Brain development begins with the formation and closure of the neural tube, the earliest nervous tissue that looks like a fat earthworm stretched out along the entire back of the embryo.
The neural tube forms from the neural plate, which begins forming just sixteen days after conception. This plate lengthens and starts folding up, forming a groove at around eighteen days, which then begins fusing shut into a tube around twenty-two days post-conception. By 27 days, the tube is fully closed and has already begun its transformation into the brain and spinal cord of the embryo.
