The triceps are located on the back of the upper arms and run from the shoulder to the elbow. The biceps are the muscles on the front of the upper arm opposite the triceps.
Each triceps muscle has three distinct parts. The long head starts at the shoulder and runs to the elbow. The lateral head starts at the top of the humerus, the long upper arm bone, and runs along the back of the arm, attaching at the elbow. The medial head originates lower down and underneath the other two sections. Each part of the triceps muscle contains different combinations of types of muscle fibers and is primarily controlled by the radial nerve.