Did anyone see the final episode of Walking Dead?

I wonder when it will resume. I just have a question concerning the plot. Dr. Jennings showed that the brains of the walkers are dead. Only the brain stem rejuvenates. Since the brain is already dead how can shooting it destroy the walkers? That seems to be a weakness in the story line Maybe the writers can come up with a plausible explanation. Ok, I know it's just a science fiction show, but I like it and a little critique won't hurt.