[RightWhale]

emulating how the neuron interacts with the outside world

That could be done within limited parameters. But your emulation program might not respond to unforeseen circumstances the way neurons do, and probably neurons are as different from each other as snowflakes so you would need several zillion emulation routines to simulate a single CNS under controlled conditions. Possible.

[PatrickHenry]

This "gradual-replacement-of-brain-cells-with-chips" scenario is a restated version of an ancient philosophical problem: Theseus' Ship.