The Brain
What weighs about 3 pounds (1.5 kilograms) and contains up to 100 billion cells? The
answer is the human brain. Thebrainis the control center of the nervous system. It’s like
the pilot of a plane. It tells other parts of the nervous system what to do. The brain is also
the most complex organ in the body. Each of its 100 billion neurons has synapses connecting
it with thousands of other neurons. All those neurons use a lot of energy. In fact, the adult
brain uses almost a quarter of the total energy used by the body. The developing brain of a
baby uses an even greater percentage of the body’s total energy.
Figure 20.5: Side view of the brain; find the location of the three major parts of the brain,
noting that the cerebrum is divided into four lobes at the upper portion of the brain: the
frontal, parietal, temporal, and occipital lobes(Left).Top view of the brain and cerebrum;
divided from front to back into two halves, these are the right and left hemispheres(Right).
( 30 )
The brain is the organ that lets us interpret what we see, hear, or sense in other ways. It
also allows us to learn, think, remember, and use language. The brain controls all of our
internal body processes and external movements, as well. As shown inFigure20.5, the
brain consists of three main parts:
- Thecerebrumisthelargestpartofthebrain. Itliesontopofthebrainstem(discussed
below). The cerebrum controls functions that we are aware of, such as problem-solving
and speech. It also controls voluntary movements, like waving to a friend. Whether
you are doing your homework or jumping hurdles, you are using your cerebrum. - The cerebellumis the next largest part of the brain. It lies under the cerebrum
and behind the brain stem. The cerebellum controls body position, coordination, and
balance. Whether you are riding a bicycle or writing with a pen, you are using your
cerebellum. - Thebrain stemis the smallest of the three main parts of the brain. It lies directly
under the cerebrum. The brain stem controls basic body functions such as breathing,
heartbeat, and digestion. The brain stem also carries information back and forth
between the cerebrum and spinal cord.