Neuron doctrine: The nervous system, as all other living systems, is built from individual separate elements (Ramon Y Cajal). He actually invented the fact that information flows along an axon to a dendrite and then to cell body. So he thought that these two elements (axon & dendrite) should be somehow connected. A neuron consists of three parts: a) the dendritic tree, b) the axon and c) the cell body (soma). Dendrites (dendritic spines) are the input devices and axons (axon terminals) are the output devices of neurons.