Neural development is the intricate sequence of events by which animals build a functional nervous system. In vertebrates it starts when signals from the mesoderm convert part of the ectoderm into neuroectoderm, forming a neural plate. This plate folds into the neural tube, whose failure to close leads to defects like spina bifida and anencephaly. The tube’s anterior region balloons into brain vesicles that subdivide into forebrain, midbrain and hindbrain territories, while embryonic cerebrospinal fluid and proliferating neural stem cells drive growth.
Patterning signals organize the tube along dorsal–ventral and head–tail axes. Molecules such as BMPs and sonic hedgehog act as gradients that specify sensory interneurons, motor neurons, and other classes, while Hox genes and retinoic acid lay out the hindbrain and spinal cord. Neural stem cells then undergo neurogenesis, influenced by epigenetic modifications, producing post-mitotic neurons that migrate by radial, tangential, axophilic or multipolar routes to assemble layered structures like the cortex.
Axons extend under the guidance of attractive and repulsive cues, forming synapses at neuromuscular junctions and throughout the central nervous system. Trophic factors such as NGF, BDNF, CNTF and GDNF determine which neurons survive. Synapses first form in excess; activity-dependent competition and synapse elimination prune connections and sharpen neural maps in sensory and motor systems. Spontaneous activity waves in visual, auditory and motor circuits, together with microglial interactions, further sculpt networks.
Modern techniques—from single-cell RNA sequencing to diffusion MRI and connectome mapping—allow these developmental processes to be traced across species and into adulthood, where neurogenesis persists in restricted brain regions.