Muscles of the shoulder originate from the clavicle and scapula to move and stabilize the arm.
The muscles of the shoulder are a complex group of muscles that control movement and maintain the stability of the glenohumeral (shoulder) joint. These muscles are categorized into two main groups: extrinsic shoulder muscles that originate from the axial skeleton and act on the scapula and humerus, and intrinsic shoulder muscles that originate from the scapula or clavicle and act directly on the humerus. Together, they enable a wide range of motions including flexion, extension, abduction, adduction, rotation, and circumduction of the arm.
The shoulder muscles are typically divided into two functional categories:
Shoulder muscles are distributed around the scapula, clavicle, and humerus. Some arise from the vertebral column or thoracic cage (extrinsic) and insert onto the scapula or humerus, while others are confined to the scapulohumeral region (intrinsic). Below is a summary of their anatomical placement and orientation:
Muscle | Origin | Insertion | Innervation |
---|---|---|---|
Deltoid | Lateral clavicle, acromion, scapular spine | Deltoid tuberosity of humerus | Axillary nerve (C5–C6) |
Teres major | Inferior angle of scapula | Medial lip of intertubercular sulcus | Lower subscapular nerve (C5–C6) |
Supraspinatus | Supraspinous fossa of scapula | Greater tubercle of humerus | Suprascapular nerve (C5–C6) |
Infraspinatus | Infraspinous fossa of scapula | Greater tubercle of humerus | Suprascapular nerve (C5–C6) |
Teres minor | Lateral border of scapula | Greater tubercle of humerus | Axillary nerve (C5–C6) |
Subscapularis | Subscapular fossa | Lesser tubercle of humerus | Upper and lower subscapular nerves (C5–C7) |
Responsible for abduction of the arm from 15° to 90°, along with flexion, extension, and rotation depending on fiber group. It provides the rounded shape to the shoulder and stabilizes the humeral head in the glenoid cavity.
Assists in adduction, extension, and medial rotation of the arm. It works synergistically with the latissimus dorsi and inserts beside it on the humerus.
Initiates the first 15° of arm abduction. It lies superior to the shoulder joint and passes beneath the acromion, making it vulnerable to impingement syndromes.
Located posteriorly, it contributes to lateral rotation of the humerus and stabilizes the shoulder joint as part of the rotator cuff.
Also involved in lateral rotation and stabilization of the shoulder joint. It is the smallest rotator cuff muscle.
The only rotator cuff muscle that medially rotates the arm. It forms the anterior wall of the axilla and inserts into the lesser tubercle of the humerus.
Shoulder muscles coordinate with one another to provide a wide range of motion while maintaining glenohumeral stability. The rotator cuff muscles compress the humeral head into the glenoid during movement, preventing dislocation. The deltoid acts with trapezius and serratus anterior to elevate the arm beyond 90° via scapulohumeral rhythm. Teres major and latissimus dorsi function to bring the arm back to the trunk (adduction and extension).
Shoulder muscles originate from the paraxial mesoderm of the somites, particularly from the hypaxial portions that contribute to limb musculature. Motor innervation from the brachial plexus is established early, and the rotator cuff muscles develop in close association with joint capsule formation. Ossification of their bony attachments completes during adolescence, and full functional maturation continues into early adulthood.