Final answer:
During embryonic development, the anterior end of the neural tube enlarges into primary vesicles, which develop into the forebrain, midbrain, and hindbrain. As the brain matures, the forebrain becomes significantly larger than the midbrain and hindbrain. These developmental processes are vital in shaping the functions and structures of the adult brain.
Step-by-step explanation:
The development of the nervous system begins with the formation of the neural tube, which eventually differentiates into various parts of the brain and the spinal cord. Around the 25th embryonic day, the anterior end of the neural tube starts developing into the brain, enlarging into primary vesicles that will become the forebrain, midbrain, and hindbrain, collectively known as the primary vesicles. These regions continue to differentiate and grow throughout embryonic development into adolescence, forming the adult brain's intricate structures.
Comparing the early embryonic brain to the adult brain, there are significant differences in the relative sizes of these regions. The forebrain, which eventually gives rise to complex structures like the cerebrum, is significantly larger in the adult brain, reflecting its role in advanced cognitive functions. In contrast, the midbrain remains relatively small, and the hindbrain develops into regions responsible for basic physiological functions and movement.
The neural crest, emanating from the neural tube, also contributes to the development of the Peripheral Nervous System (PNS) structures as well as certain non-nervous tissues. By following the developmental pattern, one can appreciate the underlying order and function that the adult brain's major regions exhibit, stemming from their embryonic origins.