Arguably, you'd need to simulate tens of billions of neurons in order to achieve human-level intelligence. So, even if you'd have correctly simulated a single neuron, there's still a lot to cover to achieve human-level AI. And even then. The few unfortunate cases where a human child has been reared outside of the normal environment (see Genie), having a human brain has turned out not to be enough to have intelligence that would be recognized as 'human-level'. So, apart from the simulated brain itself, you'd need to devise an appropriate training environment to use for training said brain to achieve human-level intelligence. Which would be a formidable feat in and of itself.