Download Muscles

Muscles
So what do muscles do?
Muscles move cows, snakes, worms and humans. Muscles move you! Without
muscles you couldn't open your mouth, speak, shake hands, walk, talk, or move
your food through your digestive system. There would be no smiling, blinking,
breathing. You couldn't move anything inside or outside you. The fact is,
without muscles, you wouldn't be alive for very long!
How do muscles move?
The cells that make up muscles contract and then relax back to original size.
Tiny microscopic fibers in these cells compress by sliding in past each other
like a sliding glass door being opened and then shut again. The cells of your
muscles use chemical energy from the food you eat to do this. Without food,
and particular kinds of nutrients, your muscles wouldn't be able to make the
energy to contract!
Some muscles are known as "voluntary" -- that is, they only work when you
specifically tell them to. Do you want to say something? Or swing a bat? Or
clap your hands? These are voluntary movements. Others, like the muscular
contracting of your heart, the movement of your diaphragm so that you can
breathe, or blinking your eyes are automatic. They're called involuntary
movements. And how do any of these muscles move? Through signals from
your nerves, and, in some cases, your brain, as well.
Bones
What would happen if humans didn't have bones?
You'd be floppy like a beanbag. Could you stand up? Forget it. Could you
walk? No way. Without bones you'd be just a puddle of skin and guts on the
floor.
Bones have two purposes. Some, like your backbone, provide the structure
which enables you to stand erect instead of lying like a puddle on the floor.
Other bones protect the delicate, and sometimes soft, insides of your body.
Your skull, a series of fused bones, acts like a hard protective helmet for your
brain. The bones, or vertebrae, of your spinal column surround your spinal
cord, a complex bundle of nerves. Imagine what could happen to your heart and
lungs without the protective armor of your rib cage!
How many bones do humans have?
When you were born you had over 300 bones. As you grew, some of these
bones began to fuse together. The result? An adult has only 206 bones!
How do my bones move?
With a lot of help. You need muscles to pull on bones so that you can move.
Along with muscles and joints, bones are responsible for you being able to
move. Your muscles are attached to bones. When muscles contract, the bones
to which they are attached act as levers and cause various body parts to move.
You also need joints which provide flexible connections between these bones.
Your body has different kinds of joints. Some, such as those in your knees,
work like door hinges, enabling you to move back and forth. Those in your
neck enable bones to pivot so you can turn your head. Still other joints like the
shoulder enable you to move your arms 360 degrees like a shower head.
Cardiovascular
What is it?
It's a big name for one of the most important systems in the body. Made up of
the heart, blood and blood vessels, the circulatory system is your body's
delivery system. Blood moving from the heart, delivers oxygen and nutrients to
every part of the body. On the return trip, the blood picks up waste products so
that your body can get rid of them.
Your Heart
About the size of your clenched fist, your heart is a muscle. It contracts and
relaxes some 70 or so times a minute at rest -- more if you are exercising -- and
squeezes and pumps blood through its chambers to all parts of the body. And it
does this through an extraordinary collection of blood vessels.
Your Blood Stream
Your blood travels through a rubbery pipeline with many branches, both big
and small. Strung together end to end, your blood vessels could circle the globe
2 1/2 times! The tubes that carry blood away from your heart are called arteries.
They're hoses that carry blood pumped under high pressure to smaller and
smaller branched tubes called capillaries. The tubes that more gently drain back
to the heart are veins.
How does your blood get oxygen?
When you inhale, you breathe in air and send it down to your lungs. Blood is
pumped from the heart to your lungs, where oxygen from the air you've
breathed in gets mixed with it. That oxygen-rich blood then travels back to the
heart where it is pumped through arteries and capillaries to the whole body,
delivering oxygen to all the cells in the body -- including bones, skin and other
organs. Veins then carry the oxygen-depleted blood back to the heart for
another ride.
Respiratory
Why do you need to breathe?
All the cells in your body require oxygen. Without it, they couldn't move, build,
reproduce, and turn food into energy. In fact, without oxygen, they and you
would die! How do you get oxygen? From breathing in air which your blood
circulates to all parts of the body.
How do you breathe?
You breathe with the help of your diaphragm and other muscles in your chest
and abdomen. These muscles literally change the space and pressure inside
your body to accomodate breathing. When your diaphragm pulls down, it not
only leaves more space for the lungs to expand but also lowers the internal air
pressure. Outside, where the air pressure is greater, you suck in air in an inhale.
The air then expands your lungs like a pair of balloons. When your diaphragm
relaxes, the cavity inside your body gets smaller again. Your muscles squeeze
your rib cage and your lungs begin to collapse as the air is pushed up and out
your body in an exhale.
So, it all starts at the nose?
Yup. About 20 times a minute, you breathe in. When you do, you inhale air and
pass it through your nasal passages where the air is filtered, heated, moistened
and enters the back of the throat. Interestingly enough, it's the esophagus or
foodpipe which is located at the back of the throat and the windpipe for air
which is located at the front. When we eat, a flap -- the epiglottis -- flops down
to cover the windpipe so that food doesn't go down the windpipe.
So -- back to breathing -- the air has a long journey to get to your lungs. It
flows down through the windpipe, past the voice box or vocal cords, to where
the lowermost ribs meet the center of your chest. There, your windpipe divides
into two tubes which lead to the two lungs which fill most of your ribcage.
Inside each of your sponge-like lungs, tubes, called bronchi, branch into even
smaller tubes much like the branches of a tree. At the end of these tubes are
millions of tiny bubbles or sacs called aleoli. Spread out flat, all the air sacs in
the lungs of an adult would cover an area about the third of a tennis court.
What do these sacs do?
They help perform an incredible magic act. Your air sacs bring new oxygen
from air you've breathed to your bloodstream. They exchange it for waste
products, like carbon dioxide, which the cells in your body have made and can't
use.
How does this exchange work?
With the help of the red blood cells in your bloodstream. Your red blood cells
are like box cars on train tracks. They show up at the sacs at just the right time,
ready to trade in old carbon dioxide that your body's cells have made for some
new oxygen you've just breathed in. In the process, these red blood cells turn
from purple to that beautiful red color as they start carrying the oxygen to all
the cells in your body.
But what happens to the carbon dioxide?
It goes through the lungs, back up your windpipe and out with every exhale. It's
a remarkable feat, this chemical exchange and breathing in and out. You don't
have to tell your lungs to keep working. Your brain does it automatically for
you.