Population is based on the de facto definition of population, which counts all residents regardless of legal status or citizenship--except for refugees not permanently settled in the country of asylum, who are generally considered part of the population of their country of origin.
The brain is made up of over 100 billion nerve cells with each brain cell connected to around 10,000 other cells, which equals around 1000 trillion connections in your brain. Your brain is actually very soft, jelly-like, and not grey but a deep red in color. The brain controls both involuntary, or lower, actions, such as heart rate, respiration, and digestion. Complex, or higher, mental activity, such as thought, reason, and abstraction, is consciously controlled.
Fire a model neuron to see how brain cells use chemical and electrical signals to communicate at incredible speeds. Where are those signals going? To the discrete pathways that enable your brain to control your body functions. When you see how parts of the brain control functions throughout body, you'll be glad that the signals travel so quickly. Your brain integrates those neurons into pathways in mysterious ways to manage its complex cognitive function. In other words, you become you when your pathways function together. Use your brain to explore your world, like a street scene filled with multisensory information or scenarios from everyday life.