Final answer:
The nonmoving, fixed part of a muscle attached to the skeleton is called the 'origin'. Muscles transfer tension via tendons to move the skeleton, with the origin remaining stabilised and the insertion moving.
Step-by-step explanation:
The part of a muscle that is nonmoving (fixed) and attached to bones or other nonmoving muscles is known as the origin. This is in contrast to the insertion of a muscle, which is the movable end attached to the bone being pulled. The interaction of skeletal muscles in the body is such that to move the skeleton, the tension from muscle fibers must be transferred to tendons, which are connected to bones. During actions like forearm flexion, muscles work together, with the origin staying fixed and the insertion moving towards the origin.