Name the muscle that extends the shoulder and its nerve supply.

Name the muscle that extends the shoulder and its nerve supply.

• A. Deltoid; axillary nerve
• B. Teres major; lower subscapular nerve
• C. Latissimus dorsi; thoracodorsal nerve
• D. Trapezius; spinal accessory nerve

Answer: (C)

Extending the shoulder mainly involves the latissimus dorsi. When this broad back muscle contracts, it pulls the humerus backward and downward, extending the arm from a flexed or raised position, and it also helps with adduction and medial rotation. Its tendon inserts into the intertubercular groove of the humerus, giving it a strong leverage to pull the arm back. The nerve supply is the thoracodorsal nerve, a branch of the posterior cord of the brachial plexus, typically carrying fibers from C6–C8. This nerve travels with the thoracodorsal vessels to reach and innervate the latissimus dorsi. Other muscles listed can assist with shoulder movement in different ways, but the latissimus dorsi is the primary extensor of the glenohumeral joint, which is why this pairing is the best answer.

Extending the shoulder mainly involves the latissimus dorsi. When this broad back muscle contracts, it pulls the humerus backward and downward, extending the arm from a flexed or raised position, and it also helps with adduction and medial rotation. Its tendon inserts into the intertubercular groove of the humerus, giving it a strong leverage to pull the arm back.

The nerve supply is the thoracodorsal nerve, a branch of the posterior cord of the brachial plexus, typically carrying fibers from C6–C8. This nerve travels with the thoracodorsal vessels to reach and innervate the latissimus dorsi.

Other muscles listed can assist with shoulder movement in different ways, but the latissimus dorsi is the primary extensor of the glenohumeral joint, which is why this pairing is the best answer.