Did you know you have more than 600 muscles in your body? They help
you do almost everything - from pumping blood throughout your body
to lifting your heavy backpack. You control some of your muscles
and others, like your heart, do their jobs without you thinking
about them at all.
Muscles are all made of the same material, a type of elastic tissue
(sort of like the material in a rubber band). Thousands, or even
tens of thousands, of small fibers make up each muscle. You have
three different types of muscles in your body: smooth muscle,
cardiac (say:
kar
-dee-ak) muscle, and skeletal (say:
skeh
-luh-tul) muscle.
Smooth Muscles
Smooth muscles are sometimes also called involuntary muscles and
they are usually in sheets, or layers, with one layer of muscle
behind the other. You can't control this type of muscle. 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.
But smooth muscles are at work all over your body. In your
stomach and digestive system, they contract (tighten up) and relax
to allow food to make its journey through the body. Your smooth
muscles come in handy if you're sick and you need to throw up.
The muscles push the food back out of the stomach so it comes up
through the esophagus (say: ih-
sah
-fuh-gus) and out of the mouth.
Smooth muscles are also found in your bladder. When they're
relaxed, they allow you to hold in urine (pee) until you can get to
the bathroom. Then they contract so that you can push the urine
out. These muscles are also in a woman's uterus, which is where
a baby develops. There they help to push the baby out of his or her
mother's body when it's time to be born.
You'll find smooth muscles at work behind the scenes in your
eyes, too. These muscles keep the eyes focused.
A Hearty Muscle
The muscle that makes up the heart is called cardiac muscle. It
is also known as the myocardium (say: my-uh-
kar
-dee-um). The thick muscles of the heart contract to pump blood out
and then relax 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. A special group of cells within the heart are
known as the pacemaker of the heart because it controls the
heartbeat.
Skeletal Muscle
Now, let's talk about the kind of muscle you think of when we
say "muscle" - the ones that show how strong you are and
let you boot a soccer ball right into the goal. These are your
skeletal muscles. They are also sometimes called striated (say:
stry
-ay-tud) muscle (striated is a fancy word meaning striped) because
the light and dark parts of the muscle fibers make them look
striped.
Skeletal muscles are voluntary muscles, which means you can
control what they do. Your leg won't bend to kick the soccer
ball unless you want it to. These muscles help to make up the
musculoskeletal (say: mus-kyuh-low-
skeh
-luh-tul) system - the combination of your muscles and your
skeleton, or bones.
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 place where two bones meet) and then attaches again to
another bone.
Skeletal muscles are held to the bones with the help of tendons
(say:
ten
-dunz). Tendons are cords made of tough tissue, and they work as
special connector pieces between bone and muscle. The tendons are
attached so well that when you contract one of your muscles, the
tendon and bone move along with it.
Skeletal muscles come in many different sizes and shapes to
allow them to do many types of jobs. Some of your biggest and most
powerful muscles are in your back, near your spine. These muscles
help keep you upright and standing tall.
They also give your body the power it needs to lift and push
things. Muscles in your neck and the top part of your back
aren't as large, but they are capable of some pretty amazing
things: Try rotating your head around, back and forth, and up and
down to feel the power of the muscles in your neck. These muscles
also hold your head high.
Face Muscles
You may not think of it as a muscular body part, but your face
has plenty of muscles. You can check them out next time you look in
the mirror. Facial muscles don't all attach directly to bone
like they do in the rest of the body. Instead, many of them attach
under the skin. This allows you to contract your facial muscles
just a tiny bit and make dozens of different kinds of faces. Even
the smallest movement can turn a smile into a frown. You can raise
your eyebrow to look surprised or wiggle your nose.
And while you're looking at your face, don't pass over
your tongue - a muscle that's attached only at one end! Your
tongue is actually made of a group of muscles that work together to
allow you to talk and help you chew food. Stick out your tongue and
wiggle it around to see those muscles at work.
Major Muscles
Because there are so many skeletal muscles in your body, we
can't list them all here. But here are a few of the major
ones:
- In each of your shoulders is a deltoid (say:
del
-toyd) muscle. Your deltoid muscles help you move your shoulders
every which way - from swinging a softball bat to shrugging your
shoulders when you're not sure of an answer.
- The pectoralis (say: pek-tuh-
rah
-lus) muscles are found on each side of your upper chest. These
are usually called pectorals (say:
pek
-tuh-rulz), or pecs, for short. When many boys hit puberty, their
pectoral muscles become larger. Many athletes and bodybuilders
have large pecs, too.
- Below these pectorals, down under your rib cage, are your
rectus abdominus (say:
rek
-tus ab-dahm-uh-nus) muscles, or abdominals (say: ab-
dahm
-un-ulz). They are also sometimes called abs for short.
- When you make a muscle in your arm, you tense your biceps
(say:
bye
-seps) muscle. When you contract your biceps muscle, you can
actually see it push up under your skin.
- Your quadriceps (say:
kwad
-ruh-seps), or quads, are the muscles on the front of your
thighs. Many people who run, bike, or play sports develop large,
strong quads.
- And when it's time for you to take a seat? You'll be
sitting on your gluteus maximus (say:
gloot
-e-us
mak
-suh-mus), the muscle that's under the skin and fat in your
behind!
Reviewed by:
Steven Dowshen, MD
Date reviewed: June 2006
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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