What function does the brachial plexus control?

The brachial plexus is a complex network of nerves that arises from the spinal cord in the neck and travels through the shoulder region, providing motor and sensory innervation to the upper limb. Its primary function is to control the movement of the arm, which includes the shoulder, forearm, and hand. The various branches of the brachial plexus innervate different muscles, facilitating a wide range of movements in the arms, such as raising, bending, and rotating at the shoulder, elbow, wrist, and fingers, making it essential for the overall mobility of the upper extremities.

While it is also involved in shoulder and hand movement, the most encompassing and accurate description of its primary control is over arm movement as a whole, making this answer the most appropriate choice.