The shoulder is comprised of bones, joints, ligaments, muscles and tendons.
Bones: clavicle (referred to as the collar bone), scapula (shoulder blade) and the humerus (upper arm bone).
The shoulder has two joints that work together to allow arm movement. The bones are joined by tendons, ligaments, and muscles (known as soft tissues).
Joints: (i) acromioclavicular (AC) joint allows the clavicle and the acromion (the part of the scapula that forms the point on the shoulder). AC joint lets us raise the arm above the head.
(ii) glenohumeral (shoulder joint) is the ball and socket type joint. The ball is the rounded upper end of the humerus, The socket is the concave part of the scapula (called the glenoid). The glenohumeral joint allows the arm to move in a circular motion + towards/away from the body. The labrum is a piece of cartilage that acts as a cushion in this ball/socket joint. (iii) sternoclavicular joint.
Two sacks called bursa are located in the shoulder. Bursa secrete lubricant that reduces friction between the joint’s moving parts.
Muscles: the deltoids (anterior deltoid, posterior deltoid and lateral deltoid) are the major shoulder muscles.