My father is a lot better offhand shot than I am; he has killed most of his deer with neck shots. I've killed--I ain't sure--maybe ten or fifteen, that way. "Hit 'em in the white spot!"
They always drop and stop. Sometimes they'll quiver a while, but they're paralyzed.
I've just taken it for granted that the physical shock of impact screws up the nerves of the spinal cord, whether the actual bone is hit or not. Whether or not that's true, doesn't matter. A 150-grain '06 in the neck is as good as a ton of anchor.