neuronal energy demand

Neuronal energy demand is the surprisingly large amount of fuel that brain cells burn just to do their job. Neurons are the cells that carry signals through your nervous system, and signaling is expensive work. Even though the brain is only about 2% of an adult's body weight, it gobbles up roughly 20% of the body's energy — making it, gram for gram, one of the hungriest organs you own. A single thinking, resting brain quietly uses about as much power as a dim household light bulb, all day, every day, whether you are solving a puzzle or fast asleep.

Most of that energy goes into one tireless chore: pumping charged particles called ions back across the neuron's outer skin (its membrane). Every time a neuron fires a signal, ions rush in and out, and the cell must immediately bail them back to where they started using tiny molecular pumps — like a boat that springs a leak with every wave and has to bail nonstop to stay afloat. Each pump runs on a molecule called ATP, the cell's rechargeable energy currency, so the bailing never stops, even at rest.

To keep that currency flowing, neurons are packed with mitochondria — the cell's miniature power plants — and they crowd especially thick at the busy junctions (synapses) where signals jump between cells. The mitochondria make ATP mainly by burning glucose, a simple sugar delivered nonstop by the blood. Here is the catch: neurons store almost no fuel of their own, so they depend on a steady minute-by-minute supply of glucose and oxygen. Cut that supply for even a few minutes — as in a stroke — and neurons quickly run out of power and begin to die, which is why the brain is so fiercely protective of its blood flow.