Final answer:
Around the 8th week of embryonic development, the human brain takes on a recognizable form. Before this, limb movements and the development of facial features occur. By the 8th week, major brain structures are formed, marking the transition from the embryonic to the fetal stage, with the fetus resembling a human.
Step-by-step explanation:
The brain begins to take on a recognizable human form around the 8th week of embryonic development. Before this point, the embryo doesn't quite look human, and it takes time for those definitive human features to develop. During the 6th week, observable changes include the start of fetal limb movements and the development of paddle-shaped hands and feet which evolve into fingers and toes through apoptosis. By the 7th week, the facial structure has a more complex design with the emergence of nostrils, outer ears, and lenses. Around the 8th week, with the head nearly the same size as the rest of the embryo's body, all major brain structures are formed, which is why the brain and the embryo begin to look characteristically human. As for the overall development, by the end of the 8th week, the embryo has grown to about 3 cm from crown to rump and weighs close to 8 g. This marks the end of the embryonic period, and the beginning of the fetal stage, where the fetus increasingly resembles a human and possesses all major body organs, albeit not yet fully developed.