In the human brain, 100 billion neurons are connected by 100 trillion synapses. And, really, this staggeringly complex structure is only the beginning. (Consider that there may be roughly one hundred thousand trillion electrical signals traversing the brain in one second.)
C. elegans was the first animal to have its genome sequenced. We can freeze it in liquid nitrogen and revive it. We can track it in 3-D. You can browse a library of its complete genome, its proteome (like the genome, but proteins) and even its whole nervous system on the internet. Science has studied this organism more thoroughly than any other -- with the possible exception of the fruit fly and the laboratory mouse -- in the entire animal kingdom.
If we can't simulate 302 neurons and 5,000 synapses, how can we hope to conquer 100,000,000,000 and 100,000,000,000,000? Let's not even get started on the 100,000,000,000,000,000 electrical signals per second that form the traffic on that neural road network.