Where Does Humanity End and Begin?

Another thing I wanna know. Let's suppose that it becomes possible for humans to integrate synthetic/mechanical machinery/technology into their very bodies and/or minds. A person with an extra mechanical arm or data storage where one of their lungs used to be would obviously still be considered to be a human. However, would a being that had modified themselves to such a point that any remaining flesh was purely vestigial and not contiguous to the continuation of their consciousness be considered a machine, human, or some other sort of being?