Remember when Meredith (Ellen Pompeo), Cristina (Sandra Oh) and Karev (Justin Chambers) were the new kids at Seattle Grace? Well, they're all grown up now, and on this Thursday's Grey's Anatomy, they're running surgeries just like real attending physicians! Can Meredith do a brain surgery without Derek's help? Can Cristina get her head screwed on straight? Will Lexie (Chyler Leigh) survive a day as everyone's scut monkey? Check out the sneak peeks below to see for yourself!