Brain Structure is a complex subject. Our brain is: 1.) intracranial (situated within the cranium), and 2.) intracerebral (contained within the cerebral cortex). The intracerebral brain is made of soft jelly-like fragile tissue with a lot of valleys and folds. The brain is 80% water. The average weight of the adult brain is 3-3.5 lbs, or about 2.4% of total body weight. Our gelatinous brain is a flesh and blood organ where 15-20% of blood flow that leaves the heart goes to the brain. Blood flow to the brain varies according to the activity going on in the brain. When there is elevated neuronal activity, there is an increase in blood flow to replenish glucose –—> a sugar molecular formula of C6H1206. Sugar is a major source of fuel for the brain. In fact, sugar is the only real source the brain uses for energy. Our brain consumes nearly 25% of our bodies total energy. A blood-sugar level increase makes for an upsurge in alertness. Our brain complies with the laws of physics, biology, and metabolism, and that makes the human brain a bio-energetic organ. On a side note: starting in Graduate School I ate a snicker bar an hour before taking a test. Maybe it was wish fulfillment on my part, but I think the ingested sugar from the bar made me more alert in taking tests.