The Human Brain
What does it do?
Our brains regulate everything we do, whether we are aware of it or
not. The brain controls involuntary actions such as breathing and
heart beat. It also manages voluntary movements, the data our senses
receive, the emotions and instincts we feel, and all the thinking
we do. Different parts of the brain control different parts of the
body.
What influences it?
The human brain is a product of millions of years of evolution. In
addition, each individual brain is shaped by a person's genes and
environment. Studying the brain includes studying the interactions
of heredity, environment, and culture. Science and technology are
helping us understand how the brain works and the best ways to make
changes when it does not work normally.
Brain
Basics
About 80% of the brain is the deeply wrinkled
gray tissue of the cerebrum. The two halves are the right and
left hemispheres, each operating a little differently. The corpus
callosum divides the cerebrum from the rest of the brain.
Beneath the corpus callosum are several small structures, such
as the thalamus. At the base of the brain is the cerebellum,
which controls automatic functions, such as breathing. The brainstem
connects to the spinal cord.
Brain
trivia
A human brain weighs less than a pound (.45 kg) at birth and
about 3 pounds (1.4 kg) by adulthood. It consists of about 100
billion neurons (nerve cells) and roughly 10 times as many other
cells. Most of it is gray matter-billions of networked neurons.
Human brain evolution
The human brain is unique among primates in that it is about
3 times larger than it would be for a non-human primate of the
same body size. Although our brain areas for seeing, smelling,
and agility are smaller than those of other primates, we have
larger areas for thinking and language. During human evolution
the major brain expansion occurred from 500,000 to 100,000 years
ago. |
 Brain
mapping
Scientists have several high-tech methods
for looking inside a working brain to see how it functions.
PET
A Positron Emission Tomography (PET) scan
shows brain areas exhibiting various degrees of activity. The
scan senses the presence of a harmless radioactive material
that has been injected into the bloodstream. This technique
helps researchers learn the function of areas in a normal brain
and see differences in diseased brains.
MRI
Magnetic Resonance Imaging (MRI) produces
a three-dimensional picture by using a magnet to align atomic
particles in body tissue and radio waves to map those tissues.
An MRI of the brain shows different tissue types and the presence
and location of unusual soft tissues, such as tumors.
fMRI
A functional MRI (fMRI) is like an MRI,
but it shows more than just tissue types. It also shows brain
activity. By sensing areas with the most oxygen, an fMRI shows
how the brain changes when an activity or stimulus changes.
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