Think back to last Halloween for a minute. Wherever you looked, there were vampires,
ghosts, or bony skeletons grinning back at you. Vampires and ghosts don't really exist,
but skeletons sure do!
Every single person has a skeleton made up of many bones. These bones give your
body structure, let you move in many ways, protect your internal organs, and more.
It's time to look at all your bones — the adult human body has 206 of them!
What Are Bones Made Of?
If you've ever seen a real skeleton or fossil in a museum, you might think that
all bones are dead. Although bones in museums are dry, hard, or crumbly, the bones
in your body are different. The bones that make up your skeleton are all very much
alive, growing and changing all the time like other parts of your body.
Almost every bone in your body is made of the same materials:
The outer surface of bone is called the periosteum (say: pare-ee-OSS-tee-um).
It's a thin, dense membrane that contains nerves and blood vessels that nourish the
The next layer is made up of compact bone. This part is smooth
and very hard. It's the part you see when you look at a skeleton.
Within the compact bone are many layers of cancellous (say: KAN-sell-us)
bone, which looks a bit like a sponge. Cancellous bone is not quite as hard as compact
bone, but it is still very strong.
In many bones, the cancellous bone protects the innermost part of the bone, the
bone marrow (say: MAIR-oh). Bone marrow is sort of like a thick jelly,
and its job is to make blood cells.
How Bones Grow
When you were a baby, you had tiny hands, tiny feet, and tiny everything! Slowly,
as you grew older, everything became a bit bigger, including your bones.
A baby's body has about 300 bones at birth. These eventually fuse (grow together)
to form the 206 bones that adults have. Some of a baby's bones are made entirely of
a special material called cartilage (say: KAR-tel-ij). Other bones
in a baby are partly made of cartilage. This cartilage is soft and flexible. During
childhood, as you are growing, the cartilage grows and is slowly replaced by bone,
with help from calcium.
By the time you are about 25, this process will be complete. After this happens,
there can be no more growth — the bones are as big as they will ever be. All
of these bones make up a skeleton that is both very strong and very light.
Your spine is one part of the skeleton that's easy to check out: Reach around to
the center of your back and you'll feel its bumps under your fingers.
The spine lets you twist and bend, and it holds your body upright. It also protects
the spinal cord, a large bundle of nerves that sends information from your brain to
the rest of your body. The spine is special because it isn't made of one or even two
bones: It's made of 33 bones in all! These bones are called vertebrae
(say: VER-tuh-bray) and each one is shaped like a ring.
There are different types of vertebrae in the spine and each does a different kind
The first seven vertebrae at the top are called the cervical
(say: SIR-vih-kul) vertebrae. These bones are in the back of your neck, just below
your brain, and they support your head and neck. Your head is pretty heavy, so it's
lucky to have help from the cervical vertebrae!
Below the cervical vertebrae are the thoracic (say: thuh-RAS-ik)
vertebrae, and there are 12 in all. These guys anchor your ribs in place. Below the
thoracic vertebrae are five lumbar (say: LUM-bar) vertebrae. Beneath
the lumbar vertebrae is the sacrum (say: SAY-krum), which is made
up of five vertebrae that are fused together to form one single bone.
Finally, all the way at the bottom of the spine is the coccyx
(say: COK-siks), which is one bone made of four fused vertebrae. The bottom sections
of the spine are important when it comes to bearing weight and giving you a good center
of gravity. So when you pick up a heavy backpack, the lumbar vertebrae, sacrum, and
coccyx give you the power. When you dance, skip, and even walk, these parts help keep
In between each vertebra (the name for just one of the vertebrae) are small disks
made of cartilage. These disks keep the vertebrae from rubbing against one another,
and they also act as your spine's natural shock absorbers. When you jump in the air,
or twist while slamming a dunk, the disks give your vertebrae the cushioning they
Your heart, lungs,
and liver are all very important, and luckily you've got ribs to keep them safe. Ribs
act like a cage of bones around your chest. It's easy to feel the bottom of this cage
by running your fingers along the sides and front of your body, a few inches below
your heart. If you breathe in deeply, you
can easily feel your ribs right in the front of your body, too. Some thin kids can
even see a few of their ribs right through their skin.
Your ribs come in pairs, and the left and right sides of each pair are exactly
the same. Most people have 12 pairs of ribs, but some people are born with one or
more extra ribs, and some people might have one pair less.
All 12 pairs of ribs attach in the back to the spine, where they are held in place
by the thoracic vertebrae. The first seven pairs of ribs attach in the front to the
sternum (say: STUR-num), a strong bone in the center of your chest
that holds those ribs in place. The remaining sets of ribs don't attach to the sternum
directly. The next three pairs are held on with cartilage to the ribs above them.
The very last two sets of ribs are called floating ribs because they aren't connected
to the sternum or the ribs above them. But don't worry, these ribs can't ever float
away. Like the rest of the ribs, they are securely attached to the spine in the back.
Your skull protects the most important part of all, the brain. You can feel your
skull by pushing on your head, especially in the back a few inches above your neck.
The skull is actually made up of different bones. Some of these bones protect your
brain, whereas others make up the structure of your face. If you touch beneath your
eyes, you can feel the ridge of the bone that forms the hole where your eye sits.
And although you can't see it, the smallest bone in your whole body is in your
head, too. The stirrup bone behind your eardrum is only .1 to .13 inches (2.5 to 3.3
millimeters) long! Want to know something else? Your lower jawbone is the only bone
in your head you can move. It opens and closes to let you talk and chew food.
Your skull is pretty cool, but it's changed since you were a baby. All babies are
born with spaces between the bones in their skulls. This allows the bones to move,
close up, and even overlap as the baby goes through the birth canal. As the baby grows,
the space between the bones slowly closes up and disappears, and special joints called
sutures (say: SOO-churs) connect the bones.
sit and type at the keyboard, while you swing on a swing, even when you pick up your
lunch, you're using the bones in your fingers, hand, wrist, and arm.
Each arm is attached to a shoulder blade or scapula (say: SKA-pyuh-luh),
a large triangular bone on the upper back corner of each side of the ribcage. The
arm is made up of three bones: the humerus (say: HYOO-muh-rus), which
is above your elbow, and the radius (say: RAY-dee-us) and ulna
(say: UL-nuh), which are below the elbow.
Each of these bones is wider at the ends and skinnier in the middle, to help give
it strength where it meets another bone. At the end of the radius and ulna are eight
smaller bones that make up your wrist. Although these bones are small, they can really
move! Twist your wrist around or wave and you'll see how the wrist can move.
The center part of your hand is made up of five separate bones. Each finger on
your hand has three bones, except for your thumb, which has two. So between your wrists,
hands, and all your fingers, you've got a grand total of 54 bones — all ready
to help you grasp things, write your name, pick up the phone, or throw a softball!
Sure, your arm, wrist, hand, and finger bones are great for picking up the phone,
but how are you supposed to run to answer it? Well, with the bones of the legs and
Your legs are attached to a circular group of bones called your pelvis.
The pelvis is a bowl-shaped structure that supports the spine. It is made up of the
two large hip bones in front, and behind are the sacrum and the coccyx. The pelvis
acts as a tough ring of protection around parts of the digestive system, parts of
the urinary system, and parts of the reproductive system.
Your leg bones are very large and strong to help support the weight of your body.
The bone that goes from your pelvis to your knee is called the femur
(say: FEE-mur), and it's the longest bone in your body. At the knee, there's a triangular-shaped
bone called the patella (say: puh-TEL-luh), or kneecap, that protects
the knee joint. Below the knee are two other leg bones: the tibia
(say: TIH-bee-uh) and the fibula (say: FIH-byuh-luh). Just like the
three bones in the arm, the three bones in the leg are wider at the ends than in the
middle to give them strength.
The ankle is a bit different from the wrist; it is where the lower leg bones connect
to a large bone in the foot called the talus (say: TAL-iss). Next
to the talus are six other bones. But the main part of the foot is similar to the
hand, with five bones. Each toe has three tiny bones, except for your big toe, which
has just two. This brings the bone total in both feet and ankles to 52!
Most people don't use their toes and feet for grabbing stuff or writing, but they
do use them for two very important things: standing and walking. Without all the bones
of the foot working together, it would be impossible to balance properly. The bones
in the feet are arranged so the foot is almost flat and a bit wide, to help you stay
upright. So the next time you're walking, be sure to look down and thank those toes!
The place where two bones meet is called a joint. Some joints move and others don't.
Fixed joints are fixed in place and don't move at all. Your skull has some of these
joints (called sutures, remember?), which close up the bones of the skull in a young
person's head. One of these joints is called the parieto-temporal
(say: par-EYE-ih-toh TEM-puh-rul) suture — it's the one that runs along the
side of the skull.
Moving joints are the ones that let you ride your bike, eat cereal, and play a
video game — the ones that allow you to twist, bend, and move different parts
of your body. Some moving joints, like the ones in your spine, move only a little.
Other joints move a lot. One of the main types of moving joints is called a hinge
joint. Your elbows and knees each have hinge joints, which let you bend and
then straighten your arms and legs. These joints are like the hinges on a door. Just
as most doors can only open one way, you can only bend your arms and legs in one direction.
You also have many smaller hinge joints in your fingers and toes.
Another important type of moving joint is the ball and socket joint.
You can find these joints at your shoulders and hips. They are made up of the round
end of one bone fitting into a small cup-like area of another bone. Ball and socket
joints allow for lots of movement in every direction. Make sure you've got lots of
room, and try swinging your arms all over the place.
Have you ever seen someone put oil on a hinge to make it work easier or stop squeaking?
Well, your joints come with their own special fluid called synovial fluid
(say: SIH-no-vee-ul) that helps them move freely. Bones are held together at the joints
by ligaments (say: LIH-guh-mints), which are like very strong rubber
Taking Care of Bones
Your bones help you out every day so make sure you take care of them. Here are
Protect those skull bones (and your brain inside!) by wearing a helmet
for bike riding and other sports. When you use a skateboard, in-line skates,
or a scooter, be sure to add wrist supports and elbow and knee pads. Your bones in
these places will thank you if you have a fall!
If you play sports like football, soccer, lacrosse, or ice hockey, always
wear all the right equipment. And never play on a trampoline. Many kids end
up with broken bones from jumping
on them. Broken bones can eventually heal, but it takes a long time and isn't much
fun while you wait.
Strengthen your skeleton by drinking milk and eating other dairy products
(like low-fat cheese or frozen yogurt). They all contain calcium, which helps
bones harden and become strong.
Be active! Another way to strengthen your bones is through exercise
like running, jumping, dancing, and playing sports.
Take these steps to be good to your bones, and they will treat you right!