The origin of a muscle is the point at which a muscle is attached to a fixed bone, while the insertion of a muscle is the point at which a muscle is attached to a bone moved by that muscle. All voluntary muscles have an origin and insertion. An example is the bicep, which originates at the scapula and inserts at the radial tuberocity on the radius.
The origin of a muscle is on the proximal bone, or the one closest to the core of the body. This bone has greater mass and is more stable during contraction than the insertion bone. The insertion of a muscle is on the distal bone of the two, or the bone furthest from the core of body. This bone has less mass, making it easier to be moved by the muscle, and has greater motion than the bone at the origin. The insertion structure is not always a bone; it can also be a tendon or subcutaneous dermal connective tissue.
Voluntary muscles are those that move the body, such as the bicep flexing the elbow, while involuntary muscles work with internal organs to do functions that are not consciously perceived, such as the heart beating.