The adult human body has 206 bones. Together, these bones form what is
called the skeleton. Although skeletons are usually something we associate
with Halloween, horror movies, or haunted houses, they are nothing to be
scared of. Every human being has a skeleton hiding underneath his or her
flesh. The bones that make up our skeleton have several key roles in the way
our body looks and functions.
Most the bones in our body are made of the same materials. Each bone
has four main layers. The outside of the bone is called the periosteum. This
layer contains nerves and blood vessels that bring nutrients to the bone. Next
is the compact bone. It is the hardest part of the bone. Inside the compact
bone is the cancellous bone. This part of the bone is light and spongy, but still
strong. The innermost layer of bone is called the marrow. This layer is almost
like a thick jelly. Bone marrow produces red blood cells, which help to bring
oxygen to all the different parts of our body, and white blood cells, which our
body uses to fight off diseases and infections.
Our skeleton also gives our body its shape and allows us to move. The
skeleton is our body’s frame; if we did not have bones, we would all flop
around like jellyfish. The special way our bones connect enable movement.
The places where our bones meet are called joints. These are the parts of
your body that you can bend and move, like your knees, elbows, shoulders,
and fingers. For an example, look at one of the legs on the diagram of the
skeleton. You will see bones called the femur, the tibia, and the fibula. The
place where these bones meet is the knee. The knee is a joint; it is protected
by the patella bone (also called the kneecap).
Finally, our bones also protect our most important organs. As you might
imagine, bones are much harder than the soft, fragile organs inside of our
body. For example, the ribs and sternum protect our heart, lungs, and major
blood vessels. The skull protects our brain. The vertebrae in our spine protect
the nerves in our spinal column. Without our bones, our bodies’ most vital
organs would be much more vulnerable.
The next time you see a skeleton while watching a scary movie or visiting
a haunted house, remember: those bones may be creepy, but you would not
be able to live without them!
"The skull contains a special kind of joint called a fibrous joint. Unlike other joints, it allows very
little movement."
Imagine that the author wanted to add this sentence to the passage. Into which paragraph
would this sentence fit best?
A
paragraph 1
B
paragraph 2
C
paragraph 3
D
paragraph 4