The Skeletal System

The Skeletal System
~~-~
Although you may not be aware of all your
bones, your body actually contains about 206 bones
of different shapes and sizes. All of these bones are
arranged in a very orderly way. They are fastened
together by stringy connective tissues called
ligaments. Together, your bones and the ligaments
that hold them in place help make up most of your
skeletal system. The skeletal system has five impor­
tant functions: it provides shape, allows movement,
protects organs, produces blood cells, and stores
certain materials.
Functions of the Skeleton
Without your skeletal system, your body would
look like little more than a mass of jelly. Besides giv­
ing the body shape and support, the skeletal system
also serves four other important function s. One of
Scapula
Sternum
Ribs
y
Vertebra
Pelvis
In
-t---Femur
Metacarpals
K"l-I'----
Patella
ft---
In
Fibula
I-+!----Tibia
h
Phalanges
Section Objective
To describe the structure and
function of the skeletal
system
Figure 12-4 You r body contains
about 206 bones. Working
together, the bones and the
muscles to which most of the
bones are attached allow you to'
do many things, including play
basketball like Magic Johnson.
What is the name of the
connective tissue that connects
bone to bone?
these is movement. Almost all of your bones are
tached to muscles. Working together, bones and
muscles allow you to walk, sit, stand, and even
Bones also protect the organs of your body.
Your brain is surrounded by a bony skull that
it from being injured. If you move your fingers
along the center of your back, you can feel your
backbone, or vertebral column. Your backbone
teets your spinal cord , which contains nerve tissue.
The spinal cord is the main message "cable" be­
tween the brain and other parts of the body. What
other organs are protected by bones?
Bones store important minerals. For example,
calcium and phosphorus are constantly deposited
bones for future use. The long bones in your
also produce many of the blood cells necessary for
healthy blood.
Figure 12-5 This X-ray shows
how the 19 bones in each of your
hands allow you to unscrew a
batt/e . What are the five functions
of the skeletal system?
Parts of the Skeleton
Su ppose you were asked to make a life-sized
model of a skeleton. Where would you start? You
may begin by thinking of the human skeleton as
HELP WANTED: ATHLETIC TRAINER
Knowledge of diving required. Must know
first aid. Previous instructional experience
and surface-diving ability desi red. Back­
ground study in anatomy and physiology
a plus .
You are enjoying the diving competition on
television. Divers twist and turn thei r bodies as
they glide through the air to the delight of their
audience.
For trained athletes diving is safe, but for
beginners it requires instruction and equipment.
Serious injury can occur to those beginners who
have not learned proper techniques, including
the best way to warm up before the com peti­
tion. The people who help prepare athletes for
the Olympics or for other athletic competitions
are called athletic trainers. Their job is to be
sure athletes keep physically fit for participation
in athletic competition. Trainers instruct ath­
letes on how to strengthen muscles by doing
special exercises and suggest special diets
keep athletes in the best of health . T
must also know when an injury or problem
pears serious and a doctor should be
If you are interested in sports and
enjoy helping athletes do w ell. you can f'n rl""t1,'>t;
a career as an athletic trainer. To receive
information. write to the National AS~50clatl()n'
for Sport and Physical Education , 1900 ASl:iOCIIJ­
tion Drive, Reston, VA 22091.
lones are at­
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backbone pronerve tissue.
"cable" be­
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For example, .
Illy deposited In
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Is necessary for
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I'
special diets to
ot health , TraIners
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To receive ~~re
Na~ional Assoclatl~n
, 1900 Assocla­
being divided into two major parts. The two major
parts of the human skeleton are the axial (AK-see­
uhl) skeleton and the appendicular (ap-uhn-DIHK­
yuh-luhr) skeleton.
AXIAL SKElETON The axial skeleton covers the
area that runs from the top of your head down
your body in a straight line to your hips. This part
includes the skull, the chest with its ribs and other
bones, and the vertebral column . The vertebral col­
umn consists of 33 separate bones. Each of these
bones is called a vertebra (vER-tuh-bruh; plural:
vertebrae) .
The appendicular skeleton
includes the bones that branch out from the axial
skeleton. These bones include the pelvis, or hip
bones, the bones of the arms and legs, the clavicle
(KLAv-uh-kuhl), or collar bone, and the scapula
(sKAP-yoo-luh), or shoulder blade.
APPENDICULAR SKELETON
"''A---Vertebra
Figure 12-6 The vertebral
column consists of 33 vertebrae, or
small bones, stacked one on top
of the other. These bones not only
protect the spinal cord, but they
also form a strong support for the
body. Is the vertebral column part
of the axial or appendicular
skeleton?
Formation of Bones
Of all our body parts, bones are the strongest
and the hardest. Perhaps this is the reason why
many people tend to think of bone as permanent
and unchanging. Actually, bone is made up partly
of living tissue. Your bones grow and change just as
your skin does. During childhood, bones are shaped
reshaped as the shape and weight of the body
Figure 12-7 X-rays of the hands
of a two year old (top left) and a
three year old (bottom left) show
that bone has not yet replaced the
cartilage in the wrist. In the X-ray
of the 14-year-old hand (center),
bone formation is almost as
complete as it is in the X-ray of a
60-year-old's hand (right). What
process changes cartilage to
bone?
279
Sharpen Your Skills
Bones as Levers
Using reference materials in
the library, find out about le­
vers. Distinguish between
first-class and second-class
levers. How do bones act as
levers? On posterboard, draw
an example of a first-class and
second-class lever. Below each
drawing, draw an example of
the bones that act like that
type of lever. In each of the
drawings, label the effort,
load, and fulcrum. At the bot­
tom of the posterboard, define
each of these terms.
changes through growth. Even in adulthood, bone'
being continually made and removed, especially
where it is under pressure.
With your index finger, touch the tip of your
nose. Now gently move the tip of your nose from
side to side. You are able to move the tip of your
nose because it contains cartilage (KAHRT-uhl-ihj).
Cartilage is a type of flexible connective tissue. It
supports such structures as the nose and ears.
lage also connects the ribs to the sternum, or breast
bone, and acts as a cushion between the bones of
the vertebral column. This connective tissue also
covers the ends of bones to keep them from rub­
bing against one another where they meet.
Most bone is made from cartilage. In the early
stages before birth, the skeleton is composed a
entirely of this flexible tissue. Then, over several
months, a great deal of cartilage disappears and is
replaced by bone . This process is called ossitlc;atJ(Jln.
(ahs-uh-fuh-KAy-shuhn) . Most of the bones in the
skeleton are formed this way.
Structure of Bones
Figure 12-8 The femur, which is
the longest bone in the body, has
two enlarged ends with a long
shaft connecting them. The ends
of the femur are made up of softer
spongy bone, while the shaft is
made up of compact bone. What
is the tough membrane that
surrounds the shaft called?
Periosteum
Bones are made up of living tissue. Yet in some
ways they are similar to such nonliving things as
rocks. Two obvious similarities are hardness and
strength. Both bones and rocks owe their hardness
and strength to chemical substances called min
Although rocks contain a wide variety of minerals,
bones are made up mainly of mineral compounds
that contain the elements calcium and phosphorus.
Marrow
Shaft
280
Spongy bone
Solid bone
Blood vessels
Dairy products are rich in calcium and phosphorus.
Next time someone suggests that you drink milk "to
keep your bones strong and healthy ," you will know
why this suggestion makes sense.
) of your
Let's take a close look at the longest bone in the
nose from
body to see what it, and other bones, are made of.
ip of your
This bone, called the femur, links your hip to your
tT-uhl-ihj).
knee. Perhaps the most obvious part of this bone is
e tissue. It .
its long shaft, or column , which is shaped something
ld ears. Cartl­
like a hollow cylinder. The shaft contains solid bone
um , or breast
and is surrounded by the periosteum (pehr-ih-AHs­
le bones of
tee-uhm). The periosteum is a tough membrane that
. tissue also
contains bone-forming cells and blood vessels. The
n from rub­
bone-forming cells aid in repairing injuries to the
meet.
bone. The blood vessels su pply food and oxygen to
1n the early
the bone's living tissue. Muscles are attached to the
;mposed almost
periosteum's surface. At each end of the shaft is an
over several.
enlarged knob. These knobs are made of a softer
appears and ~s
type of bone called spongy bone.
llled ossificatlon
Running through the middle of the thick bone is
e bones in the
a system of pipelike passageways called the
Haversian (huh-vER-shuhn) canals. They contain
blood vessels, which bring food and oxygen to the
living bone cells. These canals also contain nerves.
The nerves send messages through the canals to livparts of the bone.
Yet in some
ssue.
If you have ever broken a chicken bone in half,
.iving things as
hardness and
may have noticed that it contains a hollow cav­
"'e their hardness
or space. Inside the cavity of every bone is a soft
~~
' ll d minerals. or yellow material called marrow. Red marrow
:e.s ~(t o~' rnineral s , . ,·f\rhuops most of the body's blood cells , and yellow
tne Y d
. contains fat and blood vessels.
nera, 1 cornpoun s
hosphorus.
:) an d P
)od, bone
peciaHy
IS
>
_ """"'::lI
You walk slowly to the edge of the diving board
gaze nervously into the water. Then you raise
arms high and lower your head between them.
. slightly at the knees, you leap into the air
kick your legs out behind you , meeting the sur­
of the water with your fingertips. None of
movements would be possible if your body was
equipped with structures called joints. A joint is
place where two bones meet.
There are several types of joints. Some joints,
as the gliding, ball-and-socket, hinge, and pivot
Figure 12-9
Th e tiny openings in
this photograph of thick, compa c t
bone are the Haversian canals.
What do these canals contain?
Sharpen Your Skills
What's in a Bone?
Because bones are made up
of living tissue, they need
structures that will protect and
nourish them.
1. Obtain a large bone from
a turkey or chicken drumstick.
2. Remove all of the meat
from the bone.
3. Using a knife, cut off one
end of the bone. CAUTION: Be
careful when using a knife.
4. Examine the bone care­
fully and identify as many
parts as you can.
Draw a diagram of the bone
and label its parts. In the
human skeleton, what is this
bone called?
281
Sharpen Your Skills
First-Aid Techniques
Contact the local chapter of
the American National Red
Cross that gives first-aid in­
struction. Visit a class to ob­
serve the first-aid techniques
for fractures, dislocations, and
sprains that may occur due to
accidents. Present your find­
ings to the class in an oral
report. Be sure to mention the
meaning of the term first aid.
Also explain the first-aid treat­
ment for each of these inju­
ries. Explain how each occurs.
Figure 12-10 The actions
involved in diving require the use
of many types of joints. What
movement does the ball-and­
socket joint allow you to do?
joints, are called movable joints. Movable joints
the bones they connect to move. Others, such as
joints in the skull do not permit movement. These
joints are called immovable joints.
In the diving example, a gliding joint allows you
to lower your head as you ready yourself for your
dive into the water. The gliding joint allows the
tebrae in the neck to slide over one another.
'When you raise your arms high, the ball-and­
socket joints of your shoulders make the
possible. The ball-and-socket joints allow you to
swing your arms in a circle. These joints are made
of a bone with a rounded head that fits into the
cuplike pocket of another bone. Can you name an­
other example of a ball-and-socket joint in the
.
As you swing your arms forward, you turn them
palm side down . This movement is made possible
the pivot joint. The pivot joint permits a turning
motion in which one bone rotates on a ring-shaped
bone.
As you get ready to leap off the diving board,
you bend your knees. The knee is another type of
Neck vertebrae
Humerus
joint,
the
ment
SECTI
1. Wh
syst
2. Wh
3. Lisl
fo u
4. Wh
5. COl
ble
6. Su ~
steI
PIVOT JOINT
GLIDING JOINT
12­
~--Femur
Humerus
BALL-AND-SOCKET JOINT
282
Fibula
---'1;'.'_ _
Tibia
HINGE JOINT
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asleep
Or ar
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alive.
pump
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Ich as the
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!lows you
or your
s the ver­
~ r.
t!l-and­
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ou to
lre made
to the
name anQ the body?
turn them
possible by
It urning
ng-shaped
g board,
~ r type of
- -- Ulna
joint, a hinge joint. The hinge joint, also found at
the elbow, allows for forward and backward move­
ment. See Figure 12-10.
SECTION REVIEW
Figure 12-11 The X-ray of a
shoulder (right) shows how a bone
can be forced out of a joint in a
dislocation. In the X-ray of a lower
arm (left), you can see a break in
the radius. What is the other bone
in the lower arm called?
1. ""hat are the five functions of the skeletal
system?
2. What is a ligament?
3. List four places in the body where cartilage is
found.
4. What is marrow?
5. Compare the movements of four types of mova­
ble joints.
6. Suggest a reason why the ribs are attached to the
sternum, or breastbone, by cartilage.
PIVOT JOINT
12-3 The Muscu'lar System
- -
-
Femur
Tibia
HINGE JOINT
It is 3 A.M. and you have been asleep for several
hours. All day you walked, ran, and played , using
your muscles in a variety of ways. Now that you are
asleep, all the muscles in your body are also at rest.
Or are they?
Without waking you, many of the more than 600
muscles in your body are still working to keep you
alive. The muscles of your heart are contracting to
pump blood throughout the body. Your chest mus­
cles are working to help move air in and out of
Section Objective
To describe the three types of
muscles
283
The Skeletal System
-------=
Although you may not be aware of all your
bones, your body actually contains about 206 bones
of different shapes and sizes. All of these bones are
arranged in a very orderly way. They are fastened
together by stringy connective tissues called
ligaments. Together, your bones and the ligaments
that hold them in place help make up most of your
skeletal system. The skeletal system has five impor­
tant functions: it provides shape, allows movement,
protects organs, produces blood cells, and stores
certain materials.
Functions of the Skeleton
Without your skeletal system, your body would
look like little more than a mass of jelly. Besides giv­
ing the body shape and support, the skeletal system
al·o serves four other important functions. One of
SkUII~
~L Mandible
Clavicle
Scapula
Humerus
-5!i>-iiT-ii + - - Sternum
~~~~tJ-Ribs
Radius- - T /
Ulna­
4ia'-~rr-- Vertebra
--J#!
-n---'iT-- Pelvis
n
+---Femur
Metacarpals
t\u'----Patelia
tt----Fibula
n
I - t l - - - - Tibia
Tarsals- - ­___~
Section Objective
To describe the structure and
function of the skeletal
system
Figure 12-4 Your body contains
about 206 bones . Working
together, the bones and the
muscles to which most of the
bones are attached allow you ta
do many things, including play
basketball like Magic Johnson.
What is the name of the
connective tissue that connects
bone to bone?