Due to the complexity and multi-layered nature of the muscles in this area, it is often a region with many injury and soreness problems (second only to the lower back in injury statistics).
Rather than go into a lengthy discussion about each muscles specific function and movement, I will provide a variety of stretching exercises for this entire region of the back which are effective and important to perform to warm up for any type of exercise or activity involving the arms or upper back.
Horizontal adduction stretchOverhead Triceps and Lat stretch
Scapular Retraction stretch
Overhead Shoulder stretch