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.
In section, myelin is white whereas the gray matter is that color due to all the gray nuclei contained in the cells that make it up. The white matter is found in the inner layer of the cortex, the optic nerves, the central and lower areas of the brain or brainstem, and surrounding the central shaft of gray matter in the spinal cord.