Muscle and Tendon Work Together
Skeletal Muscles Generate Force Through Their Connecting Tendons
Sep 7, 2008
Most of the more than 600 voluntary, skeletal muscles in the human body are connected between two bones and traverse one of the body’s many joints. Not all skeletal muscles are connected to bones on both ends (the facial muscles are a prime example), but those that are, are connected to bone through an intervening connective tissue structure known as a tendon.
What Are Tendons?
Tendons are connective tissue structures that join muscles to their insertion sites in bones. Made up largely of fibrils consisting of the protein collagen, tendons show both strength and elasticity. They are able to transfer the force generated by a muscle undergoing contraction to the bone with which it is connected.
Tendons and skeletal muscles are joined together at a structure known as the myotendinous junction, which is remarkable for having high concentrations of many of the proteins that are similarly concentrated where motor nerves innervate muscle (the neuromuscular junction).
Muscles and Tendons and Joint Flexion
Most muscles act across a movable joint.
- The lower leg is straightened (extended) when the muscles of the front of the upper thigh (the quadriceps) are contracted.
- The lower leg is bent (flexed) when the muscles of the back of the thigh (the hamstring) are contracted.
This happens because these muscles are connected, through their tendons, to the bones of the lower leg and these muscle-tendon insertions pass across the knee joint.
These muscles are referred to as an antagonist pair. One muscle causes major movement of the bones and joint in one direction and these movements are opposed by the action of the other muscle. Another well known antagonist pair of muscles is the biceps and triceps muscles of the upper arm.
How Do Tendons Attach to Bones?
Tendons can be attached to the bone directly or to the fibrous membranous covering of the bone and can be joined through fiber-like, cartilage-like connections. Tendons can occur as short, thin rod like structures or as large thin sheets that extend for some distance away from the bone. These large sheet-like forms of tendon are referred to as an aponeurosis and are quite commonly found in association with the large sheet-like muscles of the abdomen and thorax.
All muscles work by contracting and passing this force through tendons to fixed points of the skeleton. Creation of force across a joint can lead to either flexion or extension of a structure. Likewise abduction (movement away from the center of the body) and adduction (movement towards the center of the body) occurs because of the action muscles exert through their tendons.
Without tendons, muscle would be unable to properly link to bones and generate the force necessary to cause movement.
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