-
Shoulder Muscles
Let’s continue with the muscles of the shoulder.
Pectoralis Major Coracobrachialis
O: Anterior Sternum, Medial 1/2 of anterior O: Coracoid Process of Scapula
Clavicle, sternal cartilage of ribs 1-7 I: Middle of the Medial Surface of the Humerus
I: Lateral lip of the Intertubercular or Bicepital A: Stabilization of the glenohumeral joint,
groove mild flexion and adduction of shoulder
A: Flexion of the shoulder, adduction of the
shoulder, medial rotation of the shoulder,
aids in deep inhalation
Biceps Brachii Triceps Brachii
O: Long Head – Supraglenoid tubercle of the O: Long Head – Infraglenoid tubercle of the
Scapula, Short Head – Coracoid Process of the Scapula, Lateral Head – Upper posterolateral
Scapula surface of the humerus, Medial Head
I: Radial Tuberosity – Posterior surface of the humerus
A: Flexion and supination of the forearm at the elbow I: Olecranon Process of the Ulna
mild flexion of shoulder, mild medial rotation of the A: Extension of the forearm at the elbow, mild
shoulder, assists in both abduction and adduction extension, adduction, and lateral rotation of
of shoulder, stabilizes glenohumeral joint the shoulder
Several muscles have listed the intertubercular or bicepital groove as an attachment. This groove is located on the front of the humerus. It is a divot in bone that house the long head of the biceps muscle. The long head of the biceps travels through this groove to the top of the humerus, then along the top of the humeral head to attach to the top of the lip of the glenoid cavity. This is a long, thin tendon.
Biceps and Triceps mostly work at the elbow, with mild actions at the shoulder. They are our first true examples of biarticular muscles, meaning they cross two joints instead of just one. Generally this description only looks at major joints. We could say that muscles like pectoralis major and latissimus dorsi are multi-articular because they cross multiple rib joints and vertebral joints, but generally they are not classified this way. Yet we have to remember that if shortened these muscles will have an effect on those smaller joints that they cross.
Also, biceps and triceps will be affected in the example I gave on Tuesday. When the head of the humerus moves forward and the scapula is pulled forward and lateral, the bones will push into the tendons of both biceps and triceps, creating tension. This tension comes not from overwork but from the misalignment at the joint.
Deltoid
O: Anterior portion – Lateral 1/2 of anterior clavicle
Middle portion – Lateral lip of Acromion Process
Posterior portion – Lateral 2/3 of inferior surface of Scapular Spine
I: Deltoid Tuberosity of humerus
A: Anterior portion – Medial rotation of shoulder, mild flexion and abduction of the shoulder
Middle portion – Abduction of the shoulder after the first 15 degrees
Posterior portion – Lateral rotation of shoulder, mild extension and abduction of the shoulder
This is our final muscle for the shoulder. Although the deltoid muscle is separated into three sections, the origins are all connected to one another. It is actually just one large muscle covering the upper shoulder. The clavicle and the acromion process come together to form a joint called the AC or acromioclavicular joint. I mentioned this joint in the video. Supraspinatus passes right underneath it. The AC joint if directly above the glenohumeral joint, but not connected to it, there is space between the two. And the acromion process becomes the scapular spine. So the origins of all three sections of the deltoid muscle form a semi-circle around the bones. The fibers of the muscle all converge, making an upside down triangle, and the point of the triangle inserts on the deltoid tuberosity of the humerus, which is located on the lateral aspect of the humerus about half way down the bone.
