Which nerve innervates both the teres major and subscapularis muscles?

• A. Upper subscapular nerve
• B. Lower subscapular nerve
• C. Thoracodorsal nerve
• D. Suprascapular nerve

Answer: (B)

The correct answer is based on the anatomy and innervation of the muscles in question. The teres major and subscapularis muscles are both innervated by the lower subscapular nerve, which arises from the posterior cord of the brachial plexus. This nerve specifically serves to provide motor innervation to these two muscles, facilitating their functions in shoulder movement and stabilization.

The teres major is responsible for actions such as internal rotation, adduction, and extension of the humerus, while the subscapularis plays a critical role in internal rotation and stabilization of the shoulder joint. The lower subscapular nerve's role in activating these muscles is essential for shoulder mechanics.

To understand the context of the other options: the upper subscapular nerve innervates only the upper part of the subscapularis; the thoracodorsal nerve innervates the latissimus dorsi; and the suprascapular nerve primarily innervates the supraspinatus and infraspinatus muscles. These nerves do not contribute to the innervation of the teres major, reinforcing the specificity of the lower subscapular nerve's function in this case. Thus, the selection of