f non-linear functions t…linear: in their normal state they actually sum up inputs to total less than the individual values. They are sub-linear. For them 2+2 = 3.5. And having many dendritic branches with sub-linear summation also lets the neuron act as two-layer neural network. A two-layer neural network that can compute a different set of non-linear functions to those computed by neurons with supra-linear dendrites. And pretty much every neuron in the brain has dendrites. So almost all neurons could, in principle, be a two-layer neural network.