Structure & Function of Tendons

Background

Tendons are a type of soft tissue that connects muscle tissue to bone, similar to the ligaments that connect bone to bone. They can be found throughout the body from the legs to the hands. They are composed almost entirely of collagen, a fibrous protein, and are often referred to as a collagenous tissue. The purpose of tendons is to transfer force between muscle and bone. This facilitates the joint movement that allows for everyday activities like walking or reaching. Tendons can have several shapes ranging from wide and flat, ribbon and fan shaped.

Structure

The structure of tendons can be divided into six major areas. The smallest component of a tendon is a collagen fibril. A collagen fibril is a group of interconnected collagen strands that are bound together. One step up in the tendon structure is the collagen fiber. The collagen fiber is a group of collagen fibrils bound in a sheath of endotenon (a substance that helps to stabilize and bind the fibrils). Fiber bundles represent the next level in the tendon. Fiber bundles are a group of collagen fibers bound together in a sheath of endotenon. A secondary fiber bundle is a group of fiber bundles bound in a sheath endotenon. A fascicle is the second largest component in the tendon structure. This is group of secondary fiber bundles that are bound together by endotenon. The endotenon that surrounds the fascicle is crimped in areas that may come under higher stress. The tendon itself is the largest structure. It is composed of a group of fascicles that are bound together by an interior sheath of endotenon and an exterior sheath of connective tissue called epitenon.

Function

The function of the tendon is to act as a stretch and recoil mechanism that transmits the force generated by a muscle to the bones or joints to which it is attached. Though an imperfect analogy, a tendon can be thought of as being similar to elastic or a rubber band. As you pull on elastic or a rubber band the material stretches, but as soon as you release it the material snaps back to its previous shape. As a muscle contracts, it exerts force on the tendon in a similar manner. The tendon will stretch and then pull back to a shorter length or recoil. This recoil transmits the energy of the muscle contraction to the joint and results in movement.