The Pocket Atlas of Human Anatomy by Chris Jarmey

Author:Chris Jarmey
Language: eng
Format: epub
Publisher: North Atlantic Books

Musculoskeletal Mechanics

Origins and Insertions

In the majority of movements, one attachment of a muscle remains relatively stationary while the attachment at the other end moves. The more stationary attachment is called the origin of the muscle, and the other attachment, the insertion. A spring that closes a gate could be said to have its origin on the gatepost and its insertion on the gate itself.

In the body, however, the attachment arrangement is rarely so clear-cut, because, depending on the activity one is engaged in, the fixed and movable ends of the muscle may be reversed. For example, muscles that attach the upper limb to the chest normally move the arm relative to the trunk, which means their origins are on the trunk and their insertions are on the upper limb. However, in climbing, the arms are fixed, while the trunk moves as it is pulled up to the fixed limbs. In this type of situation, where the insertion is fixed and the origin moves, the muscle is said to perform a reversed action. Because there are so many situations where muscles are working with a reversed action, it is sometimes less confusing to simply speak of attachments, without reference to origin and insertion.

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