Shoulder Muscles

The muscles that act on the shoulder are responsible for elevation, protraction, retraction and upward and downward rotation of the scapula.

Adjusting the position of the scapula allows a wider range of movement in the shoulder girdle and upper limb. 

These six movements are accomplished by so-called axioappendicular muscles. These shoulder muscles all originate from the axial skeleton and insert at different locations of the scapula bone to fulfill their various functions:

Pectoralis Major Muscle:

Origin: (proximal attachments)
a. Clavicular head: medial half of the clavicle.
b. Sternal head: sternum, upper costal cartilages (1-6), and the aponeurosis of the external oblique.

Actions of Pectoralis Major Muscle:

Flex the arm at the shoulder (glenohumeral) joint.

Pectoralis Minor Muscle:

Origin: (proximal attachments):
Anterior surfaces of the sternal ends of ribs 3-5

Actions on the shoulder (scapula):

Draws scapula forward and downward. (It also elevates ribs if origin & insertion are reversed).

Serratus Anterior Muscle

Attachments of Serratus Anterior Muscle: Origin & Insertion

Origin: (proximal attachments):
Anterior surfaces of the first 8 or 9 ribs.

Insertion: (distal attachments):
Anterior surface of medial border of scapula.

Actions on the Shoulder:

Abducts (protracts) scapula and upwardly rotates it while abducting the arm; stabilizes scapula by holding it to chest wall.

extrinsic muscles

extrinsic muscles: trapezius, latissimus dorsi, levator scapulae, rhomboid major and minor

The trapezius muscle is a large, diamond-shaped muscle that covers the neck and shoulder area.

Actions on the shoulder (scapula):

a. Upper fibers elevate scapula.

b. Upper fibers upwardly rotate scapula.

c. Extend neck.

d. Middle fibers adduct (retract) scapula.

e. Lower fibers scapula.

f. Lower fibers help upper fibers upwardly scapula.