The function of the triceps brachii muscle is to extend the arm at the elbow joint. Located on the back of the upper arm, the triceps brachii consists of three bundles: the long, lateral and medial heads. The triceps brachii tendon receives all three bundles at the elbow.
The long head runs from the shoulder blade to the elbow and also assists in stabilizing the shoulder joint. The lateral head of the biceps brachii originates from the back surface of the humerus bone in the upper arm, extending down to the elbow. The medial head also originates from the back surface of the humerus, but it is mostly covered by the long and medial heads.