If a guy has a prosthetic leg, is he still human?
Sure. It still does the same job, right? Does what you tell it to, walks fine?
What if he had two prosthetic legs? Artificial arms? A plastic heart? Carbon fibre bones? Silicone neurons?
Where do you stop being human?
I don't think you ever do. You could put a human mind into an entirely artificial body, and that person would still be a person.
You could download a mind out of it's eminently crappy, poorly designed squishy meatsack and into a seriously useful, functionally immortal artificial form.
I'm a dirty bastard and a moral vacuum, but my mind is something unique. So my objective is to slowly but surely, convert myself into a six armed biomechanical man-spider. Those parts I can't recreate in titanium, ceramic and silicon, I will bioengineer better versions out of stem cells - I will, for all intents and purposes, be the pinnacle of intelligent design. This of course will make me effectively the god of transhumanism, and therefore the son as well. All I need now is to nail some way of quantiying the postbiological electric field you humans call a 'soul' and I can amalgamate the holy ghost into my cold iron skeleton.