Yes, in root canal
the nerve is permanently cut down. But connection to brain is not disabled as the tooth is surrounded by bone and bony has its connection with brain too. The reason to cut down the nerve as the effective nerve is the source of infection
which spread to brain. So to prevent a very serious problem of brain infection
it is advisable to cut the nerve of effective tooth. And save the tooth. This tooth can function normally with any problem. But you need to get the crown of root canal treated tooth as after nerve removal the tooth becomes dry as it moisture supply is also cut. An dry tooth can split into pieces due to eating forces.
So dnt worry and get your root canal done by a good doctor.