Neural information processing is tightly coupled to both energy consumption and derivation from substrates.In this study,the energy function of the neuron during the action potential(AP)is described and analyzed.It has been observed that energy consumption during the AP does not match predictions of the conventional theory of neural energy dynamics.On short time scales,neural energy expenditure shifts between positive and negative phases.During the AP,the energy source switches from neuronal stores(positive expenditure or net consumption)to exploitation of external substrates,specifically the glucose and oxygen carried in cerebral blood(the negative consumption phase).Based on the idea of reductionism,this paper demonstrates how ion channels,membrane pumps and transporters,ionotropic and metabotropic receptor signaling pathways,astrocyte glycolysis and the production lactate,and the glutamate-glutamine cycle all serve to relate cerebral blood flow and neuronal metabolism to neuronal activity and so maintain neuronal energy charge during the AP.