What area does motor nerves supply in relation to the body?

The correct answer—indicating the area that motor nerves supply in relation to the body—focuses on the neck muscles, specifically the sternocleidomastoid (SCM). The SCM is a critical muscle in the neck responsible for head rotation and flexion. Motor nerves, specifically the accessory nerve (cranial nerve XI), innervate the SCM, allowing for its movement and function.

In understanding the role of motor nerves, it is essential to recognize that they carry signals from the central nervous system to the muscles, enabling voluntary and controlled movements. Each of the other options refers to different muscle groups that are indeed supplied by motor nerves but focuses on various separate muscle groups throughout the body.

For instance, while the arms and legs have significant motor nerve innervation, and the back muscles are also innervated by respective spinal nerves, the question specifically seeks to highlight the neck area, where the SCM muscle resides. Hence, this area is uniquely characterized by the specific actions of the motor nerves supplying it.