Supraspinatus and infraspinatus muscles
Supraspinatus
The supraspinatus is a triangular muscle of the shoulder girdle.
Origin: supraspinous fossa of the scapula. The muscle completely fills the supraspinous fossa and its fibers pass laterally.
Insertion: greater tubercle of the humerus.
Action: this is one of the rotator cuff muscles providing abduction of the upper arm and stabilizing the shoulder.
Innervation: suprascapular nerve, which arises from the 5th and 6th cervical nerve roots of the brachial plexus.
Blood supply: suprascapular artery, a branch of the thyrocervical trunk.
Infraspinatus
The infraspinatus is a flat, triangular shaped muscle of the shoulder girdle.
Origin: infraspinous fossa on the posterior surface of the scapula. This muscle completely fills the infraspinous fossa of the scapula and its fibers pass laterally.
Insertion: greater tubercle of the humerus.
Action: it is also one of the rotator cuff muscles that stabilizes the shoulder and provides external rotation of the upper arm.
Innervation: suprascapular nerve, which arises from the 5th and 6th cervical nerve roots of the brachial plexus.
Blood supply: suprascapular and circumflex scapular arteries.