The adult brain contains 100 billion neurons — more than the number of stars in the Milky Way galaxy. Each of the brain's neurons connects to as many as 200,000 other neurons.

At three pounds, the brain makes up only 2 percent of total body weight but consumes about 15 percent of the energy used by the entire body.

Nerve impulses carrying images from your eyes to your brain travel at almost 400 feet per second. (The speed of light is 186,000 miles per second.)