Muscle Origins, Insertions, And Actions (Shoulder Joint)

Front 1

Deltoid

Back 1

Origin:
-Anterior Fibers: anterior lateral third of the clavicle

-Middle fibers: lateral aspect of the acromion

-Posterior fibers: inferior edge of the spine of the scapula

Insertion: Deltoid tuberosity on the lateral humerus

Action:

Anterior fibers: abduction, flexion, horizontal adduction, and internal rotation of the glenohumeral joint

middle fibers: abduction of the glenohumeral joint

posterior fibers: abduction, extension, horizontal abduction, and external rotation of the glenohumeral joint

Front 2

Pectoralis major

Back 2

Origin:

Upper fibers: medial half of the anterior surface of the clavicle

Lower fibers: anterior surface of the costal cartilages of the first six ribs, and adjacent portion of the sternum

Insertion: Flat tendon 2 or 3 inches wide to the lateral lip of the intertubercular groove of the humerus

Action: Upper fibers: internal rotation, horizontal adduction, flexion to about 60 degrees, abduction and adduction past and below 90 degrees respectively

lower fibers: internal rotation, horizontal adduction, adduction and extension of the glenohumeral joint from a flexed position

Front 3

Latissimus Dorsi

Back 3

Origin: Posterior crest of the illium, back of the sacrum and spinous processes of the lumbar and lower six thoracic vertebrae (T6-T12); slips from the lower three ribs

Insertion: Medial lip of the interubercular groove of the humerus, just anterior to the insertion of the teres major

Action: Glenohumeral joint adduction, extension, internal rotation, and horizontal abduction

Front 4

Teres Major

Back 4

Origin: Posteriorly on the inferior third of the lateral border of the scapula and just superior to the inferior angle

Insertion: medial lip of the interubercular groove of the humerus just posterior to the insertion of the latissimus dorsi

Action: extension of the glenohumeral joint, internal rotation of the glenohumeral joint, adduction of the glenohumeral joint

Front 5

Subscapularis

Back 5

Origin: entire anterior surface of the subscapular fossa

Insertion: lesser tubercle of the humerus

Action: Internal rotation of the glenohumeral joint, adduction and extension as well

stabilization of the humeral head in the glenoid fossa

Front 6

Supraspinatus

Back 6

Origin: medial two-thirds of the supraspinous fossa

Insertion: Superiorly on the greater tubercle of the humerus

Action: abduction of the glenohumeral joint

stabilization of the humeral head in the glenoid fossa

Front 7

Infraspinatus

Back 7

Origin: Posterior surface of scapula below spine

Insertion: greater tubercle on posterior side of the humerus

Action: External rotation, horizontal abduction, and extension of the glenohumeral joint

stabilization of the humeral head in the glenoid fossa

Front 8

Teres minor

Back 8

Origin: posteriorly on the upper and middle aspect of the lateral border of the scapula

insertion: posteriorly on the greater tubercle of the humerus

Action: External rotation, horizontal abduction, and extension of the glenohumeral joint

Stabilization of the humeral head in the glenoid fossa

Front 9

Coracobrachialis

Back 9

Origin: Coracoid process of the scapula

Insertion: Middle of the medial border of the humeral shaft

Action: flexion, adduction, and horizontal adduction of the glenohumeral joint