Movement of the animal, movement of parts

his body relative to each other, the work of internal organs, acts of breathing,

blood circulation, digestion, excretion are carried out thanks to the action

activity of various muscle groups.

Higher animals have three types of muscles: striated

skeletal (voluntary), striated cardiac (involuntary)

nal), smooth muscles of internal organs, blood vessels and skin (involuntary).

Specialized contractile formations are considered separately.

niya - myoepithelial cells, muscles of the pupil and ciliary body of the eye.

In addition to the properties of excitability and conductivity, muscles have contractile

tenacity, i.e. the ability to shorten or change the degree of tension

nia when excited. The reduction function is possible thanks to the presence

in muscle tissue of special contractile structures.

ULTRASTRUCTURE AND BIOCHEMICAL COMPOSITION OF MUSCLES

Skeletal muscles. On the cross section

long-fibrous muscle, it is clear that it consists of primary

bundles containing 20 - 60 fibers. Each bundle is separated by connecting

the tissue shell is the perimysium, and each fiber is the endomysium.

In animal muscle there are from several hundred to several hundred

thousand fibers with a diameter from 20 to 100 microns and a length of up to 12 - 16 cm.

A separate fiber is covered with a true cell membrane - sarco-

lemma. Immediately below it, approximately every 5 µm along the length, there is a

core wives. The fibers have a characteristic cross-striation, which

is caused by the alternation of optically more and less dense areas.

The fiber is formed by many (1000 - 2000 or more) tightly packed

baths of myofibrils (diameter 0.5 - 2 µm), stretching from end to end.

Mitochondria are located in rows between the myofibrils, where

oxidative phosphorylation processes necessary to supply

muscles with energy.

Under a light microscope, myofibrils represent formations

consisting of regularly alternating dark and light

disks. Disks A are called anisotropic (have double

refraction), I disks are isotropic (almost do not have double

refraction). The length of A-disks is constant, the length of I-disks depends

from the stage of muscle fiber contraction. In the middle of each isotropic

disk there is an X-strip; in the middle of the anisotropic disk there is a less pronounced

Women's M-stripe.

Due to the alternation of isotronic and anisotropic segments, each

the myofibril has transverse striations. The ordered arrangement

The movement of myofibrils in the fiber gives the same striation to the fiber

generally.

Electron microscopy showed that each myofibril consists

from parallel filaments, or protofibrils (filaments) of different

thickness and different chemical composition. In a single myofibril there are

There are 2000 - 2500 protofibrils. Thin protofibrils have a

riverine 5 - 8 nm and length 1 - 1.2 microns, thick - respectively 10 - 15 nm and

1.5 microns.

Thick protofibrils containing myosin protein molecules form

anisotropic disks are formed. At the level of the M stripe, myosin filaments are connected

the thinnest transverse connections. Thin protofibrils consisting

mainly from the protein actin, form isotropic disks.

Actin filaments are attached to the X stripe, crossing it in both directions.

nikah; they occupy not only the I-disk area, but also enter the gaps

between the myosin filaments in the A-disc region. In these areas actin filaments

and myosin are interconnected by cross bridges extending from

myosin. These bridges, along with other substances, contain an enzyme

ATPase. The region of A-disks that does not contain actin filaments is designated

as zone N. On a cross-section of the myofibril in the region of the edges of the A-discs

it can be seen that each myosin fiber is surrounded by six actin filaments

tami.

Structural and functional contractile unit of the myofibril

is a sarcomere - a repeating section of a fibril, limited

two X stripes. It consists of half isotropic, whole anisotropic

one and half of another isotropic disk. Sarcomere size in muscles

warm-blooded is about 2 microns. Electron microphotograph of sarcomeres

appear clearly.

Smooth endoplasmic reticulum of muscle fibers, or sarcoplasm

tic reticulum forms a single system of tubes and cisterns.

Individual tubes run in the longitudinal direction, forming myo-

fibrils anastomoses, and then pass into cavities (cisterns), girdles

spreading myofibrils in a circle. A pair of adjacent tanks are almost touching

with transverse tubes (T-channels) running across from the sarcolemma

entire muscle fiber. Complex of a transverse T-channel and two

tanks symmetrically located on its sides are called a triad.

In amphibians, triads are located at the level of X-stripes, in mammals -

at the border of A-disks. Elements of the sarcoplasmic reticulum are involved

- contribute to the spread of excitation into muscle fibers, as well as

in the processes of muscle contraction and relaxation.

1 g of striated muscle tissue contains about 100 mg

contractile proteins, mainly myosin and actin, forming

actomyosin complex. These proteins are insoluble in water, but can be

extracted with salt solutions. Other contractile proteins include

tropomyosin and troponin complex (subunits T, 1, C) contain

woven in thin threads.

Muscle also contains myoglobin, glycolytic enzymes and

other soluble proteins that do not perform a contractile function

3. Protein composition of skeletal muscle

Molecular Contents.

Protein mass, dalton, protein, %

thousand

Myosin 460 55 - 60

Actin-r 46 20 - 25

Tropomyosin 70 4 - 6

Troponin complex (TnT, 76 4 - 6

Tp1, Tps)

Actinin-i 180 1 - 2

Other proteins (myoglobin, 5 - 10

enzymes, etc.)

Smooth muscles. The main structural elements of smooth muscle are

The main tissue are myodites - muscle cells of the spindle-shaped and star-shaped

flat shape with a length of 60 - 200 microns and a diameter of 4 - 8 microns. The largest

Longer cell lengths (up to 500 µm) are observed in the uterus during pregnancy.

The nucleus is located in the middle of the cells. Its shape is ellipsoidal, when contracted

cells it twists in a corkscrew shape, concentrated around the nucleus

mitochondria and other trophic components.

Myofibrils in the sarcoplasm of smooth muscle cells apparently

are missing. There are only longitudinally oriented, irregular

distributed myosin and actin protofibrils 1 - 2 μm long.

Therefore, no transverse striation of the fibers is observed. In protoplasm

cells contain a large number of vesicles containing Ca++,

which probably correspond to the sarcoplasmic reticulum transversely

riverine striated muscles.

In the walls of most hollow organs, smooth muscle cells are connected

special intercellular contacts (desmosomes) and form dense

bundles cemented by glycoprotein intercellular substance,

collagen and elastic fibers.

Such formations in which cells are in close contact, but the cytoplasm

there is no matic and membrane continuity between them (spatial

the distance between the membranes in the contact area is 20 - 30 nm),

called "functional syncytium".

The cells that form a syncytium are called unitary; excitation

can spread unhindered from one such cell to another,

although the nerve motor endings of the autonomic nervous system are divided

laid down only on some of them. In the muscle layers of some large

vessels, in the muscles that raise the hair, in the ciliary muscle of the eye there are

there are multiunitary cells equipped with individual nerve fibers

us and functioning independently of one another.

MECHANISM OF MUSCLE CONTRACTION

Under normal conditions, skeletal muscles are excited

are given by impulses that travel along the fibers of the motor neuron

new (motoneurons) located in the anterior horns of the spinal cord or

in the nuclei of the cranial nerves.

Depending on the number of terminal branches, the nerve fiber

forms synaptic contacts with a greater or lesser number of muscle

fibers

A motor neuron, its long process (axon) and a group of muscle fibers,

innervated by this axon constitute the motor, or neuromotor,

unit.

The thinner and more specialized the muscle is, the less

muscle fibers are part of the neuromotor unit. Small engines

units include only 3 - 5 fibers (for example, in the muscles of the eyeball,

small muscles of the facial part of the head), large motor units - up to

fiber (axon) of several thousand fibers (in large muscles of the trunk and

limbs). In most muscles, motor units correspond to

primary muscle bundles, each of which contains from 20 to 60

muscle fibers. Motor units differ not only in number

fibers, but also the size of neurons - large motor units include

a larger neuron with a relatively thicker axon.

The neuromotor unit works as a single unit: impulses,

coming from the motor neuron, they activate muscle fibers.

The contraction of muscle fibers is preceded by their electrical stimulation.

movement caused by the discharge of motor neurons in the area of ​​the end plates.

The terminal potential arising under the influence of the mediator

plates (PKG1), having reached the threshold level (about - 30 mV), causes

generation of an action potential propagating in both directions along

muscle fiber.

The excitability of muscle fibers is lower than the excitability of nerve fibers,

innervating muscles, although the critical level of membrane depolarization

in both cases the same. This is explained by the fact that the resting potential of the muscle

ny fibers above (about - 90 mV) the resting potential of nerve fibers

(- 70 mV). Therefore, for an action potential to occur in the muscle,

the cervical fiber needs to depolarize the membrane by a large amount,

than in a nerve fiber.

The duration of an action potential in a muscle fiber is

5 ms (in the nervous one, 0.5 - 2 ms, respectively), the speed of conduction of excitation

pressure up to 5 m/s (in myelinated nerve fibers - up to 120 m/s).

Molecular mechanisms of contraction. Downsizing is change

mechanical state of the myofibrillar apparatus of muscle fibers

influenced by nerve ampulses. Externally, the contraction manifests itself in changes

the length of the muscle or the degree of its tension, or at the same time

and another.

According to the accepted “sliding theory,” contraction is based on

interaction between actin and myosin filaments of myofibrils

due to the formation of cross bridges between them. As a result

there is a “retraction” of thin actin myofilaments between the myosi-

new.

During gliding, the actin and myosin filaments themselves do not shorten.

are chilling; the length of A-discs also remains the same, while 3-discs

and H-zones become narrower. The length of the threads does not change when stretched

As the muscles move, the degree of their mutual overlap decreases.

These movements are based on a reversible change in the conformation of the terminal

parts of myosin molecules (transverse projections with heads), in which

ligament between the thick myosin filament and the thin actin filament

are formed, disappear and appear again.

Before stimulation or during the relaxation phase, actin monomer is not available

for interaction, since this is prevented by the troponin complex and certain

nal conformation (pulling towards the filament axis) of the terminal fragments

myosin molecules.

The molecular mechanism of contraction is based on the process

called electromechanical coupling, with a key role

in the process of interaction between myosin and actin myofilaments play

Ca++ ions contained in the sarcoplasmic reticulum. This is confirmed

It is expected that in the experiment, when calcium is injected into the fibers

their reduction occurs.

The emerging potential extends not only along the surface

membrane of the muscle fiber, but also along the membranes lining the transverse

river tubules (T-fiber system). The wave of depolarization takes over

adjacent membranes of the sarcoplasmic reticulum tanks,

which is accompanied by activation of calcium channels in the membrane and the release

Ca++ ions into the interfibrillar space.

The influence of Ca+ ions on the interaction of actin and myosin is mediated by

formed by tropomyosin and troponin complex which are localized

in thin threads and constitute up to 1/3 of their mass. When binding Ca++ ions

with troponin (spherical molecules of which “sit” on actin chains)

the latter is deformed, pushing tropomyosin into the grooves between the two

actin chains. In this case, actin interaction becomes possible

with myosin heads, and the force of contraction occurs. At the same time

dit hydrolysis of ATP.

Since a single rotation of the “heads” shortens the sarcomere only

by 1/100 of its length (and with isotonic contraction, the muscle sarcomere

can be shortened by 50% of the length in tenths of a second), clearly,

that the cross bridges should make approximately 50 “stroke” movements

marriages over the same period of time. The cumulative shortening of the sequence

closely located sarcomeres of myofibrils leads to noticeable

muscle contraction.

With a single contraction, the shortening process soon ends.

The calcium pump, driven by ATP energy, reduces the concentration

Ca++ in the muscle cytoplasm up to 10 M and increases it in sarcollasma

tic reticulum up to 10 M, where Ca++ is bound by the calsec protein

Westrin.

A decrease in the level of Ca++ in the sarcoplasm suppresses ATPase activity

actomyosin activity; in this case, the myosin cross bridges are disconnected

from actin. Relaxation occurs, lengthening of the muscle, which is

passive process.

If the stimuli arrive at a high frequency (20 Hz or more),

the level of Ca++ in the sarcoplasm remains high between stimuli,

since the calcium pump does not have time to “drive” all the Ca++ ions into the system

sarcoplasmic reticulum. This is the reason for the persistent

tetanic muscle contraction.

Thus, the contraction and relaxation of a muscle represents

a series of processes unfolding in the following sequence:

incentive -> occurrence of an action potential -> electromechanical co-

tension (conduction of excitation through T-tubes, release of Ca++ and

its effect on the troponin-tropomyosin-actin system) -> education

the formation of cross bridges and the “sliding” of actin filaments along the myosin

new -> contraction of myofibrils -> decrease in the concentration of Ca++ ions

due to the work of the calcium pump -> spatial change

proteins of the contractile system -> relaxation of myofibrils.

After death, the mice remain tense, the so-called

rigor mortis. In this case, cross-links between filaments

actin and myosin are preserved and cannot break due to a decrease

level of ATP and the impossibility of active transport of Ca++ into the sarcoplasm

tic reticulum.

STRUCTURE AND FUNCTION OF THE NEURON

Material for building the central nervous system and its conduction

kov is nervous tissue, consisting of two components - nerve

cells (neurons) and neuroglia. Main functional elements

The central nervous system is made up of neurons: there are approximately 50 billion of them in the animal body,

of which only a small part is located in peripheral areas

bodies.

Neurons make up 10 - 15% of the total number of cellular elements

in the nervous system. The main part of it is occupied by neuroglial cells.

In higher animals, in the process of postnatal ontogenesis, differentiation

ciated neurons do not divide. Neurons vary significantly in

shape (pyramidal, round, star-shaped, oval), size (from 5 to

150 µm), the number of processes, but they also have common properties.

Any nerve cell consists of a body (soma, perikaryon) and processes

different types - dendrites (from lat. dendron - tree) and axon (from lat.

axon - axis). Depending on the number of processes, unipolar ones are distinguished

(single-prong), bipolar (double-prong) and multipolar

(multi-process) neurons. For the central nervous system of vertebrates, bipolar

and especially multipolar neurons.

There can be many dendrites, sometimes they are highly branched, of different

thickness and are equipped with protrusions - “spikes”, which greatly increase

their surface.

There is always one axon (neurite). It starts from the soma with an axon hillock,

covered with a special glial membrane, forms a number of axonal junctions

chaniya - terminal. The length of the axon can reach more than a meter. Axonal

the colliculus and the part of the axon not covered by the myelin sheath constitute

axon initial segment; its diameter is small (1 - 5 microns).

In the ganglia of the spinal and cranial nerves they are distributed as follows:

called pseudounipolar cells; their dendrite and axon extend from

cells in the form of a single process, which then divides in a T-shape.

Distinctive features of nerve cells are large

nucleus (up to 1/3 of the cytoplasm area), numerous mitochondria, strongly

developed reticular apparatus, the presence of characteristic organelles - tigroid

substances and neurofibrils. The tigroid substance has the appearance of basophilic

lumps and is a granular cytoplasmic network with multi-

nature of ribosomes. The function of the tigroid is associated with the synthesis of cellular proteins.

With prolonged irritation of the cell or cutting of axons, this substance

disappears. Neurofibrils are filamentous, clearly defined structures

located in the body, dendrites and axon of the neuron. Even more educated

thin elements - neurofilaments during their aggregation with neurotubules.

They apparently perform a supporting function.

There are no ribosomes in the cytoplasm of the axon, but there are mitochondria,

endoplasmic reticulum and well-developed neurofilament apparatus and

neurotubules. It has been established that axons are very complex

transport systems, and for certain types of transport (proteins,

metabolites, mediators) are apparently answered by different subcellular

structures.

Some parts of the brain have neurons that produce granules

secretion of mucoprotein or glycoprotein nature. They possess at the same time

physiological signs of neurons and glandular cells. These cells

are called neurosecretory.

The function of neurons is to perceive signals from receptors

or other nerve cells, storage and processing of information and re-

giving nerve impulses to other cells - nerve, muscle or secretory.

Accordingly, specialization of neurons takes place. They are divided into

3 groups:

sensitive (sensory, afferent) neurons that perceive signals

from the external or internal environment;

associative (intermediate, intercalary) neurons connecting different

nerve cells with each other;

motor (effector) neurons transmitting descending influences from

upstream parts of the central nervous system to downstream ones or from the central nervous system

to the working bodies.

The bodies of sensory neurons are located outside the central nervous system: in the spinal cord

ganglia and their corresponding ganglia of the brain. These neurons

have a pseudounipolar shape with an axon and an axon-like dendrite.

Afferent neurons also include cells, axons

which make up the ascending tracts of the spinal cord and brain.

Association neurons are the most numerous group of neurons.

They have a smaller size, a stellate shape and axons with numerous

long branches; located in the gray matter of the brain. Implementation

connection between different neurons, for example sensory and motor

significant within one brain segment or between adjacent segments;

their processes do not extend beyond the central nervous system.

Motor neurons are also located in the central nervous system. Their axons are involved

involve the transmission of downward influences from higher-lying areas

brain to lower ones or from the central nervous system to working organs (for example,

motor neurons in the anterior horns of the spinal cord). There are effector-

ny neurons in the autonomic nervous system. The features of these

The rons are an extensive network of dendrites and one long axon.

The perceptive part of the neuron is mainly branching

dendrites equipped with a receptor membrane. As a result of the summation

local processes of excitation in the most easily excitable triger

in the axon zone, nerve impulses (action potentials) arise, which

spread along the axon to the terminal nerve endings. This way

So, the excitation passes through the neuron in one direction - from the dendrites

to the soma and axon.

Neuroglia. The bulk of nervous tissue consists of glial cells

elements that perform auxiliary functions and fill almost

all the space between neurons. Anatomically, they are distinguished

neuroglial cells in the brain (oligodendrocytes and astrocytes) and Schwann cells

cells in the peripheral nervous system. Oligodendrocytes and Schwann cells

cells form myelin sheaths around axons.

Between glial cells and neurons there are gaps as wide as

15 - 20 nm, which communicate with each other, forming an interstitial

space filled with liquid. Through this space

there is an exchange of substances between the neuron and glial cells, and

also supplying neurons with oxygen and nutrients through

diffusion. Glial cells apparently perform only supporting and

protective functions in the central nervous system, and are not, as assumed, the source

com their food or information keepers.

Glial cells differ from neurons in their membrane properties:

they react passively to electric current; their membranes do not generate

They are responsible for the propagating impulse. Between neuroglial cells there is a

There are tight contacts (low resistance areas), which

These provide direct electrical communication. Membrane poten-

cial of glial cells is higher than that of neurons and depends mainly

on the concentration of K+ ions in the medium.

When, during active activity of neurons in the extracellular space,

concentration increases

K+, part of it is absorbed by depolarized glial elements.

This buffering function of glia provides a relatively constant external

cellular K+ concentration.

Glial cells - astrocytes - are located between the bodies of neurons

and the wall of the capillaries, their processes are in contact with the wall of the latter.

These perivascular processes are elements of the hematoencephalic

sky barrier.

Microglial cells perform a phagocytic function, their number is sharp

increases with damage to brain tissue.

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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 with 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

Plant and animal organisms differ not only externally, but also, of course, internally. However, the most important distinguishing feature of the way of life is that animals are able to actively move in space. This is ensured due to the presence of special tissues in them - muscle tissue. We will look at them in more detail later.

Animal tissue

In the body of mammals, animals and humans, there are 4 types of tissues that line all organs and systems, form blood and perform vital functions.

The combined combination of all of these types ensures the normal structure and functioning of living beings.

Muscle tissue: classification

A specialized structure plays a special role in the active life of humans and animals. Its name is muscle tissue. Its structure and functions are very unique and interesting.

In general, this fabric is heterogeneous and has its own classification. It should be considered in more detail. There are such types of muscle tissue as:

• smooth;
• striated;
• cardiac.

Each of them has its own location in the body and performs strictly defined functions.

The structure of a muscle tissue cell

All three types of muscle tissue have their own structural features. However, it is possible to identify general patterns of cell structure of such a structure.

Firstly, it is elongated (sometimes reaching 14 cm), that is, it stretches along the entire muscular organ. Secondly, it is multinuclear, since it is in these cells that the processes of protein synthesis, formation and breakdown of ATP molecules occur most intensively.

Also, the structural features of muscle tissue are that its cells contain bundles of myofibrils formed by two proteins - actin and myosin. They provide the main property of this structure - contractility. Each thread-like fibril includes stripes that are visible under a microscope as lighter and darker. They are protein molecules that form something like strands. Actin forms light ones, and myosin forms dark ones.

The peculiarity of muscle tissue of any type is that their cells (myocytes) form entire clusters - bundles of fibers, or symplasts. Each of them is lined from the inside with entire clusters of fibrils, while the smallest structure itself consists of the proteins mentioned above. If we consider figuratively this structural mechanism, it turns out like a nesting doll - less in more, and so on down to the very bundles of fibers united by loose connective tissue into a common structure - a certain type of muscle tissue.

The internal environment of the cell, that is, the protoplast, contains all the same structural components as any other in the body. The difference is in the number of nuclei and their orientation not in the center of the fiber, but in the peripheral part. Also, division occurs not due to the genetic material of the nucleus, but thanks to special cells called satellites. They are part of the myocyte membrane and actively perform the function of regeneration - restoring tissue integrity.

Properties of muscle tissue

Like any other structures, these types of tissues have their own characteristics not only in structure, but also in the functions they perform. The main properties of muscle tissue due to which they can do this:

• reduction;
• excitability;
• conductivity;
• lability.

Thanks to the large number of blood vessels and capillaries that supply the muscles, they can quickly perceive signal impulses. This property is called excitability.

Also, the structural features of muscle tissue allow it to quickly respond to any irritation, sending a response impulse to the cerebral cortex and spinal cord. This is how the property of conductivity manifests itself. This is very important, since the ability to respond in a timely manner to threatening influences (chemical, mechanical, physical) is an important condition for the normal safe functioning of any organism.

Muscle tissue, the structure and functions that it performs - all this generally comes down to the main property, contractility. It implies a voluntary (controlled) or involuntary (without conscious control) decrease or increase in the length of the myocyte. This happens due to the work of protein myofibrils (actin and myosin filaments). They can stretch and thin almost to the point of invisibility, and then quickly restore their structure again.

This is the peculiarity of muscle tissue of any type. This is how the work of the human and animal heart, their blood vessels, and the eye muscles that rotate the apple are structured. It is this property that provides the ability for active movement and movement in space. What could a person do if his muscles could not contract? Nothing. Raising and lowering your arm, jumping, squatting, dancing and running, performing various physical exercises - only muscles help you do all this. Namely, myofibrils of actin and myosin nature, forming tissue myocytes.

The last property that needs to be mentioned is lability. It implies the ability of tissue to quickly recover after stimulation and return to full performance. Only axons can do this better than myocytes -

The structure of muscle tissue and the possession of the listed properties are the main reasons for their performance of a number of important functions in animal and human organisms.

Smooth fabric

One of the types of muscle. It is of mesenchymal origin. It is arranged differently from others. Myocytes are small, slightly elongated, resembling fibers thickened in the center. The average cell size is about 0.5 mm in length and 10 µm in diameter.

The protoplast is distinguished by the absence of a sarcolemma. There is one nucleus, but there are many mitochondria. Localization of genetic material, separated from the cytoplasm by the karyolemma, is in the center of the cell. The plasma membrane has a fairly simple structure; complex proteins and lipids are not observed. Myofibril rings containing actin and myosin in small quantities, but sufficient for tissue contraction, are scattered near the mitochondria and throughout the cytoplasm. The endoplasmic reticulum and Golgi complex are somewhat simplified and reduced compared to other cells.

Smooth muscle tissue is formed by bundles of myocytes (spindle-shaped cells) of the described structure and is innervated by efferent and afferent fibers. Subject to the control of the autonomic nervous system, that is, it contracts and is excited without conscious control of the body.

In some organs, smooth muscle is formed due to individual single cells with special innervation. Although this phenomenon is quite rare. In general, two main types of smooth muscle cells can be distinguished:

The first group of cells is poorly differentiated, contains many mitochondria, and a well-defined Golgi apparatus. Bundles of contractile myofibrils and microfilaments are clearly visible in the cytoplasm.

The second group of myocytes specializes in the synthesis of polysaccharides and complex combinative high-molecular substances, from which collagen and elastin are subsequently built. They also produce a significant part of the intercellular substance.

Locations in the body

Smooth muscle tissue, the structure and functions it performs, allow it to be concentrated in different organs in unequal quantities. Since innervation is not subject to control by the directed activity of a person (his consciousness), then the localization locations will be appropriate. Such as:

• walls of blood vessels and veins;
• most of the internal organs;
• leather;
• eyeball and other structures.

In this regard, the nature of the activity of smooth muscle tissue is fast-acting and low.

Functions performed

The structure of muscle tissue leaves a direct imprint on the functions they perform. So, smooth muscles are needed for the following operations:

The gallbladder, the junction of the stomach into the intestine, the bladder, lymphatic and arterial vessels, veins and many other organs - all of them are able to function normally only due to the properties of smooth muscles. Management, let us make a reservation once again, is strictly autonomous.

Striated muscle tissue

The ones discussed above are not subject to control by the human consciousness and are not responsible for his movement. This is the prerogative of the next type of fiber - cross-striped.

First, let's figure out why they were given such a name. When examined under a microscope, you can see that these structures have a clearly defined striation across certain strands - filaments of actin and myosin proteins that form myofibrils. This was the reason for the name of the fabric.

Transverse muscle tissue has myocytes that contain many nuclei and are the result of the fusion of several cellular structures. This phenomenon is referred to as “symplast” or “syncytium”. The appearance of the fibers is represented by long, elongated cylindrical cells, tightly connected to each other by a common intercellular substance. By the way, there is a certain tissue that forms this environment for the articulation of all myocytes. Smooth muscle also has it. Connective tissue is the basis that can be either dense or loose. It also forms a whole series of tendons, with the help of which striated skeletal muscles are attached to the bones.

The myocytes of the tissue in question, in addition to their significant size, have several more features:

• the sarcoplasm of cells contains a large number of clearly distinguishable microfilaments and myofibrils (actin and myosin at the base);
• these structures are combined into large groups - muscle fibers, which, in turn, directly form the skeletal muscles of different groups;
• there are many nuclei, a well-defined reticulum and Golgi apparatus;
• Numerous mitochondria are well developed;
• innervation is carried out under the control of the somatic nervous system, that is, consciously;
• fiber fatigue is high, but so is performance;
• lability is above average, rapid recovery after refraction.

In the body of animals and humans, striated muscles are red. This is explained by the presence of myoglobin, a specialized protein, in the fibers. Each myocyte is covered on the outside with an almost invisible transparent membrane - the sarcolemma.

At a young age, animals and humans contain more dense connective tissue between myocytes. Over time and aging, it is replaced by loose and fatty tissue, so the muscles become flabby and weak. In general, skeletal muscles occupy up to 75% of the total mass. It is what makes up the meat of animals, birds, and fish that humans eat. The nutritional value is very high due to the high content of various protein compounds.

A type of striated muscle, in addition to skeletal, is cardiac. The peculiarities of its structure are expressed in the presence of two types of cells: ordinary myocytes and cardiomyocytes. Ordinary ones have the same structure as skeletal ones. Responsible for the autonomous contraction of the heart and its vessels. But cardiomyocytes are special elements. They contain a small amount of myofibrils, and therefore actin and myosin. This indicates low contractility. But that is not their task. The main role is to perform the function of conducting excitability through the heart, implementing rhythmic automation.

Cardiac muscle tissue is formed due to the repeated branching of its constituent myocytes and the subsequent association of these branches into a common structure. Another difference from striated skeletal muscle is that cardiac cells contain nuclei in their central part. Myofibrillar areas are localized along the periphery.

What organs does it form?

All skeletal muscles of the body are striated muscle tissue. A table reflecting the locations of this tissue in the body is given below.

Importance for the body

The role played by striated muscles is difficult to overestimate. After all, it is she who is responsible for the most important distinctive property of plants and animals - the ability to actively move. A person can perform a lot of the most complex and simple manipulations, and all of them will depend on the work of skeletal muscles. Many people engage in thorough training of their muscles and achieve great success in this due to the properties of muscle tissue.

Let's consider what other functions the striated muscles perform in the body of humans and animals.

1. Responsible for complex facial contractions, expression of emotions, external manifestations of complex feelings.
2. Maintains body position in space.
3. Performs the function of protecting the abdominal organs (from mechanical stress).
4. Cardiac muscles provide rhythmic contractions of the heart.
5. Skeletal muscles are involved in the acts of swallowing and form the vocal cords.
6. Regulate tongue movements.

Thus, we can draw the following conclusion: muscle tissue is an important structural element of any animal organism, endowing it with certain unique abilities. The properties and structure of different types of muscles provide vital functions. The structure of any muscle is based on the myocyte - a fiber formed from the protein filaments of actin and myosin.

Muscle as an organ, auxiliary organs of muscles.

Movement in vertebrates is carried out by muscles built from transversely striated muscle tissue.

The main structural elements of skeletal cross-striated muscle tissue are skeletal myocytes, on which cambial poorly differentiated cells are located. In addition, muscle as an organ includes elements of fibrous connective tissue, adipose tissue, and nerve fibers with endings. Each muscle contains blood and lymphatic vessels that form a microvasculature in the organ.

Musculature in its structure is a typical parenchymal organ. The working tissue or parenchyma will be the muscle tissue itself, and the stroma (framework) will be the connective tissue membranes:

1. Endomysium(endomysium) is the loose connective tissue that surrounds each muscle fiber.

2. Perimysium (perimysium) is a dense connective tissue that unites several muscle fibers into one bundle; blood vessels and nerves extend from the thickness of the perimysium.

3.Epimysium (epimysium) is the outer shell consisting of dense connective tissue with a small amount of adipose tissue.

Muscle types:

1. Unipinnate- these are muscles in which the bundles of muscle fibers run obliquely in relation to the length of the muscle.

2. Bipinnate- these are muscles in which bundles of muscle fibers approach the center of the tendon from two opposite sides.

3. Multipinnate- these are muscles in which bundles of muscle fibers go in different directions, as a result of which the tendon can be divided into three or more plates.

Accessory and auxiliary organs of muscles are tendons (aponeuroses), fascia, mucous bursae, synovial sheaths, sesamoid bones and pulleys.

Tendon (tendo) is located at the ends of the muscle belly, has a connective tissue skeleton, tendon parenchyma, and consists of dense connective tissue fibers that are located strictly to each other.

The shape of the tendons corresponds to the shape of the muscle.

Properties of the tendon: low fatigue and high resistance to stretching.

3 sheaths of the connective tissue skeleton of the tendon:

1. Endotenon (endotenonium) surrounds the tendon fiber itself.

2. Peritenon (peritenonium) surrounds the first tendon bundle.

3. Epithenon (epitronium) surrounds the tendon like a sheath.

Synovial bursae (bursasynovialis) are small sacs filled with synovial fluid. The cavities of the synovial bursae and those located near the joints often communicate with each other.

Function: To prevent friction of muscles, tendons or ligaments with other organs.

According to development features and topography they are divided into: permanent And acquired, axillary, subtendinous, subglottic, subcutaneous.

Synovial vaginas (vaginasynovialis) are similar in structure and purpose to bursae. Their wall consists of two membranes - synovial and fibrous. Synovial has two leaves. The visceral connects to the tendon, and the parietal is adjacent to the fibrous membrane. The area where the parietal layer transitions to the visceral layer is called mesentery of tendon (mesotendineum). Vessels and nerves pass through it to the tendon. Between the visceral and parietal layers there is a slit-like cavity filled with synovial fluid.

Fascia (f ascia) surround individual muscles (special fascia) or groups of muscles (deep fascia) or the entire body (superficial fascia). They consist of dense connective tissue.

Sesamoid bones (ossasesamoidea) are secondary bone structures. They can form both inside tendons and in the wall of the capsule of some joints. In this case, the sesamoid bones are located at the top of the joint or where it is necessary to change the direction of the force of muscle contraction.

Blocks (trochleae) located above the protruding parts of the bone where it is necessary to change the course of the muscle or the direction of action of the force of their contractions. To eliminate friction, they are covered with hyaline cartilage. In the area of ​​the block, as a rule, synovial bursae and synovial sheaths are located.

The anatomy of human muscles, their structure and development, perhaps, can be called the most pressing topic that arouses maximum public interest in bodybuilding. Needless to say, the structure, work and function of muscles is a topic that a personal trainer should pay special attention to. As in the presentation of other topics, we will begin the introduction to the course with a detailed study of the anatomy of muscles, their structure, classification, work and functions.

Maintaining a healthy lifestyle, proper nutrition and systematic physical activity help develop muscles and reduce body fat levels. The structure and work of human muscles will be understood only by sequentially studying first the human skeleton and only then the muscles. And now that we know from the article that it also functions as a frame for attaching muscles, it’s time to study what main muscle groups form the human body, where they are located, what they look like and what functions they perform.

Above you can see what the human muscle structure looks like in the photo (3D model). First, let's look at the musculature of a man's body with terms applied to bodybuilding, then the musculature of a woman's body. Looking ahead, it is worth noting that the muscle structure of men and women is not fundamentally different; the musculature of the body is almost completely similar.

Human muscle anatomy

Muscles are called organs of the body that are formed by elastic tissue, and the activity of which is regulated by nerve impulses. The functions of muscles include movement and movement in space of parts of the human body. Their full functioning directly affects the physiological activity of many processes in the body. Muscle function is regulated by the nervous system. It promotes their interaction with the brain and spinal cord, and also participates in the process of converting chemical energy into mechanical energy. The human body forms about 640 muscles (various methods of counting differentiated muscle groups determine their number from 639 to 850). Below is the structure of human muscles (diagram) using the example of a male and female body.

Muscle structure of a man, front view: 1 – trapezoid; 2 – serratus anterior muscle; 3 – external oblique abdominal muscles; 4 – rectus abdominis muscle; 5 – sartorius muscle; 6 – pectineus muscle; 7 – long adductor muscle of the thigh; 8 – thin muscle; 9 – tensor fascia lata; 10 – pectoralis major muscle; 11 – pectoralis minor muscle; 12 – anterior head of the humerus; 13 – middle head of the humerus; 14 – brachialis; 15 – pronator; 16 – long head of the biceps; 17 – short head of the biceps; 18 – palmaris longus muscle; 19 – extensor muscle of the wrist; 20 – adductor carpi longus muscle; 21 – long flexor; 22 – flexor carpi radialis; 23 – brachioradialis muscle; 24 – lateral thigh muscle; 25 – medial thigh muscle; 26 – rectus femoris muscle; 27 – long peroneal muscle; 28 – extensor digitorum longus; 29 – tibialis anterior muscle; 30 – soleus muscle; 31 – calf muscle

Muscle structure of a man, rear view: 1 – posterior head of the humerus; 2 – teres minor muscle; 3 – teres major muscle; 4 – infraspinatus muscle; 5 – rhomboid muscle; 6 – extensor muscle of the wrist; 7 – brachioradialis muscle; 8 – flexor carpi ulnaris; 9 – trapezius muscle; 10 – rectus spinalis muscle; 11 – latissimus muscle; 12 – thoracolumbar fascia; 13 – biceps femoris; 14 – adductor magnus muscle of the thigh; 15 – semitendinosus muscle; 16 – thin muscle; 17 – semimembranosus muscle; 18 – calf muscle; 19 – soleus muscle; 20 – long peroneal muscle; 21 – abductor hallucis muscle; 22 – long head of the triceps; 23 – lateral head of the triceps; 24 – medial head of the triceps; 25 – external oblique abdominal muscles; 26 – gluteus medius muscle; 27 – gluteus maximus muscle

The structure of a woman's muscles, front view: 1 – scapular hyoid muscle; 2 – sternohyoid muscle; 3 – sternocleidomastoid muscle; 4 – trapezius muscle; 5 – pectoralis minor muscle (not visible); 6 – pectoralis major muscle; 7 – serratus muscle; 8 – rectus abdominis muscle; 9 – external oblique abdominal muscle; 10 – pectineus muscle; 11 – sartorius muscle; 12 – long adductor muscle of the thigh; 13 – tensor fascia lata; 14 – thin muscle of the thigh; 15 – rectus femoris muscle; 16 – vastus intermedius muscle (not visible); 17 – vastus lateralis muscle; 18 – vastus medialis muscle; 19 – calf muscle; 20 – tibialis anterior muscle; 21 – long extensor of the toes; 22 – long tibialis muscle; 23 – soleus muscle; 24 – anterior bundle of deltas; 25 – middle bundle of deltas; 26 – brachialis muscle; 27 – long biceps bundle; 28 – short biceps bundle; 29 – brachioradialis muscle; 30 – extensor carpi radialis; 31 – pronator teres; 32 – flexor carpi radialis; 33 – palmaris longus; 34 – flexor carpi ulnaris

Muscle structure of a woman, rear view: 1 – posterior bundle of deltas; 2 – long triceps bundle; 3 – lateral triceps bundle; 4 – medial triceps bundle; 5 – extensor carpi ulnaris; 6 – external oblique abdominal muscle; 7 – extensor of the fingers; 8 – fascia lata; 9 – biceps femoris; 10 – semitendinosus muscle; 11 – thin muscle of the thigh; 12 – semimembranosus muscle; 13 – calf muscle; 14 – soleus muscle; 15 – short peroneus muscle; 16 – flexor pollicis longus; 17 – teres minor muscle; 18 – teres major muscle; 19 – infraspinatus muscle; 20 – trapezius muscle; 21 – rhomboid muscle; 22 – latissimus muscle; 23 – spinal extensors; 24 – thoracolumbar fascia; 25 – gluteus minimus; 26 – gluteus maximus muscle

Muscles have quite a variety of shapes. Muscles that share a common tendon but have two or more heads are called biceps (biceps), triceps (triceps), or quadriceps (quadriceps). The functions of the muscles are also quite diverse, these are flexors, extensors, abductors, adductors, rotators (inward and outward), levator, depressor, straightener and others.

Types of muscle tissue

Characteristic structural features allow us to classify human muscles into three types: skeletal, smooth and cardiac.

Types of human muscle tissue: I - skeletal muscles; II - smooth muscles; III - cardiac muscle

• Skeletal muscles. The contraction of this type of muscle is completely controlled by the person. Combined with the human skeleton, they form the musculoskeletal system. This type of muscle is called skeletal precisely because of its attachment to the bones of the skeleton.
• Smooth muscles. This type of tissue is present in the cells of internal organs, skin and blood vessels. The structure of human smooth muscles implies that they are located mostly in the walls of hollow internal organs, such as the esophagus or bladder. They also play an important role in processes that are not controlled by our consciousness, for example in intestinal motility.
• Heart muscle (myocardium). The work of this muscle is controlled by the autonomic nervous system. Its contractions are not controlled by human consciousness.

Since the contraction of smooth and cardiac muscle tissue is not controlled by human consciousness, the emphasis in this article will be focused specifically on skeletal muscles and their detailed description.

Muscle structure

Muscle fiber is a structural element of muscles. Separately, each of them represents not only a cellular, but also a physiological unit that is capable of contracting. The muscle fiber has the appearance of a multinucleated cell; the fiber diameter ranges from 10 to 100 microns. This multinucleated cell is located in a membrane called the sarcolemma, which in turn is filled with sarcoplasm, and within the sarcoplasm there are myofibrils.

Myofibril is a thread-like formation that consists of sarcomeres. The thickness of myofibrils is usually less than 1 micron. Taking into account the number of myofibrils, white (aka fast) and red (aka slow) muscle fibers are usually distinguished. White fibers contain more myofibrils but less sarcoplasm. It is for this reason that they contract faster. Red fibers contain a lot of myoglobin, which is why they got their name.

Internal structure of human muscle: 1 – bone; 2 – tendon; 3 – muscular fascia; 4 – skeletal muscle; 5 – fibrous membrane of skeletal muscle; 6 – connective tissue membrane; 7 – arteries, veins, nerves; 8 – bundle; 9 – connective tissue; 10 – muscle fiber; 11 – myofibril

The work of muscles is characterized by the fact that the ability to contract faster and stronger is characteristic of white fibers. They can develop force and speed of contraction 3-5 times higher than slow fibers. Anaerobic physical activity (working with weights) is performed primarily by fast-twitch muscle fibers. Long-term aerobic physical activity (running, swimming, cycling) is performed primarily by slow-twitch muscle fibers.

Slow fibers are more resistant to fatigue, while fast fibers are not adapted to prolonged physical activity. As for the ratio of fast and slow muscle fibers in human muscles, their number is approximately the same. In most of both sexes, about 45-50% of the muscles of the limbs are slow muscle fibers. There are no significant gender differences in the ratio of different types of muscle fibers in men and women. Their ratio is formed at the beginning of a person’s life cycle, in other words, it is genetically programmed and practically does not change until old age.

Sarcomeres (components of myofibrils) are formed by thick myosin filaments and thin actin filaments. Let's look at them in more detail.

Actin– a protein that is a structural element of the cell cytoskeleton and has the ability to contract. It consists of 375 amino acid residues and makes up about 15% of muscle protein.

Myosin- the main component of myofibrils - contractile muscle fibers, where its content can be about 65%. The molecules are formed by two polypeptide chains, each of which contains about 2000 amino acids. Each of these chains has a so-called head at the end, which includes two small chains consisting of 150-190 amino acids.

Actomyosin– a complex of proteins formed from actin and myosin.

FACT. For the most part, muscles consist of water, proteins and other components: glycogen, lipids, nitrogen-containing substances, salts, etc. Water content ranges from 72-80% of the total muscle mass. Skeletal muscle consists of a large number of fibers, and characteristically, the more fibers there are, the stronger the muscle.

Muscle classification

The human muscular system is characterized by a variety of muscle shapes, which in turn are divided into simple and complex. Simple: spindle-shaped, straight, long, short, wide. Complex muscles include the multicipital muscles. As we have already said, if the muscles have a common tendon, and there are two or more heads, then they are called biceps (biceps), triceps (triceps) or quadriceps (quadriceps), and multitendon and digastric muscles are also multi-headed. The following types of muscles with a certain geometric shape are also complex: quadrate, deltoid, soleus, pyramidal, round, serrated, triangular, rhomboid, soleus.

Main functions muscles are flexion, extension, abduction, adduction, supination, pronation, raising, lowering, straightening and more. The term supination means outward rotation, and the term pronation means inward rotation.

By grain direction muscles are divided into: rectus, transverse, circular, oblique, unipennate, bipennate, multipennate, semitendinosus and semimembranosus.

In relation to the joints, taking into account the number of joints through which they are thrown: single-joint, double-joint and multi-joint.

Muscle work

During contraction, actin filaments penetrate deep into the spaces between myosin filaments, and the length of both structures does not change, but only the total length of the actomyosin complex is reduced - this method of muscle contraction is called sliding. The sliding of actin filaments along myosin filaments requires energy, and the energy required for muscle contraction is released as a result of the interaction of actomyosin with ATP (adenosine triphosphate). In addition to ATP, water plays an important role in muscle contraction, as well as calcium and magnesium ions.

As already mentioned, muscle function is completely controlled by the nervous system. This suggests that their work (contraction and relaxation) can be controlled consciously. For the normal and full functioning of the body and its movement in space, muscles work in groups. Most of the muscle groups in the human body work in pairs and perform opposite functions. It looks like this: when the “agonist” muscle contracts, the “antagonist” muscle stretches. The same is true vice versa.

• Agonist- a muscle that performs a specific movement.
• Antagonist- a muscle that performs the opposite movement.

Muscles have the following properties: elasticity, stretching, contraction. Elasticity and stretching give the muscle the ability to change in size and return to its original state, the third quality makes it possible to create force at its ends and lead to shortening.

Nerve stimulation can cause the following types of muscle contraction: concentric, eccentric and isometric. Concentric contraction occurs in the process of overcoming the load when performing a given movement (lifting up when pulling up on a bar). Eccentric contraction occurs in the process of slowing down movements in the joints (lowering down when pulling up on a bar). Isometric contraction occurs at the moment when the force created by the muscles is equal to the load exerted on them (keeping the body hanging on the bar).

Muscle functions

Knowing the name and location of this or that muscle or group of muscles, we can move on to studying the block - the function of human muscles. Below in the table we will look at the most basic muscles that are trained in the gym. As a rule, six main muscle groups are trained: chest, back, legs, shoulders, arms and abs.

FACT. The largest and strongest muscle group in the human body is the legs. The largest muscle is the gluteus. The strongest is the calf muscle; it can hold weight up to 150 kg.

Conclusion

In this article, we examined such a complex and voluminous topic as the structure and functions of human muscles. When we talk about muscles, we of course also mean muscle fibers, and the involvement of muscle fibers in the work involves the interaction of the nervous system with them, since the execution of muscle activity is preceded by the innervation of motor neurons. It is for this reason that in our next article we will move on to consider the structure and functions of the nervous system.