The human muscle in relation to its total mass is about 40%. Their main function in the body is to ensure movement through the ability to contract and relax. For the first time the structure of muscles (grade 8) begins to be studied in school. There, knowledge is given at a general level, without much deepening. The article will be interesting to those who wish to go beyond this framework a little.
Structure of muscles: general information
Muscle tissue is a group that unites cross-striped, smooth and cardiac varieties. Differing in origin and structure, they are combined on the basis of the function performed, that is, the ability to contract and lengthen. In addition to the listed varieties, which are formed from the mesenchyme (mesoderm), in the human body there is also muscle tissue having an ectodermal origin. These are myocytes of the iris of the eyes.
The structural, general structure of the muscles is as follows: they consist of an active part called the abdomen, and tendon ends (tendons). The latter are formed from dense connective tissue and perform the function of attachment. They differ in characteristic whitish-yellow color and shine. In addition, they possess a considerable fortress. Usually, with their tendons, the muscles are attached to the links of the skeleton, the connection with which is movable. However, some can be attached to the fascia, to various organs (eyeball, cartilage of the larynx, etc.), to the skin (on the face). Blood supply to the muscles varies and depends on the loads they are experiencing.
Regulation of the muscles
Control over their work is carried out, as in other organs, by the nervous system. Receptors or effectors terminate its fibers in the muscles. The first are also located in the tendons, have the form of terminal branches of the sensory nerve or neuromuscular spindle, which has a complex device. They react to the degree of contraction and stretching, so that a person has a certain feeling, which, in particular, helps to determine the position of the body in space. Effector nerve endings (the second name - motor plaques) belong to the motor nerve.
The structure of muscles is also characterized by the presence in them of fiber endings of the sympathetic nervous system (vegetative).
The structure of the striated muscle tissue
It is often called skeletal or striated. The structure of the skeletal muscle is not easy enough. It is formed by fibers having a cylindrical shape, a length of 1 mm to 4 cm and more, a thickness of 0.1 mm. Each is a special complex, consisting of myosatellite and myosymplast, covered with a plasma membrane called the sarcolemma. Outside, the basal membrane (plate), formed of the finest collagen and reticular fibers, adjoins it. Myosymplast consists of a large number of ellipsoidal nuclei, myofibrils and cytoplasm.
The structure of muscles of this type is distinguished by a well developed sarcotubular network formed of two components: the tubules of EPS and T-tubes. The latter play an important role in accelerating the implementation of the action potential to microfibrils. Myosatellitocytes are located directly above the sarcolemma. Cells have a flattened shape and a large nucleus rich in chromatin, as well as a centrosome and a small number of organelles, myofibrils are absent.
Sarcoplasma of skeletal muscle is rich in a special protein - myoglobin, which, like hemoglobin, has the ability to bind with oxygen. Depending on its content, presence / absence of myofibrils and fiber thickness, two types of striated muscle are distinguished. The specific structure of the skeleton, the muscles - all these are the elements of the person's adaptation to the erection, their main functions are support and movement.
Red Muscle Fibers
They have a dark color, are rich in myoglobin, sarcoplasm and mitochondria. However, they contain few myofibrils. These fibers are reduced slowly enough and can stay in such a state for a long time (in other words, in a working state). The structure of the skeletal muscle and the functions it performs are worth considering as parts of the whole, mutually conditioning each other.
White Muscular Fibers
They differ in light color, contain much less amount of sarcoplasm, mitochondria and myoglobin, but they are characterized by a high content of myofibrils. This causes them to contract much more intensively than the red ones, but they also "get tired" too quickly.
The structure of a person's muscles is different in that there is one and the other kind in the body. Such a set of fibers determines the speed of the reaction of the muscles (contraction) and their long working capacity.
Smooth muscle tissue (unspecified): structure
It is built of myocytes stationed in the walls of the lymph, blood vessels, and constituting the contractile apparatus in the inner hollow organs. This elongated cells with a spindle shape, without cross-striations. Their location group. Every miocic surrounds the basal membrane, collagen and reticular fibers, among which are elastic. Among themselves cells are linked by the nexus. The structural features of the muscles of this group are that each myocite surrounded by connective tissue, suited one nerve fiber (for example, the sphincter of the pupil), and momentum are transported from one cell to another using a nexus. Its speed of 8-10 cm/s.
In smooth miocytes, the rate of contraction is much less than that of myocytes of striated muscle tissue. But energy is spent sparingly. This structure allows them to make long-term tonic abrasions (for example, sphincters of blood vessels, hollow, tubular organs) and slow enough movements, which are often rhythmic.
Cardiac muscle tissue: features
According to the classification, it belongs to the cross-striped, but the structure and function of the muscles of the heart differ markedly from the skeletal ones. Cardiac muscle tissue consists of cardiomyocytes, which form complexes, connecting with each other. Reduction of the heart muscle is not subject to control by the human consciousness. Cardiomyocytes are cells having an irregular cylindrical shape, with 1-2 nuclei, a large number of large mitochondria. Between them they are connected by intervening disks. This is a special zone, which includes the cytolemma, the areas of attachment of myofibrils to it, desmos, and nexus (through them there is a transfer of nervous excitation and ion exchange between cells).
Classification of muscles depending on the form and size
1. Long and short. The first occur where the largest swing in motion. For example, the upper and lower limbs. And short muscles, in particular, are located between separate vertebrae.
2. Broad muscles (in the photo - the stomach). They are mainly located on the body, in the cavity walls of the body. For example, the superficial muscles of the back, chest, abdomen. When multilayered, their fibers tend to go in different directions. Therefore, they provide not only a great variety of movements, but also strengthen the walls of the body cavities. In broad muscles, the tendons are flat and occupy a large surface, they are called stretchings or aponeuroses.
3. Circular muscles. They are around the body's orifices and contract with their contractions, resulting in the name "sphincters". For example, the circular muscle of the mouth.
Complex muscles: features of the structure
Their names correspond to their structure: two-, three- (pictured) and four-headed. The structure of the muscles of this species differs in that their origin is not uniform, but divided into 2, 3 or 4 parts (heads), respectively. Starting from different points of the bone, they then shift and unite in the common abdomen. It can also be divided by an intermediate tendon across. Such a muscle is called a two-abdominal muscle. The direction of the fibers can be parallel to the axis or be at an acute angle to it. In the first case, the most common, the muscle is sufficiently shortened by contraction, thus providing a large swing in the movements. And in the second - the fibers are short, located at an angle, but they are much larger in number. Therefore, the muscle is shortened only slightly with contraction. Its main advantage lies in the fact that it develops a great deal of strength. In the case of fibers approaching the tendon only on one side, the muscle has the name of a single-bump, if with two - two-pinnate.
Auxiliary apparatus of muscles
The structure of the muscles of a person is unique and has its own characteristics. So, for example, under the influence of their work, auxiliary devices are formed from the surrounding connective tissue. There are four in total.
1. Fascia, which is nothing but a shell of dense, fibrous fibrous tissue (connective). They cover both single muscles, and whole groups, as well as some other organs. For example, kidneys, vascular bundles, etc. They affect the direction of traction during contraction and do not allow the muscles to move to the sides. The density and strength of the fascia depends on their location (they differ in different parts of the body).
2. Bursal (pictured). The role and structure of many, perhaps, will remember from school lessons (Biology, 8th grade: “Building muscles”). They represent a kind of bags, the walls are formed by connective tissue and thin enough. Inside the fluid-filled type synovitis. As a rule, they are formed where tendons are in contact among themselves or experiencing a lot of friction on the bone when the muscle contraction, and the friction of her skin (e.g., elbows). Thanks to the synovial fluid is improved and easier to slide. They develop mainly after birth, and over the years the cavity increases.
3. Synovial vaginas. Their development occurs within the osteo-fibrous or fibrous channels, with which the tendons of the long muscles are surrounded in places of sliding along the bone. In the structure of the synovial vagina, two petals are distinguished: the inner lobe, covering the tendon on all sides, and the outer tendon lining the walls of the fibrous canal. They prevent the friction of the tendons against the bone.
4. Sesamoid bones. As a rule, they ossify inside ligaments or tendons, strengthening them. This facilitates the work of the muscle by increasing the arm of the application of force.