Layered structure and leveled function of a human brain

If stretched out to a flat plain, the cortex of a brain in an adult human may have a surface area of around 2,000 square centimeters. It contains 1-2 billion neurons in six distinguishable layers, adding up to the 2-3 mm thick “grey matter”. For the rest of the brain, its majority volume is made of “white matter” of neural fibers (axons and dendrites) and other cells, e.g., glial cells, which provide brain homeostasis and may help neurons to live and work well [1, 2]. On the cortex, researchers have recognized over two hundred local areas that specially assign for different functions and may excite under different statuses [3, 4]. Recently, it is found that intensively arranged parallel axons form effective isolation walls for separate motion and diffusion modes of intracellular fluidics in a brain [5]. Yet to date the working mechanisms of the cortex and human brain remains not fully clear.