The rotator cuff is a critical component of the shoulder that takes part in almost every movement of this joint. As described in an article published in "American Family Physician," the rotator cuff is composed of four muscles--the subscapularis, the infraspinatus, the supraspinatus and the teres minor--as well as the tendons that attach them to the bones of the shoulder joint. The rotator cuff wraps around the humerus, or upper arm bone, to attach it to the scapula bone, or shoulder blade. This helps to stabilize and support the shallow grooved shoulder joint. Strength and flexibility in each of the four muscles that make up the rotator cuff is important for healthy shoulder joint function.
Subscapularis
The subscapularis muscle originates on the scapula and extends to the humerus. It stabilizes and rotates the shoulder joint to turn the arm inward. The subscapularis is mainly located between the scapula and the rib cage and is the deepest muscle of the rotator cuff. It is innervated by the upper and lower subscapular nerves.
Infraspinatus
The infraspinatus muscle originates on the edge of the scapula bone and connects to the upper end of the humerus bone. This muscle helps to stabilize and rotate the shoulder joint externally or outward so that the palms are faced forward. The suprascapular nerve innervates, or provides nerves to, the infraspinatus muscle.
Supraspinatus
As described by the Nicholas Institute of Sports Medicine and Athletic Trauma, the supraspinatus muscle originates at the scapula and inserts at the humerus bone. It is innervated by the suprascapular nerve. This muscle abducts the shoulder joint to raise the arm out to the side of the body. The supraspinatus muscle helps to provide a wide range of movement in the shoulder joint.
Teres Minor
As described at MayoClinic.com, the teres minor originates at the bottom outside corner of the scapula and inserts at the humerus bone. It works with the infraspinatus muscle to rotate the shoulder joint outward. The axillary nerve innervates the teres.
