Final answer:
The lateral pectoral nerve is associated with arm movement, as it innervates muscles like the pectoralis major that contribute to the movement and function of the upper limbs.
Step-by-step explanation:
The lateral pectoral nerve is associated primarily with arm movement (A). It innervates some of the muscles in the anterior compartment of the shoulder and chest, such as the pectoralis major, which is directly involved in the movement and stabilization of the upper limb. This nerve's functions tie into the broader actions of the muscles associated with the pectoral girdle, which also help to transfer force from the muscles acting on the upper limb to the thorax. The lateral corticospinal tract, where the neurons reside, is responsible for the movement of arm and leg muscles. The wider ventral horns found in the cervical spinal cord reflect the greater number of motor neurons needed for the finer control of upper limb musculature.