Trapezius is a superficial broad triangular muscle at neck and upper back, one of the largest superficial muscles at the upper back. It attaches to the base of the skull and extends down to the neck, the upper back until mid back; laterally it inserts to the shoulder blades. There are three functional regions to the muscle: the Upper, middle, and lower trapezius, and each region has its own function: upper region moves the shoulder blades and support the arms; the middle region retracts the shoulder blades and the lower region rotates and depresses the shoulder blades. Trigger points present in trapezius is a common cause of upper back pain.
Rhomboid major and minor muscles
Below Levator scapulae muscle are Rhoboids including rhomboids minor and rhomboids major. Rhomboid minor and Rhomboids major are muscles on the back connecting the shoulder blade with the spinal column. Rhomboids major is just below the rhomboid minor. They are deeper to the trapezius starting from spinal column C7 to T5 and inserting to the medial border of the shoulder blade. They keep the shoulder blade pressed against the back and retracted the shoulder blade toward the spinal column. The innervation to these two muscles is from C4-C6 nerve root on the neck.