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Thursday, 7 July 2011

Human brain

Human brain


Human brain
Skull and brain normal human.svg
Human brain and skull
Cerebral lobes.png
Cerebral lobes: the frontal lobe (pink), parietal lobe (green) and occipital lobe (blue)
Latin Cerebrum
Gray's subject #184 736
System Central nervous system
Artery Anterior communicating artery, middle cerebral artery
Vein Cerebral veins, external veins, basal vein, terminal vein, choroid vein, cerebellar veins
The human brain is the center of the human nervous system. Enclosed in the cranium, the human brain has the same general structure as that of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size.[1] Most of the spatial expansion comes from the cerebral cortex, a convoluted layer of neural tissue which covers the surface of the forebrain. Especially expanded are the frontal lobes, which are associated with executive functions such as self-control, planning, reasoning, and abstract thought. The portion of the brain devoted to vision, the occipital lobe, is also greatly enlarged in human beings.
Brain evolution, from the earliest shrew-like mammals through primates to hominids, is marked by a steady increase in encephalization, or the ratio of brain to body size. Estimates vary for the number of neuronal and non-neuronal cells contained in the brain, ranging from 80 or 90 billion (~85 109) non-neuronal cells (glial cells) and an approximately equal number of (~86 109) neurons,[2] of which about 10 billion (1010) are cortical pyramidal cells, to over 120 billion neuronal cells, with an approximately equal number of non-neuronal cells.[3] These cells pass signals to each other via as many as 1000 trillion (1015, 1 quadrillion) synaptic connections.[4] Due to evolution, however, the modern human brain has been shrinking over the past 28,000 years.

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