Muscle is an active element of the musculoskeletal system.
Classification of muscles is carried out according to various criteria: position in the human body, shape, direction of fibers, functions, relation to joints, etc.
Main muscle types
The classification of human and vertebrate muscles suggests three different types: striated skeletal muscle, striated cardiac muscle (myocardium), and smooth muscles that make up the walls of blood vessels and hollow internal organs.
The purpose of the striated muscles is to set the bones in motion, participate in the formation of the walls of the oral, chest, and abdominal cavities. They are part of the auxiliary parts of the organs of the eye, affect the auditory ossicles. The work of skeletal muscles ensures that the human body is kept in balance, moving in space, performing respiratory and swallowing movements, and the presence of facial expressions.
Skeletal muscles: structure
Almost 40% of adult body weight is muscle tissue. There are more than 400 skeletal muscles in the body.
Skeletal muscle units are a motor neuronand muscle fibers innervated by this neuromotor unit. With the help of impulses sent by the motor neuron, muscle fibers come into action.
Skeletal muscles are represented by a large number of muscle fibers. They have an elongated shape. The classification of human muscles suggests that their diameter is 10-100 microns, and the length ranges from 2-3 to 10-12 cm.
The muscle cell is surrounded by a thin membrane - the sarcolemma, containing sarcoplasm (protoplasm) and a large number of nuclei. The contractile part of the muscle fiber is represented by long muscle filaments - myofibrils, which consist mainly of a substance called actin.
Myosin contained in cells is in a dispersed state. It contains a lot of protein, which plays an important role in maintaining the tonic contraction. Even the relative rest of the skeletal muscle does not imply its complete relaxation. At this time, moderate tension is maintained, i.e. muscle tone.
Auxiliary Muscle Apparatus
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 structures that make up auxiliary devices, which consist of fascia, tendon sheath, synovial bags and blocks. Fascia is a cover consisting of connective tissue that provides support to the muscle belly when it contracts, and prevents the muscles from rubbing against each other. In case of pathology, the presence of fascia prevents the spreadpus and blood in case of 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 differ greatly in structure, which determines their functional diversity. Muscle strength can be determined by the number of muscle bundles, since they determine the size of the physiological diameter. It is its relation to the anatomical diameter that makes it possible to judge one or another strength of dynamic and static characteristics.
Classification of skeletal muscles according to differences in these ratios divides skeletal muscles into dynamic, static-dynamic and static.
The simplest structure is characteristic of dynamic muscles. In the presence of a gentle remysium, their long fibers run along the longitudinal axis of the muscle or at an angle to it, which causes the anatomical diameter to coincide with the physiological one. These muscles perform a large dynamic load. They have a large amplitude, but they do not differ in strength. These muscles are considered fast, agile, but also fatigued quickly.
In statodynamic muscles, the perimysium (internal and external) is more strongly developed than in dynamic ones, and the muscle fibers are shorter. They go in different directions, i.e., unlike dynamic ones, they form a set of physiological diameters. If there is one common anatomical diameter, a muscle can have 2, 3, or 10 physiological diameters. This issuggests that statodynamic muscles are stronger than dynamic ones. Their role is mainly to maintain a static function during support, to keep the joints extended when standing. They are distinguished by great strength and considerable endurance.
Classification of muscles suggests a third type. These are static muscles. They can develop in the process of a large static load falling on them. The lower the location of the muscles on the body, the more static they differ in structure. Great static work when standing and supporting the limb on the ground in motion, fixing the joints in a certain position is included in their direct tasks.
Classification of muscles according to the direction of muscle fibers and their relation to tendons
Muscles, the fibers of which are parallel to the longitudinal axis, are called fusiform, or parallel. When the fibers are at an angle to the axis, such a muscle is called pennate. In the limbs, it is mainly the fusiform and feathery muscles that are localized.
Intramuscular tendon layers, or rather their number, and the direction of the muscle layers serve as criteria by which pennate muscles are divided into several types:
- one-feathered, which lack tendon layers, the attachment of muscle fibers to the tendon is present only on one side;
- two-pinned; they have one tendon layer and bilateral attachment of muscle fibers to the tendon;
- multi-pinnate, in which there are two or more tendon layers, which causes interlacing of musclebundles, they approach the tendon from several sides.
How are muscles divided by shape?
Classification of muscles by shape distinguishes several main types in their variety.
- Long. They are located mainly in the limbs. Their shape resembles a spindle. Each muscle is conditionally divided into three parts: the middle part is called the abdomen; the beginning of the muscle is called the head, the end opposite to the beginning is the tail. Their tendons have a ribbon-like shape. There are such long muscles that have not one, but several heads on different bones, which is necessary to strengthen their support. Such muscles are called multi-headed.
- Short. They are located where there is not too much range of motion. These are the junctions of individual vertebrae, the places between the vertebrae and ribs, etc.
- 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 a motor function, but also a supporting and protective one.
- Muscles of other shapes: square, circular, deltoid, dentate, trapezius, fusiform, etc.
Division of muscles into groups depending on the number of heads and location
The structure and classification of muscles are interrelated. So, one of their parts has several heads. They are named according to the number of heads: two-headed (biceps), three-headed (triceps), etc.
Depending on the location,which muscles occupy in the body, they are superficial and deep, medial and lateral, external and internal.
Muscles according to impact on joints
Classification of muscles in relation to joints implies the presence of single-joint (affect only one joint), bi-joint (spread over two joints), and multi-joint muscles (act on three or more joints).
Classification of muscles by function
According to this criterion, muscles-synergists and muscles-antagonists are distinguished. Synergists move the joint in only one direction (flexors or extensors), while antagonists act on the joint in two opposite directions (flexors and extensors).
Classification of muscles by function includes other options. Also, the muscles are adductor, abductor. They can perform rotational functions, compress, narrow, expand, raise, lower, strain, delay.
