Energy-Hungry Organ

Your brain is only about 2 percent of your body weight, yet it consumes around 20 percent of your total energy. Passing signals from neuron to neuron is expensive work, so the brain demands a steady supply of glucose and oxygen, delivered by an extensive network of tiny blood vessels packed into your skull.

The brain's energy demand is so steep that just five minutes without oxygen can cause permanent damage. Unlike muscles, neurons store almost no energy reserves, so they depend on continuous blood flow. That dependence is why strokes are so devastating and why every second counts.