Bones. The structure of the bones

Bone tissue (textus ossei) is a specialized type of connective tissue with a high mineralization of intercellular organic matter containing about 70% of inorganic compounds, mainly calcium phosphates. More than 30 microelements (copper, strontium, zinc, barium, magnesium, etc.) have been found in bone tissue, which play an important role in metabolic processes in the body.

Organic matter - the matrix of bone tissue - is represented mainly by proteins of the collagen type and lipids. Compared to cartilage, it contains a relatively small amount of water, chondroitin sulfuric acid, but a lot of citric and other acids that form complexes with calcium, which impregnates the organic matrix of the bone.

Thus, the solid intercellular substance of bone tissue (in comparison with cartilaginous tissue) gives the bones higher strength, and at the same time, fragility.

Organic and inorganic components in combination with each other determine the mechanical properties of bone tissue - the ability to resist stretching and compression.

Despite the high degree of mineralization, in the bone tissues there is a constant renewal of their constituent substances, constant destruction and creation, adaptive rearrangements to changing operating conditions. The morphological and functional properties of bone tissue change depending on age, physical activity, nutritional conditions, as well as under the influence of the activity of the endocrine glands, innervation and other factors.

Classification

Exists two main types of bone tissue:

reticulofibrous (coarse-fibrous),
lamellar.

These types of bone tissue differ in structural and physical properties, which are mainly due to the structure of the intercellular substance. In coarse fibrous tissue, collagen fibers form thick bundles running in different directions, and in lamellar tissue, bone substance (cells, fibers, matrix) form systems of plates.

Bone tissue also includes dentin and cementum of the tooth, which are similar to bone tissue in terms of a high degree of mineralization of the intercellular substance and a supporting, mechanical function.

Bone cells: osteoblasts, osteocytes and osteoclasts. They all develop from the mesenchyme, like cartilage cells. More precisely, from the mesenchymal cells of the sclerotome of the mesoderm. However, osteoblasts and osteocytes are related in their differon in the same way as fibroblasts and fibrocytes (or chondroblasts and chodrocytes). And osteoclasts have a different, hematogenous origin.

Bone differon and osteohistogenesis

Development bone tissue in the embryo is carried out in two ways:

1) directly from the mesenchyme, - direct osteogenesis;
2) from the mesenchyme at the site of a previously developed cartilaginous bone model - this is indirect osteogenesis.

Postembryonic development of bone tissue occurs during its physiological and reparative regeneration.

In the process of bone tissue development, a bone differon is formed:

stem cells,
half-stem cells (preosteoblasts),
osteoblasts (a type of fibroblast)
osteocytes.

The second structural element is osteoclasts (a kind of macrophages) that develop from blood stem cells.

Stem and semi-stem osteogenic cells are not morphologically identified.

Osteoblasts (from the Greek. osteon - bone, blastos - germ), are young cells that create bone tissue. In bone, they are found only in the periosteum. They are capable of proliferation. In the resulting bone, osteoblasts cover the entire surface of the developing bone beam in an almost continuous layer.

The shape of osteoblasts is different: cubic, pyramidal or angular. Their body size is about 15-20 microns. The nucleus is round or oval, often located eccentrically, contains one or more nucleoli. In the cytoplasm of osteoblasts, the granular endoplasmic reticulum, mitochondria, and the Golgi apparatus are well developed. It reveals significant amounts of RNA and high activity of alkaline phosphatase.

Osteocytes (from the Greek osteon - bone, cytus - cell) are mature (definitive) cells of bone tissue that have lost the ability to divide. They have a process shape, a compact, relatively large nucleus and a weakly basophilic cytoplasm. Organelles are poorly developed. The presence of centrioles in osteocytes has not been established.

Bone cells lie in bone lacunae that follow the contours of the osteocyte. The length of the cavities ranges from 22 to 55 microns, the width is from 6 to 14 microns. The tubules of the bone lacunae are filled with tissue fluid, anastomose with each other and with the perivascular spaces of the vessels that go inside the bone. The exchange of substances between osteocytes and blood is carried out through the tissue fluid of these tubules.

Osteoclasts (from the Greek osteon - bone and clastos - fragmented) are cells of a hematogenous nature that can destroy calcified cartilage and bone. Their diameter reaches 90 microns or more, and they contain from 3 to several tens of nuclei. The cytoplasm is weakly basophilic, sometimes oxyphilic. Osteoclasts are usually located on the surface of the bone bars. That side of the osteoclast, which is adjacent to the destroyed surface, is rich in cytoplasmic outgrowths (corrugated border); it is the area of synthesis and secretion of hydrolytic enzymes. Along the periphery of the osteoclast there is a zone of tight adherence of the cell to the bone surface, which, as it were, seals the area of action of enzymes. This zone of the cytoplasm is light, contains few organelles, with the exception of microfilaments consisting of actin.

The peripheral layer of the cytoplasm above the corrugated edge contains numerous small vesicles and larger vacuoles.

It is believed that osteoclasts release CO2 into the environment, and the enzyme carbonic anhydrase promotes the formation of carbonic acid (H2CO3) and the dissolution of calcium compounds. The osteoclast is rich in mitochondria and lysosomes, whose enzymes (collagenase and other proteases) break down collagen and proteoglycans of the bone tissue matrix.

It is believed that one osteoclast can destroy as much bone as 100 osteoblasts create in the same time. The functions of osteoblasts and osteoclasts are interconnected and regulated by hormones, prostaglandins, functional load, vitamins, etc.

The intercellular substance (substantia intercellularis) consists of a basic amorphous substance impregnated with inorganic salts, in which collagen fibers are located, forming small bundles. They contain mainly protein - collagen I and V types. Fibers can have a random direction - in reticulofibrous bone tissue, or a strictly oriented direction - in lamellar bone tissue.

bone tissue osteohistogenesis blood cell

Bone tissue is reticulofibrous and lamellar.

Reticulofibrous (coarse fibrous) bone tissue

reticulofibrous bone tissue textus osseus reticulofibrosus) occurs mainly in embryos. In adults, it can be found at the site of overgrown cranial sutures, at the points of attachment of tendons to bones. Randomly arranged collagen fibers form thick bundles in it, clearly visible microscopically even at low magnifications.

In the main substance of the reticulofibrous bone tissue, there are elongated-oval bone lacunae with long anastomosing tubules, in which osteocytes with their processes lie. From the surface, the coarse fibrous bone is covered with periosteum.

lamellar bone tissue

Lamellar bone tissue ( textus osseus lamellaris) - the most common type of bone tissue in the adult body. It is made up of bone records (lamellae ossea). The thickness and length of the latter ranges from several tens to hundreds of micrometers. They are not monolithic, but contain fibrils oriented in different planes.

In the central part of the plates, the fibrils have predominantly longitudinal direction, along the periphery - tangential and transverse directions are added. The plates can delaminate, and the fibrils of one plate can continue into the neighboring ones, creating a single fibrous bone base. In addition, the bone plates are permeated with individual fibrils and fibers oriented perpendicular to the bone plates, woven into the intermediate layers between them, due to which greater strength of the lamellar bone tissue is achieved. Both compact and spongy matter are built from this tissue in most flat and tubular bones of the skeleton.

Histological structure of the tubular bone as an organ

The tubular bone as an organ is mainly built from lamellar bone tissue, except for tubercles. Outside, the bone is covered with periosteum, with the exception of the articular surfaces of the epiphyses, covered with hyaline cartilage.

Periosteum, or periosteum ( periosteum). There are two layers in the periosteum: outer(fibrous) and interior(cellular). The outer layer is formed mainly by fibrous connective tissue. The inner layer contains osteogenic cambial cells, preosteoblasts, and osteoblasts of varying degrees of differentiation. Spindle-shaped cambial cells have a small amount of cytoplasm and a moderately developed synthetic apparatus. Preosteoblasts are vigorously proliferating oval-shaped cells capable of synthesizing mucopolysaccharides. Osteoblasts are characterized by a highly developed protein-synthesizing (collagen) apparatus. Vessels and nerves supplying the bone pass through the periosteum.

The periosteum connects the bone with the surrounding tissues and takes part in its trophism, development, growth and regeneration.

The structure of the diaphysis

The compact substance that forms the diaphysis of the bone consists of bone plates, [the thickness of which varies from 4 to 12-15 microns]. Bone plates are arranged in a certain order, forming complex formations - osteons, or Haversian systems. There are three layers in the diaphysis:

outer layer of common lamellae,
middle, osteon layer, and
inner layer of common lamellae.

External common (general) plates do not form complete rings around the diaphysis of the bone, they overlap on the surface with the following layers of plates. The internal common plates are well developed only where the compact substance of the bone directly borders the medullary cavity. In the same places where the compact substance passes into the spongy one, its internal common plates continue into the plates of the crossbars of the spongy substance.

Perforating (Volkmann) channels lie in the outer common plates, through which vessels enter the bone from the periosteum into the bone. From the side of the periosteum, collagen fibers penetrate into the bone at different angles. These fibers are called perforating (Sharpey) fibers. Most often, they branch only in the outer layer of the common lamellae, but they can also penetrate into the middle osteon layer, but they never enter the osteon lamellae.

In the middle layer, bone plates are located in osteons. In the bone plates are collagen fibrils soldered into a calcified matrix. The fibrils have different directions, but they are predominantly oriented parallel to the long axis of the osteon.

Osteons(Haversian systems) are the structural units of the compact substance of the tubular bone. They are cylinders, consisting of bone plates, as if inserted into each other. In the bone plates and between them are the bodies of bone cells and their processes, immured in the bone intercellular substance. Each osteon is delimited from neighboring osteons by the so-called cleavage line formed by the main substance that cements them. In the central canal of the osteon, blood vessels pass with their accompanying connective tissue and osteogenic cells.

In the diaphysis of a long bone, osteons are located predominantly parallel to the long axis. The osteon channels anastomose with each other. , in places of anastomoses, the plates adjacent to them change their direction. Such channels are called perforating, or nourishing. The vessels located in the osteon channels communicate with each other and with the vessels of the bone marrow and periosteum.

Most of the diaphysis is the compact substance of tubular bones. On the inner surface of the diaphysis, bordering the medullary cavity, the lamellar bone tissue forms the bone crossbars of the cancellous bone. The cavity of the diaphysis of tubular bones is filled with bone marrow.

Endost (endosteum) - a membrane covering the bone from the side of the bone marrow cavity. In the endosteum of the formed bone surface, an osmiophilic line is distinguished on the outer edge of the mineralized bone substance; osteoid layer, consisting of an amorphous substance, collagen fibrils and osteoblasts, blood capillaries and nerve endings, a layer of squamous cells that indistinctly separate the endosteum from the elements of the bone marrow. The thickness of the endosteum exceeds 1-2 microns, but less than that of the periosteum.

In areas of active bone formation, the thickness of the endosteum increases by 10-20 times due to the osteoid layer due to an increase in the synthetic activity of osteoblasts and their precursors. During bone remodeling, osteoclasts are found in the endosteum. In the endosteum of aging bone, the population of osteoblasts and progenitor cells decreases, but the activity of osteoclasts increases, which leads to thinning of the compact layer and restructuring of the cancellous bone.

Between the endosteum and the periosteum, there is a certain microcirculation of fluid and minerals due to the lacunar-canal system of bone tissue.

Bone vascularization. Blood vessels form a dense network in the inner layer of the periosteum. From here, thin arterial branches originate, which, in addition to blood supply to osteons, penetrate into the bone marrow through nutrient holes and take part in the formation of a network of capillaries that feed it. Lymphatic vessels are located mainly in the outer layer of the periosteum.

Bone innervation. In the periosteum, myelinated and unmyelinated nerve fibers form a plexus. Part of the fibers accompanies the blood vessels and penetrates with them through the nutrient holes into the channels of the same name, and then into the osteon channels and then reaches the bone marrow. Another part of the fibers ends in the periosteum with free nerve ramifications, and also participates in the formation of encapsulated bodies.

The growth of tubular bones.

Bone growth is a very long process. It begins in humans from the early embryonic stages and ends on average by the age of 20. During the entire period of growth, the bone increases both in length and in width.

Long bone growth in length ensured by the presence metaepiphyseal cartilaginous plate, in which two opposite histogenetic processes are manifested. One is the destruction of the epiphyseal plate with the formation of bone tissue, and the other is the incessant replenishment of cartilage tissue by neoplasm of cells. However, over time, the processes of cartilage destruction begin to prevail over the processes of neoplasm, as a result of which the cartilage plate becomes thinner and disappears.

There are three zones in the metaepiphyseal cartilage:

border zone (intact cartilage),
zone of columnar (actively dividing) cells and
a zone of vesicular (dystrophically changed) cells.

The border zone, located near the epiphysis, consists of round and oval cells and single isogenic groups, which provide a connection between the cartilaginous plate and the bone of the epiphysis. In the cavities between the bone and cartilage there are blood capillaries that provide nutrition to the cells of the deeper zones of the cartilage plate. The columnar cell zone contains actively proliferating cells that form columns located along the axis of the bone and ensure its growth and length. The proximal ends of the columns are composed of maturing, differentiating cartilage cells. They are rich in glycogen and alkaline phosphatase. Both of these zones are most reactive under the action of hormones and other factors that affect the processes of ossification and bone growth. The bubble cell zone is characterized by hydration and destruction of chondrocytes, followed by endochondral ossification. The distal part of this zone borders on the diaphysis, from where osteogenic cells and blood capillaries penetrate into it. The longitudinally oriented columns of endochondral bone are essentially bony tubules where osteons are formed.

Subsequently, the centers of ossification in the diaphysis and epiphysis merge and the growth of the bone in length ends.

Long bone growth wide carried out by the periosteum. From the side of the periosteum, fine-fibered bone begins to form very early in concentric layers. This appositional growth continues until the completion of bone formation. The number of osteons immediately after birth is small, but by the age of 25 in the long bones of the limbs, their number increases significantly.

Some terms from practical medicine:

osteodystrophy-- degeneration of bone tissue, caused by a violation of the processes of interstitial metabolism; characterized by restructuring of the bone structure with the replacement of bone elements with osteoid and fibrous tissue, sometimes by increased osteogenesis;
meloreostosis(syn.: Leri disease, osteosis eburnisans, osteopathia hyperostotica, rhizomonomeloreostosis) is a congenital disease characterized by severe sclerosis, hyperostosis and deformation of one or more long tubular bones (femur, tibia, humerus);

Bone tissue develops from the mesenchyme and is a form of connective tissue in which the intercellular substance is calcified. The intercellular substance consists of the main substance, in which fibers and inorganic salts are located. Fibers such as collagen fibers of the connective tissue are called ossein. The fibers and the main substance between them are impregnated with salts of calcium, phosphorus, magnesium, etc., which form complex compounds.
In the intercellular substance there are cavities connected by the thinnest bone tubules. Osteocytes lie in these cavities - process-shaped cells incapable of mitosis, with weakly expressed organelles. The processes of osteocytes penetrate into the tubules, which are of great importance in the delivery of nutrients to the cells and the ground substance. The tubules are connected to channels within the bone that contain blood vessels, providing pathways for the exchange of materials between osteocytes and the blood.
In addition to osteocytes, osteoblasts are found in bone tissue. Their cytoplasm is basophilic and contains a large amount of RNA. Well developed organelles. Osteoblasts form bone tissue; releasing the intercellular substance and immuring in it, they turn into osteocytes. Accordingly, in the formed bone, osteoblasts are found only in areas of growth and regeneration of bone tissue.
Another form of bone cells are osteoclasts - large multinucleated cells. Their cytoplasm contains a large number of lysosomes. These cells form microvilli directed towards the microfoci of bone or cartilage destruction.
The osteoclast secretes enzymes, which can explain the dissolution of bone substance by it. These cells take an active part in the destruction of the bone. With pathological processes in the bone tissue, their number increases sharply. They are also important in the process of bone development: in the process of building the final form of the bone, they destroy the calcified cartilage and even the newly formed bone: “correcting” its primary form. In the process of bone formation, blood vessels take an active part, providing the formation of an osteogenic site.
Bone tissue builds the skeleton and, therefore, performs a supporting function. The skeletal material is strong only when the organic and inorganic components of the bone are combined (removal of organic substances makes the bone brittle, inorganic - softness). Bones also take part in metabolism, because they are a kind of depot of calcium, phosphorus and other substances.
Bone tissue, despite its strength and density, constantly renews its constituent substances, there is a restructuring of the internal structure of the bone and even a change in its external shape.
There are two types of bone tissue: coarse fibrous and lamellar (Fig. 25, a, b).
coarse fibrous bone. In this bone, in the ground substance, powerful bundles of ossein fibers pass in various directions. Osteocytes are also located without a specific orientation. The bones of the skeleton of fish and amphibians are built from such tissue. In higher vertebrates, in the adult state, coarse-fibred bone is found in places where the cranial sutures are overgrown and where tendons are attached to the bone.
lamellar bone. Most of the adult skeleton is built from lamellar bone tissue. The diaphysis of a tubular bone consists of three layers - a layer of outer general plates, a layer of haversian systems (osteons) and a layer of internal general plates. External general plates are located under the periosteum; internal - from the side of the bone marrow. These plates cover the entire bone, forming a concentric layering. Channels pass through the general plates into the bone, in which blood vessels go. Each plate is a characteristic basic substance of the bone, in which bundles of ossein (collagen) fibers run in parallel rows. Osteocytes lie between the plates.

a - coarse fibrous: I - bone cells (osteocytes) - 2 - intercellular substance; b - lamellar: I - osteon, 2 - internal general plates, 3 - external general plates, 4 - osteons (havers) channel.

Video: Histological preparation "Coarse fibrous bone tissue"

In the middle layer, the bone plates are arranged concentrically around the canal, where the blood vessels pass, forming an osteon (Haversian system). The osteon is, as it were, a system of cylinders inserted one into the other. This design gives the bone extreme strength. In two adjacent plates, bundles of ossein fibers run in different directions, almost at right angles to each other. Intercalated (intermediate) plates are located between the osteons. These are parts of former osteons, evidence of active restructuring of bone tissue. The periosteum is a fibrous connective tissue containing osteoblasts, blood vessels, and nerve endings. Osteoblasts are activated during bone fractures and take part in bone formation.

Attention, only TODAY!

Musculoskeletal system The human body is made up of bones and skeletal muscles. Due to the ability to contract, the muscles set the bones of the skeleton in motion, as a result of which the human body or its parts can move in space and perform this or that work. Muscle contraction occurs under the influence of nerve impulses coming from the central nervous system. Skeletal muscles are one of the main effector apparatuses of the nervous system, which has been convincingly shown by physiologists.

THEM. Sechenov wrote: "All the endless variety of external manifestations of brain activity is finally reduced to a single phenomenon - muscle movement." In addition to the bone skeleton and muscles, the system of organs of movement and support includes joints, cartilage, tendons, ligaments, fascia.

Main function bones- providing a solid support for the human body. Along with this mechanical function, bones also take part in mineral metabolism, since they contain the main supply of calcium, phosphorus, and other minerals. The bones contain red bone marrow - the main organ of hematopoiesis. Bone is an organ built primarily from bone tissue. The composition of each bone also includes a number of tissues that are in certain ratios.

For example, consider the structure of a tubular bones, namely the human femur. It consists of lamellar bone tissue, periosteum (periosteum), endosteum, articular cartilage, synovial endothelium, vessels and nerves. The cavity of the diaphysis, as well as the spaces of the spongy substance of the epiphyses, are filled with bone marrow. The compact substance of the bone is represented by lamellar bone tissue. Outside the diaphysis of the bone there is a periosteum (periosteum), followed by the outer surrounding (general) plates.

From the inside from the side medullary cavity internal surrounding (general) plates are located, covered with endo-stoma. The main part of the tubular bone, located between the outer and inner surrounding plates, is made up of osteons and intercalated plates (residual osteons) filling the gaps between them.

Osteon is a three-dimensional cylindrical system of concentrically arranged bone plates and osteocytes surrounding the central canal of the osteon. In bone plates, ossein fibrils are tightly and parallel to each other. Bone-lamellar cylinders, as it were, are inserted one into the other. In adjacent concentric bone plates, osseous new fibrils run at a different angle. Due to this, exceptional strength of osteons is achieved. The complex structure of osteons is formed in the process of bone tissue histogenesis and its constant restructuring.

Part osteons is destroyed. Their remains are intercalated plates. Along with this, new osteons arise. Their source is cambial cells located in loose connective tissue around vessels in osteon channels. A large role in the process of restructuring, and especially in the mechanisms of the reception of physical loads, is assigned to piezoelectric effects. When the bone plates are bent, + and - charges arise on their surface. It is believed that a positive charge causes differentiation of osteoclasts, and a negative charge - osteoblasts.

Thus, in bone tissue the processes of creation and destruction proceed harmoniously, thanks to which mechanical strength and physiological regeneration of the bone are achieved.

Tubular growth bones in length usually ends by the age of 20 years. Until this time, the metaepiphyseal growth plate, located between the epiphysis and the diaphysis, functions. In the metaepiphyseal plate, a border zone is distinguished, located closer to the bone tissue of the epiphysis. This zone is also called the zone of resting cartilage. Next, a zone of proliferating young cartilage, or a zone of columnar cells, is isolated. Here, new chondroblasts are formed to replace those cartilage cells that die off at the diaphyseal surface of the plate.

The next zone in the metaepiphyseal record called the zone of maturing cartilage, or the zone of vesicle cells. It is characterized by destruction of chondrocytes followed by endochondral ossification. Allocate another zone of cartilage calcification. It directly borders on the bone tissue of the diaphysis. Capillaries and osteogenic cells penetrate into it. The latter turn into osteoblasts, which form bone crossbars on the diaphyseal side of the metaepiphyseal plate.

In this way, interstitial cartilage growth on the epiphyseal side of the metaepiphyseal plate, it pushes the epiphysis away from the diaphysis, but the metaepiphyseal plate does not increase in thickness, since from the side of the diaphysis it constantly undergoes resorption and is replaced by bone tissue. Due to this, the growth of tubular bones in length occurs.

Lesson number 10

Traffic. The structure of the musculoskeletal system. Prevention of her diseases

II. Skeleton

III. Muscular apparatus

Muscle structure

2) muscle groups

I. Functional structure of the musculoskeletal system

1) body support

2) Movement of a body or its parts in space

3) Protective(protection of internal organs, brain and spinal cord, etc.)

Basic principles of the system functioning

1) The basic principles of the functioning of the skeleton: works in accordance with the laws of mechanics

2) The basic principles of the functioning of the muscular apparatus:

A) arbitrary (conscious) nature of contraction

B) most muscles are grouped into functional complexes - agonists (carry out the movement of the body or its part in one direction) and antagonists (carry out the movement of the body or its part in opposite directions); the coordinated work of these muscle complexes is achieved due to the coordination of the processes of excitation and inhibition in the neurons of the corresponding somatic arcs)

C) with excessive loads on the muscles, a state of fatigue develops in them; the resulting muscle pain and fatigue are associated with a relative lack of oxygen in the muscle tissue (delivery lags behind consumption), activation of glycolysis, the formation of excess amounts of lactic acid and its release into the general circulation

3) Regulatory mechanisms

A) nervous regulation of the musculoskeletal system is carried out by the somatic department of the nervous system

B) the main principle of regulation is reflex (somatic reflex arcs close at the level of the spinal cord and brain stem)

C) the midbrain plays an important role in the activity of the somatic nervous system

C) the highest link in the system of regulation of movements is the cerebral cortex of the telencephalon (musculocutaneous zones located on both sides of the central sulcus)

D) along with the above nervous structures, the cerebellum, the basal nuclei of the telencephalon, and the limbic system play an important role in the regulation of motor activity.

II. Skeleton

Has over 200 bones. The structure of the bones.

1) Classification of bones:

Flat bones (eg: frontal and parietal bones of the skull, scapula, sternum)

Tubular bones (eg: femur, humerus)

Anatomical structure of bones

Flat bones: consist of two thin plates, between which is a spongy substance

Long bones: in a long bone, two epiphyses are distinguished, formed by a spongy substance, and a diaphysis, built from a compact substance. The epiphyses are covered with hyaline cartilage on the outside (part of the articular apparatus)

The diaphysis is covered from the outside by the periosteum, from the inside, from the side of the bone marrow cavity - by the endosteum; the periosteum performs protective and trophic functions, and also provides growth (in thickness) and regeneration of the bone.

Histological structure of bones

The bones of an adult consist of lamellar bone tissue; coarse-fibred bone tissue is found only in the cranial sutures and places of attachment of tendons to bones. The general plan of the microscopic structure of bone tissue: an elementary structural block of lamellar bone tissue is a bone plate, consisting of many parallel-oriented collagen fibers impregnated with calcium phosphate, and cells (mainly osteocytes). Structures of a higher order are formed from bone plates - osteons, general plates and bone packages. The osteon is a system of concentric cylinders, the wall of which is formed by a bone plate, in the center of which there is a channel containing blood vessels and nerve fibers. It is important to note that the directions of the fibers in adjacent cylinders do not coincide, which ensures high mechanical strength of the structure as a whole. Osteons form the basis of the compact substance of tubular bones. The general plates are a set (usually up to ten) of extended bone plates located along the outer and inner perimeters of the diaphysis of tubular bones. The bone package is a complex of several bone plates. Many bone packages form the spongy substance of flat bones and the epiphyses of tubular bones, it should be emphasized that the internal architecture of the bones is such that all their structural elements are organized in space in accordance with the direction of the lines of force, due to which significant strength is achieved with a relatively small thickness of the bones.

Bone joints

A) Continuous: characterized by the presence of a lining between the bones, consisting of connective tissue (eg: ligaments of the spine), cartilage (eg: intervertebral discs), bone tissue (eg: joints of the frontal and parietal bones of the skull),

B) Discontinuous: characterized by the following structure: between the bones there is a cavity containing a fluid that reduces the friction of the articular surfaces (the latter, as mentioned above, are covered with hyaline cartilage). The articular apparatus includes auxiliary structures, in particular, an articular bag made of connective tissue. Varieties of discontinuous joints: cylindrical (ex: joint between I and II cervical vertebrae), block-shaped (ex: interphalangeal joint), ellipsoid (ex: wrist joint), saddle-shaped (ex: carpometacarpal joint of the thumb), flat (ex.: joint between flat processes of vertebrae), spherical (ex.: hip joint)

Departments of the skeleton

A) The skeleton of the head (skull) includes: the brain section consists of six bones - one frontal, two parietal, two temporal, one occipital), the facial section is formed by five main bones - one upper jaw, one lower jaw, two zygomatic bones, one palatine bone.

B) The skeleton of the body is represented by:

The spine, built from individual vertebrae connected by intervertebral discs (they consist of fibrous cartilage, provide flexibility to the spine, and perform a shock-absorbing function). A single vertebra is a bony ring. The spine consists of five sections: cervical (7 vertebrae), thoracic (12 vertebrae), lumbar (5 vertebrae), sacral (5 fused vertebrae), coccygeal (4-5 fused vertebrae). The spine is characterized by an S-shape, has four bends: two back (kyphosis) and two forward (lordosis).

The chest, which includes the thoracic spine, sternum, 12 pairs of ribs (10 of them are connected to the sternum, 2 are oscillating)

C) the skeleton of the limbs, represented by the upper limbs, consisting of the girdle of the upper limbs: 2 shoulder blades, 2 collarbones. Skeleton of a free limb: shoulder (humerus), forearm (ulna and radius), hand (carpus, metacarpus, fingers). The lower extremities are represented by the girdle of the lower extremities, consisting of the pelvis (a bone ring consisting of two pelvic bones and the sacrum). Skeleton of the free limb: femur (femur), lower leg (tibia and fibula), foot (tarsus, metatarsus, fingers).

III. Muscular apparatus

Has over 400 muscles

Muscle structure

A) anatomical structure. Muscle - an organ in which a contractile part (or a body consisting of a head, abdomen and tail) and a tendon (built from a dense, formed connective tissue) are distinguished, with which it is attached to bones and other structures; outside the muscle is covered with fascia. Types of muscles:

depending on the number of heads (biceps, for example, biceps brachii), triceps, for example, triceps brachii, quadriceps, for example, quadriceps femoris)

shape (long, for example, biceps brachii, short, for example, short finger flexors, wide, for example, diaphragm)

Histological structure of muscles:

The basis of skeletal muscles is striated skeletal muscle tissue, the structural unit of which is the muscle fiber (symplast)

The muscle fiber is covered with a thin connective tissue sheath, in which the vessels and nerves pass.

Groups of muscle fibers form bundles of various ranks, separated by layers of connective tissue

In the center of the muscle fiber is its contractile apparatus - many parallel-oriented myofibrils (organelles of special importance)

The nuclei and most organelles of general importance are located on the periphery of the muscle fiber.

Myofibrils are characterized by transverse striation - a regular alternation of light (I) and dark (A) disks.

Dark disks are formed by myosin fibrils, light - by actin fibrils (the latter are attached to a plate passing in the middle of the I-disk - Z-strip)

The smallest repeating unit of a myofibril capable of contraction is the sarcomere, which includes half of the I-disk, A-disk and half of the I-disk (its formula is as follows: 1/2 I + A + 1/2

Contraction mechanism: thin actin fibrils are pulled by thick myosin fibrils deep into the A-disk (sliding theory); the process needs ATP and Ca ions

Groups of mice

A) muscles of the head

Group I - facial muscles: frontal, circular muscles of the eyes and mouth

Group II - chewing muscles: temporal, chewing, internal and external pterygoid

B) neck muscles

Subcutaneous muscle (platysma), sternocleidomastoid muscles, hyoid muscles.

B) back muscles

Distinguish between superficial (trapezius muscle, latissimus dorsi, rhomboid muscle, serratus muscles and muscles that lift the shoulder blades) and deep (rectifier muscles of the spine, etc.)

D) abdominal muscles

Straight, transverse and oblique muscles of the abdomen (all these muscles have wide and flat tendons, which, when connected to each other, form a white line of the abdomen).

The muscles of the abdominal wall together form the abdominal press, which plays an important role in the acts of defecation and urination, as well as in labor.

D) chest muscles

Large and small pectoral muscles, external and internal intercostal muscles, diaphragm (with holes for the esophagus and accompanying vagus nerves, trachea, aorta, inferior vena cava, sympathetic nerve trunk and some other nerves and vessels)

E) muscles of the shoulder girdle

Deltoid muscles.

G) shoulder muscles

Biceps brachii, brachialis, triceps brachii.

H) muscles of the forearm

brachioradialis muscle, flexors of the hand and fingers, extensors of the hand and fingers.

I) hand muscles

Muscles of the I-th finger, V-th finger, the middle group of muscles that provides flexion, extension and abduction of the phalanges.

K) muscles of the pelvic girdle

Large, medium and small gluteal muscles

L) thigh muscles

Quadriceps femoris, sartorius, biceps femoris, semitendinosus, semimembranosus.

M) leg muscles

Tibialis muscle, peroneal muscles, triceps muscle of the lower leg (consists of two muscles: gastrocnemius and soleus).

H) muscles of the foot.

Short extensors of the fingers, internal, middle and external muscles that provide flexion and lateral movements of the fingers.

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