Shoulder Muscles

Question 1

Posterior Deltoid

Answer 1

Origin -
Inferior edge of the scapular spine

Insertion -
The deltoid tuberosity on the lateral surface of the proximal humeral shaft

Actions -
Extension of the arm at the shoulder
Assists with external rotation of the arm at the shoulder

Question 2

Anterior Deltoid

Answer 2

Origin -
Anterior border of the lateral third of the clavicle

Insertion -
The deltoid tuberosity on the lateral surface of the proximal humeral shaft

Actions -
Flexion of the arm at the shoulder

Question 3

Middle Deltoid

Answer 3

Origin -
Lateral border of the acromion process of the scapula

Insertion -
The deltoid tuberosity on the lateral surface of the proximal humeral shaft

Actions -
Abduction of the arm at the shoulder