Hi, my book says that in the brain and skeletal muscle cells, it only yields a total of 36 ATP because NADH + H+ cannot enters the brain and skeletal muscle cells' mitochondria. But why FADH2 can is not stated. Can someone tell me why? Also, since NADH + H+ is formed inside the mitochondria why would NADH + H+ cannot be used in the brain? They are still formed inside the mitochondria right? Also, i would like to ask if my understanding is correct. NADH + H+'s H+ is used to push hydrogen against the concentration so that it will go through a gradient and ATP is synthesized from the ATP synthetase. Is this right? Lots of question, thanks for the help.