& Healing Centre
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Brain Function.
The human brain is the center of the human nervous system and
is a highly complex organ. Enclosed in the cranium, it has the same general
structure as the brains of other mammals, but is over three times as large as
the brain of a mammal with an equivalent body size. 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 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. The human brain has been estimated to contain 50–100 billion
neurons, of which about 10 billion are cortical pyramidal cells. These
cells pass signals to each other via approximately 100 trillion synaptic
connections.
In spite of the fact that it is protected by the thick bones of the skull,
suspended in cerebrospinal fluid, and isolated from the bloodstream by the
blood-brain barrier, the delicate nature of the human brain makes it susceptible
to many types of damage and disease. The most common forms of physical damage
are closed head injuries such as a blow to the head, a stroke, or poisoning by a
wide variety of chemicals that can act as neurotoxins. Infection of the brain is
rare because of the barriers that protect it, but is very serious when it
occurs. More common are genetically based diseases, such as Parkinson's disease,
multiple sclerosis, and many others. A number of psychiatric conditions, such as
schizophrenia and depression, are widely thought to be caused at least partially
by brain dysfunctions, although the nature of such brain anomalies is not well
understood.