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You have been entrusted with the care and
feeding of the most extraordinary and
complex creation in the universe. Home to
your mind and personality, your brain houses
your cherished memories and future hopes. It
orchestrates the symphony of consciousness
that gives you purpose and passion, motion
and emotion.
But what do you really
know about it?
The brain is the most complex part of the
human body. This three-pound organ is the
seat of intelligence, interpreter of the
senses, initiator of body movement, and
controller of behavior. Lying in its bony
shell and washed by protective fluid, the
brain is the source of all the qualities
that define our humanity. The brain is the
crown jewel of the human body.
For centuries, scientists and philosophers
have been fascinated by the brain, but until
recently they viewed the brain as nearly
incomprehensible. Now, however, the brain is
beginning to relinquish its secrets.
Scientists have learned more about the brain
in the last 10 years than in all previous
centuries because of the accelerating pace
of research in neurological and behavioral
science and the development of new research
techniques.
Together, the brain and spinal cord make up
the central nervous system. They are covered
by three layers of membranes called meninges
and bathed in protective cerebrospinal
fluid, which acts as a "shock absorber" to
help prevent injury.
The largest part of the brain is comprised
of the cerebrum,
which is split into right and left
hemispheres. The cerebrum controls voluntary
actions, thought, speech, and memory. Most
mammals have a relatively small cerebrum,
but in humans it makes up most of the brain.
This allows us to perform much more
complicated actions than other species can.
The cortex, or "gray
matter," is the outer layer of the
cerebrum, made up mostly of the cell bodies
of neurons, or nerve cells. Most of the
brain's work of processing information is
done in the folds of gray matter. This is
where the blueprints are stored that contain
the vital information of our intelligence,
memory, personality, emotion, speech, and
ability to move and function in familiar and
complex ways. Nerve fibers found in the
cortex's underlying
white matter carry messages into the
brain for additional processing. These
messages are then relayed to other parts of
the nervous system, which carry them out.
The midbrain,
located deeper within the brain's structure,
acts as a cellular switchboard, keeping the
different areas of the brain communicating
with one another. This is necessary for the
brain to carry out its most complicated
functions, because its simultaneous commands
require proper routing and coordination.
The central structure of the brain contains
the thalamus,
hypothalamus,
and pituitary gland.
The thalamus
carries messages from the sensory organs to
the brain. The
hypothalamus regulates automatic
functions such as changes in pulse rate,
thirst, appetite, and sexual and sleep
patterns. It also regulates the
pituitary gland's
production of multiple hormones that play
roles in growth, metabolism, fluid and
mineral balance, sexual function, and the
body's response to stress. Four ventricles
(cavities within the brain) contain
cerebrospinal fluid, which protects the
brain's delicate structure, nourishes brain
tissue, and carries away waste materials.
The back of the brain is divided into three
parts. The cerebellum
(Latin for "little brain") is located below
the cerebral hemispheres and controls our
ability to make coordinated and balanced
motor movements. The
medulla oblongata, which connects the
brain to the very top of the spinal cord,
controls many of the involuntary actions of
our bodies, such as the regulation of
heartbeat, breathing, and digestion. The
pons is a
specialized band of nerve fibers that links
the midbrain with the medulla oblongata and
acts as a high-functioning switchboard.
The spinal cord
is a long shaft of tissue made up of neurons
and supporting cells that
is
covered by
meningeal membranes. Extending from the
bottom of the medulla oblongata, the spinal
cord is surrounded and protected by a
stacked set of ring-shaped bones called the
vertebrae, which together make up the spinal
column. The spinal column is classified by
region: cervical (neck), thoracic (rib
cage/upper back), lumbar (mid-/lower back)
and sacral (tailbone). Nerves branch off
from the spinal cord, passing through the
bony vertebrae and extending out to the
organs and body parts to which they are
specifically "wired." In the spaces between
the vertebrae is a rubbery material called
cartilage. These cartilage cushions, called
spinal disks, allow flexible movement
between the vertebrae so that our backs can
bend and absorb shock when we run, jump, and
otherwise exert ourselves.
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