Answer:
At just six weeks, the embryo's brain and nervous system begin to develop, although the complex parts of the brain continue to grow and develop through the end of pregnancy, with development ending around the age of 25.
Step-by-step explanation:
The brain begins with the neural tube, formed in the first month of the embryo’s growth. The neural tube closes around week 6 or 7, at which point the brain separates into three parts: front brain, midbrain, and hindbrain. These three parts will eventually develop into the specialized parts of the brain, and the cerebrum will fold into the left and right halves of the brain.
From the time the neural tube closes, around week 7, the brain will grow at a rate of 250,000 neurons per minute for the next 21 weeks. Ultrasounds can reveal the embryo moving as early as 6 weeks after conception (or 8 pregnancy weeks), detecting the electrical impulses that govern movement and indicating that the brain is beginning to function.