This chapter contains basic information about the muscles present in the human body and their structure.
A person has three types of muscle tissue:
- striated (striated),
- heart striated
- unstriated (smooth).
Of these three types of muscle tissue for bodybuilding, the most interesting is striated (striated) muscle tissue, since it is it that is part of the skeletal muscles and forms their basis.
The structure of striated muscle tissue
The construction of striated muscle tissue
If we talk about the total number of muscles, we can say that in the human body there are about 600 muscles. Most of them are paired and are located symmetrically on both sides of the body.
The total muscle mass is:
- in men — 42% of body weight$
- in women — 35%$
- among athletes — 45-52%.
More than 50% of the weight of all muscles is located on the lower extremities, 25-30% on the upper limbs, 20-25% in the trunk and head. Under the influence of systematic training, structural restructuring of the muscles, an increase in their weight and volume occur. This process is called functional hypertrophy.
The main structural unit of the muscle is muscle fiber. A single muscle fiber has a length of 0.1 to 2-3 cm (in the tailor muscle up to 12 cm) and a thickness of 0.01 to 0.2 mm. The muscle fiber is surrounded by a sheath — a sarcolemma, on the surface of which the ends of the motor nerves are located. Several nerve endings may approach one fiber.
The nerve endings located in the muscles are called receptors and effectors. Receptors perceive the degree of contraction and extension of the muscle, speed and strength of movement. From receptors, information enters the central nervous system, signaling the state of the muscles. According to the effectors, impulses from the central nervous system enter the muscles, causing their excitation. The strength of contraction of excited muscles varies depending on the frequency of nerve impulses. The higher the frequency of nerve impulses, the greater the intensity of contraction.
Sarcolemma, (the membrane surrounding the muscle fiber) blocks the internal contents of the muscle fiber from the intercellular fluid washing it. The entire internal space of the muscle fiber is occupied by sarcoplasm, which is a colloidal protein structure in which glycogen clumps, fat droplets and some other inclusions are interspersed. There are various subcellular particles in the sarcoplasm: nuclei, mitochondria, myofibrils, ribosomes stanozolol prezzo, etc. Their function is to regulate the metabolism in the muscle fiber by affecting the synthesis of specific muscle proteins.
Myofibrils are long specialized muscle cell organelles that perform a contraction function. There are more than 2000 of them inside each fiber. In untrained muscles, myofibrils are scattered, and in trained muscles they are grouped in Congame bundles. The process of bundling myofibrils into bundles is called intramuscular coordination. Thanks to this process, at the initial stages of training, an increase in muscle strength occurs without a significant increase in muscle diameter.
Mitochondria located between myofibrils are particles having bilayer membranes. In the membranes of mitochondria, biological oxidation enzymes are located. Mitochondria are energy centers, they produce 80-90% of all the necessary muscle energy (in the form of adenosine triphosphoric acid or, in short, ATP).
Inside the sarcoplasm there is a system of longitudinal and transverse tubules, membranes, vesicles, called the sarcoplasmic reticulum or sarcoplasmic reticulum, which divides the sarcoplasm into separate compartments where various biochemical processes take place. Bubbles and tubes of the sarcoplasmic reticulum braid each myofibril. Through the tubes connected with the outer cell membrane (T — system), a direct exchange of substances between cellular organelles and intercellular fluid is possible. The tubes can also serve to propagate the excitation wave from the outer membrane to the inner zones.
If we consider the chemical composition of muscle fibers, we can see that 70 to 80% of water is contained in muscle tissue. The functions of water in the cell are diverse:
- water serves as a solvent for many substances;
- as part of colloidal particles, water enters into cellular structures;
- Water is an indispensable participant in many chemical reactions.
Of the solids, 80-85% is protein. About 40% of all muscle proteins are in myofibrils, about 30% — in the sarcoplasm, about 14% — in the mitochondria, about 15% — in the sarcolemma, the rest in the nuclei and other cellular organelles.