|Glencoe Health 2nd Edition. Mission Hills: Glencoe Inc., 1989: 252.||"Weighing around three pounds (1.35kg), the brain contains nearly 100 billion cells."||100 billion|
|World Book 2001. Chicago: World Book Inc., 2001: 551.||"The human brain has from 10 billion to 100 billion neurons."||10–100 billion|
|Magill's Medical Guide Revised Edition. Salem Press, 1998: 221.||"It has been estimated that the adult brain has around one hundred billion neurons and an even larger number of glial cells."||100 billion|
|The Science Times Book of the brain. New York: The Lyons Press, 1987: 150.||"The human brain holds about 100 billion nerve cells."||100 billion|
|The Scientific American Book of the Brain. New York: Scientific American, 1999: 3.||"An adult human brain has more than 100 billion neurons"||> 100 billion|
One of the most remarkable aspects of the adult nervous system is the human brain. The human brain controls memory, vision, learning, thought, consciousness and other activities. By means of electrochemical impulses the brain directly controls conscious or voluntary behavior. It also monitors, through feedback circuitry, most involuntary behavior and influences automatic activities of the internal organs.
During fetal development the foundations of the mind are laid as billions of neurons form appropriate connections and patterns. No aspect of this complicated structure has been left to chance. The basic wiring plan is encoded in the genes. It has been shown from previous studies that in developing embryos of animals, nerve cells are created in or travel to designated regions of the brain, and once in place send out axons along preprogrammed paths to make contact with specific targets.
The brain's billions of neurons connect with one another in complex networks. All physical and mental functioning depends on the establishment and maintenance of neuron networks. A person's habits and skills -- such as nail-biting or playing a musical instrument -- become embedded within the brain in frequently activated neuron networks. When a person stops performing an activity, the neural networks for the activity fall into disuse and eventually may disappear.
Differences in weight and size of a person's brain does not correlate with differences in mental ability. The adult human brain normally weighs from 1.0 to 1.5 kg (2¼ to 3¼ lbs).
The work of the brain is similar to a combination of a computer and a chemical factory. So take good care of your PC!
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