Which nerve innervates the pectoralis major muscle?

• A. Medial pectoral nerve
• B. Lateral pectoral nerve
• C. Long thoracic nerve
• D. Thoracodorsal nerve

Answer: (B)

The lateral pectoral nerve is primarily responsible for innervating the pectoralis major muscle. This nerve arises from the brachial plexus and specifically arises from the lateral chord, which is formed by the anterior rami of the upper trunk roots (C5, C6, and C7). The pectoralis major plays a vital role in movements such as flexion, adduction, and internal rotation of the shoulder, and effective innervation is crucial for these functions.

The medial pectoral nerve also provides innervation to the pectoralis major, but its primary role is associated more with the pectoralis minor muscle. The long thoracic nerve primarily innervates the serratus anterior muscle and is vital for shoulder movement, while the thoracodorsal nerve innervates the latissimus dorsi muscle. Thus, the lateral pectoral nerve is correctly identified as the main nerve for the pectoralis major's innervation.