Describe the origins of the three heads of the triceps brachii, their insertion, and their actions.

• A. Origins: long head infraglenoid tubercle; lateral head posterior humerus above the radial groove; medial head posterior humerus below the radial groove. Insertion: olecranon of the ulna. Actions: elbow extension; the long head also extends and adducts the shoulder.
• B. Origins: all heads originate from the scapula; Insertion: radial tuberosity; Actions: elbow flexion.
• C. Origins: long head infraglenoid tubercle; lateral head from anterior humerus; medial head from radial groove; Insertion: olecranon; Actions: elbow flexion.
• D. Origins: long head infraglenoid tubercle; lateral head from posterior humerus; medial head from anterior humerus; Insertion: coracoid process.

Answer: (A)

The main concept here is how the three heads of the triceps brachii are positioned to create their actions: each head has a distinct origin, they all insert on the olecranon of the ulna, and the long head crosses the shoulder joint to influence shoulder movement while the other heads mainly extend the elbow. The long head originates from the infraglenoid tubercle of the scapula, while the lateral head comes from the posterior aspect of the humerus above the radial groove and the medial head from the posterior humerus below the radial groove. All three insert onto the olecranon. Their primary action is elbow extension, with the long head also capable of extending and adducting the shoulder. The option that matches this pattern correctly lists those exact origins, the olecranon insertion, and the elbow-extension action—with the long head additionally enabling shoulder extension and adduction. The other choices contain incorrect origins (such as from the scapula or from the anterior/posterior humeral regions not near the radial groove), incorrect insertion (like insertion on the radial tuberosity or coracoid), or incorrect actions (elbow flexion instead of extension).