The myosin filaments are then able to bind with the actin filament and contraction occurs. Skeletal muscles responsible for movement of the limbs can be classified according to their function. Those which cause the joint to close up are flexors . Their opposite, or antagonistic muscles are called extensors , which cause the joint to stretch out. For example, biceps in the arm are flexors, while triceps extending from the shoulder to the elbow are extensors.
Adductor muscles move a limb toward the body, while abductors move it away from the body.
The point of attachment of a flexor or extensor on the moving bone is called the insertion , and the point of attachment on the stationary bone is the origin . Voluntary skeletal muscles are attached to bones either directly or by means of straps of connective tissue called tendons . Movable joints are held together by ligaments , flexible bands of connective tissue, that hold muscles and tendons in place.