The structure of skeletal muscle. Muscle as an organ

It is impossible to do without at least a superficial knowledge of how muscles are structured and physiological processes when it comes to such key things in training as: intensity, muscle growth, increasing strength and speed, proper nutrition, proper weight loss, aerobic exercise. It is difficult to explain to a person who knows nothing about the structure and functioning of the body why some bodybuilders have ridiculous endurance, why marathon runners cannot have great muscle mass and strength, why it is impossible to remove fat only in the waist area, why it is impossible to pump up huge arms without training the whole body , why proteins are so important for increasing muscle mass and many, many other topics.

Any physical exercise always has something to do with muscles. Let's take a closer look at the muscles.

Human muscles

A muscle is a contractile organ consisting of special bundles of muscle cells that ensures the movement of skeletal bones, body parts, and substances in body cavities. As well as fixation of certain parts of the body relative to other parts.

Usually the word “muscle” refers to the biceps, quadriceps or triceps. Modern biology describes three types of muscles in the human body.

Skeletal muscles

These are exactly the muscles that we think of when we say the word “muscles.” Attached to the bones by tendons, these muscles provide movement of the body and maintain a certain posture. These muscles are also called striated, because when viewed through a microscope, their transverse striations are striking. A more detailed explanation of this striation will be given below. Skeletal muscles are controlled by us voluntarily, that is, at the command of our consciousness. In the photo you can see individual muscle cells (fibers).

Smooth muscle

This type of muscle is found in the walls of internal organs such as the esophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels and even the skin (in which they provide hair movement and overall tone). Unlike skeletal muscles, smooth muscles are not under the control of our consciousness. They are controlled by the autonomic nervous system (the unconscious part of the human nervous system). The structure and physiology of smooth muscles differs from that of skeletal muscles. In this article we will not touch on these issues.

Heart muscle (myocardium)

This muscle powers our heart. It is also not controlled by our consciousness. However, this type of muscle is very similar to skeletal muscles in its properties. In addition, the heart muscle has a special area (sinoatrial node), also called a pacemaker (pacemaker). This area has the property of producing rhythmic electrical impulses that ensure a clear periodicity of myocardial contraction.

In this article I will talk only about the first type of muscle - skeletal. But you should always remember that there are two other varieties.

Muscles in general

There are about 600 skeletal muscles in humans. In women, muscle mass can reach 32% of body weight. In men, even 45% of body weight. And this is a direct consequence of hormonal differences between the sexes. I believe this importance is even greater for bodybuilders, since they purposefully build muscle tissue. After 40 years, if you do not exercise, muscle mass in the body begins to gradually decrease by about 0.5-1% per year. Therefore, physical exercise becomes simply necessary as you age, unless, of course, you want to turn into a wreck.

A separate muscle consists of an active part - the abdomen, and a passive part - tendons, which are attached to the bones (on both sides). Different types of muscles (by shape, by attachment, by function) will be discussed in a separate article devoted to the classification of muscles. The abdomen consists of many bundles of muscle cells. The bundles are separated from each other by a layer of connective tissue.

Muscle fibers

Muscle cells (fibers) have a very elongated shape (like threads) and come in two types: fast (white) and slow (red). There is often evidence of a third intermediate type of muscle fiber. We will discuss the types of muscle fibers in more detail in a separate article, but here we will limit ourselves to only general information. In some large muscles, the length of muscle fibers can reach tens of centimeters (for example, in the quadriceps).

Slow muscle fibers

These fibers are not capable of fast and powerful contractions, but they are capable of contracting for a long time (hours) and are associated with endurance. Fibers of this type have many mitochondria (cell organelles in which the main energy processes occur), a significant supply of oxygen in combination with myoglobin. The predominant energy process in these fibers is aerobic oxidation of nutrients. Cells of this type are entangled in a dense network of capillaries. Good marathon runners tend to have more of this type of fiber in their muscles. This is partly due to genetic reasons, and partly due to training habits. It is known that during special endurance training over a long period of time, exactly this (slow) type of fiber begins to predominate in the muscles.

In the article I talked about the energy processes occurring in muscle fibers.

Fast muscle fibers

These fibers are capable of very powerful and rapid contractions, however, they cannot contract for a long time. This type of fiber has fewer mitochondria. Fast fibers are entangled with fewer capillaries compared to slow fibers. Most weightlifters and sprinters tend to have more white muscle fibers. And this is quite natural. With special strength and speed training, the percentage of white muscle fibers in the muscles increases.

When they talk about taking sports nutrition drugs such as, we are talking about the development of white muscle fibers.

Muscle fibers stretch from one tendon to another, so their length is often equal to the length of the muscle. At the junction with the tendon, the muscle fiber sheaths are firmly connected to the collagen fibers of the tendon.

Each muscle is abundantly supplied with capillaries and nerve endings coming from motor neurons (nerve cells responsible for movement). Moreover, the finer the work performed by the muscle, the fewer muscle cells there are per motor neuron. For example, in the eye muscles there are 3-6 muscle cells per motor neuron nerve fiber. And in the triceps muscle of the leg (gastrocnemius and soleus) there are 120-160 or even more muscle cells per nerve fiber. The process of the motor neuron connects to each individual cell with thin nerve endings, forming synapses. Muscle cells innervated by a single motor neuron are called a motor unit. Based on a signal from a motor neuron, they contract simultaneously.

Oxygen and other substances enter through the capillaries that entangle each muscle cell. Lactic acid is released into the blood through capillaries when it is formed in excess during intense exercise, as well as carbon dioxide, metabolic products. Normally, a person has about 2000 capillaries per 1 cubic millimeter of muscle.

The force developed by one muscle cell can reach 200 mg. That is, when contracting, one muscle cell can lift a weight of 200 mg. When contracting, a muscle cell can shorten by more than 2 times, increasing in thickness. Therefore, we have the opportunity to demonstrate our muscles, for example, biceps, by bending our arm. As you know, it takes on the shape of a ball, increasing in thickness.

Look at the picture. Here you can clearly see exactly how the muscle fibers are located in the muscles. The muscle as a whole is contained in a connective tissue sheath called the epimysium. The bundles of muscle cells are also separated from each other by layers of connective tissue, which contain numerous capillaries and nerve endings.

By the way, muscle cells belonging to the same motor unit can lie in different bundles.

Glycogen (in the form of granules) is present in the cytoplasm of the muscle cell. Interestingly, there may be even more muscle glycogen in the body than glycogen in the liver due to the fact that there are a lot of muscles in the body. However, muscle glycogen can only be used locally, within a given muscle cell. And liver glycogen is used by the entire body, including muscles. We will talk about glycogen separately.

Myofibrils are the muscles of muscles

Please note that the muscle cell is literally packed with contractile cords called myofibrils. Essentially, these are muscles of muscle cells. Myofibrils occupy up to 80% of the total internal volume of a muscle cell. The white layer enveloping each myofibril is nothing more than the sarcoplasmic reticulum (or, in other words, the endoplasmic reticulum). This organelle entangles each myofibril with a thick openwork mesh and is very important in the mechanism of muscle contraction and relaxation (pumping Ca ions).

As you can see, myofibrils are made up of short cylindrical sections called sarcomeres. One myofibril usually contains several hundred sarcomeres. The length of each sarcomere is about 2.5 micrometers. Sarcomeres are separated from each other by dark transverse partitions (see photo). Each sarcomere consists of the thinnest contractile filaments of two proteins: actin and myosin. Strictly speaking, four proteins are involved in the act of contraction: actin, myosin, troponin and tropomyosin. But let's talk about this in a separate article on muscle contraction.

Myosin is a thick protein filament, a huge long protein molecule, which is also an enzyme that breaks down ATP. Actin is a thinner protein filament that is also a long protein molecule. The contraction process occurs thanks to the energy of ATP. When a muscle contracts, thick filaments of myosin bind to thin filaments of actin, forming molecular bridges. Thanks to these bridges, thick myosin filaments pull up actin filaments, which leads to shortening of the sarcomere. In itself, the reduction of one sarcomere is insignificant, but since there are a lot of sarcomeres in one myofibril, the reduction is very noticeable. An important condition for the contraction of myofibrils is the presence of calcium ions.

The thin structure of the sarcomere explains the cross-striations of muscle cells. The fact is that contractile proteins have different physical and chemical properties and conduct light differently. Therefore, some areas of the sarcomere appear darker than others. And if we take into account that the sarcomeres of neighboring myofibrils lie exactly opposite each other, then hence the transverse striation of the entire muscle cell.

We will take a more detailed look at the structure and function of sarcomeres in a separate article on muscle contraction.

Tendon

This is a very dense and inextensible formation, consisting of connective tissue and collagen fibers, which serves to attach the muscle to the bones. The strength of the tendons is evidenced by the fact that it takes a force of 600 kg to rupture the quadriceps femoris tendon, and 400 kg to rupture the triceps surae tendon. On the other hand, if we talk about muscles, these are not such big numbers. After all, muscles develop forces of hundreds of kilograms. However, the body's lever system reduces this force to gain speed and range of motion. But more on this in a separate article on body biomechanics.

Regular strength training leads to stronger tendons and bones where muscles attach. Thus, the tendons of a trained athlete can withstand more severe loads without rupture.

The connection between tendon and bone does not have a clear boundary, since the cells of the tendon tissue produce both tendon substance and bone substance.

The connection of the tendon with muscle cells occurs due to a complex connection and mutual penetration of microscopic fibers.

Between the cells and fibers of the tendons near the muscles lie special microscopic Golgi organs. Their purpose is to determine the degree of muscle stretching. In essence, the Golgi organs are receptors that protect our muscles from excessive stretching and tension.

Muscle structure:

A - appearance of the 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, 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 actively participate in metabolic processes and the 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 by a large number of 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.

The stroma of the muscle, represented by the external and internal perimysium and endomysium, contains muscle tissue (muscle fibers that form muscle bundles), 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 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, based on 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 the 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 with 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 “bags”) formed in vulnerable places under the ligaments are called subglottis, under muscles - axillary, under 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 one. 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 muscle, or muscle, is an organ of voluntary movement. It is built from striated muscle fibers, which are able to shorten under the influence of impulses from the nervous system and, as a result, produce work. Muscles, depending on their function and location on the skeleton, have different shapes and different structures.

The shape of the muscles is extremely varied and difficult to classify. Based on their shape, it is customary to distinguish between two main groups of muscles: thick, often fusiform, and thin, lamellar, which, in turn, have many variations.

Anatomically, in a muscle of any shape, a muscle belly and muscle tendons are distinguished. When the muscle belly contracts, it produces work, and the tendons serve to attach the muscle to the bones (or to the skin) and to transmit the force developed by the muscle belly to the bones or folds of skin.

Muscle structure (Fig. 21). On the surface, each muscle is covered with connective tissue, the so-called common sheath. Thin connective tissue plates extend from the common membrane, forming thick and thin bundles of muscle fibers, as well as covering individual muscle fibers. The common shell and plates make up the connective tissue skeleton of the muscle. Blood vessels and nerves pass through it, and with abundant feeding, adipose tissue is deposited.

Muscle tendons consist of dense and loose connective tissue, the ratio between which varies depending on the load experienced by the tendon: the more dense connective tissue there is in the tendon, the stronger it is, and vice versa.

Depending on the method of attachment of bundles of muscle fibers to tendons, muscles are usually divided into single-pinnate, bi-pinnate and multi-pinnate. Unipennate muscles have the simplest structure. Bunches of muscle fibers run in them from one tendon to another approximately parallel to the length of the muscle. In bipinnate muscles, one tendon is split into two plates that lie superficially on the muscle, and the other comes out from the middle of the abdomen, while bundles of muscle fibers go from one tendon to the other. Multipinnate muscles are even more complex. The meaning of this structure is as follows. With the same volume, there are fewer muscle fibers in unipennate muscles compared to bi- and multi-pennate muscles, but they are longer. In bipennate muscles, the muscle fibers are shorter, but there are more of them. Since muscle strength depends on the number of muscle fibers, the more there are, the stronger the muscle. But such a muscle can perform work over a shorter distance, since its muscle fibers are short. Therefore, if a muscle works in such a way that, expending a relatively small force, it provides a large range of movement, it has a simpler structure - single-pinnate, for example, the brachiocephalic muscle, which can throw the leg far forward. On the contrary, if the range of movement does not play a special role, but great force must be exerted, for example, to keep the elbow joint from bending when standing, only the multipennate muscle can perform this work. Thus, knowing the working conditions, it is possible to theoretically determine what structure the muscles will be in a particular area of ​​the body, and, conversely, by the structure of the muscle one can determine the nature of its work, and therefore its position on the skeleton.

Rice. 21. Structure of skeletal muscle: A - cross section; B - ratio of muscle fibers and tendons; I—unipinnate; II - bipinnate and III - multipinnate muscle; 1 - common shell; 2 - thin plates of the skeleton; 3 — cross-section of blood vessels and nerves; 4 - bundles of muscle fibers; 5—muscle tendon.

The evaluation of meat depends on the type of muscle structure: the more tendons in the muscle, the worse the quality of the meat.

Vessels and nerves of muscles. Muscles are abundantly supplied with blood vessels, and the more intense the work, the more blood vessels there are. Since the movement of an animal is carried out under the influence of the nervous system, the muscles are also equipped with nerves that either conduct motor impulses into the muscles, or, on the contrary, carry out impulses arising in the receptors of the muscles themselves as a result of their work (contraction forces).

Human muscles in relation to his total mass are approximately 40%. Their main function in the body is to provide movement through the ability to contract and relax. For the first time, muscle structure (8th grade) begins to be studied at school. There, knowledge is given at a general level, without much in-depth. The article will be of interest to those who want to go a little beyond this framework.

Muscle structure: general information

Muscle tissue is a group that includes striated, smooth and cardiac varieties. Differing in origin and structure, they are united based on the function they perform, that is, the ability to contract and lengthen. In addition to the listed varieties, which are formed from mesenchyme (mesoderm), the human body also has muscle tissue of ectodermal origin. These are the myocytes of the iris.

The structural, general structure of the muscles is as follows: they consist of an active part, called the abdomen, and tendon ends (tendon). The latter are formed from dense connective tissue and perform the function of attachment. They have a characteristic whitish-yellow color and shine. In addition, they have significant strength. Usually, with their tendons, muscles are attached to the links of the skeleton, the connection with which is movable. However, some can also attach to the fascia, to various organs (eyeball, laryngeal cartilage, etc.), to the skin (on the face). The blood supply to muscles varies and depends on the loads they experience.

Regulating muscle function

Their work is controlled, like other organs, by the nervous system. Its fibers in the muscles end as receptors or effectors. The former are also located in the tendons and have the form of terminal branches of the sensory nerve or neuromuscular spindle, which has a complex structure. They react to the degree of contraction and stretching, as a result of which a person develops a certain feeling, which, in particular, helps to determine the position of the body in space. Effector nerve endings (also known as motor plaques) belong to the motor nerve.

The structure of the muscles is also characterized by the presence in them of the endings of fibers of the sympathetic nervous system (autonomic).

The structure of striated muscle tissue

It is often called skeletal or striated. The structure of skeletal muscle is quite complex. It is formed by fibers that have a cylindrical shape, a length from 1 mm to 4 cm or more, and a thickness of 0.1 mm. Moreover, each is a special complex consisting of myosatellitocytes and myosymplast, covered with a plasma membrane called sarcolemma. Adjacent to it outside is a basement membrane (plate), formed from the finest collagen and reticular fibers. Myosymplast consists of a large number of ellipsoidal nuclei, myofibrils and cytoplasm.

The structure of this type of muscle is distinguished by a well-developed sarcotubular network, formed from two components: ER tubules and T-tubules. The latter play an important role in accelerating the conduction of action potentials to microfibrils. Myosatellite cells are located directly above the sarcolemma. The cells have a flattened shape and a large nucleus, rich in chromatin, as well as a centrosome and a small number of organelles; there are no myofibrils.

The sarcoplasm of skeletal muscle is rich in a special protein - myoglobin, which, like hemoglobin, has the ability to bind with oxygen. Depending on its content, the presence/absence of myofibrils and the thickness of the fibers, two types of striated muscles are distinguished. The specific structure of the skeleton, muscles - all these are elements of a person’s adaptation to upright walking, their main functions are support and movement.

Red muscle fibers

They are dark in color and rich in myoglobin, sarcoplasm and mitochondria. However, they contain few myofibrils. These fibers contract quite slowly and can remain in this state for a long time (in other words, in working condition). The structure of skeletal muscle and the functions it performs should be considered as parts of a single whole, mutually determining each other.

White muscle fibers

They are light in color, contain a much smaller amount of sarcoplasm, mitochondria and myoglobin, but are characterized by a high content of myofibrils. This means that they contract much more intensely than red ones, but they also “get tired” quickly.

The structure of human muscles differs in that the body contains both types. This combination of fibers determines the speed of muscle reaction (contraction) and their long-term performance.

Smooth muscle tissue (unstriated): structure

It is built from myocytes located in the walls of lymphatic and blood vessels and forming the contractile apparatus in the internal hollow organs. These are elongated cells, spindle-shaped, without transverse striations. Their arrangement is group. Each myocyte is surrounded by a basement membrane, collagen and reticular fibers, among which are elastic. Cells are connected by numerous nexuses. The structural features of the muscles of this group are that one nerve fiber (for example, the pupillary sphincter) approaches each myocyte, surrounded by connective tissue, and the impulse is transported from one cell to another using nexuses. The speed of its movement is 8-10 cm/s.

Smooth myocytes have a much slower contraction rate than myocytes of striated muscle tissue. But energy is also used sparingly. This structure allows them to make long-term contractions of a tonic nature (for example, sphincters of blood vessels, hollow, tubular organs) and fairly slow movements, which are often rhythmic.

Cardiac muscle tissue: features

According to the classification, it belongs to the striated muscle, but the structure and functions of the heart muscles are noticeably different from skeletal muscles. Cardiac muscle tissue consists of cardiomyocytes, which form complexes by connecting with each other. The contraction of the heart muscle is not subject to the control of human consciousness. Cardiomyocytes are cells that have an irregular cylindrical shape, with 1-2 nuclei and a large number of large mitochondria. They are connected to each other by insertion disks. This is a special zone that includes the cytolemma, areas of attachment of myofibrils to it, desmos, nexuses (through them the transmission of nervous excitation and ion exchange between cells occurs).

Classification of muscles depending on shape and size

1. Long and short. The first ones are found where the range of motion is greatest. For example, upper and lower limbs. And the short muscles, in particular, are located between individual vertebrae.

2. Broad muscles (stomach in the photo). They are mainly located on the body, in the cavity walls of the body. For example, superficial muscles of the back, chest, abdomen. With a multilayer arrangement, their fibers, as a rule, go in different directions. Therefore, they provide not only a wide variety of movements, but also strengthen the walls of body cavities. In the broad muscles, the tendons are flat and occupy a large surface area; they are called sprains or aponeuroses.

3. Circular muscles. They are located around the openings of the body and, through their contractions, narrow them, as a result of which they are called “sphincters”. For example, the orbicularis oris muscle.

Complex muscles: structural features

Their names correspond to their structure: two-, three- (pictured) and four-headed. The structure of muscles of this type is different in that their beginning is not single, but divided into 2, 3 or 4 parts (heads), respectively. Starting from different points of the bone, they then move and unite into a common abdomen. It can also be divided transversely by the intermediate tendon. This muscle is called digastric. The direction of the fibers can be parallel to the axis or at an acute angle to it. In the first case, the most common, the muscle shortens quite strongly during contraction, thereby providing a large range of movements. And in the second, the fibers are short, located at an angle, but there are much more of them in number. Therefore, the muscle shortens slightly during contraction. Its main advantage is that it develops great strength. If the fibers approach the tendon only on one side, the muscle is called unipennate, if on both sides it is called bipennate.

Auxiliary apparatus of muscles

The structure of human muscles is unique and has its own characteristics. For example, under the influence of their work, auxiliary devices are formed from the surrounding connective tissue. There are four of them in total.

1. Fascia, which is nothing more than a shell of dense, fibrous fibrous tissue (connective). They cover both single muscles and entire groups, as well as some other organs. For example, kidneys, neurovascular bundles, etc. They influence the direction of traction during contraction and prevent the muscles from moving to the sides. The density and strength of fascia depends on its location (they differ in different parts of the body).

2. Synovial bursae (pictured). Many people probably remember their role and structure from school lessons (Biology, 8th grade: “Muscle structure”). They are peculiar bags, the walls of which are formed by connective tissue and are quite thin. Inside they are filled with fluid such as synovium. As a rule, they are formed where the tendons come into contact with each other or experience great friction against the bone during muscle contraction, as well as in places where the skin rubs against it (for example, the elbows). Thanks to the synovial fluid, gliding improves and becomes easier. They develop mainly after birth, and over the years the cavity increases.

3. Synovial vagina. Their development occurs within the osteofibrous or fibrous canals that surround the long muscle tendons where they slide along the bone. In the structure of the synovial vagina, two petals are distinguished: the inner one, covering the tendon on all sides, and the outer one, lining the walls of the fibrous canal. They prevent the tendons from rubbing against the bone.

4. Sesamoid bones. Typically, they ossify within the ligaments or tendons, strengthening them. This facilitates the work of the muscle by increasing the shoulder of force application.

Muscle as an organ

There are 3 types of muscle tissue in the human body:

Skeletal

Striated

Striated skeletal muscle tissue is formed by cylindrical muscle fibers with a length of 1 to 40 mm and a thickness of up to 0.1 μm, each of which is a complex consisting of myosymplast and myosatelite, covered with a common basement membrane, reinforced by thin collagen and reticular fibers. The basement membrane forms the sarcolemma. Under the plasmalemma of the myosymplast there are many nuclei.

The sarcoplasm contains cylindrical myofibrils. Between the myofibrils there are numerous mitochondria with developed cristae and glycogen particles. Sarcoplasm is rich in proteins called myoglobin, which, like hemoglobin, can bind oxygen.

Depending on the thickness of the fibers and the myoglobin content in them, they are distinguished:

Red fibers:

Rich in sarcoplasm, myoglobin and mitochondria

However, they are the thinnest

Myofibrils are arranged in groups

Oxidative processes are more intense

Intermediate fibers:

Poorer in myoglobin and mitochondria

Thicker

Oxidative processes are less intense

White fibers:

- the thickest

- the number of myofibrils in them is greater and they are evenly distributed

- oxidative processes are less intense

- even lower glycogen content

The structure and function of fibers are inextricably linked. This way the white fibers contract faster, but also tire quickly. (sprinters)

Red ways to a longer contraction. In humans, muscles contain all types of fibers; depending on the function of the muscle, one or another type of fiber predominates in it. (stayers)

The structure of muscle tissue

The fibers are distinguished by transverse striations: dark anisotropic disks (A-disks) alternate with light isotropic disks (I-disks). Disc A is divided by a light zone H, in the center of which there is a mesophragm (line M), disk I is divided by a dark line (telophragm - Z line). The telophragm is thicker in the myofibrils of red fibers.

Myofibrils contain contractile elements - myofilaments, among which are thick (myosive), occupying the A disk, and thin (actin), lying in the I-disc and attached to the telophragms (Z-plates contain the protein alpha-actin), and their ends penetrate into A-disk between thick myofilaments. The section of muscle fiber located between two telophragms is a sarconner - a contractile unit of myofibrils. Due to the fact that the boundaries of the sarcomeres of all myofibrils coincide, regular striations arise, which are clearly visible on longitudinal sections of the muscle fiber.

On cross sections, myofibrils are clearly visible in the form of rounded dots against the background of light cytoplasm.

According to the theory of Huxley and Hanson, muscle contraction is the result of the sliding of thin (actin) filaments relative to thick (myosin) filaments. In this case, the length of the filaments of disk A does not change, disk I decreases in size and disappears.

Muscles as an organ

Muscle structure. A muscle as an organ consists of bundles of striated muscle fibers. These fibers, running parallel to each other, are bound by loose connective tissue into first-order bundles. Several such primary bundles are connected, in turn forming bundles of the second order, etc. in general, muscle bundles of all orders are united by a connective tissue membrane, making up the muscle belly.

The connective tissue layers present between the muscle bundles, at the ends of the muscle belly, pass into the tendon part of the muscle.

Since muscle contraction is caused by an impulse coming from the central nervous system, each muscle is connected to it by nerves: afferent, which is the conductor of the “muscle feeling” (motor analyzer, according to K.P. Pavlov), and efferent, which leads to nervous excitation. In addition, sympathetic nerves approach the muscle, thanks to which the muscles in a living organism are always in a state of some contraction, called tone.

A very energetic metabolism occurs in the muscles, and therefore they are very richly supplied with blood vessels. The vessels penetrate the muscle from its inner side at one or more points called the muscle gate.

The muscle gate, along with the vessels, also includes nerves, with which they branch in the thickness of the muscle according to the muscle bundles (along and across).

A muscle is divided into an actively contracting part, the belly, and a passive part, the tendon.

Thus, skeletal muscle consists not only of striated muscle tissue, but also of various types of connective tissue, nervous tissue, and the endothelium of muscle fibers (vessels). However, the predominant one is striated muscle tissue, the property of which is contractility; it determines the function of the muscle as an organ - contraction.

Muscle classification

There are up to 400 muscles (in the human body).

According to their shape they are divided into long, short and wide. The long ones correspond to the movement arms to which they are attached.

Some long ones begin with several heads (multi-headed) on different bones, which enhances their support. There are biceps, triceps and quadriceps muscles.

In the case of fusion of muscles of different origin or developed from several myotons, intermediate tendons, tendon bridges, remain between them. Such muscles have two or more bellies - multiabdominal.

The number of tendons with which the muscles end also varies. Thus, the flexors and extensors of the fingers and toes each have several tendons, due to which contractions of one muscle belly produce a motor effect on several fingers at once, thereby achieving savings in muscle work.

Vastus muscles - located primarily on the torso and have an enlarged tendon called a tendon sprain or aponeurosis.

There are various forms of muscles: quadratus, triangular, pyramidal, round, deltoid, serratus, soleus, etc.

According to the direction of the fibers, determined functionally, muscles are distinguished with straight parallel fibers, with oblique fibers, with transverse fibers, and with circular ones. The latter form sphincters, or sphincters, surrounding the openings.

If the oblique fibers are attached to the tendon on one side, then the so-called unipennate muscle is obtained, and if on both sides, then the bipennate muscle. A special relationship of fibers to tendon is observed in the semitendinosus and semimembranosus muscles.

Flexors

Extensors

Adductors

Abductors

Rotators inwards (pronators), outwards (supinators)

Onto-phylogenetic aspects of the development of the musculoskeletal system

Elements of the musculoskeletal system of the body in all vertebrates develop from the primary segments (somites) of the dorsal mesoderm, lying on the sides and neural tube.

The mesenchyme (sclerotome) arising from the medioventral part of the somite goes to form around the skeletal notochord, and the middle part of the primary segment (myotome) gives rise to muscles (the dermatome is formed from the dorsolateral part of the somite).

During the formation of the cartilaginous and subsequently the bone skeleton, the muscles (myotomes) receive support on the solid parts of the skeleton, which are therefore also located metamerically, alternating with muscle segments.

Myoblasts elongate, merge with each other and turn into segments of muscle fibers.

Initially, the myotomes on each side are separated from each other by transverse connective tissue septa. Also, the segmented arrangement of the trunk muscles in lower animals remains for life. In higher vertebrates and humans, due to more significant differentiation of muscle masses, segmentation is significantly smoothed out, although traces of it remain in both the dorsal and ventral muscles.

Myotomes grow in the ventral direction and are divided into dorsal and ventral parts. From the dorsal part of the myotomes arises the dorsal muscles, from the ventral part - the muscles located on the front and lateral sides of the body and called ventral.

Adjacent myotomes can fuse with each other, but each of the fused myotomes holds the nerve related to it. Therefore, muscles originating from several myotomes are innervated by several nerves.

Types of muscles depending on development

Based on innervation, it is always possible to distinguish autochthonous muscles from other muscles that have moved into this area - aliens.

Some of the muscles that have developed on the body remain in place, forming local (autochthonous) muscles (intercostal and short muscles along the processes of the vertebrae.

The other part in the process of development moves from the trunk to the limbs - truncofugal.

The third part of the muscles, having arisen on the limbs, moves to the torso. These are the truncopetal muscles.

Limb muscle development

The muscles of the limbs are formed from the mesenchyme of the kidneys of the limbs and receive their nerves from the anterior branches of the spinal nerves through the brachial and lumbosacral plexuses. In lower fish, muscle buds grow from the myotae of the body, which are divided into two layers located on the dorsal and ventral sides of the skeleton.

Similarly, in terrestrial vertebrates, the muscles in relation to the skeletal rudiment of the limb are initially located dorsally and ventrally (extensors and flexors).

Trunctopetal

With further differentiation, the rudiments of the muscles of the forelimb grow in the proximal direction and cover the autochthonous muscles of the body from the chest and back.

In addition to this primary musculature of the upper limb, truncofugal muscles are also attached to the girdle of the upper limb, i.e. derivatives of the ventral muscles, which serve for movement and fixation of the belt and moved to it from the head.

The girdle of the hind (lower) limb does not develop secondary muscles, since it is immovably connected to the spinal column.

Head muscles

They arise partly from the cephalic somites, and mainly from the mesoderm of the gill arches.

Third branch of the trigeminal nerve (V)

Intermediate facial nerve (VII)

Glossopharyngeal nerve (IX)

Superior laryngeal branch of the vagus nerve (X)

Inferior laryngeal branch of the vagus nerve (X)

Muscle work (elements of biomechanics)

Each muscle has a moving point and a fixed point. The strength of a muscle depends on the number of muscle fibers included in its composition and is determined by the area of ​​the cut in the place through which all muscle fibers pass.

Anatomical diameter - the cross-sectional area perpendicular to the length of the muscle and passing through the abdomen in its widest part. This indicator characterizes the size of the muscle, its thickness (in fact, it determines the volume of the muscle).

Absolute muscle strength

Determined by the ratio of the mass of the load (kg) that a muscle can lift and the area of ​​its physiological diameter (cm2)

In the calf muscle – 15.9 kg/cm2

For the triceps - 16.8 kg/cm2