Our nerves, central, (our brains and so on) but also those in your hands feet and even those in your mouth. It is a complex whole that has been written about a lot scientifically.
Great when this interests you and when you can understand that substance. But when you don't understand and want to? Then what are you doing?

Eric Chudler is an American professor who, in addition to his high quality research, is also trying to make this kind of knowledge understandable to everyone.
His site is not really optimally designed, but the information you find there... Great! (and I used it a lot in my role as a teacher of physiotherapy, so also great for the more advanced!)

For the writers among us... He even has a neurological poetry contest and a writing match on the site! (again for children but well, you can only get inspiration from somewhere)