Which of These Statements Correctly Describes the Corticospinal System

Which of these statements correctly describes the corticospinal system?

A) It consists of fibres that originate within the primary motor cortex and terminate on motor neurons.
B) It involves the motor regions of the cortex, the cerebellum, the basal nuclei, and the thalamus.
C) It is concerned primarily with regulation of overall body posture.
D) It consists of fibres that originate within the parietal lobe and terminate on the posterior grey horn of the spinal cord.