Difference Between Muscles And Tendons
The strength and skill displayed by athletes depend on well-developed muscles. The gymnast balancing on a wooden beam and the ballet dancer pirouetting across the stage rely on the muscles in their legs to precisely perform their steps. The football quarterback throwing a pass relies on upper-body muscles for his success. But muscles are also responsible for the essential but almost invisible metabolic activities that occur day after day within the body: the regular beating of the heart, the digestion of food, even the breathing of air.
The body contains more than 600 different muscles, each responsible for a specific task, some working together, others on their own. The main function of most muscles is to provide motion. By alternately contracting and relaxing, muscles make the various parts of the body move. For example, some muscles move the arms and legs, while others open and close the eyelids. But muscles also protect organs—the outer and inner walls of the stomach are formed by muscles—and they also help the blood flow efficiently throughout the body. Muscles are an important component in what makes the body of one person look different from the body of another. Because they perform so many different jobs, muscles vary greatly in size and shape. They range from the great latissimus dorsi, which is the broadest muscle of the back, to a threadlike ear muscle that is only about 0.25 inch (5 millimeters) long.
Muscles are often more effective when combined with tendons, bands of connective tissue that attach the ends of muscles to bones. Tendons are quite flexible and immensely strong. Some tendons are very conspicuous, such as those that pass behind the knees, or the Achilles tendon that runs from the muscle of the calf of the leg down to the projecting heel bone.
People often confuse tendons with ligaments, which are also found at joints and made up of connective tissue. Ligaments, however, do not attach muscles to bones, but hold one bone to another. That is, they articulate, or join, the parts of the skeleton.
Tendons transmit the force exerted by muscle fibers. Suppose that a given muscle is called on to perform a strenuous task. As described earlier, each muscle fiber exerts a definite amount of force—never more, never less. To get more force, more fibers are needed. But if all the required fibers were arranged side by side, there would not be room enough on the bones for all the muscular attachments involved. Therefore, in many muscles the fibers are set at an angle, and their force is carried by a tendon running the length of the muscle. This arrangement gives the muscle the appearance of a feather—the tendon being the quill, and the fibers the branches; in other words, tendons economize space that would otherwise be occupied by muscle fibers. An example of this type of arrangement is the temple muscle.
Another example of tendons supporting muscles is illustrated by the hands and fingers, which can perform numerous and infinitely varied movements. The hand can strike a hard blow with the clenched fist, apply light pressure to a glass being washed, or delicately poise the fingers to thread a needle. Such a variety of movements requires many muscles—more than there is room for on the bones of the hands.
The problem has been solved very ingeniously. Many of the muscles involved in moving the hands and fingers start in the upper part of the forearm. Near the wrist a great number of fibers are attached to a very few tendons. The forearm muscles manipulate the fingers of the hand by means of these intervening tendons.
Tendons also help muscles to withstand sideways forces. Where muscles rub against each other or against bone, they develop protective tendon patches. There are always tendons where muscles have to turn corners, as in passing from the leg to the foot. Here the muscles are shielded by the tendons, and the tendons in turn are protected against friction by bags of connective tissue called tendon sheaths.