Structure and classification of human muscles

The muscle is an active element of the musculoskeletal system.

Classification of muscles is carried out on different grounds: position in the human body, shape, direction of fibers, functions, attitude to the joints, etc.

The main types of muscles

The classification of the muscles of man and vertebrates presupposes the presence of three different types: striated skeletal muscles, striated cardiac muscle (myocardium) and smooth muscles, of which the walls of blood vessels and hollow internal organs are composed.

The purpose of the striated muscles is to bring the bones into motion, to participate in the formation of the walls of the oral, thoracic, abdominal cavities. They are part of the auxiliary parts of the eye, affect the auditory ossicles. The work of skeletal muscles ensures the retention of the human body in equilibrium, movement in space, the performance of respiratory and swallowing movements, the presence of facial expressions.

Skeletal muscles: structure

Almost 40% of the body weight of adults is just muscle tissue. Skeletal muscles in the body are more than 400.

Units of skeletal muscles are motoneuron and muscle fibers innervated by this neuromotor unit. With the help of impulses sent by motoneuron, muscle fibers come into action.

Skeletal muscles are represented by a large number of muscle fibers. They have an elongated shape. Classification of human muscles suggests that their diameter is 10-100 microns, and the length varies from 2-3 to 10-12 cm.

The muscle cell is surrounded by a thin membrane - a sarcolemma containing sarcoplasm (protoplasm) and a large number of nuclei. The contractile part of the muscle fiber is represented by long muscle threads - myofibrils, which consist mainly of a substance called actin.

The myosin contained in the cells is in a dispersed state. It has a lot of protein, which plays an important role in maintaining tonic contraction. Even, the relative calm of the skeletal muscle does not imply its complete relaxation. At this time, a moderate tension is maintained, i.e. Muscular tone.

Auxiliary apparatus of muscles

The structure and classification of skeletal muscles determine their functionality. So, they are able to perform certain actions only with the help and with the participation of special anatomical formations that make up auxiliary devices, which consist of fascia, tendon sheaths, synovial bags and blocks. The fascia is a veil consisting of connective tissue, supports the muscular abdomen, when it shrinks, prevent the friction of the muscles from each other. In the case of pathology, the presence of fascias prevents the spread of pus and blood during hemorrhage.

Classification of skeletal muscles by dynamic and static properties

Skeletal muscles, based on the nature of the relationship between muscle bundles and intramuscular connective tissue formations, can vary greatly in structure, which determines their functional diversity. The strength of muscles can be determined by the number of muscle beams, since they determine the value of the physiological diameter. It is his attitude to the anatomical diameter that allows one to judge about this or that force of dynamic and static characteristics.

Classification of skeletal muscles from differences in these ratios divides the skeletal muscles into dynamic, static and static ones.

The simplest structure is characteristic for dynamic muscles. In the presence of gentle permutation, their long fibers pass along the longitudinal axis of the muscle or at an angle to it, which determines the coincidence of the anatomical diameter with the physiological one. These muscles perform a great dynamic load. They have a large amplitude, but they do not differ in strength. These muscles are considered quick, agile, but also quickly fatiguing.

Stethodynamic muscles of perimises (inner and outer) are more developed than in dynamic muscles, and muscle fibers are shorter. They go in different directions, that is, they form, in contrast to the dynamic, a lot of physiological widths. If there is one common anatomical diameter in the muscle, there may be 2, 3, or 10 physiological widths. This allows us to state that the statodynamic muscles are stronger than the dynamic ones. Their role is mainly in maintaining the static function during the support, keeping the joints unbent when standing. They are distinguished by great strength and considerable endurance.

Classification of muscles involves the presence of a third type. These are static muscles. They can develop in the process of a large static load falling on them. The lower the arrangement of muscles on the body, the greater the static they differ in structure. A large static work when standing and supporting the limb on the soil in motion, fixing the joints in a certain position, is part of their direct tasks.

Classification of muscles in the direction of muscle fibers and their relation to tendons

Muscles, whose fibers are located parallel to the longitudinal axis, are called spindle-shaped, or parallel. When the fibers are at an angle to the axis, such a muscle is called pinnate. In the extremities are localized, mainly just fusiform and pinnate muscles.

Intramuscular tendon interlayers, or rather their number, and the directions of the muscle layers serve as criteria by which the pinnate muscles are divided into several types:

• Single-pleated, in which there are no tendon layers, attachment of muscle fibers to the tendon, there is only one side;
• Two-pinnate; They have one tendon interlayer and bilateral attachment of muscle fibers to the tendon;
• Multi-pleated, with two or more tendon layers, which causes the interweaving of muscle bundles, they approach the tendon from several sides.

How do the muscles divide in shape?

Classification of muscles in form distinguishes several basic types in their variety.

1. Long. They are located mainly in the limbs. Their shape resembles a spindle. Each muscle is divided into three parts: the middle part is called the abdomen; The beginning of the muscle is called the head, the opposite end is the tail - it's the tail. Their tendons have a ribbon-like shape. There are such long muscles, in which not one, but several heads on different bones, which is necessary to strengthen their support. Such muscles are called multi-headed.
2. Short. They are where there is not too much scope for movement. These are the joints of separate vertebrae, the spaces between the vertebrae and the ribs, and so on.
3. Flat wide. They are localized mainly on the trunk and belts of the upper and lower extremities. They have enlarged tendons, called aponeuroses. Flat muscles perform not only motor function, but also support and protective.
4. Muscles of other forms: square, circular, deltoid, dentate, trapezoidal, fusiform, etc.

The division of muscles into groups, depending on the number of heads and location

The structure and classification of muscles are interrelated. So, one part has several heads. They are given a name in accordance with the number of heads: biceps (biceps), triceps (triceps), etc.

Depending on the place that the muscles occupy in the body, they are superficial and deep, medial and lateral, external and internal.

Muscles in accordance with the effect on the joints

Classification of the muscles with respect to the joints implies the presence of single-joint (affect only one joint), bipartite (it is thrown through two joints), and multi-joint muscles (act on three or more joints).

Classification of muscles by function

By this criterion, muscle synergists and muscle antagonists are isolated. Synergists bring the joint into motion in only one direction (flexors or extensors), and the antagonists act on the joint in two opposite directions (flexors and extensors).

Classification of muscles by function includes other options. Also, muscles are leading, withdrawing. Can perform rotational functions, compress, narrow, expand, lift, lower, stretch, pull.