Tendini e fascia profonda

Tendons are anatomical structures that connect muscles to other structures, such as bone and cartilage, but also to other structures. Given their function of transmitting force, they must be highly resistant to traction and have little elasticity to avoid absorbing the tension generated by the muscle. These properties are determined by the tendon's structure: they are composed of dense, regular connective tissue, and type 1 collagen fibers constitute at least 60% of the tendon's dry weight. They are organized into fascicles, which in turn can form secondary and tertiary fascicles, creating a veritable hierarchy of parallel bundles. Each of these fascicles is surrounded by a very thin film of loose connective tissue called the endotenon, which is continuous with the perimysium of the muscle and allows the fascicles to slide over each other and continue to transmit muscle tension despite changes in joint angle and, therefore, the orientation of the bone on which they insert. Externally, it is surrounded by the epitenon, a layer of tissue that is continuous with the epimysium of the muscle. Tenocytes, the tendon cells, are located between the collagen fibers. These are fibroblasts trapped in the tendon's purely fibrous matrix. Externally, some tendons are surrounded by other structures: -tenosynovial sheaths or tendon sheaths -paratenon Tendons can be classified based on their length (short and long), or based on their approximate shape: cylindrical (like the Achilles tendon), ribbon-like (like the tendons of the rotator cuff in the shoulder, for example), or flattened, in which case they are called aponeuroses. The myotendinous junction is formed by digits of the muscle belly that meet complementary digits of the tendon. Instead of anchoring to a Z-shaped disc, the terminal thin filaments of the muscle cells are inserted into a protein plate similar to the adherens junction I discussed in the lesson on epithelial tissue. On this plate, the collagen fibers of the tendon bind, via other proteins, on the other side. The osteotendinous junction, also called the enthesis, can be of two types: -fibrocartilaginous or indirect -fibrous or direct Vascular supply comes primarily from the muscle and the surrounding loose connective tissue. It never comes from the bone, with the sole exception of the Achilles tendon, which also receives blood vessels from the osteotendinous junction. Many tendons have areas of reduced vascularization, primarily due to mechanical stress, which are called CRITICAL AREAS. Innervation is purely sensory and is primarily provided by specialized endings called Golgi tendon organs, located mostly near the myotendinous junction and registering muscle tension. Another important connective tissue structure in the musculoskeletal system is the deep fascia. The deep fascia is located directly beneath the hypodermis and should not be confused with the superficial fascia, which is the middle layer of the hypodermis and which we will discuss in another lesson on the integumentary system. However, the superficial fascia and deep fascia are linked by the DEEP RETINACULUM CUTIS within the deepest layer of the hypodermis. This connects the superficial and deep fascia with sparse bundles of collagen fibers oriented obliquely to the deep fascia. In a similar manner, but with vertical bundles of collagen fibers, the dermis and the superficial fascia are linked, forming the superficial retinaculum cutis. Beneath the deep fascia, we find the muscle. The visceral surface of the deep fascia is separated from the epimysium of the underlying muscle by only a very thin layer of loose connective tissue. The deep fascia is composed of dense, regular connective tissue formed by layers of collagen fibers that run parallel to each other but are oriented differently from one layer to the next, reaching an average thickness of approximately 1 mm and enveloping the entire musculoskeletal system. From the visceral surface of the fascia, intermuscular septa can arise, which, inserting into the bone, divide the body region into what are called MUSCLE LOCATES or COMPARTMENTS. At the joints, the deep fascia tends to thicken, forming retinacula, then fuse with the periosteum and joint capsules, and then continue into other fasciae. 00:00 Intro to Tendons and Mechanical Properties 00:46 Tendon Structure 01:57 Tenocytes 02:26 Tenosynovial Sheaths and Paratenon 03:43 Tendon Classification 04:25 Myotendinous Junction and Enthesis 06:14 Tendon Vascularization and Innervation 07:43 Fascia Location 09:27 Fascia Structure, Septa, and Muscle Lodges