Roller Coaster Fears-Cedar Point?

I love roller coasters and I love riding them. In a few weeks I will be going to Cedar Point and I was wondering how safe their roller coasters are. Top Thrill Dragster and Millenium Force are the main two. I just don't see how they can be safe. What kind of restraints hold you in and what keeps you from dying on them? or what about internal bleeding and brain damage?