The nervous system as a system of power The problem of power and organization is the main problem in the activity of the nervous system. The tasks of this system are reduced to the organization and management of the processes occurring inside the organism and between the organism and its environment. That fact,

In the human body, everything is interconnected and arranged very wisely. The skin and muscles, internal organs and skeleton, all this clearly interacts with each other, thanks to the efforts of nature. Below is a description of the human skeleton and its function.

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A skeleton made of bones of different sizes and shapes, on which the human body is fixed, is called a skeleton. It serves as a support and provides reliable security for important internal organs. What a human skeleton looks like can be seen in the photo.

Described organ connecting with muscle tissue, it is the musculoskeletal system of homo sapiens. Thanks to this, all individuals can move freely.

The finally developed bone tissue consists of 20% water and is the strongest in the body. Human bones include inorganic substances, thanks to which they have strength, and organic, giving flexibility. That is why bones are strong and resilient.

Human Bone Anatomy

Examining the organ in more detail, it can be seen that it consists of several layers:

• External. Forms high strength bone tissue;
• Connective. The layer tightly covers the outside of the bones;
• Loose connective tissue. Complex interlacing of blood vessels is located here;
• Cartilage tissue. It has settled on the ends of the organ, due to it, the bones have the opportunity to grow, but up to a certain age;
• Nerve endings. They carry signals from the brain and vice versa, like wires.

The bone marrow is placed in the cavity of the bone tube; it is red and yellow.

Functions

Without exaggeration, we can say that the body will die if the skeleton ceases to perform its important functions:

• Support... The solid bone-cartilaginous skeleton of the body is formed by the bones, to which fascia, muscles and internal organs are attached.
• Protective... Containers have been created for the maintenance and protection of the spinal cord (spine), the brain (cranium) and for the rest, no less important, organs of human life (rib cage).
• Motor... Here, bones are exploited by muscles as levers to move the body with the help of tendons. They predetermine the coherence of joint movements.
• Cumulative... In the central cavities of the long bones, fat is accumulating - this is the yellow bone marrow. The growth and strength of the skeleton depends on it.
• In metabolism bone tissue plays an important role, it can be safely called a storehouse of phosphorus and calcium. It is responsible for the exchange of additional minerals in the human body: sulfur, magnesium, sodium, potassium and copper. When there is a shortage of any of these substances, they are released into the bloodstream and spread throughout the body.
• Hematopoietic... Red bone marrow is actively involved in hematopoiesis and bone formation, filled with blood vessels and nerves. The skeleton contributes to the creation of blood and its renewal. The process of hematopoiesis takes place.

Skeleton organization

In the structure of the skeleton includes several groups of bones. One contains the spine, cranium, thorax and is the main group, which is a supporting structure and forms a frame.

The second, additional group, includes bones that form the arms, legs, and bones that provide connection to the axial skeleton. Each group is described in more detail below.

Main or axial skeleton

Skull - is the bone base of the head... In shape, it is half an ellipsoid. The brain is located inside the cranium, and the senses have found a place here. Serves as a solid support for the elements of the respiratory and digestive apparatus.

The rib cage is the bony base of the chest. It resembles a compressed truncated cone. It is not only a support, but also a mobile device, participating in the work of the lungs. The internal organs are located in the chest.

Spine- an important part of the skeleton, it provides a stable vertical position of the body and contains the back of the brain, protecting it from damage.

Accessory skeleton

Upper limb girdle - allows the upper limbs to attach to the axial skeleton. It includes a pair of shoulder blades and a pair of collarbones.

Upper limbs - unique working tool, which is indispensable. It consists of three sections: shoulder, forearm and hand.

Lower limb belt - connects the lower limbs to the axial frame, and is also a convenient container and support for the digestive, reproductive and urinary systems.

Lower limbs - mainly perform supporting, motor and spring functions human body.

The skeleton of a person with the name of bones, as well as how many of them are in the body and each section, is described below.

Skeleton departments

In an adult, the skeleton contains 206 bones. Usually his anatomy debuts with a skull. Separately, I would like to note the presence of the external skeleton - the dentition and nails. The human skeleton consists of many paired and unpaired organs, forming separate skeletal parts.

Skull anatomy

The cranium also includes paired and unpaired bones. Some are spongy while others are mixed. There are two main sections in the skull, they differ in their functions and development. Right there, in the temporal region, is the middle ear.

The cerebral section creates a cavity for part of the sensory organs and the brain of the head. It has a vault and a base. There are 7 bones in the department:

• Frontal;
• Wedge-shaped;
• Parietal (2 pcs.);
• Temporal (2 pcs.);
• Lattice.

The facial section includes 15 bones. It contains most of the senses. This is where it starts parts of the respiratory and digestive system.

The middle ear contains a chain of three small bones that transmit vibrations of sound from the eardrum to the labyrinth. There are 6 of them in the cranium. On the right there are 3 and on the left 3.

• Hammer (2 pcs.);
• Anvil (2 pcs.);
• The stirrup (2 pcs.) Is the smallest bone of 2.5 mm.

Torso anatomy

This includes the spine starting at the neck. The chest is attached to it. They are very related in their location and the functions they perform. Consider separately vertebral column, then the chest.

Vertebral column

The axial skeleton consists of 32–34 vertebrae. They are interconnected by cartilage, ligaments and joints. The spine is divided into 5 sections and there are several vertebrae in each section:

• Cervical (7 pcs.) This includes an epistrophy and an atlas;
• Breast (12 pcs.);
• Lumbar (5 pcs.);
• Sacral (5 pcs.);
• Coccygeal (3-5 accrete).

The vertebrae are separated by 23 intervertebral discs. This combination has a name: partially movable joints.

Rib cage

This part of the human skeleton is formed from the sternum and 12 ribs, which are attached to the 12 thoracic vertebrae. Flattened from front to back and widened in the transverse direction, the ribcage forms a mobile and strong rib cage. It protects the lungs, the heart and major blood vessels from damage.

Sternum.

It has a flat shape and spongy structure. It contains a rib cage in front.

Upper limb anatomy

With the help of the upper limbs, a person performs a lot of elementary and complex actions. Hands include many small parts and are divided into several departments, each of which conscientiously does its job.

To the free part of the upper limb includes four sections:

• The upper limb belt includes: 2 shoulder blades and 2 collarbones.
• Shoulder bones (2 pcs.);
• Elbow (2 pcs.) And radial (2 pcs.);
• Brush. This complex part is made up of 27 small pieces. Bones of the wrist (8 x 2), metacarpus (5 x 2) and phalanges of the fingers (14 x 2).

The hands are an exceptional apparatus for fine motor skills and precise movements. Human bones are 4 times stronger than concrete, so you can perform rough mechanical movements, the main thing is not to overdo it.

Lower limb anatomy

The bones of the pelvic girdle form the skeleton of the lower extremities. Human legs are made up of many small parts and are subdivided into sections:

The skeleton of the leg is similar to the skeleton of the arm. Their structure is the same, and the difference is seen in details and size. The entire weight of the human body when moving around rests on its feet. Therefore, they are stronger and stronger than hands.

Bone shapes

In the human body, bones are not only of different sizes, but also shapes. There are 4 types of bone shapes:

• Wide and flat (like a skull);
• Tubular or long (in the limbs);
• Composite, asymmetrical (pelvic and vertebrae);
• Short (bones of the wrist or feet).

Having considered the structure of the human skeleton, one can come to the conclusion that it is an important structural component of the human body. Performs functions due to which the body carries out the normal process of its life.

Skeletal system combines the bones and joints of the body. Bone is a fairly complex organ, consisting of a large number of cells, fibers and minerals. The skeleton provides support and protection for the soft tissues, attachment points to realize movement in the joints. Inside the bones, new red marrow is produced. They also act as a reservoir for ... [Read below]

• Head and neck
• Chest and upper back
• Pelvis and lower back
• Arm and hand bones
• Legs and feet

[Top start]… calcium, iron and energy in the form of fat. Finally, the skeleton grows throughout childhood and provides support for the rest of the body.

Human skeletal system includes two hundred and six separate bones, which are located in two sections: the axial skeleton and the appendicular skeleton. The axial skeleton runs along the midline of the body axis and consists of eighty bones in regions of the body: skull - hypoid, auditory ossicles, ribs, sternum, and spine; the appendicular skeleton consists of one hundred twenty-six bones: upper and lower limbs, pelvic girdle, chest (shoulder) girdle.

Consists of twenty-two bones connected together, except for the lower jaw. These twenty-one fused bones are split apart so that the skull and brain can grow. The lower jaw remains movable and forms the only movable joint in the skull with the temporal bone.

The bones in the upper part of the skull are designed to protect the brain from damage. Bones of the lower and front of the skull - facial bones: support the nose and mouth, eyes.

Sublingual and auditory bones

The hyoid bone is a small, U-shaped bone located just below the mandible. The hyoid bone is the only bone that does not form a connection with any other bone; it is a floating bone. The function of the hyoid bone is to keep the trachea open and to form connection points for the muscles of the tongue.
Hammer, incus and stapes known collectively as the auditory ossicles, are the smallest bones in the body. Located in a small cavity inside the temporal bone, they serve to amplify and transmit sound from the eardrum to the inner ear.

Vertebrae

Twenty-six vertebrae form the spinal column of the human body. They are named by region:
cervical (neck) -, thoracic (chest) -, lumbar (lower back) -, - 1 vertebra and coccygeal (coccyx) - 1 vertebra.
With the exception of the sacrum and coccyx, the vertebrae are named after the first letter of their region and its position along the upper axis. For example, the uppermost thoracic vertebra is called T1 and the lower one is called T12.

The structure of the human vertebrae

Ribs and sternum

It is a thin, knife-shaped bone located along the midline of the chest. The sternum is attached to the ribs by thin strips of cartilage called rib cartilage.

There are twelve pairs of edges generating.
The first 7 ribs are true ribs because they connect the thoracic vertebrae directly to the sternum via. Ribs eight, nine and ten are all connected to the sternum through cartilage that connects to the cartilage of the seventh pair of ribs, so they are considered "false". Ribs 11 and 12 are also false, but are also considered "floating" because they have no attachment to cartilage and sternum at all.

Chest (shoulder) girdle

Consists of left and right and left and right, connects the upper limb (arm) and the bones of the axial skeleton.

Is the upper arm. It forms a hinge and enters the socket, forming with the lower bones of the hand. The radius and ulna are the bones of the forearm. The ulnar is located on the inside of the forearm and forms a hinge joint with the humerus at the elbow joint. Radial allows the forearm and arm to move in the wrist joint.

Arm bones (lower) form the wrist joint with, a group of eight small bones that provide additional flexibility to the wrist. The wrist is connected to the five metacarpal bones, which form the bones of the hand and connect to each finger. The toes have three bones known as phalanges, only the thumb includes two phalanges.

and lower limb belt

Formed by the left and right bones, the pelvic girdle connects the lower limbs (legs) and the bones of the axial skeleton.

Femur is the largest bone in the body and the only bone in the femur. The femur forms a hinge and fits into the socket, and also forms with the knee cap. The patella is a special bone because it is one of the few bones not present at birth.

and bones are the bones of the shin. The tibia is much larger than the fibula and carries almost all of the body's weight. It is used to maintain balance. The tibia and fibula with bone (one of the seven bones of the tarsus) form the ankle joint.

represent a group of seven small bones that form the back of the foot and heel. They form connections with the five long bones of the foot. Then, each of the metatarsal bones forms a connection with one of the many phalanges in the toes. Each finger has three phalanges, with the exception of the thumb, which has only two phalanges.

Microscopic bone structure

The skeleton makes up approximately 30-40% of the body weight of an adult. The skeletal mass consists of a non-living bone matrix and many small bone cells. About half of the mass of the bone matrix is ​​water, while the other half is made up of collagen protein and hard crystals of calcium carbonate and calcium phosphate.

Living bone cells are found at the edges of bones and in small cavities within the bone matrix. Although these cells make up a very small percentage of total bone mass, they have several very important roles in the function of the skeletal system. Bone cells allow bones to: grow and develop, and be repaired after injury.

Bone types

All bones of the body can be broken down into 5 types: short, long, flat, irregular, and sesamoid.

Long
Long bones are longer than their width and are the main bones of the limbs. Long bones grow for a significant time longer than other bones and are responsible for our growth rates. The medullary cavity is located in the center of the long bones and serves as a storage area for the bone marrow. Examples of long bones include thighs, tibiae, fibula, metatarsus, and phalanges.

Short
The short bones are broad and often round or cube-shaped. Carpal bones and tarsus bones are short bones.

Permanent
Flat bones vary greatly in size and shape, but have a common tendency to be very thin. Because flat bones do not contain a marrow cavity like long bones. The frontal, parietal, and occipital bones of the skull, along with the ribs and pelvic bones, are examples of flat bones.

Wrong
Irregular bones have a shape that does not match the pattern of long, flat and short bones. The sacrum is the vertebrae and the coccyx of the spine, as well as the sphenoid, ethmoid and zygomatic bones of the skull, all bones of an irregular shape.

Sesamoid
They form inside the tendons that run through the joints. The sesamoid bones are formed to protect the tendons from stress and strain in the joint and to help give a mechanical advantage to the muscles that pull the tendons. The patella and pisiform bones and wrist bones are the only sesamoid bones that count as part of the body's two hundred and six bones. Other sesamoid bones form in the joints of the arms and legs.

Parts of bones

Long bones have several parts due to their gradual development. At birth, each of the long bones contains three bones separated by hyaline cartilage. The end of the bone is the pineal gland (EPI = further; physis = grow) while the middle bone is called the diaphysis (diameter = passage). Epiphysis and diaphysis elongate towards each other and eventually merge into a common bone. The area of ​​growth and possible fusion is called the metaphysis (meta = after). After the long pieces of bone have been joined together, a single hyaline cartilage remains in the bone and sits at the ends of the bones that form joints with other bones. The articular cartilage acts as a shock absorber and sliding bearing on the surface between the bones to facilitate movement in the joint.
Considering bone cross section, then there are several different layers that make up the bones. Outside, the bone is covered with a fairly thin layer of dense, irregular connective tissue called the periosteum. The periosteum contains many strong collagen fibers to firmly attach tendons and muscles to bones. Osteoblast cells and stem cells in the periosteum are involved in the growth and repair of the outer part of the bone as a result of injury. The vessels present in the periosteum provide energy to the cells on the surface of the bone and penetrate into the bone itself to nourish the cells inside the bone. The periosteum also contains nerve tissue to provide bone sensitivity when injured.
Deep under the periosteum there is a compact bone which makes up the hard, mineralized part of the bone. Compact bone is made of a matrix of hard mineral salts reinforced with tough collagen fibers. Many tiny cells called osteocytes live in small spaces in the matrix and help maintain the strength and integrity of compact bone.
Below the compact layer of bone the area of ​​cancellous bone is located where bone grows in thin columns called trabeculae, with gaps for red bone marrow in between. Trabeculae grow in a pattern to resist external stresses, with the least mass possible, while keeping bones light but strong. Long bones have a hollow medullary cavity in the middle of the diaphysis. The medullary cavity contains red bone marrow during childhood, eventually developing into yellow bone marrow after puberty.

A joint is the point of contact between bones, between bone and cartilage, or between bone and tooth.
Synovial joints are the most common type and have a small gap between the bones. This gap allows for increased range of motion and space for synovial fluid - the lubricant of the joint. Fibrous joints exist where the bones are very tightly connected and there is little or no movement between the bones. The fibrous joints also hold the teeth in their bony cells. Finally, cartilage joints form where bone meets cartilage or where there is a layer of cartilage between two bones. These joints provide a small amount of flexibility in the joint due to the gel-like consistency of the cartilage.

Human skeleton functions

Support and protection

The main function of the skeletal system is to form a solid foundation that supports and protects the organs of the body and anchors the skeletal muscles. The bones of the axial skeleton act as a hard shell to protect internal organs such as the brain and heart from damage caused by external forces. The bones of the appendicular skeleton provide support and flexibility to the joints and anchor the muscles that move the limbs.

Traffic

The bones of the skeletal system act as anchorage points for skeletal muscles. Almost every skeletal muscle works by pulling two or more bones either closer together or further apart. The joints act as anchor points for the movement of bones. The areas of each bone where muscles provide movement grow larger and stronger to support the extra muscle strength. In addition, the total mass and thickness of bone increases when it is under great stress from lifting weights or maintaining body weight.

Hematopoiesis

Red bone marrow produces red and white blood cells in a process known as hematopoiesis. Red bone marrow is found in a cavity inside the bones known as the marrow cavity. Children tend to have more red bone marrow compared to their body size than adults, due to the constant growth and development of their bodies. The amount of red bone marrow drops at the end of puberty and is replaced by yellow bone marrow.

Storage

The skeletal system stores many different essential substances to facilitate growth and repair of the body. The skeletal cell matrix acts as a calcium storage reservoir by storing and releasing calcium ions into the blood as needed. Adequate levels of calcium ions in the blood are essential for the normal functioning of the nervous and muscular systems. Bone cells also secrete osteocalcin, a hormone that helps regulate blood sugar and fat storage. The yellow bone marrow inside our hollow long bones is used to store energy in the form of lipids. Finally, the red bone marrow stores some iron in the form of a ferritin molecule and uses this iron to form hemoglobin in red blood cells.

Growth and development

The skeleton begins to form in the early stages of fetal development as a flexible framework of hyaline cartilage and dense irregular fibrous connective tissue. These tissues act as bases for the skeleton to replace them. As it grows, blood vessels begin to grow in the soft skeleton of the fetus, delivering stem cells and nutrients for bone growth. Bone tissue slowly replaces cartilage and fibrous tissue in a process called calcification. Calcified areas spread from their blood vessels replacing old tissue until they reach the border of another bone. At birth, the skeleton of a newborn has over 300 bones; as a person matures, these bones grow together and fuse into larger bones, retaining only 206 bones.

The structure of the bones of the human skeleton

The skeleton is a system of regularly connected bones and cartilage, developing from the mesoderm, constituting the basis of the body and a rigid supporting structure, which, in combination with the muscles, provides the statics and dynamics of the animal. Already from this definition, one can imagine that the skeleton is a polyfunctional system. But its leading function is movement, which ensures animal life: finding food and a relative, salvation from enemies, animal migration. The bones of the skeletal system, as levers of movement, have a varied shape that has developed in the process of evolution. They serve as a place for the application of muscle force and the transformation of this force into translational movements, and only the high reliability of the skeleton, as a strong and elastic structure, can provide the necessary mobility of the animal. This is especially important for wild animals, since even a short-term failure of the organs of movement leads to their death. Therefore, the general direction of the evolution of the locomotor apparatus in wild relatives of our domestic animals was the development of the maximum running speed, as well as the improvement of statics - the ability to rest while standing. Thus, the skeleton performs not only the function of movement, but also of support.

Other mechanical functions of the skeletal system are the protection of a number of critical organs. The skeleton, being the receptacle of the brain and spinal cord, protects them from external influences, and thanks to its elasticity and springiness, it protects against shocks and shocks. At the beginning of its appearance, the skeleton served as an organ of protection from the effects of the external environment and from enemies. In modern animals, the skeleton forms a protective wall for such vital organs located in the chest cavity as the heart, lungs, and in the pelvic cavity - the reproductive organs.

The springiness and elasticity of the skeleton ensures the smoothness of the translational movements of animals in conditions of gravity and is carried out, first of all, by organs such as joints. Bones, as you know, in the joints articulate at angles of various sizes and the epiphyses of the bones involved in the formation of joints have a spongy structure. The cancellous bones, which form the basis of the spinal column, carpal and tarsal joints, as well as the movable and elastic bone-cartilaginous basis of the chest, are also important spring elements of the skeletal system.

The skeleton also performs a number of biological functions.

He participates in mineral metabolism, containing huge reserves of inorganic compounds: salts; calcium, phosphorus, iron, etc. Mineralization and demineralization of the skeleton is an integral part of complex metabolic processes in the body, especially mineral metabolism, on which the growth of the animal and its productivity largely depend. The veterinarian should take into account that the quantitative ratios of mineral salts in the skeletal system change with age, depend on the sex of the animal, pregnancy, feeding and housing conditions, the nature of mineral feeding and the intensity of use of the dairy herd. The desire to get the maximum milk or other product without the appropriate care for the preservation of the health of the animal can lead to a weakening of constitutional and productive qualities and, ultimately, to metabolic diseases. When there are not enough vitamins and minerals in the feed, the body draws calcium from the bones. On this soil, the bones of the skeleton lose their hardness, are deformed (bent), rickets develop in young animals, and osteomalacia in cows. In these diseases, the entire skeletal system is affected.

First of all, the least loaded bones (for example, the last caudal vertebrae, etc.) are demineralized and absorbed.

Blood cells are produced in the cancellous bone. Moreover, the function of hematopoiesis largely depends on the motor activity of the animal, which contributes to a better metabolism in the bone marrow as an organ of hematopoiesis. The skeleton serves as an organ of biological defense of the body, since protective (immune) bodies are developed here, which are directly related to the preservation of the natural resistance of the animal body to diseases.

By virtue of its function, the skeleton of animals is one of the most accurate indicators of the development of the organism, and the bone tissue, despite its apparent stability, is in a state of continuous restructuring, depending on the functional state of the organism.

The skeleton as a whole gives a certain character to the external appearance of animals (exterior), certain proportions of the body, determining the typical features of the constitution (a set of morphological and functional characteristics of the organism). This is important from a practical point of view, since such valuable qualities as health, adaptability, vitality, ability to fatten, sexual activity, early maturity of animals are associated with this or that type of constitution. Bones, their tubercles and processes serve not only as a place of attachment of muscles, but also as landmarks for determining the topography of internal organs and for performing zootechnical measurements, And when studying anatomy, the skeleton, as Academician V.V. it is easy to navigate by it in the location of all organs. And even A. S. Pushkin in his poem "Message to Delvig" said in a heartfelt way:

"... skeleton

A subject dear to philosophers,

The subject is pleasant and useful

For the eyes and heart ... "

It is known, for example, that more than half of the labeled atoms of radioactive calcium introduced into the body of an animal is found in the bone tissue within a day. Radioactive strontium also tends to accumulate in bones, which served as the basis for studying the patterns of skeletal ossification by autoradiography.

Recent studies have shown that the skeletal system is an extensive blood depot, where up to 50% of all blood contained in the body is concentrated. Meanwhile, the relationship between the circulatory and skeletal systems has not yet been fully disclosed, therefore, the problem of the depositing and blood-conducting functions of bones is currently in the focus of research.

Thus, the skeleton is a living system, which in the process of individual life undergoes profound changes depending on the living conditions, lifestyle, nature of nutrition and operation, conditions and system of maintenance, changes in connection with the hematopoietic function, adaptation of organisms to respiration. This explains the differences in the degree of skeletal development.

In the anatomical and functional terms, an axial and peripheral skeleton is distinguished. The axial skeleton, in turn, is subdivided into the skeleton of the head (skull) and the skeleton of the trunk, consisting of the spinal column, ribs and sternum. The peripheral skeleton is represented by the bones of the thoracic and pelvic limbs.

Internal organs, skin, blood vessels.

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

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

From a functional point of view, motor neurons, which send nerve impulses to muscle fibers, can also be attributed to the motor apparatus. The bodies of motor neurons that innervate the skeletal muscles with axons are located in the anterior horns of the spinal cord, and those that innervate the muscles of the maxillofacial region are located in the motor nuclei of the brainstem. The motor neuron axon branches at the entrance to the skeletal muscle, and each branch is involved in the formation of a neuromuscular synapse on a separate muscle fiber (Fig. 1).

Rice. 1. Branching of the axon of a motor neuron into axonal terminals. Electronogram

Rice. Human skeletal muscle structure

Skeletal muscle is made up of muscle fibers that combine to form muscle bundles. The set of muscle fibers innervated by branches of the axon of one motor neuron is called a motor (or motor) unit. In the eye muscles, 1 motor unit can contain 3-5 muscle fibers, in the muscles of the trunk - hundreds of fibers, in the soleus muscle - 1500-2500 fibers. Muscle fibers of 1 motor unit have the same morphological and functional properties.

Skeletal muscle function are:

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

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

In addition, striated muscles play a role in the production of heat that maintains thermal homeostasis and in the deposition of certain nutrients.

Rice. 2. Function of skeletal muscle

Physiological properties of skeletal muscle

Skeletal muscle has the following physiological properties.

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

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

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

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

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

Rice. Human skeletal muscle

Physical properties of skeletal muscle

Skeletal muscle is characterized by extensibility, elasticity, strength, and the ability to do work.

Elongation - the ability of a muscle to change length under the action of a tensile force.

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

- the ability of a muscle to lift a load. To compare the strength of various muscles, their specific strength is determined by dividing the maximum mass by the number of square centimeters of its physiological section. Skeletal muscle strength depends on many factors. For example, on the number of motor units excited at a given time. It also depends on the synchronization of the motor units. Muscle strength also depends on the original length. There is a certain average length at which the muscle develops maximum contraction.

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

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

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

Supporting properties of skeletal muscle

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

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

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

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

Single cut

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

The amplitude of a single contraction of an isolated muscle fiber does not depend on the strength of stimulation, i.e. obeys the law "all or nothing". However, the contraction of an entire muscle, consisting of many fibers, during direct irritation depends on the strength of the irritation. At a threshold current, only a small number of fibers are involved in the reaction, so muscle contraction is barely noticeable. With an increase in the strength of stimulation, the number of fibers engulfed in excitement increases; contraction increases until all fibers are contracted ("maximum contraction") - this effect is called the Bowditch ladder. Further increase in the irritating current does not affect muscle contraction.

Rice. 3. Single muscle contraction: A - the moment of muscle irritation; a-6 - latent period; 6-in - reduction (shortening); c-d - relaxation; dd - successive elastic vibrations.

Tetanus muscle

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

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

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

Optimal is called the frequency of irritation at which each subsequent irritation enters the phase of increased muscle excitability. At the same time, tetanus of the maximum size (optimal) develops.

Pessimal is called such a frequency of irritation at which each subsequent stimulation is carried out in the phase of reduced excitability of the muscle. In this case, the size of tetanus will be minimal (pessimal).

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

Muscle contraction modes

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

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

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

Are reduced by similar mechanisms.

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