What anatomical fact explains why the left side of the body is controlled by the right brain?

The correct option highlights that the motor-pyramidal tracts decussate in the medulla. This means that as motor signals travel from the brain to the body, they cross over to the opposite side at a specific level in the brainstem, which is the medulla oblongata. Consequently, neural signals that control movement on the left side of the body originate from the right hemisphere of the brain and vice versa.

This anatomical feature is significant because it explains the phenomenon of contralateral control, which is the basis for how the brain communicates with the limbs. When an injury occurs to one side of the brain, it often affects the opposite side of the body due to this crossover, leading to deficits in motor function on the contralateral side.

The option indicating that the left brain is responsible for all motor functions is misleading because both hemispheres contribute to various aspects of motor control, and it does not clarify the crossing over that leads to contralateral control. The statement about the motor-pyramidal tracts crossing over at the spinal cord inaccurately represents the specific location of this decussation, while the choice mentioning symmetrical control oversimplifies the complex relationship between the brain hemispheres and bodily control without addressing the anatomical mechanism involved