Shoulder Muscles

Deltoid

Origin: Clavicle (collarbone), acromion, and spine of the scapula.

Insertion: Deltoid tuberosity of the humerus (upper arm bone).

Action: The deltoid muscle is responsible for shoulder abduction when the arm is moved away from the body, as well as flexion and extension.

Supraspinatus

Origin: Supraspinous fossa of the scapula.

Insertion: Greater tubercle of the humerus.

Action: Initiates shoulder abduction and helps stabilize the shoulder joint.

Infraspinatus

Origin: Infraspinous fossa of the scapula.

Insertion: Greater tubercle of the humerus.

Action: Performs external rotation of the shoulder joint.

Teres Minor

Origin: Lateral border of the scapula.

Insertion: Greater tubercle of the humerus.

Action: Assists in external rotation of the shoulder.

Subscapularis

Origin: Subscapular fossa of the scapula.

Insertion: Lesser tubercle of the humerus.

Action: Performs internal rotation of the shoulder joint.

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