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.
The stuff between our ears comes in two shades: white and grey. The difference between the two is all in the fat content. The white matter of the brain is made up primarily of axon tracts, the long, spindly appendages of some brain cells. These tracts transmit the electrical signals that the brain cells, called neurons, use to communicate.