Help me please! I am terrified of my brother!?

I understand it it normal to have an occasional brawl and all but he is very dangerous. I am 14 almost 15 and he is 16 going on 17. He is a junior in high school and ever sine I could remember he has been incredibly abusive to me and my sister. He just got finished hitting me and i have a large purple bruise on my back and it hurts to walk. He's even chocked me to unconciousness and has made me convulse on more than one occasion. I'm afraid to tell my mom because i dont want her to stress about it, but I'm feeling like I have no choice because he tends to aim at my head and I,m starting to have really bad head aches and my grades are lowering incredibly. I use to be a strait A student now I'm getting C's and It's very hard to stay awake in class. What should I do? I have already spoken to him about it but he only shrugged and told me I deserve everything I get.