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.

Distinguish fasciae own (fasciae propriae), forming a connective tissue case for a given muscle; superficial (fasciae superficiales), covering the muscles from above; The deep (fasciae profundae), separating one group of muscles from the other. Each region has its fascia (for example, the shoulder is fascia brachii, the forearm is fascia antebrachii). If the muscles lie in several layers, then between the adjacent layers are located fascia plates: between the superficial muscles - the surface lamina (lamina superficialis), between the deep - the deep plate (lamina profunda). The superficial fascia (plate) is located under the skin, delimits the muscles from the subcutaneous basis (cellulose), envelops the muscles of this or that part of the body (for example, the muscles of the limb). Between groups of muscles (usually of various functional purposes) pass intermuscular septa (septa intermuscularia), connecting the superficial fascia with the bone (periosteum). At the junction of the fascia with one another thickenings are formed, the so-called fascial nodes, to which a significant place is assigned in strengthening the fascia and protecting the vessels and nerves from compression. Fascia, intermuscular septum firmly fuse with the periosteum of bones, make a soft base for muscles and other organs, participating in the formation of a soft core, or soft skeleton.

The structure of the fascia developing from embryonic connective tissue in the formation of muscles depends on the functions of the muscles, the pressure that the muscles exert on the fascia with their contraction. In places where the muscles partially begin on the fascia, the fascia is well developed, dense, supported by tendon fibers and resembles a thin broad tendon (wide fascia of the thigh, fascia of the shin) in appearance. However, this is not a tendon, not an aponeurosis, as they were incorrectly called, but a fascia of the tendon type. Muscles performing a lesser load have a weak, loose fascia, without a definite orientation of connective tissue fibers. Such thin, loose fascia are called fascia fasciae.

In some places, there are formations, which are thickened fascia. These include the tendon arc (arcus tendineus), which is formed as a local compaction of the fascia over the underlying vascular-neural bundle or other anatomical formation. In the region of some joints (ankle, wrist), where the muscles and tendons, according to the structure of the limb, change their direction, the fasciae are also thickened. Attaching to the bony protrusions, the fascia forms fibrous bridges - retinacula retinaculae. Holders prevent the tendons from shifting to the sides and give them the right direction when contracting the muscles.

Channels formed between the holders and the underlying bones, in which the long thin tendons of the muscles pass, are called bone-fibrous. Tendons in such canals are surrounded by a dense fibrous connective tissue, which forms a fibrous vagina of tendons (vagina fibrosa tendinum). Such a fibrous vagina may be common to several tendons or divided fibrous bridges into several independent vaginas for each tendon.

The tendon movement in its fibrous vagina (osteo-fibrous canal) occurs with the participation of the synovial vagina, which eliminates the friction of the tendon in motion about the fixed walls of the canal. The synovial vagina is formed by the synovial membrane, the synovial layer (stratum synoviale), which has two plates (leaf) - the inner and outer. The internal (visceral) plate (lamina visceralis) envelops the tendon from all sides, fuses with it, with its connective tissue membrane - peritendinium. The outer (parietal) plate (lamina parietalis) is located from the inside to the walls of the fibrous vagina (bone-fibrous canal). Between the visceral and parietal (parietal) plates there is a narrow slit containing a small amount of mucoid-like fluid - synovia.

The visceral and parietal plates of the synovial membrane pass into each other at the ends of the tendon sheath, as well as all over the vagina, forming a mesotendinium tendon. Mesotendinium consists of two leaves of the synovial membrane that connect the visceral and parietal plates, contains blood vessels and nerves that feed the tendon. During muscle contraction, its tendon, covered with the visceral plate of the synovial membrane, slides freely along the outer (parietal) plate, like a piston inside the cylinder, due to the presence of a synovium in the slit-shaped cavity of the synovial vagina. The synovial layer may surround one tendon or several if they lie in one fibrous vagina (canal).

In places where the tendon or muscle is attached to the ossicle, there are synovial bags that perform the same functions as the synovial sheaths of the tendons - eliminate friction.

The synovial bag (bursa synovialis) has the form of a flattened connective tissue sac, inside which there is a small amount of synovial fluid. The walls of the synovial sac on one side are fused with the moving organ (muscle, tendon), on the other - with a bone or other tendon. The sizes of bags vary - from a few millimeters to several centimeters. The cavity of the synovial bag located next to the joint can communicate with the joint cavity. Often, the synovial pouch lies between the tendon and the bony ridge, which has a groove covered with a cartilage for the tendon. This protrusion is called the muscle block (trochlea muscularis). The block changes the direction of the tendon, serves as a support for it and simultaneously increases the angle of attachment of the tendon to the bone, thereby increasing the lever of force application. The same function is performed by sesamoid bones that develop in the thickness of some tendons or are fused to the tendon. Among these sesamoid bones are the pea-shaped bone on the hand, and the patella is the largest sesamoid bone.

[1], [2], [3], [4]