Final answer:
The embryonic origin of CNS neurons is the neuroectoderm, which undergoes folding and converging to form the neural tube, developing into the brain and spinal cord.
Step-by-step explanation:
The embryonic origin of central nervous system (CNS) neurons is the neuroectoderm. During embryonic development, a specialized region of ectoderm differentiates into neuroectoderm, which forms the precursor tissue for the nervous system. The neuroectoderm then undergoes folding and converging to form the neural tube, which eventually develops into the brain and spinal cord.