Structure of neural network is a very crucial matter. Single neuron is a simple mechanism and it's not able to do much by itself. Only a compound of neurons makes complicated operations possible. Because of our little knowledge about actual rules of human's brain functioning many different architectures were created, which try to imitate the structure and behaviour of human's nervous system. Most often one-way, one-layer type of network architecture is used. It is determined by the fact that all neurons must participate in the rivalry with the same rights. Because of that each of them must have as many inputs as the whole system.
Neural network
2-D map of neurons