How do you remember the way to your friend's house? Why do
your eyes blink without you ever thinking about it? Where do
dreams come from? Your brain is the one responsible for these
things and a whole lot more. Your brain is the boss of your body.
It runs the show by controlling just about everything you do.
It is more powerful and much faster than any computer you've ever used.
It is large and in charge - so large that it fills the upper half of your head.
It looks like a soft, wrinkly gray sponge, and it's almost as heavy as
a carton of orange juice! By the time you're grown up, it will weigh
about 3 pounds.
The Brain Team
The largest player on the brain team is the cerebrum (say: ser-ee-brum).
The cerebrum makes up 85% of the brain's weight, and it's easy
to see why. This is the thinking part of the brain. It lets you solve
math problems, play video games, feed your fish, do a dance, remember
your sister's birthday, and draw pictures. It's the cerebrum that makes
human beings more intelligent than animals because it's the part that
lets us reason. Imagine if your dog tried to read the paper after he
fetched it. It wouldn't work out too well for him, because compared
with you, the thinking part of his brain is very small!
The cerebrum is made up of two halves, with one on either side of
the head. Some scientists think that the right half helps you think
about abstract things, like music, colors, or shapes. The left half is
said to be more analytical, helping you with math, logic, and speech.
Scientists do know for sure that the right half of the cerebrum controls
the left side of your body, and the left half controls the right side.
One part of the cerebrum is called the motor area. It runs across the
two halves of the cerebrum like headphones, from ear to ear. The
motor area controls your voluntary muscles - the muscles in your body
that move when you want them to. Next time you're playing soccer and
take a shot on goal, thank your motor area!
Next up is the cerebellum (say: ser-eh-bell-um). The cerebellum is
at the back of the brain, below the cerebrum. It is a lot smaller than
the cerebrum - only 1/8 of its size. But don't let the cerebellum's small
size fool you - it is working very hard behind the scenes, controlling
balance, movement, and coordination (how your muscles work together).
Because of your cerebellum, you can stand upright, keep your balance,
and move around. Think about a surfer riding the waves on his surfboard.
What does he need to stay balanced? The best surfboard? The coolest
wetsuit? Nope - he needs his cerebellum!
Another brain part that's small but mighty is the brain stem.
The brain stem is beneath the cerebrum and in front of the cerebellum.
The brain stem connects the rest of the brain to the spinal cord, which
runs down your neck and back. The brain stem controls all the functions
that are necessary for your body to stay alive, like breathing air, digesting
food, and circulating blood. It's in charge of your involuntary muscles
- the ones that work automatically, without you even thinking about it.
There are involuntary muscles in the heart and stomach, and it's the
brain stem that tells your heart to pump more blood when you're biking,
or your stomach to start digesting that piece of birthday cake you just
ate. (Remember, the cerebrum has control over the voluntary muscles.
Controlling all of the body's muscles is too big a job for one brain part!)
The brain stem is also responsible for sorting through the millions of
messages that the brain and the rest of the body send back and forth.
Whew! It's a big job being the brain's secretary!
The hippocampus (say: hip-po-camp-us) is a part that's amazingly
cool, because you use it to remember the way to school! The
hippocampus is part of the cerebrum, and it's the area of your brain
that deals with memory. There are different kinds of memory: two of
them are called short-term and long-term. Try to remember what
you had for breakfast today - that's an example of short-term memory.
It's information your brain just received. Now think about your very
first day of school or last year's birthday party. Those are examples
of events that are stored in your long-term memory. Your hippocampus
has the big job of transferring information between short-term and
long-term memory. It's a lot of work, but the hippocampus is always
there, making sure you remember little things, like where you left your
yo-yo, and big things, like your camping vacation two summers ago.
The pituitary gland (say: pit-oo-it-tary) is very small - only about the
size of a pea! Its job is to produce and release hormones into your body.
If your clothes from last year are too small, it's because your pituitary
gland released special hormones that made you grow. This gland is a
major player in puberty, too. This is the time when boys' and girls'
bodies go through major changes as they slowly become men and women
- all thanks to hormones released by the pituitary gland.
Last but not least is the hypothalamus (say: hi-poh-tha-luh-muss).
It sits right in the center of your brain, in the middle of the action.
The hypothalamus is like your brain's inner thermometer. It knows
what temperature your body should be (about 98.6 degrees Fahrenheit
or 37 degrees Celsius), and it sends messages telling your body to
either sweat or shiver. Sweating when you're hot or shivering when
you're cold is your body's way of trying to keep your temperature the
same. Remember the last time you ran around and got really sweaty?
Your hypothalamus could tell that your body temperature was going
up from all that running, and it sent a message to your skin to sweat.
When you began sweating, your body started to cool off.
You've Got Some Nerve!
So the bossy brain sends all these messages around the body.
How? By using nerves. Nerves are bundles of thin threads that carry
messages throughout the body, a lot like how phone lines carry
conversations. The name for this entire system of bundles is the
nervous system, and it runs through the whole body just like those
phone lines run through a city. Some of the messages go straight
to the big boss, but a lot of them first go through a long bundle of
nerves called the spinal cord. The spinal cord is inside your spine
(reach around and feel the bumps in your back - that's your spine).
Your eyes, ears, and skin are even working for your brain, sending
messages through the nervous system about what's going on
outside your body. Want an example of how all these parts work
Your Brain vs. Spiky Cactus
Suppose you were at a friend's house, and his spiky cactus fell off the
windowsill and was headed right for your leg. Yikes! Your eyes would
go to work right away, sending a message through your nerves to your
brain: "WARNING, BOSS! SPIKY CACTUS HEADED TOWARD THE LEGS!"
The brain would use the spinal cord and nerves to send a message to
your leg muscles, telling them: "GET OUT OF THE WAY!" The brain even
tells the muscles which way to move and how fast to move, all in a split
second. This is an example of a voluntary movement. Your brain was
hard at work to keep you from getting pricked by the cactus.
The Boss Is Always Busy
The brain is always working - even when you're sleeping, it's doing all
kinds of cool things. It's always yearning for learning, since it's in
charge of learning and mastering new things. It's even in control of all
your feelings and emotions! Treat your brain well by eating good foods,
exercising, and getting enough sleep. Protect your brain by always
wearing a helmet when playing sports or riding your bicycle. And don't
drink alcohol take drugs, or use tobacco - the cells in your brain hate
this stuff, because it kills them! Take care of the boss of your body and
it won't let you down - it's the hardest worker around!
Sleep is like a time-out for your body, so you can feel rested and
prepared for the next day. But your brain never sits on the bench!
Even as it's telling your body to sleep, parts of your brain are awake,
taking control of how you sleep. There are five stages of sleep, and
your brain is in charge of every one.
In the first stage, as you're drifting off to sleep, your brain tells your
heart to beat slower and tells your body to lower its temperature
slightly. It sends messages to your muscles to relax.
In the second stage, you're in a light sleep. You might wake up from
a noise or touch. But if your dog doesn't jump on the bed or start to
bark, you progress to stage three.
Now you're in a deep sleep. Your brain tells your blood pressure to
go down, and you won't be very sensitive to the temperature of the
air around you, either.
Then it's time for stage four, the deepest sleep yet. This is the stage
where some people sleepwalk or sleeptalk. It's difficult to be awakened
from this stage of sleep. The very last stage is called REM sleep. REM
stands for Rapid Eye Movement, because even though your muscles
are totally relaxed, your eyes move back and forth quickly and your
heartbeat increases. This is the stage when you dream.
As the night goes on, you repeat stages two, three, four, and REM
every 90 minutes - that's about four or five times a night! No wonder
the brain is so busy!
When you go into REM sleep, your eyes may start to flutter behind
your eyelids - this means you're dreaming! Everybody has dreams,
but some people can't remember them as well as other people. What's
your brain doing when you're having a dream? Some scientists think
that dreams are your brain's way of sorting through what happened
during the day. The things that are important get stored in memory,
and the rest goes away - like sorting through mail. The good stuff is
what gets saved, and the bad junk mail gets thrown out.
Yearning for Learning
When you were very small, you couldn't do too much - you weren't able
to tell time, get dressed, or even talk! But your brain was ready to learn
all these things and much more, because it's armed with neurons
(say: nur-onz). The nervous system is made up of millions and millions
of these microscopic cells. Each neuron has tiny branches coming off it
that allow it to connect to many other neurons. When you were first
born, your brain came with all the neurons it will ever have, but many
of them were not connected to each other. When you learn things, the
messages travel from one neuron to another, over and over. Eventually,
the brain starts to create connections (or pathways) between the
neurons, so things become easier and you can do them better and
Think back to the first time you rode a bike. Your brain had to think
about pedaling, staying balanced, steering with the handlebars,
watching the road, and maybe even hitting the brakes - all at one time.
Hard work, right? But eventually, as you got more practice, the neurons
sent messages back and forth until a pathway was created in your brain.
Now you can ride your bike without thinking about it, because the
neurons have successfully created a "bike" pathway.
Maybe you got the exact toy you wanted for your birthday, and you're
really happy. Or your friend is sick, and you feel sad and afraid. Or your
little brother messed up your room, so you're really angry! Have you
ever wondered where those feelings come from? They all come from your
brain, which controls all the emotions you feel.
Your brain has a little bunch of cells on each side called the amygdala
(say am-ig-duh-luh). The word "amygdala" is Latin for almond, and
that's what this area looks like. Scientists believe that the amygdala
is responsible for emotion. So when you feel sad about a friend moving
away, your amygdala is hard at work. But they're not all bad - the
amygdala is also at work when you're really excited about winning
your soccer game.
It's normal to feel all different kinds of emotions, good and bad.
Sometimes you might feel a little sad and wonder why. And sometimes
you might feel anxious, or silly, or even frustrated. These feelings are
all part of what makes us human.