Shoulder Muscles: Origin, Insertion, and Action

Rhomboid major and minor

Origin: Minor: ligamentum nuchae; spinous processes of vertebrae C7 and T1; Major: spionous processes of vertebrae T2-T5. Insertion: medial border of scapula. Action: elevates, retracts, and inferiorly rotates scapula. Innervation: dorsal scapular nerve

Infraspinatus

Origin: infraspinous fossa of scapula. Insertion: greater tubercle of humerus. Action: lateral rotation of arm.

Serratus anterior

Origin: external surfaces of ribs 1-8. Insertion: medial border of scapula. Action: protraction and superior rotation of scapula; holds scapula against thoracic wall. Innervation: long thoracic nerve from ventral primary rami

Pectoralis minor

Origin: external surfaces of ribs 3-5. Insertion: coracoid process of scapula. Action: depression and inferior rotation of scapula.

Teres minor

Origin: lateral border of scapula. Insertion: greater tubercle of humerus. Action: lateral rotation of arm.

Deltoid

Origin: lateral third of clavicle; acromion process; spine of scapula. Insertion: deltoid tuberosity of humerus. Action: Anterior fibers: medial rotation and flexion of arm; middle fibers: abduction of arm; posterior fibers: lateral rotation and extension of arm; anterior and posterior fibers: act together to adduct the arm.

Pectoralis major

Origin: medial half of clavicle; sternum; costal cartilages of ribs 1-6. Insertion: lateral lip of intertubercular groove on humerus. Action: flexion, medial rotation, and adduction of the arm. Innervation: lateral and medial pectoral nerves

Trapezius

Origin: posterior surface of occipital bone; ligamentum nuchae; spinous processes of thoracic vertebrae. Insertion: lateral third of clavicle; acromion process; spine of scapula. Action: Superior fibers: elevates scapula; middle fibers: retracts scapula; inferior fibers: depress scapula. Innervation: motor: spinal accessory (XI), proprioception: C3-C4

Teres major

Origin: scapula, near inferior angle. Insertion: medial lip of intertubercular groove. Action: extension, adduction, and medial rotation of arm.

Latissimus dorsi

Origin: spinous processes of vertebrae T6-T12; thoracolumbar fascia; iliac crest; inferior three ribs. Insertion: intertubercular groove of humerus. Action: extension, adduction, and medial rotation of arm. Innervation: thoracodorsal nerve (C7,8) from the posterior cord of the brachial plexus

Subscapularis

Origin: subscapular fossa of scapula. Insertion: lesser tubercle of humerus. Action: adduction and medial rotation of arm.

Supraspinatus

Origin: supraspinous fossa of scapula. Insertion: greater tubercle of humerus. Action: abduction of arm.