Tendons are a type of regularly arranged dense connective tissue that connects muscles to bone. This fibrous and flexible tissue is also called sinew. The material properties of the connective tissue have made animal sinew a traditional component of bows and threads.
Tendon Structure
This soft tissue is made of more than 80% type I collagen by weight. The collagen is arranged in fibrils, which are made up of microfibrils in a hierarchical structure. The fibrils form a fascicle, which is made up of not only the basic tendon fibril, but also fibroblasts in parallel rows. Fibroblasts are involved in the production of collagen. The fascicle is covered by the fascicular membrane, making the structure known as the tendon.
Tendons also contain some elastin fibers, but a low concentration, and proteoglycan matrix, a proteinaceous filler between connective tissue fibers. The flexibility of this tissue is due to the inherent flexibility of collagen.
How Tendons Attach to Bone and Muscle
The connective tissue merges with the periosteum, the thin membrane covering the bone. This is referred to as the insertion point and is a movable attachment. The tendon also merges with the thin membrane covering the muscle, called the fascia. This is referred to as the origin, as it is this point that determines the tendon’s function, i.e. which muscle it acts upon. The origin is a stationary attachment.
The tendon receives some blood supply from the microvasculature of the muscle fascia at the origin. However, tendons tend to have relatively poor vascularization and do not heal well when injured. Tendons in the fingers and other joints that bend sharply are directed within a tendon sheath.
Tendon Function
Each muscle usually has two tendons binding to two different bones, with the muscle crossing the joint. This allows the tendon to act as a pulley.
The tendons function to carry tensile forces from the muscle to the bone. When a muscle contracts it pulls on the tendon, which then pulls on the bone, resulting in movement. The bones are held together at the joints by ligaments and other connective tissues, so the actions of tendons result in specific movements, depending on the muscle and joints involved.
- Visit The Electronic Textbook of Hand Surgery for a list of human tendons.
- For more on joints, see Human Skeletal Movement
Resources:
Scanlon and Sanders. Essentials of Anatomy and Physiology, 4th edition, 2003.
SUNY Downstate Medical Center. “Connective Tissue”, Histology Lab Manual Online, updated March 2008. Accessed April 19, 2010.
University of Michigan College of Engineering. “BME/ME 456 Biomechanics: Structure and function of ligaments and tendons”. Accessed April 20, 2010.
Wayne State University. “ME 518: Orthopedic soft tissues”. Accessed April 20, 2010.
Alicia Mae Prater - Alicia received her doctorate in Experimental Pathology in 2007. She has been a freelance writer and scientific editor since 2008.
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