Every skeletal muscle in the human body is attached to a bone or other connective tissue structure, crossing at least one joint. Usually, we describe the muscle attachment by locating its origin and insertion point.
The origin is a point of attachment of the muscle to the immovable or less movable bone - a point where the muscle is anchored to the bone. The insertion is a point of attachment of the muscle to the movable bone. When the muscle contracts, the insertion is usually pulled towards the origin, creating the movement.
Some muscles cross more than two joints, thus their action can be more complex. Other muscles have interchangeable origins and insertions, depending on the action being performed. Thus, when describing a muscle, it is important to consider the type of movement it can perform.
Figure 1: The origin and insertion point of the upper arm muscle. The origin point is placed on the immovable bone, and the insertion point is placed on the movable bone. When muscle contracts, it pulls the insertion point towards the origin point.