Download The Skeletal Muscles

The Skeletal Muscles
Types of Muscle
What Are Muscles Made of?
Since you have 650 muscles in your body, you might think that all together, they're pretty
heavy. And you're right! Your muscles make up about one half of your body's weight.
For example, that means if you weigh 60 pounds, about 30 pounds of you is pure muscle!
Muscles are all made of the same material, a type of muscle fiber that is elastic (sort of
like the material in a rubber band). Hundreds or even thousands of these small fibers
make up each muscle. You have three different types of muscles in your body: smooth
muscle, cardiac (say: car-dee-ack) muscle, and skeletal (say: skell-ih-tull) muscle.
Cardiac Muscle
Have you ever thought about why your heart can pump blood day in and day out? It's
because the heart is a - you guessed it - muscle. The muscle that makes up the heart is
called the myocardium (say: my-oh-car-dee-um). It is sometimes also called cardiac
muscle. The thick muscles of the heart contract (tighten up) to pump blood out and then
relax (loosen up) to let blood back in after it's circulated through the body.
Just like smooth muscle, cardiac muscle works all by itself with no help from you. The
brain and nervous system tell the heart muscle what to do and how fast to pump blood,
and the heart muscle does the rest. This means pumping blood every minute of the day,
every day of their lives.
Skeletal Muscles
Skeletal muscles help you move your body and do things like… kick a soccer ball or
spoon dog food into your dog's dish?
Skeletal muscles are also known as voluntary muscles - these are the muscles that you
can control. Your leg won't bend to kick the ball unless you want it to, and your dog's
dinner won't find its way into the dish unless you tell your muscles to make it happen.
Together, the skeletal muscles work with your bones to give your body power and
strength. In most cases, a skeletal muscle is attached to one end of a bone. It stretches all
the way across a joint (the "hinged" place where two bones meet), and then attaches again
to another bone.
Want to see a skeletal muscle in action? Try making a muscle with your arm. The muscle
in the top half of your arm contracts, and it pulls the bones in the lower half of your arm
along with it. After you make the muscle, let your arm relax. What happens to the lower
part of your arm as you relax your upper arm?
Smooth Muscles
Smooth muscles are sometimes also called involuntary muscles. You can't control this
type of muscle - these muscles work involuntarily, which means that your brain and body
tell these muscles what to do without you even thinking about it. You can't use your
smooth muscles to make a muscle in your arm or jump into the air.
So what are smooth muscles good for then, you ask? Lots! Smooth muscles are in your
stomach, and they work by contracting (this means they tighten up) and relaxing to allow
food to pass into your small intestine. If you're like a lot of kids and you've ever thrown
up, then you've felt the smooth muscles in your stomach at work. The muscles push the
food back out of the stomach so it comes up through the esophagus (say: ee-sof-a-gus)
and out of the mouth. Because they are involuntary muscles, you don't have any say in
the deal. Luckily, ‘puking’ doesn't happen very often.
All smooth muscles are usually set up in sheets, with one behind the other. Smooth
muscles are also found in your bladder, and they contract to allow you to hold urine in
until you're ready to urinate. They are also found in a woman's uterus, which is where a
baby develops - these involuntary muscles help to push the baby out of his mother's body
when it's time for him to be born. Smooth muscles are at work behind the scenes in your
eyes to keep them focused. And tiny smooth muscles are even found in the walls of some
of your blood vessels.
Smooth muscles found in:
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Stomach
Bladder
Uterus
Eyes (for focus)
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Walls of some blood vessels
Esophagus