The main muscles of the upper arm include the biceps, brachialis, coracobrachilis, and the triceps. All but the triceps are located in the anterior, or front, compartment of the arm; the triceps is in the posterior compartment. The other muscle that exists in the upper arm is the deltoid. The muscles of the arms are responsible for manipulating the forearm.
The biceps is the most well-known muscle of the upper arm. It gets its name from the two heads, both of which attach to the scapula, or shoulder blades. The biceps is responsible for supination of the forearm, as well as flexing.
The brachialis, a smaller muscle located closest to the elbow, acts as the primary flexor of the elbow when the rest of the arm is not being moved. It connects to the ulna, or the smaller bone of the forearm. The coracobrachialis, on the other hand, is the muscle responsible for flexing the arm at the shoulder. Like the biceps, it connects to the scapula.
The triceps, which is located on the posterior of the arm, has three heads. Two of them lie closer to the surface than the other one, so the third head is usually not visible. The triceps is responsible for the extension of the forearm, acting as an opposing pair with the biceps.