Muscles of the shoulder and arm: attachments, nerves and actions
The arm has an anterior compartment of flexors supplied by the musculocutaneous nerve and a posterior compartment of extensors supplied by the radial nerve. The deltoid covers the shoulder joint and is supplied by the axillary nerve.
| Muscle | Origin | Insertion | Innervation | Action |
|---|---|---|---|---|
| Deltoid | Anterior fibres: lateral third of the clavicle. Middle fibres: acromion. Posterior fibres: spine of the scapula. | Deltoid tuberosity on the lateral shaft of the humerus. | Axillary nerve (C5-C6). | Middle fibres abduct the arm (from about 15 to 90 degrees, after supraspinatus starts the movement). Anterior fibres flex and medially rotate; posterior fibres extend and laterally rotate. |
| Biceps brachii | Short head: tip of the coracoid process of the scapula. Long head: supraglenoid tubercle of the scapula. | Radial tuberosity; bicipital aponeurosis into the deep fascia of the medial forearm. | Musculocutaneous nerve (C5-C6). | Flexes the elbow and supinates the forearm (strongest with the elbow bent); weakly flexes the shoulder; the long head helps stabilise the shoulder joint. |
| Brachialis | Distal half of the anterior surface of the humerus and the adjacent intermuscular septa. | Coronoid process and tuberosity of the ulna. | Musculocutaneous nerve (C5-C6); the lateral part also receives a small branch from the radial nerve. | Flexes the elbow in all positions of the forearm. |
| Coracobrachialis | Tip of the coracoid process of the scapula (with the short head of biceps). | Middle third of the medial surface of the humeral shaft. | Musculocutaneous nerve (C5-C7). | Flexes and adducts the arm at the shoulder; helps resist dislocation of the humeral head. |
| Triceps brachii | Long head: infraglenoid tubercle of the scapula. Lateral head: posterior humerus above the radial groove. Medial head: posterior humerus below the radial groove. | Posterior surface of the olecranon of the ulna through a common tendon. | Radial nerve (C6-C8). | Extends the elbow; the long head also extends and adducts the arm at the shoulder. |
Frequently asked questions
Which nerve supplies the anterior compartment of the arm?
The musculocutaneous nerve.
Which nerve supplies the triceps?
The radial nerve.
See each muscle in 3D
Last updated September 30, 2026. Educational use only. See our editorial policy.