ABOUT HUMAN BRAIN

Human brain

The human brain is the center of the human nervous system and is a highly complex organ. It has the same general structure as the brains of other mammals, but is over five times as large as the "average brain" of a mammal with the same body size.^{[citation needed]} Most of the expansion comes from the cerebral cortex, a convoluted layer of neural tissue that covers the surface of the forebrain. Especially expanded are the frontal lobes, which are involved in executive functions such as self-control, planning, reasoning, and abstract thought. The portion of the brain devoted to vision is also greatly enlarged in humans.

Brain evolution, from the earliest shrewlike mammals through primates to hominids, is marked by a steady increase in encephalization, or the ratio of brain to body size. The human brain has been estimated to contain 50–100 billion (10¹¹) neurons^{[citation needed]}, of which about 10 billion (10¹⁰) are cortical pyramidal cells.^{[citation needed]} These cells pass signals to each other via around 100 trillion (10¹⁴)^{[citation needed]} synaptic connections.