Ligaments are stretchy bands of tissue
that, in most cases, hold one bone to another. They are a key part of what
allows most joints to move, help control their range of motion, and stabilize
them so that the bones move in proper alignment. Some parts of the peritoneum,
the membrane that surrounds the abdominal cavity, are also called ligaments
although they perform a different function.
Structure
Proteins known as collagen make up the tissue in most
ligaments. Groups of these proteins form long, flexible, thread-like strands,
or fibers. Collagen fibers are found throughout the bodies of humans and other
warm-blooded animals, as they help the skin stay elastic and also make up most
types of connective tissue. The composition of these fibers allows them to
stretch significantly when they move, such as when the elbow is bent or
straightened. Collagen fibers are often arranged in crossing patterns, which
helps prevent the joint from moving past its normal range of motion despite the
ligament's flexibility.
Types and Function
Connective tissues generally serve to protect organs,
store energy, support body structures, or connect other tissues. Most ligaments
fulfill the last function and help flex or extend a body part; these are called
joint or articular ligaments. In the elbow, for example, the ulnar collateral, radial
collateral, and annular ligaments work together to allow the joint to move.
They are found in the head and neck, pelvis, wrist, and knee, among other
places. Each joint typically contains at least three, with the knee having
eight.
Other ligaments, such as those found in the back,
mainly provide stability to bone or cartilage. If the structure primarily
strengthens or supports other ligaments, it is called an accessory ligament.
Injuries and Treatments
Because ligaments play an important role in
stabilizing the joints, they are very susceptible to injury due to overuse or
sudden movement. Regular stretching can increase the length and flexibility of
the muscles and by extension the ligaments. This strengthens the joints,
helping to prevent injury and allowing them to move farther and support more
activity.
TENDON
Tendon or sinew
is a tough band of fibrous connective tissue that usually
connects muscle
to bone
and is capable of withstanding tension.
Tendons are similar to ligaments;
both are made of collagen. Ligaments join one bone to another bone, while
tendons connect muscle to bone.
A tendon, or sinew, is a cord of tissue that attaches the end of
a muscle to a bone or other part of the body. It is composed of bundles of
white fibrous tissue surrounded by a sheath. This tissue enters the bone and
blends with the fibers of the bone. A tendon is inelastic but flexible and very
strong.
Many tendons are located near the skin surface. Perhaps the most
familiar is the Achilles tendon, which connects the calf muscles to the heel
bone. It enables the foot to push against the ground when a person walks. The
hamstring tendons are the great tendons of the thigh muscles. They are located
behind and at each side of the knee joint.
Their strength and toughness make some animal tendons useful as
sutures in surgery. Such sutures may be dissolved by body fluids and absorbed.
