O/I/A/I's Posterior Muscles Acting on Shoulder and Arms

Trapezius Origin

Occipital protuberance, nuchal ligament, spinous processes of C7-T12

Trapezius Insertion

Clavicle, acromion process, spine of scapula

Trapezius Innervation

Accessory (XI) nerve

Trapezius Action

Extends and abducts head, rotates and adducts scapula, fixes scapula

Latissimus dorsi Origin

T7-12, L1-5, sacrum, iliac crest, ribs 10-12

Latissimus dorsi Insertion

Intertubercular groove of humerus 

Latissimus dorsi Innervation

Thoracodorsal nerve

Latissimus dorsi Action

Extends, adducts, and medially rotates arm; depresses shoulder 

Deltoid Origin

Clavicle, acromion process, spine of scapula 

Deltoid Insertion

Deltoid tuberosity of humerus

Deltoid Innervation

Axillary nerve

Deltoid Action

Abducts, flexes, and extends arm; medially and laterally rotates arm

Rhomboideus major Origin

Spines of T1-4

Rhomboideus major Insertion

Inferior, medial border of scapula

Rhomboideus major Action

Adducts scapula

Rhomboideus major Innervation

Dorsal scapular nerve

Rhomboideus minor Origin

Nuchal ligament, spines of C6-7 C1-4

Rhomboideus minor Insertion

Medial border of scapula at scapular spine

Rhomboideus minor Action

Adducts scapula

Rhomboideus minor Innervation

Dorsal scapular nerve

Levator scapulae Origin

C1-4

Levator scapulae Insertion

Superior angle of scapula

Levator scapulae Action

Elevates scapula, abducts and rotates neck

Levator scapulae Innervation

Spinal nerves C3-5, dorsal scapular nerve

Suprasinatus Origin

Supraspinous fossa

Suprasinatus Insertion

Greater tubercle of humerus

Suprasinatus Action

Abducts arm (stabilizes shoulder joint)

Suprasinatus Innvervation

Suprascapular nerve

Infraspinatus Origin

Infraspinous fossa

Infraspinatus Insertion

Greater tubercle of humerus

Infraspinatus Action

Extends and laterally rotates arm (stabilizes shoulder joint)

Infraspinatus Innervation

Suprascapular nerve

Subscapularis Origin

Subscapular fossa

Subscapularis Insertion

Lesser tubercle of humerus

Subscapularis Action

Extends and medially rotates arm (stabilizes shoulder joint)

Subscapularis Innervation

Subscapular nerve

Teres minor Origin

Lateral border of scapula

Teres minor Insertion

Greater tubercle of humerus

Teres minor Action

Extends, laterally rotates, and adducts arm (stabilizes joint shoulder)

Teres minor Innervation

Axillary nerve

Teres major Origin

Lateral border of scapula

Teres major Insertion

Crest of lesser tubercle of humerus

Teres major Action

Extends, adducts, and medially rotates arm

Teres major Innervation

Subscapular nerve

Triceps brachii Origin

Infraglenoid tuberosity of scapula, lateral and posterior surface of humerus

Triceps brachii Insertion

Olecranon process of ulna

Triceps brachii Action

Extends and adducts arm, extends forearms

Triceps brachii Innervation

Radial nerve