Structure and functions of the muscular system
The muscular system consists of about 600 muscles that provide movement of the body in space, maintaining the posture, breathing, chewing, swallowing, speech, participating in the work of internal organs, circulation, heat regulation, metabolism, and playing an important role in human perception body and its parts in space. The muscle is an integral organ consisting of striated muscle tissue, and also of dense and loose connective tissue. The innervation and blood supply of the muscle is provided by the vessels and nerves passing through it.
In the structure of the muscle, the abdomen and tendon are identified (Figure 3.13). The muscular abdomen serves to contract and consists of bundles of striated muscular tissue - muscle fibers running parallel to each other and connected together by a loose connective tissue. The connective tissue located between the muscular tufts, but the ends of the muscular abdomen, passes into the tendon - the passive part of the muscle with which it is attached to the bones. The abdomen of the muscle has a reddish-brown color, a tendon consisting of a dense connective tissue, has a brilliant light golden color and is located at both ends of the muscle. It is dense, contains few blood vessels and has a lower level of metabolism. Most tendons move away from the head of the muscle in the form of white strands and firmly hold the tendon on the bone, penetrating the periosteum and attaching to the compact layer of bone. Long tendons of the hand or foot are surrounded by a vagina in which there is an oily synovial fluid. It lubricates the tendons, making it easier to slip when the muscles of the forearm or tibia pull the fingers or feet. Tendons of a flat form that not only connect muscles to bones but also muscles to each other (for example, connections of facial muscles) are called aponeuroses. Some muscles do not have tendons, they start from the bone and are attached to it by the abdomen (such muscles have been called sedentary).
Fig. 3.13. The structure of the muscle
The main properties of muscle tissue - contractility, excitability and elasticity - are inherent and muscle as an organ. The contractility of the muscles is regulated by the nervous system. In the muscles are nerve endings - receptors and effectors. Receptors are sensitive nerve endings that perceive the degree of contraction and stretching of the muscle, speed, acceleration, strength of motion. They can be free (in the form of terminal branchings of the sensory nerve) or unfree (in the form of a complexly constructed neuromuscular spindle). From the receptors, information about the state of the muscle and the realization of the motor program enters the central nervous system. Impulses from the central nervous system come to the muscles by effector, causing their excitement. The nerves that regulate metabolic processes and muscle tone at rest also fit the muscles. This relationship allows the nervous system to regulate muscle activity and metabolic processes in them and ultimately perform the tasks of adaptation and functioning in the environment.
The degree of development of the musculature depends on various factors: heredity, sex, exercise, nutrition, etc. Regular physical activity leads to an increase in the weight and volume of muscles (the so-called functional hypertrophy).
Muscles are divided into topographic groups: muscles of the head, neck, back, chest, abdomen; muscles of the upper extremity belt, shoulder, forearm, hand; muscles of the pelvis, hips, legs, feet. In these groups, the anterior and posterior muscle groups are distinguished, superficial and deep, external and internal muscles. In Fig. 3.14 represents the main muscles of the human body.
Fig. 3.14. Human muscles :
1 - front view :
1 - frontal abdomen of the cervical-frontal muscle; 2 - the circular muscle of the mouth; 3 - chin; 4 - sterno-hyoid; 5 - trapezoidal; 6 - three-headed shoulders; 7 - a straight belly; 8 - an external oblique abdomen; 9 - the beam flexor of the brush; 10 - pulling the wide fascia of the thigh; 11 - the anus and lumbar; 12 - scallop; 13 - long leading; 14 - tailoring; 15 - straight thigh; 16 - gentle; 17 - inner wide; 18 - diverting the thumb; 19 - the tendon of the long muscle that extends the fingers; 20 a long muscle that extends fingers; 21 - soleus; 22 - anterior tibia; 23 - the calf; 24 - the outer wide; 25 - a short muscle that extends the thumb; 26 - a long muscle that reclines the thumb; 27 - the elbow extensor of the hand; 28 - short radius extensor of the hand; 29 - extensor of the fingers; 30 - long extensor of the hand; 31 - a brachium; 32 - three-headed shoulders; 33 - the front dentate; 34 - double-headed shoulders; 35 - large chest; 36 - deltoid; 37 - front staircase; 38 - the average ladder; 39 - sternocleidosus; 40 - lowering the corner of the mouth; 41 - chewing; 42 - a large zygomatic; 43 - temporal;
2 - rear view:
1 - the occipital abdomen of the occipitus-frontal muscle; 2 - is trapezoid; 3 - deltoid; 4 - three-headed shoulders; 5 - biceps brachium; 6 - a round pronator; 7 and 23 - the brachiculus; 8 - the beam flexor of the brush; 9 - long palm; 10 - ulnar flexor of the hand; 11 - the superficial flexor of the fingers; 12 and 16 - semimembranous; 13 - is a semitendinous; 14 - gentle; 15 - double-headed hips; 17 - calf; 18 - sole; 19 - a large buttock; 20 - a short muscle that removes the thumb; 21 - mean gluteal gland; 22 - an external oblique abdomen; 24 - the widest back; 25 - Front gear; 26 - a large round one; 27 - small round; 28 - subacute; 29 - is sternocostile-lumpy; 30 - a belt of the head; 31 - chewing; 32 - half-baked head; 33 - temporal
The action of skeletal muscles is carried out according to the laws of levers and is aimed at changing the position of a part of the body in space or in opposing the forces of gravity while holding a static posture. The tendons of the muscle attach to different bones, the muscle contraction leads to a change in the position of the bone or, on the contrary, to its retention in a certain position. Any movement is carried out not by one but by several muscles, the action of which can be unidirectional (muscles synergists ) or multidirectional (muscles - antagonists). strong> Complex complex of muscle contractions leads to a smooth and harmonious movement. Muscles, providing certain movements, have received the name of a functional group. For example, a group of muscles flexing the joint works simultaneously with a group of muscles extending the joint, and the action of any muscle can occur only when the antagonist muscle relaxes at the same time. Such coordination is called muscular coordination. For example, the concerted work of paired antagonists of the biceps and triceps of the shoulder allows you to raise and lower your arms, bend and unbend them at the elbow (Figure 3.15).
Fig. 3.15. Muscle-antagonists of the shoulderMuscles have an intensive metabolism, so they have a well developed blood circulation, through which oxygen is delivered to the muscles, nutrients and biologically active substances, metabolic products and carbon dioxide are removed. Blood flow in the muscle is continuous, but its activity depends on the nature and intensity of the muscle. In the absence of muscular load, about a third of all capillaries function, with increasing the number of capillaries increases significantly. It is established that the major muscles of the body are "assistants" heart, acting as a pump in the movement of blood through the vessels. Therefore, the load on the cardiac muscle with physical activity in people with a well developed muscular system is less than that of untrained people.
In the body, each skeletal muscle is always in a state of a certain tension, readiness for action, which has received the name of a muscle tone. In children, muscle tone is lower than that of adults, women are lower than men, and all depend heavily on exercise for all.
Influence of the load on the human muscular apparatus
The load has a shaping effect on the muscles. Strengthened muscle work contributes to an increase in the mass of muscle tissue, a certain degree of which is called muscle hypertrophy. Depending on the characteristics of physical exertion, a significant part of the muscles of the body or their individual groups may become hypertrophied. This phenomenon is based on an increase in the mass of muscle fibers and the number of myofibrils contained in them, which leads to an increase in muscle diameter, activation of metabolic processes, increase in strength and rate of contraction, and the total muscle mass in trained people can reach 50% of body weight instead of the usual 30- 40%.The opposite process is muscle atrophy, which develops with prolonged inactivity: if the tendon or nerve is damaged, the plaster cast on the limb, or the long stay in bed due to illness. The diameter of the muscle fibers and the activity of metabolic processes in them with atrophy decrease. After the resumption of muscle activity, atrophy gradually disappears.
Fatigue - a temporary decrease in the working capacity of the body or any organ that occurs as a result of work and disappears after rest. Muscle fatigue with prolonged exercise is caused by the depletion in the muscle tissue of the energy reserves necessary for muscle fiber contraction and the accumulation of slags that do not have time to be discharged " - metabolic products that inhibit the activity of muscle fibers. In addition, an important role is played by fatigue arising in the nerve centers that control the work of this group of muscles. In the works of IM Sechenov (1903) it was shown that restoration is best accomplished not with passive, but with active rest (change of activity).
The fatigue of the child is directly dependent on the age and is due to the age characteristics of the nervous activity, since the muscle itself can contract without fatigue for a sufficiently long time. In infancy, the active active wakefulness is about 1.5-2 hours, then increases slightly. It can develop and, if necessary, prolong the inhibition of motor activity. Restoration of muscular efficiency at rest most quickly occurs in 7-9 years, in the pubertal period (by 13-15 years) decreases and again rises to 16-18 years. The adaptation of muscles to physical loads against the background of increasing fatigue is called endurance, it also undergoes certain changes in ontogeny: the greatest increase in endurance with muscular load is noted at 7-10 years, in boys at age 17 the endurance is twice higher than at age 7, to the endurance of adolescents reaches 85% of this value in adults, the endurance peak is at the age of 20-29 years, then it gradually decreases and by about 70 years it is about 25% of the maximum level.
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