What portion of a muscle is attached to an immovable section of the skeleton?

The origin of a muscle is the portion that is attached to the immovable section of the skeleton. It serves as the stable point of attachment when a muscle contracts. During muscle action, the origin remains fixed while the other end, which is typically attached to a moveable part (the insertion), pulls the bone closer to the origin. This relationship is critical for understanding how muscles function during movement, as it allows for efficient leverage and force generation.

The belly refers to the fleshy central part of the muscle, which is involved in contractions but does not provide stable attachment. Tendons are the connective tissue structures that connect muscles to bones but do not define the specific points of muscle attachment. The insertion is the point where the muscle attaches to the bone that moves, contrasting the stability provided by the origin. Understanding these terms is essential for grasping how muscular and skeletal systems work together in movement.