Lets see if I can explain this well. Block schedule is what ASDOH follows. It basically means that you learn in "blocks", for example: instead of taking an anatomy course and learning the anatomy of the entire body, then relearning it when you take physiology, then again in histology etc... you learn everything by systems. So say you are learning about the digestive system. In the block schedule, they will bring a national specialist to teach you everything there is to know about that system. They will teach the anatomy, phys, biochem, histology, etc for that one system, then after you know everything there is to know about that system they move on to another system with another lecturer.
My personal opinion about this type of learning, is that it is brilliant. It cuts out so much wasted time reviewing things that you have already learned in earlier years, plus you are taught by some of the most knowledgeable people on the subject. I don't know exactly how USN will implement the system, but that is the basic run down. I hope my explanation wasn't too confusing.