In this exercise, we will examine the shoulder and its associated muscles, joints, nerves and vessels. You will need to change the orientation of the cadaver from supine to a prone position when you change from anterior to posterior structures.
We can easily classify the muscles of the shoulder into three groups:
I: Axioscapular - muscles that run from the axial skeleton (vertebrae, sternum and ribs) to the scapula are primarily involved with the movements of the scapula and do not directly affect movement at the true glenohumeral joint. They include the pectoralis minor, trapezius, rhomboid major and minor, the levator scapulae and the serratus anterior.
II: Axiohumeral - muscles whose origin's or proximal attachments are on the axial skeleton, and run to, or insert on, the humerus. These muscles are involved with the movements of the humerus, and thus the true shoulder (glenohumeral) joint. They include the pectoralis major and the latissimus dorsi.
III: Scapulohumeral - sometimes called intrinsic shoulder muscles because they originate and insert within the confines of the "shoulder." These muscles have a direct effect upon the shoulder joint and include the deltoid, teres major and minor, supraspinatus and infraspinatus and the subscapularis.
Except for the trapezius, which receives motor supply from cranial nerve XI (the spinal accessory nerve), all of the muscles of the shoulder receive their motor nerve supply from branches of the brachial plexus. Figure 11-1 of the brachial plexus will help in visualizing these nerves.
Nerves and the muscles receiving motor input are: