types can be roughly distinguished: 1) Long muscles correspond to long levers of movement and therefore are found mainly on the limbs. They have a spindle-shaped shape, the middle part is called the abdomen, the end corresponding to the beginning of the muscle is the head, and the opposite end is the tail. The longus tendon has the shape of a ribbon. Some long muscles begin with several heads (multiceps)

on various bones, which enhances their support.

2) Short muscles are located in those areas of the body where the range of movements is small (between individual vertebrae, between vertebrae and ribs, etc.).

3) Flat (wide) the muscles are located mainly on the torso and limb girdles. They have an extended tendon called an aponeurosis. Flat muscles have not only a motor function, but also a supporting and protective function.

4) Other forms of muscles are also found: square, circular, deltoid, serrated, trapezoidal, spindle-shaped, etc.

ACCESSORY ORGANS OF MUSCLES

When muscles work, conditions are often created that reduce the efficiency of their work, especially on the limbs, when the direction of muscle force during contraction occurs parallel to the direction of the lever arm. (The most beneficial action of muscle force is when it is directed at right angles to the lever arm.) However, the lack of this parallelism in muscle work is eliminated by a number of additional devices. For example, in places where force is applied, bones have bumps and ridges. Special bones are placed under the tendons (or set between the tendons). At joints, the bones thicken, separating the muscle from the center of movement at the joint. Simultaneously with the evolution of the muscular system of the body, auxiliary devices develop as an integral part of it, improving the working conditions of the muscles and helping them. These include fascia, bursae, synovial sheaths, sesamoid bones, and special blocks.

Accessory muscle organs:

A - fascia in the area of ​​the distal third of the horse's leg (on a transverse section), B - retinaculum and synovial sheaths of muscle tendons in the area of ​​the horse's tarsal joint from the medial surface, B - fibrous and synovial sheaths on longitudinal and B" - transverse sections;

I - skin, 2 - subcutaneous tissue, 3 - superficial fascia, 4 - deep fascia, 5 own muscle fascia, 6 - tendon own fascia (fibrous sheath), 7 - connections of the superficial fascia with the skin, 8 - interfascial connections, 8 - vascular - nerve bundle, 9 - muscles, 10 - bone, 11 - synovial sheaths, 12 - extensor retinaculum, 13 - flexor retinaculum, 14 - tendon;

a - parietal and b - visceral layers of the synovial vagina, c - mesentery of the tendon, d - places of transition of the parietal layer of the synovial vagina into its visceral layer, e - cavity of the synovial vagina

Fascia.

Each muscle, muscle group and all the musculature of the body is covered with special dense fibrous membranes called fasciae - fasciae. They tightly attract muscles to the skeleton, fix their position, helping to clarify the direction of the force of action of the muscles and their tendons, which is why surgeons call them muscle sheaths. Fascia demarcates muscles from each other, creates support for the muscle belly during its contraction, and eliminates friction between muscles. Fascia is also called the soft skeleton (considered a remnant of the membranous skeleton of vertebrate ancestors). They also help in the supporting function of the bone skeleton - the tension of the fascia during support reduces the load on the muscles and softens the shock load. In this case, the fascia takes on the shock-absorbing function. They are rich in receptors and blood vessels, and therefore, together with the muscles, they provide muscle-joint sensation. They play a very significant role in regeneration processes. So, if, when removing the affected cartilaginous meniscus in the knee joint, a flap of fascia is implanted in its place, which has not lost connection with its main layer (vessels and nerves), then with some training, after some time, an organ with the function of the meniscus is differentiated in its place, the work of the joint and the limbs as a whole are restored. Thus, by changing the local conditions of biomechanical load on the fascia, they can be used as a source of accelerated regeneration of structures of the musculoskeletal system during autoplasty of cartilage and bone tissue in restorative and reconstructive surgery.

With age, fascial sheaths thicken and become stronger.

Under the skin, the torso is covered with superficial fascia and connected to it by loose connective tissue. Superficial or subcutaneous fascia- fascia superficialis, s. subcutanea- Separates the skin from the superficial muscles. On the limbs, it can have attachments on the skin and bone protrusions, which, through contractions of the subcutaneous muscles, contributes to the implementation of shaking of the skin, as is the case in horses when they are freed from annoying insects or when shaking off debris stuck to the skin.

Located on the head under the skin superficial fascia of the head - f. superficialis capitis, which contains the muscles of the head.

Cervical fascia – f. cervicalis lies ventrally in the neck and covers the trachea. There are fascia of the neck and thoracoabdominal fascia. Each of them connects to each other dorsally along the supraspinous and nuchal ligaments and ventrally along the midline of the abdomen - linea alba.

The cervical fascia lies ventrally, covering the trachea. Its surface sheet is attached to the petrous part of the temporal bone, the hyoid bone and the edge of the atlas wing. It passes into the fascia of the pharynx, larynx and parotid. Then it runs along the longissimus capitis muscle, gives rise to intermuscular septa in this area and reaches the scalene muscle, merging with its perimysium. A deep plate of this fascia separates the ventral muscles of the neck from the esophagus and trachea, is attached to the intertransverse muscles, anteriorly passes to the fascia of the head, and caudally reaches the first rib and sternum, following further as the intrathoracic fascia.

Associated with the cervical fascia cervical subcutaneous muscle - m. cutaneus colli. It goes along the neck, closer to

her ventral surface and passes to the facial surface to the muscles of the mouth and lower lip.Thoracolumbar fascia – f. thoracolubalis lies dorsally on the body and is attached to the spinous

processes of the thoracic and lumbar vertebrae and maklok. The fascia forms a superficial and deep plate. The superficial one is attached to the macular and spinous processes of the lumbar and thoracic vertebrae. In the area of ​​the withers, it is attached to the spinous and transverse processes and is called the transverse spinous fascia. The muscles that go to the neck and head are attached to it. The deep plate is located only on the lower back, is attached to the transverse costal processes and gives rise to some abdominal muscles.

Thoracic fascia – f. thoracoabdominalis lies laterally on the sides of the chest and abdominal cavity and is attached ventrally along the white line of the abdomen - linea alba.

Associated with the thoracoabdominal superficial fascia pectoral, or cutaneous, muscle of the trunk - m. cutaneus trunci - quite extensive in area with longitudinally running fibers. It is located on the sides of the chest and abdominal walls. Caudally it gives off bundles into the knee fold.

Superficial fascia of the thoracic limb - f. superficialis membri thoraciciis a continuation of the thoracoabdominal fascia. It is significantly thickened in the wrist area and forms fibrous sheaths for the tendons of the muscles that pass here.

Superficial fascia of the pelvic limb - f. superficialis membri pelviniis a continuation of the thoracolumbar and is significantly thickened in the tarsal area.

Located under the superficial fascia deep, or fascia itself - fascia profunda. It surrounds specific groups of synergistic muscles or individual muscles and, attaching them in a certain position on a bone base, provides them optimal conditions for independent contractions and prevents their lateral displacement. In certain areas of the body where more differentiated movement is required, intermuscular connections and intermuscular septa extend from the deep fascia, forming separate fascial sheaths for individual muscles, which are often referred to as their own fascia (fascia propria). Where group muscle effort is required, intermuscular partitions are absent and the deep fascia, acquiring particularly powerful development, has clearly defined cords. Due to local thickenings of the deep fascia in the area of ​​the joints, transverse, or ring-shaped, bridges are formed: tendon arches, retinaculum of muscle tendons.

IN areas of the head, the superficial fascia is divided into the following deep ones: The frontal fascia runs from the forehead to the dorsum of the nose; temporal - along the temporal muscle; parotid-masticatory covers the parotid salivary gland and the masticatory muscle; the buccal goes in the area of ​​the lateral wall of the nose and cheek, and the submandibular - on the ventral side between the bodies of the lower jaw. The buccal-pharyngeal fascia comes from the caudal part of the buccinator muscle.

Intrathoracic fascia – f. endothoracica lines the inner surface of the thoracic cavity. Transverse abdominal fascia – f. transversalis lines the inner surface of the abdominal cavity. Pelvic fascia – f. pelvis lines the inner surface of the pelvic cavity.

IN In the area of ​​the thoracic limb, the superficial fascia is divided into the following deep ones: fascia of the scapula, shoulder, forearm, hand, fingers.

IN area of ​​the pelvic limb, the superficial fascia is divided into the following deep ones: gluteal (covers the croup area), fascia of the thigh, lower leg, foot, fingers

During movement, fascia plays an important role as a device for sucking blood and lymph from underlying organs. From the muscle bellies, the fascia passes to the tendons, surrounds them and is attached to the bones, holding the tendons in a certain position. This fibrous sheath in the form of a tube through which the tendons pass is called fibrous tendon sheath - vagina fibrosa tendinis. The fascia may thicken in certain areas, forming band-like rings around the joint that attract a group of tendons that pass over it. They are also called ring ligaments. These ligaments are especially well defined in the area of ​​the wrist and tarsus. In some places, the fascia is the site of attachment of the muscle that tenses it,

IN in places of high tension, especially during static work, the fascia thickens, its fibers acquire different directions, not only helping to strengthen the limb, but also acting as a springy, shock-absorbing device.

Bursae and synovial vaginas.

In order to prevent friction of muscles, tendons or ligaments, soften their contact with other organs (bone, skin, etc.), facilitate sliding during large ranges of movement, gaps are formed between the sheets of fascia, lined with a membrane that secretes mucus or synovium, depending on which synovial and mucous bursae are distinguished. Mucous bursae - bursa mucosa – (isolated “sacs”) formed in vulnerable places under the ligaments are called subglottic, under the muscles - axillary, under the tendons - subtendinous, under the skin - subcutaneous. Their cavity is filled with mucus and they can be permanent or temporary (calluses).

The bursa, which is formed due to the wall of the joint capsule, due to which its cavity communicates with the joint cavity, is called synovial bursa - bursa synovialis. Such bursae are filled with synovium and are located mainly in the areas of the elbow and knee joints, and their damage threatens the joint - inflammation of these bursae due to injury can lead to arthritis, therefore, in differential diagnosis, knowledge of the location and structure of synovial bursae is necessary, it determines the treatment and prognosis of the disease.

Somewhat more complexly built synovial tendon sheaths – vagina synovialis tendinis , in which long tendons pass, throwing over the carpal, metatarsal and fetlock joints. The synovial tendon sheath differs from the synovial bursa in that it has much larger dimensions (length, width) and a double wall. It completely covers the muscle tendon moving in it, as a result of which the synovial sheath not only performs the function of a bursa, but also strengthens the position of the muscle tendon over a significant extent.

Horse subcutaneous bursae:

1 - subcutaneous occipital bursa, 2 - subcutaneous parietal bursa; 3 - subcutaneous zygomatic bursa, 4 - subcutaneous bursa of the angle of the mandible; 5 - subcutaneous presternal bursa; 6 - subcutaneous ulnar bursa; 7 - subcutaneous lateral bursa of the elbow joint, 8 - subglottic bursa of the extensor carpi ulnaris; 9 - subcutaneous bursa of the abductor of the first finger, 10 - medial subcutaneous bursa of the wrist; 11 - subcutaneous precarpal bursa; 12 - lateral subcutaneous bursa; 13 - palmar (statar) subcutaneous digital bursa; 14 - subcutaneous bursa of the fourth metacarpal bone; 15, 15" - medial and lateral subcutaneous bursa of the ankle; /6 - subcutaneous calcaneal bursa; 17 - subcutaneous bursa of the tibial roughness; 18, 18" - subfascial subcutaneous prepatellar bursa; 19 - subcutaneous sciatic bursa; 20 - subcutaneous acetabular bursa; 21 - subcutaneous bursa of the sacrum; 22, 22" - subfascial subcutaneous bursa of the maclocus; 23, 23" - subcutaneous subglottic bursa of the supraspinous ligament; 24 - subcutaneous prescapular bursa; 25, 25" - subglottic caudal and cranial bursa of the nuchal ligament

Synovial sheaths form within fibrous sheaths that anchor long muscle tendons as they pass through joints. Inside, the wall of the fibrous vagina is lined with synovial membrane, forming parietal (outer) leaf this shell. The tendon passing through this area is also covered with a synovial membrane, its visceral (inner) sheet. Sliding during tendon movement occurs between the two layers of the synovial membrane and the synovium located between these leaves. The two layers of the synovial membrane are connected by a thin two-layer and short mesentery - the transition of the pariental layer to the visceral layer. The synovial vagina, therefore, is a thin two-layer closed tube, between the walls of which there is synovial fluid, which facilitates the sliding of a long tendon in it. In case of injuries in the area of ​​​​the joints where there are synovial sheaths, it is necessary to differentiate the sources of the released synovium, finding out whether it flows from the joint or the synovial sheath.

Blocks and sesamoid bones.

Blocks and sesamoid bones help improve muscle function. Blocks - trochlea - are certain shaped sections of the epiphyses of tubular bones through which muscles are thrown. They are a bony protrusion and a groove in it where the muscle tendon passes, due to which the tendons do not move to the side and the leverage for applying force increases. Blocks are formed where a change in the direction of muscle action is required. They are covered with hyaline cartilage, which improves muscle gliding; there are often synovial bursae or synovial sheaths. The blocks have a humerus and a femur.

Sesamoid bones - ossa sesamoidea - are bone formations that can form both inside muscle tendons and in the wall of the joint capsule. They form in areas of very strong muscle tension and are found in the thickness of the tendons. Sesamoid bones are located either at the top of a joint, or on the protruding edges of articulating bones, or where it is necessary to create a kind of muscle block in order to change the direction of muscle efforts during its contraction. They change the angle of muscle attachment and thereby improve their working conditions, reducing friction. They are sometimes called “ossified tendon areas,” but it must be remembered that they only go through two stages of development (connective tissue and bone).

The largest sesamoid bone, the patella, is set into the tendons of the quadriceps femoris muscle and slides along the epicondyles of the femur. Smaller sesamoid bones are located under the digital flexor tendons on the palmar and plantar sides of the fetlock (two for each) joint. On the joint side, these bones are covered with hyaline cartilage.

Skeletal muscles are the active part of the musculoskeletal system. It consists of skeletal muscles and their auxiliary devices, which include fascia, bursae, synovial tendon sheaths, pulleys, and sesame bones.

In the body of an animal there are about 500 skeletal muscles. Most of them are paired and are located symmetrically on both sides of the animal’s body. Their total mass is 38-42% for a horse of body weight, in cattle 42-47%, in pigs 30-35% of body weight.

The muscles in the animal’s body are not located randomly, but in a regular manner, depending on the effect of the animal’s gravity and the work performed. They exert their effect on those parts of the skeleton that are movably connected, i.e. muscles act on joints and syndesmoses.

The main places of muscle attachment are bones, but sometimes they are attached to cartilage, ligaments, fascia, and skin. They cover the skeleton so that the bones only in some places lie directly under the skin. Fixed on the skeleton, as on a system of levers, the muscles, when contracted, cause various movements of the body, fix the skeleton in a certain position and give shape to the animal’s body

The main functions of skeletal muscles:

1) The main function of muscles is dynamic. When contracting, the muscle shortens by 20-50% of its length and thereby changes the position of the bones associated with it. Work is performed, the result of which is movement.

2) Another muscle function - static. It manifests itself in fixing the body in a certain position, in maintaining the shape of the body and its parts. One of the manifestations of this function is the ability to sleep standing (horse).

3) Participation in metabolism and energy. Skeletal muscles are “heat sources” because when they contract, about 70% of the energy is converted into heat and only 30% of the energy provides movement. Skeletal muscles hold about 70% of the body's water, which is why they are also called “water sources.” In addition, adipose tissue can accumulate between muscle bundles and inside them (especially during fattening pigs).

4) At the same time, during their work, skeletal muscles help the heart function by pushing venous blood through the vessels. In experiments, it was possible to find out that skeletal muscles act like a pump, ensuring the movement of blood through the venous bed. Therefore, skeletal muscles are also called “peripheral muscle hearts.”

The structure of muscle from a biochemist's point of view

Skeletal muscle is composed of organic and inorganic compounds. Inorganic compounds include water and mineral salts (calcium, phosphorus, magnesium salts). Organic matter is mainly represented by proteins, carbohydrates (glycogen), lipids (phosphatides, cholesterol). Table 2.

Chemical composition of skeletal muscle

Knowledge of the basics of anatomy and the structure of your own body, together with an understanding of the meaning and structure of training, allows you to increase the effectiveness of sports many times over - after all, any movement, any athletic effort is performed with the help of muscles. In addition, muscle tissue is a significant part of body weight - in men it accounts for 42-47% of dry body mass, in women - 30-35%, and physical activity, especially planned strength training, increases the proportion of muscle tissue, and physical inaction, on the contrary, reduces it.

Types of muscles

There are three types of muscles in the human body:

• skeletal (they are also called striated);
• smooth;
• and myocardium, or heart muscle.

Smooth muscle form the walls of internal organs and blood vessels. Their distinctive feature is that they work independently of a person’s consciousness: it is impossible to stop, for example, peristalsis (contractions) of the intestine by force of will. The movements of such muscles are slow and monotonous, but they work continuously, without rest, throughout their lives.

Skeletal muscles responsible for maintaining the body in balance and performing a variety of movements. Do you feel like you are “just” sitting in a chair and relaxing? In fact, dozens of your skeletal muscles are working during this time. The work of skeletal muscles can be controlled by willpower. Striated muscles are capable of contracting quickly and relaxing just as quickly, but intense activity leads to fatigue relatively quickly.

Heart muscle uniquely combines the qualities of skeletal and smooth muscles. Just like skeletal muscles, the myocardium is capable of working intensively and contracting rapidly. Just like smooth muscles, it is practically tireless and does not depend on a person’s volitional effort.

By the way, strength training not only “sculpts the relief” and increases the strength of our skeletal muscles - it also indirectly improves the quality of smooth muscle and cardiac muscle work. By the way, this will also lead to the effect “ feedback“—strengthened, developed through endurance training, the heart muscle works more intensely and efficiently, which is reflected in improved blood supply to the entire body, including skeletal muscles, which can therefore withstand even greater loads. Trained, developed skeletal muscles form a powerful “corset” that supports internal organs, which does not play a role last role in the normalization of digestive processes. Normal digestion, in turn, means normal nutrition of all organs of the body, and muscles in particular.

Different types of muscles differ in their structure, but we will take a closer look at the structure of skeletal muscle, as it is directly related to the process of strength training.

Let's focus on skeletal muscles

The main structural component of muscle tissue is the myocyte - a muscle cell. One of the distinguishing features of a myocyte is that its length is hundreds of times greater than its cross section, which is why the myocyte is also called a muscle fiber. From 10 to 50 myocytes are connected into a bundle, and the muscle itself is formed from the bundles - in the biceps, for example, up to a million muscle fibers.

Between the bundles of muscle cells pass the smallest blood vessels - capillaries, and nerve fibers. Bundles of muscle fibers and the muscles themselves are covered with dense membranes of connective tissue, which at their ends become tendons that attach to the bones.

The main substance of a muscle cell is called sarcoplasm. The thinnest muscle filaments are immersed in it - myofibrils, which are the contractile elements of the muscle cell. Each myofibril consists of thousands of elementary particles - sarcomeres, the main feature of which is the ability to contract under the influence of a nerve impulse.

During targeted strength training, both the number of muscle fiber myofibrils and their cross-sectional area increases. First, this process leads to an increase in muscle strength, then to an increase in its thickness. However, the number of muscle fibers themselves remains the same - it is determined by the genetic characteristics of the development of the body and does not change throughout life. From this we can conclude that athletes have different physical prospects - those whose muscles consist of more fibers have a better chance of increasing muscle thickness through strength training than those athletes whose muscles contain fewer fibers.

So, the strength of a skeletal muscle depends on its cross-section - that is, on the thickness and number of myofibrils that form the muscle fiber. However, strength indicators increase and muscle mass not the same: when muscle mass doubles, muscle strength becomes three times greater, and scientists do not yet have a single explanation for this phenomenon.

Types of skeletal muscle fibers

The fibers that form skeletal muscles are divided into two groups: “slow”, or ST-fibers (slow twitch fibers) and “fast”, FT-fibers (fast twitch fibers). ST fibers contain a large number of myoglobin protein, which is red in color, which is why they are also called red fibers. These are endurance fibers, but they work at a load within 20-25% of the maximum muscle strength. In turn, FT fibers contain little myoglobin, which is why they are also called “white” fibers. They contract twice as fast as the “red” fibers and are capable of developing 10 times more force.

At loads less than 25% of the maximum muscle strength, the ST fibers work first, and then, when they become depleted, the FT fibers come into play. When they also use up the energy resource, they will become exhausted and the muscles will need rest. If the load is initially large, both types of fibers work simultaneously.

However, you should not mistakenly associate the types of fibers with the speed of movements that a person performs. Which type of fibers is predominantly involved in work at a given moment depends not on the speed of the movement performed, but on the effort that must be expended on this action. Related to this is the fact that different types muscles that perform various functions have a variable ratio of ST and FT fibers. In particular, the biceps, a muscle that performs predominantly dynamic work, contains more FT fibers than ST. In contrast, the soleus muscle, which experiences primarily static loads, consists primarily of ST fibers.

By the way, like the total number of muscle fibers, the ratio of ST/FT fibers in muscles specific person is genetically determined and remains constant throughout life. This also explains the innate abilities for certain sports: in the most “talented”, outstanding sprinters, the calf muscles consist of 90% “fast” fibers, while in marathon runners, on the contrary, up to 90% of these fibers are slow.

However, despite the fact that the natural number of muscle fibers, as well as the ratio of their fast and slow varieties, cannot be changed, well-planned and persistent training will force the muscles to adapt to the load and will certainly bring results.

Skeletal (somatic) muscles are represented by a large number (more than 200) muscles. Each muscle has a supporting part - the connective tissue stroma and a working part - the muscle parenchyma. The more static load a muscle performs, the more developed its stroma is.

On the outside, the muscle is covered with a connective tissue sheath, which is called the external perimysium - perimysium. It has different thicknesses on different muscles. Connective tissue septa extend inward from the external perimysium - the internal perimysium, surrounding muscle bundles of various sizes. The greater the static function of a muscle, the more powerful the connective tissue partitions are located in it, the more of them there are. On the internal partitions in the muscles, muscle fibers can be attached, vessels and nerves pass through. Between the muscle fibers there are very delicate and thin connective tissue layers called endomysium.

In this stroma of the muscle, represented by the external and internal perimysium and endomysium, muscle tissue (muscle fibers forming muscle bundles) is naturally packed, forming a muscle belly of various shapes and sizes. The muscle stroma at the ends of the muscle belly forms continuous tendons, the shape of which depends on the shape of the muscles. If the tendon is cord-shaped, it is simply called a tendon - tendo. If the tendon is flat, coming from a flat muscular belly, then it is called an aponeurosis.

The tendon is also distinguished between outer and inner sheaths (mesotendineum). The tendons are very dense, compact, form strong cords that have high tensile strength. Collagen fibers and bundles in them are located strictly longitudinally, due to which the tendons become a less fatigued part of the muscle. The tendons are attached to the bones, penetrating into the thickness of the bone tissue in the form of Sharpey's fibers (the connection with the bone is so strong that the tendon is more likely to rupture than it is torn off from the bone). Tendons can move to the surface of the muscle and cover them at a greater or lesser distance, forming a shiny sheath called the tendon mirror.

In certain areas, the muscle includes vessels that supply it with blood and nerves that innervate it. The place where they enter is called the organ gate. Inside the muscle, vessels and nerves branch along the internal perimysium and reach its working units - muscle fibers, on which the vessels form networks of capillaries, and the nerves branch into:

1) sensory fibers - come from the sensitive nerve endings of the proprioceptors, located in all parts of the muscles and tendons, and carry out an impulse sent through the spinal ganglion cell to the brain;

2) motor nerve fibers that carry impulses from the brain: a) to muscle fibers, ending on each muscle fiber with a special motor plaque, b) to muscle vessels - sympathetic fibers, carrying impulses from the brain through the sympathetic ganglion cell to the smooth muscles of the blood vessels, c) trophic fibers ending on the connective tissue base of the muscle.

Since the working unit of muscles is the muscle fiber, it is their number that determines the strength of the muscle; The strength of the muscle depends not on the length of the muscle fibers, but on the number of them in the muscle. The more muscle fibers there are in a muscle, the stronger it is. The length of muscle fibers usually does not exceed 12-15 cm, the lifting force of the muscle is on average 8-10 kg per 1 cm 2 of physiological diameter. When contracting, the muscle shortens by half its length. To count the number of muscle fibers, a cut is made perpendicular to their longitudinal axis; the resulting area of ​​transversely cut fibers is the physiological diameter. The area of ​​the cut of the entire muscle perpendicular to its longitudinal axis is called the anatomical diameter. In the same muscle there can be one anatomical and several physiological diameters, formed if the muscle fibers in the muscle are short and have different directions. Since muscle strength depends on the number of muscle fibers in them, it is expressed by the ratio of the anatomical diameter to the physiological one. There is only one anatomical diameter in the muscle belly, but physiological ones can have different numbers (1:2, 1:3,..., 1:10, etc.). A large number of physiological diameters indicates muscle strength.

Muscles are light and dark. Their color depends on their function, structure and blood supply. Dark muscles are rich in myoglobin (myohematin) and sarcoplasm, they are more resilient. Light muscles are poorer in these elements; they are stronger, but less resilient. In different animals, at different ages, and even in different parts of the body, the color of the muscles can be different: they are the darkest in horses, much lighter in pigs; young animals are lighter than adults; darker on the limbs than on the body; wild animals are darker than domestic ones; In chickens the pectoral muscles are white, in wild birds they are dark.