The brain contains around neurons, each creating approximately synapses, totaling synapses. The precise organization into functional areas is vital for brain functionality, starting early in neural development with steps like cell identity acquisition and migration. Early embryonic development stages in vertebrates include fertilization, cleavage, gastrulation, and neurulation. Neurulation involves the formation of the neural plate and subsequent neural tube, leading to the development of CNS ventricles. The anterior neural tube differentiates into five areas: telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon, with patterning signals like Emx2 and Pax6 guiding this organization. Cortical neurons are specified based on their birthplace and birthdate, influencing their final layer position. Neuronal migration involves radial glia support. The visual system's wiring demonstrates both molecular guidance and the importance of experience, as shown in experiments by Roger Sperry and Hubel & Wiesel, highlighting the roles of chemorepellents and activity in visual circuit development.