When having the nerve is helped by having the muscle.

Suppose just now you had picked up this journal, flipped it open and started to read this article. When this started to happen we might assume that there would be some physiological changes in the brain to support this extra brain work and indeed neuroscientists can now put together a rather plausible description of what they might be. On the basis of evidence from the study of the brain, not only in vitro, but also in vivo, with tools like positron emission tomography and magnetic resonance spectroscopy, the story goes something like this. The arousal associated with reading and making sense of the words would have activated various areas of your brain and the fuel metabolism of neurons (and almost immediately of astrocytes also) would have increased to support the increased nervous activity. Release and re-uptake of neurotransmitters, and pumping of ions across cell membranes and between sub-cellular compartments is energetically expensive. Accordingly, soon after an activating stimulus it is possible to detect markedly increased glycolytic lactate production, probably occurring almost exclusively in astroglia in response to glutamate stimulation, followed by a rise in accumulation of extracellular lactate, then a fall as it is taken up and oxidised completely in neurons. The initial burst of glycolysis probably takes place at the expense of blood glucose transported rapidly through the blood-brain barrier, but there is a substantial back-up of astroglial glycogen which can be used if the demand exceeds the supply of glucose for a variety of reasons (or if there is hypoxia when glycolysis is the only energy-producing process).