Final answer:
The axons of neurons in the developing forebrain bundle together to form three major white matter systems: the dorsal column, the anterior column, and the lateral column, which correspond to sensory and motor pathways.
Step-by-step explanation:
Neurons in the developing forebrain extend axons to communicate with other parts of the nervous system, and these axons bundle together to form three major white matter systems. In the context of the spinal cord, which serves as a model for understanding these white matter systems, there are three columns of white matter. These are the dorsal column, which relays sensory information to the brain, the anterior column, which conveys motor commands to the motor neurons, and the lateral column, which conveys both sensory and motor information between the spinal cord and brain. In the brain itself, similar pathways and tracts form as the result of developmental processes governed by the embryonic neural tube, determining the organization of the neuronal networks.