Skeletal muscles, attached to the bones, set them in motion, participate in the formation of the walls of the body cavities: the oral, thoracic, ventral, pelvis, are part of the walls of some internal organs (pharynx, upper part of the esophagus, larynx), are among the auxiliary organs of the eye (oculomotor muscles), have an effect on the auditory ossicles in the tympanum. With the help of skeletal muscles, the human body is kept in balance, moves in space, respiratory, chewing and swallowing movements are carried out, facial expressions are formed. The total mass of skeletal muscles is 28 kg for men and 17 kg for women. In an adult human muscle mass is about 30% in men, about 20% in women (20-22% in newborns). In older and older people, the mass of muscle tissue, compared with a younger age, decreases somewhat.
There are about 400 muscles in the human body, consisting of striated (transversely striated, skeletal) muscle tissue, which shrinks accordingly to our will. Under the influence of impulses coming along the nerves of the central nervous system, the skeletal muscles contract, move the bone levers, actively change the position of the human body.
Structure of muscles
Each muscle (museums) consists of bundles of striated (transversely striated) muscle fibers, each of which has a thin connective tissue envelope - endomysium (endomysium). Between the bundles of muscle fibers are connective tissue layers that form the shells of these bundles - internal perimysium (perimysium internum). The shell of the whole muscle is the outer permutation, or epimisis (perimysium externum, s.epimysium), which continues on the tendon called peritendineum (peritendineum). Muscle bundles form the fleshy part of the organ - the abdomen of the muscle (venter), which passes into the tendon. With the help of muscle beams or the proximal tendon, which is called the head of the muscle (caput), the muscle originates from the bone. The distal end of the muscle or its distal tendon, which is also referred to as the "tail", the muscle is attached to another bone. It is generally accepted that the beginning of the muscle is closer to the median axis of the body (proximal) than the attachment point, which is distal. Tendons in different muscles vary in shape, thickness, and length.
Classification of muscles
Skeletal muscles are subdivided according to their position in the human body, in the shape, direction of the muscle bundles, in function, in relation to the joints.
According to the location, the muscles are superficial and deep, medial and lateral, external and internal.
Auxiliary apparatus of muscles
Muscles, contracting, perform their function with the participation and assistance of anatomical formations, which should be considered as auxiliary apparatus of muscles. These include the fascia, the vagina of tendons, synovial bags and muscle blocks.
Fascia (fascia) is a connective tissue cover of the muscle. Forming the cases for the muscles, the fascia delineate them from each other, create a support for the muscular abdomen when it shrinks, eliminate the friction of the muscles against each other. Having a case-like structure, the fascias in pathology limit the spread of pus, blood during a hemorrhage, enable "local" local anesthesia . Between the surface of the muscle, its membrane (epimisia) and fasciae is a thin layer of loose fiber. In some places (on the lower leg, forearm), the fascia serves as the starting point for the muscles, and then it is difficult to separate the muscle from the fascia.
Work and strength of muscles
The main property of muscle tissue that forms skeletal muscles - contractility leads to a change in the length of the muscle under the influence of nerve impulses. Muscles act on the bones of the levers, which are connected with the help of joints. In this case, each muscle acts on the joint in only one direction. In the uniaxial joint (cylindrical, block-shaped), the motion of the bone levers occurs only around one axis, so the muscles are located in relation to such a joint on both sides and act on it in two directions (flexion-extension, reduction-retraction, rotation). For example, at the elbow joint, some muscles are flexors, others are extensors.
Work of muscles. Since the ends of the muscle are attached to the bones, the points of its beginning and attachment become closer to each other during contraction, while the muscles themselves perform a certain work. Thus, the body of a person or a part of it with the reduction of the corresponding muscles changes their position, they move, overcome resistance to gravity, or, on the contrary, yield to this force. In other cases, when the muscles contract, the body is held in a certain position without performing the movement. Proceeding from this, distinguish overcoming, inferior and retaining the work of muscles.
Development of muscles
The source of the entire skeletal, striated muscle of the body in humans, as well as in animals, is the middle embryonic leaf - the mesoderm. However, the development of muscles within the trunk, head and limbs has a number of characteristics, which are easier to understand, following the initial stages of embryogenesis. Musculature of the trunk develops mainly from the dorsal, para-axial (near-axis) section of the mesoderm, which forms the primary segments of the body - the somite. Somites are located on the sides of the axial organs of the embryo - the neural tube and spinal cord. At the 4th week of development, there are about 40 pairs of somites: from 3 to 5 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4-5 tail. Further, each somite is divided into 3 parts: sclerotome, dermatome and myotome; from the latter develop the muscles of the trunk.
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