The driving force behind every one of us is the most powerful organ in the natural world: the human brain. Our central processing unit generates as many electrical impulses in a single day as all the telephones in the world combined. With new state-of-the-art imagery of this complex, mysterious machine, we reveal how our brain accelerates when faced with intense stress or danger, and taps into its deepest layers to unlock prehistoric survival instincts.

The human body is engineered for strength, power and endurance. Bone is sturdy as concrete but flexible enough to resist breaking and light enough to allow us to be quicker off the mark than a racehorse. Our muscles, ligaments and joints have far greater strength and endurance than we know. In this episode, we feature extraordinary tales of human strength told with stunning see-through "anatomy in motion."

Less than one-twentieth of an inch below the surface of the skin are the "antennae" that allow us to sense the world around us. This vital layer is the gateway to the original information superhighway -- the nervous system. Millions of nerves carry sensations across the body and up to the brain at hundreds of miles an hour. But our nervous system also has abilities almost beyond imagining.