This time-lapse shows neurulation, the early developmental process where a flat sheet of cells folds and seals to form the neural tube, which later becomes the brain and spinal cord. Cells change shape, pull together, and bend in a coordinated pattern, guided by chemical signaling gradients and mechanical tension. The timing and closure sequence are critical. When this folding and sealing process fails, neural tube defects such as spina bifida can occur. | William Wallace, Ph.D.