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.
What Are Muscles Made of?
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-a-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-ul) 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!
Updated and reviewed by:
Elana
Pearl Ben-Joseph, MDDate reviewed:
September 2004
Originally reviewed by: Steven
Dowshen, MD