Muscles
Muscles are important structures in the human body acting on bones to produce motion. Each muscle has an origin on one bone, an insertion on another bone, and crosses a joint in order to produce motion.
The Deltoid is a very active muscle within the shoulder complex. This muscle has three parts. The origin of the anterior part of the deltoid is the lateral third of the clavicle. The origin of the middle part of the deltoid is the acromion of the scapula. The origin of the posterior part of the deltoid is the spine of the scapula. All three of these parts insert on the deltoid tuberosity of the humerus.
Because this muscle has origins in three different locations, it is involved in several actions. This muscle completes shoulder extension, abduction, internal rotation, external rotation, horizontal abduction and horizontal adduction. Pectoralis major is a very large muscle superficial to pectoralis minor and subscapularis on the anterior side of the body. This muscle has origins across the anterior inferior surface of the clavicle, the side of the sternum and ribs 1-6. The insertion of this muscle is the greater tubercle of the humerus.
Similar to the deltoid, pectoralis's many origins allow a wide variety of motions. These motions include houlder flexion, extension, adduction, internal rotation, and horizontal adduction of the shoulder. |
Teres major is a muscle of the shoulder with its origin on the posterior surface of the scapula. Its insertion is on the lesser tubercle of the humerous. This muscle produces flexion, extension, adduction, and internal rotation of the shoulder.
Latissimus dorsi is a very large muscle with many locations of orgin. These origins include the spinous process of T6-T12 and L1-L5. There are also places of origin on the lower 3-4 ribs, the iliac crest and the inferior angle of the scapula. The insertion of this muscle is located at the intertuberclar groove on the humerus. The motions produced by this muscle is shoulder adduction and internal rotation of the shoulder. Supraspinatus, infraspinatus, and teres minor are all part of the rotator cuff discussed below. |
Rotator Cuff
As mentioned in the bones and structures page, the glenoid fossa is very shallow. While this is a great advantage in terms of range of motion, this is a great disadvantage in terms of stability. The rotator cuff comes in very important in ensuring greater stability within the shoulder joint so that the head of the humerus does not become dislocated from the glenoid fossa.
The supraspinatus muscle is most superior of the rotator cuff muscles located superior to the spine of the scapula. This muscle has its origin at the supraspinous fossa of the scapula and inserts at the lesser tubercle of the humerus. This muscle produces shoulder abduction.
The infraspinatus is located on the posterior side of the body, inferior to the spine of the scapula. This muscle has its origin at the infrapinous fossa and inserts at the greater tubercle of the humerus.The motions produced by this muslce includeexternal rotation and horizontal abduction of the shoulder.
Teres Minor is also located on the posterior side of the body, inferior to the infraspinatus muscle. Teres minor has its origin on the posterior surface of the scapula's inferior angle. Its insertion is on the greater tubercle of the humerus.This muscle produces the same actions as the infraspinatus; external rotation and horizontal abduction of the shoulder.
Finally, subscapularis is a rotator cuff muscle located on the anterior side of the body. This muscle has its origin on the subscapular fossa and its insertion on the lesser tubercle of the humerus. Subscapularis produces internal rotation of the shoulder.
The supraspinatus muscle is most superior of the rotator cuff muscles located superior to the spine of the scapula. This muscle has its origin at the supraspinous fossa of the scapula and inserts at the lesser tubercle of the humerus. This muscle produces shoulder abduction.
The infraspinatus is located on the posterior side of the body, inferior to the spine of the scapula. This muscle has its origin at the infrapinous fossa and inserts at the greater tubercle of the humerus.The motions produced by this muslce includeexternal rotation and horizontal abduction of the shoulder.
Teres Minor is also located on the posterior side of the body, inferior to the infraspinatus muscle. Teres minor has its origin on the posterior surface of the scapula's inferior angle. Its insertion is on the greater tubercle of the humerus.This muscle produces the same actions as the infraspinatus; external rotation and horizontal abduction of the shoulder.
Finally, subscapularis is a rotator cuff muscle located on the anterior side of the body. This muscle has its origin on the subscapular fossa and its insertion on the lesser tubercle of the humerus. Subscapularis produces internal rotation of the shoulder.