 In this video, I will identify the muscles that move the glenohumeral joint, which is commonly referred to as the shoulder joint, and list the origin insertion and action of the major muscles that move the glenohumeral joint. I'll start by going through some of the large superficial muscles. On the anterior here, we have pectoralis major in the mammary region, and the action of pectoralis major is to abduct and flex the glenohumeral joint. Then the deltoid is a triangular shape muscle giving shape to the shoulder, the acromial or deltoid region. And the action of the deltoid is to abduct, flex, or extend the glenohumeral joint. And so while pectoralis major abducts the glenohumeral joint, the deltoid is an antagonist to the pectoralis major when the deltoid performs abduction, ABduction. Then latissimus dorsi is another muscle that abducts the glenohumeral joint. So latissimus dorsi and pectoralis major are synergists that work together for the action of abduction at the glenohumeral joint. And the deltoid is an antagonist to both pectoralis major and latissimus dorsi when it performs abduction, abduction of the glenohumeral joint. So the origin of pectoralis major is along the clavicle as well as along the sternum. And the insertion of pectoralis major is on the greater tubercle of the humerus. The action of pectoralis major is to abduct or flex the glenohumeral joint. The deltoid muscle has three portions, an anterior portion that has its origin from the clavicle at the lateral end of the clavicle or the acromial end of the clavicle. So this is also known as the clavicular portion of the deltoid. Then there's a middle portion of the deltoid with its origin from the acromion of the scapula. So that's also known as the acromial portion of the deltoid. And then around to the posterior of the scapula, the deltoid has an origin from the scapular spine. So the spinous portion of the deltoid is this posterior portion of the deltoid. When all three portions of the deltoid contract together, the action is to abduct. So the insertion of the deltoid is down onto the humerus at the deltoid tuberosity. And when all three portions of the deltoid contract, they perform the action of abduction. But if just the clavicular most anterior portion contracts, the action would be flexion. And if just the most posterior portion, the spinous portion of the deltoid contracts, the action would be extension of the glenohumeral joint. So the deltoid has a diversity of actions depending on which portions contract. The deltoid can either perform abduction, flexion, or extension of the glenohumeral joint. Lettucemus dorsi has its origin from the spinous processes of the thoracic and lumbar vertebrae in a band of connective tissue known as the lumbodorsal fascia, or thoracodorsal fascia. The insertion of lettucemus dorsi is on the humerus at the intertubercular sulcus. And the action of lettucemus dorsi is to abduct or extend the glenohumeral joint. Now we'll move to the deeper muscles that move the glenohumeral joint, starting with teres major. On the posterior, just deep to the trapezius, we can see the teres major has an origin on the scapula there at the inferior angle. The teres major has the action of medial rotation and abduction at the glenohumeral joint. Then superior to the teres major is a muscle group known as the rotator cuff. The rotator cuff consists of four muscles, and the rotator cuff is important functionally to help stabilize the glenohumeral joint, to hold the head of the humerus into the glenoid cavity. And the four muscles can be remembered with this pneumonic device. S-I-T-S is an acronym, SITS is an acronym for supraspinatus, infraspinatus, teres minor, and subscapularis. So I wrote out subscapularis because we won't be able to see subscapularis from this posterior view. But here we have supraspinatus, and the action of supraspinatus is abduction of the glenohumeral joint. Here we have infraspinatus, the action of infraspinatus is lateral rotation of the glenohumeral joint. And then here we have teres minor, located just superior to teres major. And teres minor has the action of lateral rotation at the glenohumeral joint. The last rotator cuff muscle subscapularis is located on the anterior of the scapula with its origin from the subscapular fossa. So it cannot be viewed from this illustration, but the action of subscapularis is medial rotation of the glenohumeral joint. And together the rotator cuff muscles help to stabilize the glenohumeral joint, and the rotator cuff muscles are commonly injured, which can lead to instability of the glenohumeral joint. The origin of teres major is on the inferior angle of the scapula, and the insertion of teres major is on the intertubercular sulcus of the humerus. Then the action of teres major is to medial rotate or adduct the glenohumeral joint. So the origin of supraspinatus is the supraspinus fossa of the scapula, and the insertion of supraspinatus is the greater tubercle of the humerus. The action of supraspinatus is to abduct and stabilize the glenohumeral joint. The origin of infraspinatus is the infraspinus fossa of the scapula. The insertion is the greater tubercle of the humerus, just inferior to the insertion of the supraspinatus, and the action is to lateral rotate. The origin of teres minor is the lateral border of the scapula. The insertion is the greater tubercle, just inferior to the insertion for infraspinatus, and the action is to lateral rotate the glenohumeral joint. In this illustration we have an anterior view that allows us to see the subscapularis. This is a deep view with Pectoralis major removed so that we can see subscapularis on the anterior surface of the scapula, where it has its origin from the subscapular fossa. The action of subscapularis is to medial rotate and stabilize the glenohumeral joint. The origin of subscapularis is the subscapular fossa, the insertion is the lesser tubercle of the humerus, and the action is to medial rotate the glenohumeral joint.