Muscle structure. Muscle as an organ

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).

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.

A cross-striated (striated) or skeletal muscle fiber or myocyte, as a structural unit with a length of 150 microns to 12 cm, contains in the cytoplasm from 1 to 2 thousand myofibril , located without strict orientation, some of them are grouped into bundles. This is especially pronounced in trained people. Therefore, the more organized the fibrous structure is, the more force this muscle can develop.

Muscle fibers are united into bundles of the 1st order endomysium, which regulates the degree of its contraction according to the principle of a spiral (nylon stocking), the more the spiral stretches, the more it compresses the myocyte. Several such bundles of 1st order are combined internal perimysium into bundles of 2nd order, and so on up to 4th order. The last order of connective tissue surrounds the active part of the muscle as a whole and is called epimysium (external perimysium). The endo- and perimysium of the active part of the muscle passes to the tendon part of the muscle and is called peritendinium, which ensures the transfer of forces from each muscle fiber to the tendon fibers. Injuries most often occur at the border of these 2 tissues (in dancers and ballerinas).

Tendons do not transmit the total traction of muscle fibers to bones. Tendons are attached to bone by intertwining their fibers with the collagen fibers of the periosteum. Tendons are attached to bones either in a concentrated manner or dispersedly. In the first case, a tubercle or ridge forms on the bone, and in the second, a depression. Tendons are very strong. For example, the calcaneal (Achilles) tendon can withstand a load of 400 kg, and the quadriceps tendon can withstand a load of 600 kg. This leads to the fact that, under excessive loads, the tuberosity of the bone is torn off, but the bone itself remains intact. Tendons have a rich innervation apparatus and are abundantly supplied with blood. It has been established that the blood supply to muscle tissue is somewhat mosaic: in the outer areas, vascularization is 2 times greater than in the deep ones. Usually there are from 300-400 to 1000 capillaries per 1 mm3.

The structural and functional unit of muscle is mion – a motor neuron with an innervated group of muscle fibers.

Each nerve fiber approaching the muscle branches and ends in motor plaques. The number of muscle fibers associated with one nerve cell ranges from 1 to 350 in the brachioradialis muscle and 579 in the triceps surae muscle.

Thus, a muscle is an organ consisting of several tissues, the leading of which is muscle tissue, which has a certain shape, structure and function.

Classification of muscles.

Created 03/24/2016

Perhaps you can’t start strength training without knowing the names of the muscles and where they are located.

After all, knowing the structure of the body and understanding the meaning and structure of training significantly increases the effectiveness of strength training.

Types of muscles

There are three types of muscle tissue:

smooth muscle

Smooth muscles form the walls of internal organs, respiratory passages and blood vessels. Slow and uniform movements of smooth muscle move substances through organs (for example, food through the stomach or urine through the bladder). Smooth muscles are involuntary, that is, they work independently of our consciousness, continuously throughout life.

heart muscle (myocardium)

Responsible for pumping blood throughout the body. Just like smooth muscles, it cannot be controlled consciously. The heart muscle contracts rapidly and works intensely throughout life.

skeletal (striated) muscles

The only muscle tissue that is controlled by consciousness. There are more than 600 skeletal muscles and they make up about 40 percent of the human body weight. In older people, skeletal muscle mass decreases to 25-30%. However, with regular high muscle activity, muscle mass is maintained until old age.

The main function of skeletal muscles is to move bones and maintain body posture and position. The muscles responsible for maintaining body posture have the greatest endurance of any muscle in the body. In addition, skeletal muscles perform a thermoregulatory function, being a source of heat.

Structure of skeletal muscles

Muscle tissue contains many long fibers (myocytes) connected into a bundle (from 10 to 50 myocytes in one bundle). From these bundles the belly of the skeletal muscle is formed. Each bundle of myocytes, as well as the muscle itself, is covered with a dense sheath of connective tissue. At the ends, the shell passes into tendons, which are attached to the bones at several points.

Blood vessels (capillaries) and nerve fibers pass between the bundles of muscle fibers.

Each fiber consists of smaller filaments - myofibrils. They are made up of even smaller particles called sarcomeres. They contract voluntarily under the influence of nerve impulses sent from the brain and spinal cord, producing joint movement. Although our movements are under our conscious control, the brain can learn movement patterns so that we can perform certain tasks, such as walking, without thinking.

Strength training helps increase the number of muscle fiber myofibrils and their cross-section. First, the strength of the muscle increases, and then its thickness. But the number of muscle fibers themselves does not change and it is genetically determined. Hence the conclusion: those whose muscles contain more fibers are more likely to increase muscle thickness through strength training than those whose muscles contain fewer fibers.

The thickness and number of myofibrils (the cross-section of the muscle) determines the strength of the skeletal muscle. Strength and muscle mass do not increase equally: when muscle mass doubles, muscle strength becomes three times greater.

There are two types of skeletal muscle fibers:

• slow (ST fibers)
• fast (FT fibers)

Slow fibers are also called red fibers because they contain large amounts of the red protein myoglobin. These fibers are durable, but work at a load within 20-25% of the maximum muscle strength.

Fast fibers contain little myoglobin and are therefore also called white fibers. They contract twice as fast as slow-twitch fibers and can produce ten times more force.

When the load is less than 25% of maximum muscle strength, slow-twitch fibers work. And when they become depleted, fast fibers begin to work. When their energy is used up, exhaustion sets in and the muscle needs rest. If the load is immediately large, then both types of fibers work simultaneously.

Different types of muscles that perform different functions have different ratios of fast-twitch and slow-twitch fibers. For example, the biceps contains more fast-twitch fibers than slow-twitch fibers, and the soleus muscle consists mainly of slow-twitch fibers. Which type of fiber will be predominantly involved in the work at a given moment depends not on the speed of the movement, but on the effort that needs to be spent on it.

The ratio of fast and slow fibers in the muscles of each person is genetically determined and remains unchanged throughout life.

Skeletal muscles got their names based on their shape, location, number of attachment sites, location of attachment, direction of muscle fibers, and functions.

Classification of skeletal muscles

according to form

• fusiform
• square
• triangular
• ribbon-like
• circular

by number of heads

• double-headed
• triceps
• quadriceps

by number of abdomens

• digastric

in the direction of muscle bundles

• unipinnate
• bipinnate
• multipinnate

by function

• flexor
• extensor
• rotator-lifter
• constrictor (sphincter)
• abductor (abductor)
• adductor (adductor)

by location

• superficial
• deep
• medial
• lateral

Human skeletal muscles are divided into large groups. Each large group is divided into muscles of separate areas, which can be arranged in layers. All skeletal muscles are paired and located symmetrically. Only the diaphragm is an unpaired muscle.

heads

• facial muscles
• masticatory muscles

torso

• neck muscles
• back muscles
• chest muscles
• diaphragm
• abdominal muscles
• perineal muscles

limbs

• shoulder girdle muscles
• shoulder muscles
• forearm muscles
• hand muscles

• pelvic muscles
• thigh muscles
• calf muscles
• foot muscles

Skeletal muscles are not equally located in relation to the joints. The location is determined by their structure, topography and function.

• single-joint muscles- are attached to adjacent bones and act on only one joint
• biarticular, multi-articular muscles- spread over two or more joints

Multi-joint muscles are usually longer than single-joint muscles and are located more superficially. These muscles begin on the bones of the forearm or lower leg and are attached to the bones of the hand or foot, to the phalanges of the fingers.

Skeletal muscles have numerous auxiliary devices:

• fascia
• fibrous and synovial tendon sheaths
• bursae
• muscle blocks

Fascia- connective membrane that forms the muscle sheath.

Fascia separates individual muscles and muscle groups from each other and performs a mechanical function, facilitating muscle function. Typically, muscles are connected to fascia using connective tissue. Some muscles start from the fascia and are firmly fused with them.

The structure of the fascia depends on the function of the muscles and on the force that the fascia experiences when the muscle contracts. Where the muscles are well developed, the fascia is denser. Muscles that bear little load are surrounded by loose fascia.

Synovial vagina separates the moving tendon from the stationary walls of the fibrous vagina and eliminates their mutual friction.

Synovial bursae, which are present in areas where a tendon or muscle passes over a bone, through an adjacent muscle, or where two tendons meet, also eliminate friction.

Block is a fulcrum for the tendon, ensuring a constant direction of its movement.

Skeletal muscles rarely work on their own. Most often they work in groups.

4 types of muscles according to the nature of their action:

agonist- directly performs any specific movement of a certain part of the body and bears the main load during this movement

antagonist- performs the opposite movement in relation to the agonist muscle

synergist- gets involved in the work together with the agonist and helps him complete it

stabilizer- support the rest of the body while performing the movement

Synergists are located on the side of the agonists and/or close to them. Agonists and antagonists are usually located on opposite sides of the bones of the working joint.

Contraction of an agonist can lead to reflex relaxation of its antagonist - mutual inhibition. But this phenomenon does not occur with all movements. Sometimes joint compression occurs.

Biomechanical properties of muscles:

Contractility- the ability of a muscle to contract when excited. The muscle shortens and a traction force occurs.

Muscle contraction occurs in different ways:

-dynamic reduction- tension in a muscle that changes its length

Thanks to this, movements occur in the joints. Dynamic muscle contraction can be concentric (the muscle shortens) or eccentric (the muscle lengthens).

-isometric contraction (static)- tension in a muscle at which its length does not change

When tension occurs in the muscle, no movement occurs in the joint.

Elasticity- the ability of a muscle to restore its original length after eliminating the deforming force. When a muscle is stretched, elastic deformation energy occurs. The more a muscle is stretched, the more energy it stores.

Rigidity- the ability of a muscle to resist applied forces.

Strength- determined by the magnitude of the tensile force at which the muscle ruptures.

Relaxation- a property of a muscle that manifests itself in a gradual decrease in traction force at a constant muscle length.

Strength training promotes the growth of muscle tissue and increases the strength of skeletal muscles, improves the functioning of smooth muscles and cardiac muscle. Due to the fact that the heart muscle works more intensely and efficiently, the blood supply not only to the entire body, but also to the skeletal muscles themselves improves. Thanks to this, they are able to carry more load. Well-developed muscles, thanks to training, provide better support for internal organs, which has a beneficial effect on the normalization of digestion. In turn, good digestion provides nutrition to all organs, and in particular muscles.

Skeletal muscle functions and training exercises

Upper body muscles

Biceps brachii (biceps)- bends the arm at the elbow, rotates the hand outward, strains the arm at the elbow joint.

Resistance exercises: all types of arm curls; rowing movements.

Pull-ups, rope climbing, rowing.

Pectoralis major muscle: clavicular sternal (chest)- brings the hand forward, inward, up and down.

Resistance Exercises: Bench presses at any angle, prone flyes, push-ups, overhead rows, dips, cross-arms on blocks.

Sternocleidomastoid muscle (neck)- tilts his head to the sides, turns his head and neck, tilts his head forward and back.

Resistance exercises: head strap exercises, wrestling bridge, partner resistance exercises and self-resistance exercises.

Wrestling, boxing, football.

Coracobrachialis muscle- raises his hand to his shoulder, pulls his hand towards his body.

Resistance exercises: flyes, raises, bench press.

Throwing, bowling, arm wrestling.

Brachialis muscle (shoulder)- brings the forearm to the shoulder.

Resistance exercises: all types of curls, reverse curls, rowing movements.

Pull-ups, rope climbing, arm wrestling, weightlifting.

Forearm muscle group: brachioradialis, extensor carpi radialis longus, extensor carpi ulnaris, abductor muscle and extensor pollicis (forearm) - brings the forearm to the shoulder, flexes and straightens the hand and fingers.

Resistance exercises: wrist curls, wrist roller exercises, Zottman curls, holding barbell plates in your fingers.

All types of sports, competitions of security forces using hands.

Rectus abdominis (abdominals)- tilts the spine forward, tightens the anterior wall of the abdomen, spreads the ribs.

Exercises with resistance: all types of lifting the body from a lying position, the same with a reduced amplitude, lifting on a “Roman chair”.

Gymnastics, pole vaulting, wrestling, diving, swimming.

Serratus anterior major muscle (serratus muscles)- turns the scapula down, spreads the shoulder blades, expands the chest, raises the arms above the head.

Resistance exercises: pullovers, standing presses.

Weightlifting, throwing, boxing, pole vaulting.

External obliques (obliques)- bend the spine forward and to the sides, tighten the anterior wall of the abdominal cavity.

Resistance exercises: side bends, torso crunches, crunches.

Shot put, javelin throw, wrestling, football, tennis.

Trapezius muscle (trapezius)- raises and lowers the shoulder girdle, moves the shoulder blades, moves the head back and tilts to the sides.

Resistance exercises: shoulder raises, barbell cleans, overhead presses, overhead raises, rowing movements.

Weightlifting, wrestling, gymnastics, handstand.

Deltoid muscle group: front head, side head, back head (deltoids) - raise the arms to a horizontal position (each head raises the arm in a specific direction: front - forward, side - to the sides, back - back).

Exercises with resistance: all presses with a barbell, dumbbells; bench presses (front deltoid); lifting dumbbells forward, sideways and backwards; pull-ups on the bar (rear delta).

Weightlifting, gymnastics, shot put, boxing, throwing.

Triceps muscle (triceps)- straightens his hand and takes it back.

Resistance exercises: arm straightening, cable presses, close grip bench presses; all exercises that involve straightening the arms. Plays an auxiliary role in rowing exercises.

Handstand, gymnastics, boxing, rowing.

Latissimus dorsi (latissimus dorsi)- move the arm down and back, relax the shoulder girdle, promote increased breathing, and bend the torso to the side.

Resistance exercises: all types of pull-ups and rows, rowing movements, pullovers.

Weightlifting, rowing, gymnastics.

Back muscle group: supraspinatus muscle, teres minor muscle, teres major muscle, rhomboid (back) - rotate the arm outward and inward, help in abducting the arm back, rotate, raise and retract the shoulder blades.

Resistance exercises: squats, deadlifts, rowing movements, sit-ups.

Weightlifting, wrestling, shot put, rowing, swimming, football defense, dance moves.

Muscles of the lower body

Quadriceps: vastus externus, rectus femoris, vastus externus, sartorius (quadriceps) - straighten legs, hip joint; bend the legs, hip joint; turn the leg out and in.

Resistance Exercises: All forms of squats, leg presses and leg extensions.

Rock climbing, cycling, weightlifting, track and field, ballet, football, skating, European football, powerlifting, sprints, dancing.

Biceps hamstrings: semimembranosus, semitendinosus (biceps femoris) - various actions: leg flexion, hip rotation in and out, hip extension.

Resistance exercises: leg curls, straight-legged deadlifts, wide-footed Gakken squats.

Wrestling, sprinting, skating, ballet, steeplechase, swimming, jumping, weightlifting, powerlifting.

Gluteus maximus (buttocks)- straightens and rotates the thigh outward.

Resistance exercises: squats, leg presses, deadlifts.

Weightlifting, powerlifting, skiing, swimming, sprints, cycling, rock climbing, dancing.

Calf muscle (shin)- straightens the foot, promotes tension in the knee, “switching off” the knee joint.

Resistance exercises: standing calf raises, donkey raises, half squats or quarter squats.

All forms of jumping and running, cycling, ballet.

Soleus muscle

Resistance exercises: seated calf raises.

Anterior shin group: tibialis anterior, peroneus longus - straightens, flexes and rotates the foot.

Resistance exercises: standing and sitting calf raises, toe raises.

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.