sx05_TE_(NC7-8)302-339.fm Page 322 Thursday, July 14, 2005 3:18 PM
Section
4
4
The Muscular
System
Objectives
The Muscular System
Reading Preview
After this lesson, students will be able to
D.1.4.1 Identify the types of muscles found
in the body.
D.1.4.2 Explain why skeletal muscles work
in pairs.
Key Concepts
• What types of muscles are found
in the body?
• Why do skeletal muscles work in
pairs?
Key Terms
Target Reading Skill
Previewing Visuals Explain that looking
at the visuals before they read helps students
activate prior knowledge and predict what
they are about to read.
Answers
Sample answers:
How does skeletal muscle help my body
move? (Skeletal muscles are attached to the
ends of bones and provide the force to move
them.) Where is smooth muscle found?
(The inside of many internal organs) Why is
cardiac muscle considered a special type?
(It is found only in the heart; it is like smooth
muscle because it is involuntary and like
skeletal muscle because it is striated.)
Teaching Resources
• involuntary muscle
• voluntary muscle
• skeletal muscle
• tendon
• striated muscle
• smooth muscle
• cardiac muscle
Target Reading Skill
Previewing Visuals When you
preview, you look ahead at the
material to be read. Preview
Figure 15. Then, in a graphic
organizer like the one below, write
two questions that you have about
the diagram. As you read, answer
your questions.
Types of Muscle
Q. How does skeletal muscle
help my body move?
A.
• Transparency D7
Q.
Preteach
Build Background
Knowledge
How Do Muscles Work?
1. Grip a spring-type clothespin
with the thumb and index
finger of your writing hand.
Squeeze the clothespin open
and shut as quickly as possible
for two minutes. Count how
many times you can squeeze
the clothespin before your muscles tire.
2. Rest for one minute. Then, repeat Step 1.
Think It Over
Predicting What do you think would happen if you repeated
Steps 1 and 2 with your other hand? Give a reason for your
prediction. Then, test your prediction.
A rabbit becomes still when it senses danger. The rabbit sits so
still that it doesn’t seem to move a muscle. Could you sit without moving any muscles? Saliva builds up in your mouth. You
swallow. You need to breathe. Your chest expands to let air in.
All of these actions involve muscles. It is impossible to sit absolutely still without muscle movement.
There are about 600 muscles in your body. Muscles have
many functions. For example, they keep your heart beating, pull
your mouth into a smile, and move the bones of your skeleton.
The girl doing karate on the next page uses many of her muscles
to move her arms, legs, hands, feet, and head. Other muscles
expand and contract her chest and allow her to breathe.
Types of Muscle
Some of your body’s movements, such as smiling, are easy to
control. Other movements, such as the beating of your heart,
are impossible to control completely. That is because some of
your muscles are not under your conscious control. Those
muscles are called involuntary muscles. Involuntary muscles
are responsible for such essential activities as breathing and
digesting food.
L2
How Muscles Move
Ask each student to hold a science book in
one hand. Have students stand and hold
the books down at their sides. Ask them to
lift the books while feeling their arm muscles
with the opposite hand. Ask: What muscles
did you feel contract? What else did you
notice? (Sample answer: Muscles in the upper
arm; fibers [tendons] stood out through
the skin.) Record their observations on
the board.
322 ◆
L1
Skills Focus Predicting
Materials spring-type clothespin
Time 15 minutes
Tips Caution students not to move so fast
that they lose their grip; otherwise they
might pinch their fingers in the spring.
Expected Outcome The muscles can
respond repetitively but tire easily. Most
322
students will find that the number of times
they are able to squeeze the clothespin
decreases in Step 2.
Think It Over Students might predict
that repeating the steps with the other
hand would produce the same pattern, but
that they will not be able to squeeze the
clothespin as many times as in the first
trial because the writing hand is stronger.
sx05_TE_(NC7-8)302-339.fm Page 323 Thursday, July 14, 2005 3:18 PM
The muscles that are under your conscious control are
called voluntary muscles. Smiling, turning a page in a book,
and getting out of your chair when the bell rings are all actions
controlled by voluntary muscles.
Your body has three types of muscle tissue—skeletal
muscle, smooth muscle, and cardiac muscle. Some of these
muscle tissues are involuntary, and some are voluntary. In
Figure 15, you see a magnified view of each type of muscle in
the body. Both skeletal and smooth muscles are found in many
places in the body. Cardiac muscle is found only in the heart.
Each muscle type performs specific functions in the body.
Instruct
Types of Muscle
Teach Key Concepts
FIGURE 15
Types of Muscle
Your body has three types of
muscle tissue: skeletal muscle,
smooth muscle, and cardiac
muscle. Classifying Which type of
muscle is found only in the heart?
Cardiac muscle
Smooth muscle
Skeletal muscle
L2
Classifying Muscles
Focus Tell students that muscles are found
everywhere in the body.
Teach Ask: What is the difference between
voluntary and involuntary muscles?
(Voluntary muscles are under your conscious
control; involuntary muscles are not.) Point
out that a person does not have to think all
the time about moving voluntary muscles,
for example, when walking. But the person
does decide when to start and stop walking.
Refer students to Figure 15. Ask: How are
skeletal and cardiac muscles alike? (Both
have a striped appearance.) Where is the
smooth muscle located in the figure? (In
the stomach) Ask: Are skeletal muscles
voluntary or involuntary? (Voluntary)
Smooth muscles? (Involuntary) Cardiac?
(Involuntary)
Apply Ask: How does cardiac muscle
compare with skeletal muscle? (Like skeletal
muscle, cardiac muscle is striated. Unlike
skeletal muscle, cardiac muscle contracts
repeatedly without getting tired.) learning
modality: visual
Independent Practice
L2
Teaching Resources
• Guided Reading and Study Worksheet:
The Muscular System
Student Edition on Audio CD
Chapter 8
◆
323
Differentiated Instruction
L1
Special Needs
Experiencing Voluntary and
Involuntary Movements Have students
wave their hands. Tell them this movement
is voluntary. Then, help them find their
pulse. Point to the heart in Figure 12, and
explain that their pulse is caused by
muscles in the heart. Explain that the
beating of their heart is involuntary.
learning modality: kinesthetic
L1
Less Proficient Readers
Developing a Study Aid As students
read the section, have them write ten
questions about the muscular system.
Suggest they write a mixture of short
answer, fill-in-the-blank, and matching
questions. Have partners exchange the
questions and answer them. Urge them to
reread the appropriate passages to find
answers to questions. learning modality:
Monitor Progress
L2
Oral Presentation Have students describe
the difference between voluntary and
involuntary muscle.
Answer
Figure 15 Cardiac
verbal
323
sx05_TE_(NC7-8)302-339.fm Page 324 Thursday, July 14, 2005 3:18 PM
PHSchool.com
For: More on muscle
types
Visit: PHSchool.com
Web Code: ced-4014
Students can review the types of muscles in an
online interactivity.
L3
Observing Muscle Tissue
Materials prepared slides of skeletal,
smooth, and cardiac muscle; microscope
Time 20 minutes
Focus Review the three types of muscle.
Teach
CAUTION: Tell students to be careful
handling the slides. Ask them to observe
the slides with a low-power lens, then at high
power. Have them sketch each type of muscle,
noting whether cells contain striations, and
labeling the nucleus and cytoplasm for each
cell type. The cell membrane may or may
not be distinguishable because cells may be
tightly packed.
Apply Ask students how the nuclei of
striated muscle tissue differ from the nuclei
of cardiac and smooth. (Striated have more
nuclei.) Tell students that skeletal muscle
tissue is actually many individual cells, each
with a nucleus, that have joined to make one
muscle fiber. A muscle fiber can be several
centimeters long. Smooth and cardiac
muscle tissues are composed of individual
cells, each with its own nucleus. learning
Get a Grip
Are skeletal muscles at work
when you’re not moving?
1. Hold a stirrer in front of
you, parallel to a table
top. Do not touch the
table.
2. Have a partner place a
hairpin on the stirrer.
3. Raise the stirrer until the
“legs” of the hairpin just
touch the table. The
“head” of the hairpin
should rest on the stirrer.
4. Hold the stirrer steady for
20 seconds. Observe what
happens to the hairpin.
5. Grip the stirrer tighter and
repeat Step 4. Observe.
Skeletal Muscle Every time you walk across a room, you are
using skeletal muscles. Skeletal muscles are attached to the
bones of your skeleton and provide the force that moves your
bones. At each end of a skeletal muscle is a tendon. A tendon is a
strong connective tissue that attaches muscle to bone. Skeletal
muscle cells appear banded, or striated. For this reason, skeletal
muscle is sometimes called striated (STRY ay tid) muscle.
Because you have conscious control of skeletal muscles,
they are classified as voluntary muscles. One characteristic of
skeletal muscles is that they react very quickly. Think about
what happens during a swim meet. Immediately after the starting gun sounds, a swimmer’s leg muscles push the swimmer
off the block into the pool. However, another characteristic of
skeletal muscles is that they tire quickly. By the end of the race,
the swimmer’s muscles are tired and need a rest.
Smooth Muscle The inside of many internal organs, such
as the stomach and blood vessels, contain smooth muscles.
Smooth muscles are involuntary muscles. They work automatically to control certain movements inside your body, such as
those involved in digestion. For example, as the smooth muscles of your stomach contract, they produce a churning action.
The churning mixes the food with chemicals, and helps to
digest the food.
Unlike skeletal muscles, smooth muscle cells are not striated. Smooth muscles behave differently than skeletal muscles,
too. Smooth muscles react more slowly and tire more slowly.
Inferring Are the skeletal
muscles in your hand at work
when you hold your hand
still? Explain.
Where is smooth muscle found?
modality: visual
Help Students Read
L1
Anticipation Guide Before students read
the next two sections, write these statements
on the board:
• Muscle cells shorten and lengthen to
move a muscle.
• Exercise causes more muscle cells to
be produced.
Ask students whether they agree with the
statements. Discuss their responses, and then
have them read the sections and evaluate
their initial answers. (Both statements are
false. Muscle cells shorten only, and exercise
makes individual muscle cells grow in size.)
324
324 ◆
L2
Skills Focus Inferring
Materials wooden stirrer, hairpin
Time 10 minutes
Tips Ask students to predict what may
happen to the hairpin as they hold the
stirrer out in front of them.
Expected Outcome Even when students
hold their hands still, some of the muscles
are at work as evidenced by the movement,
or “walking,” of the hairpin.
Extend Have students rest a hand on their
desks, make a fist, and then extend the
index finger. Tell them to hold the index
finger still. If students watch carefully, they
can probably see the finger trembling
slightly. learning modality: kinesthetic
sx05_TE_(NC7-8)302-339.fm Page 325 Monday, July 18, 2005 12:46 PM
Muscles at Work
Cardiac Muscle The tissue called cardiac muscle is found
only in your heart. Cardiac muscle has some characteristics in
common with both smooth muscle and skeletal muscle. Like
smooth muscle, cardiac muscle is involuntary. Like skeletal
muscle, cardiac muscle cells are striated. However, unlike skeletal muscle, cardiac muscle does not get tired. It can contract
repeatedly. You call those repeated contractions heartbeats.
Teach Key Concepts
PHSchool.com
For: More on muscle types
Visit: PHSchool.com
Web Code: ced-4014
Muscles at Work
Has anyone ever asked you to “make a muscle”? If so, you probably tightened your fist, bent your arm at the elbow, and made
the muscles in your upper arm bulge. Like other skeletal muscles, the muscles in your arm do their work by contracting,
becoming shorter and thicker. Muscle cells contract when they
receive messages from the nervous system. Because muscle
cells can only contract, not extend, skeletal muscles must
work in pairs. While one muscle contracts, the other muscle
in the pair relaxes to its original length.
Muscles Work in Pairs Figure 16 shows the muscle
action involved in bending the arm at the elbow. First, the
biceps muscle on the front of the upper arm contracts to
bend the elbow, lifting the forearm and hand. As the biceps
contracts, the triceps on the back of the upper arm relaxes
and returns to its original length. Then, to straighten the
elbow, the triceps muscle contracts. As the triceps contracts
to extend the arm, the biceps relaxes and returns to its original length. Another example of muscles that work in pairs are
those in your thigh that bend and straighten the knee joint.
FIGURE 16
Muscle Pairs
Because muscles can only contract,
or shorten, they must work in
pairs. To bend the arm at the
elbow, the biceps contracts while
the triceps returns to its original
length. Interpreting Diagrams
What happens to each muscle to
straighten the arm?
Biceps
contracts
Triceps
returns to
original
length
L2
Muscles Work in Pairs
Focus Refer students to Figure 16.
Teach Ask students to bend their elbows so
they can feel their muscles contract and relax
as shown in the figure. Explain that muscles
can only contract, or become shorter. They
cannot extend, or become longer. Ask: How
does your biceps change as you bend your
arm? (It gets shorter and thicker and feels
firmer.) What happens to your arm when
your triceps contracts? (The arm straightens
and the biceps returns to its original length.)
Apply Explain that the nervous system
determines the strength of muscle
contractions. If a person lifts something
light, only a few muscle cells will contract;
if the object is heavy, many muscle cells will
contract. learning modality: kinesthetic
Teaching Resources
• Transparency D8
L2
Triceps
contracts
Modeling How Skeletal Muscles Work
Biceps
returns
to original
length
Materials strips of cardboard; thick, long
elastic bands; brass fasteners
Time 25 minutes
Focus Review how muscles work in pairs.
Teach Have students work in small groups
to build models to show how muscle pairs
work together, and then have them
demonstrate and explain the model.
Apply Ask students to examine a diagram
of a human skeleton and list the bones that
are moved by muscle pairs. learning
modality: kinesthetic
Chapter 8
◆ 325
Monitor Progress
Differentiated Instruction
L1
Less Proficient Readers
Comparing and Contrasting Ask
students to organize the information on
types of muscle tissue in a compare/
contrast table. Columns are Type of Tissue,
How It Is Controlled, and Where It Is
Found. learning modality: visual
L3
Gifted and Talented
Improving Flexibility Flexibility is the
ability to use a muscle throughout its
entire range of motion. Flexibility is just as
important as having strong muscles. Have
students ask a physical education teacher
to show them how to correctly perform
stretches for flexibility. Students can lead
the class in performing the stretches.
learning modality: kinesthetic
L2
Drawing Have students observe which
muscles contract when they stand and bend a
knee. Then have them sketch the
bones and muscles in the thigh in
each position and indicate which
muscle is contracted. Have students place
their drawings in their portfolios.
Answers
Figure 16 The triceps contracts and the
biceps returns to its original length.
On the inside of many
internal organs
325
sx05_TE_(NC7-8)302-339.fm Page 326 Thursday, July 21, 2005 2:50 PM
Monitor Progress
L2
Muscular Strength and Flexibility Regular exer-
Answer
Stretch and warm up
thoroughly.
Assess
Reviewing Key Concepts
1. a. Skeletal, smooth, and cardiac b. A
person can control voluntary muscles, such
as skeletal muscles. A person cannot control
involuntary muscles, such as smooth or
cardiac muscles. Also, voluntary muscles tire
more easily than involuntary muscles.
c. The person would not be able to move the
finger because the muscle would not be
connected to the bone.
2. a. Attached to the bones of the skeleton;
for example, in the upper arms and thighs
b. To bend the arm, the biceps shortens,
pulling the forearm up toward the shoulder.
To straighten the arm, the triceps contracts
while the biceps returns to its original
length. c. Sample answer: Because paired
muscles must work together, and exercise
makes individual muscle cells grow in size,
exercising both muscles in a pair will make
them grow equally strong.
Reteach
L1
Name several different body parts, including
internal organs, and ask students to identify
the type of muscle found there and its
function.
Performance Assessment
Writing Have students write a paragraph
explaining why having involuntary muscles
is important.
Teaching Resources
• Section Summary: The Muscular System
• Review and Reinforce: The Muscular
System
• Enrich: The Muscular System
FIGURE 17
Preventing Muscle Injuries
When you warm up before exercising, you
increase the flexibility of your muscles.
What are two ways to prepare the muscles
for exercise?
4
Section 4 Assessment
Target Reading Skill Previewing Visuals Refer to your
questions and answers about Figure 15 to help you answer
Question 1 below.
Reviewing Key Concepts
1. a. Identifying What are the three types of muscle tissue?
b. Comparing and Contrasting How do voluntary and
involuntary muscles differ? Give an example of each
type of muscle.
c. Predicting The muscles that move your fingers are
attached to the bones in your fingers by tendons.
Suppose one of the tendons in a person’s index finger
were cut. How would it affect movement in the finger?
2. a. Identifying Where might you find muscle pairs?
b. Describing Describe how the muscles in your upper
arm work together to bend and straighten your arm.
c. Applying Concepts When exercising to build muscular
strength, why is it important to exercise both muscles
in a muscle pair equally?
Comparison Paragraph Write a
paragraph comparing smooth
muscle tissue and skeletal muscle
tissue. Include whether these
muscle tissues are voluntary or
involuntary, where they are found
and what their functions are. In
addition, describe what you might
expect to see if you looked at these
muscle tissues under a microscope.
326 ◆
Keep Students on Track Models
should be complete or nearly so.
Provide time for testing and revising
of designs. Suggest that students try
different materials if some materials
aren’t working. Before conducting the
tests, have students review the criteria
they will use to evaluate their model’s
performance.
326
cise is important for maintaining both muscular
strength and flexibility. Exercise makes individual muscle cells grow in size. As a result, the whole muscle
becomes thicker. The thicker a muscle is, the stronger
the muscle is. When you stretch and warm up thoroughly before exercising, your muscles become more
flexible. Stretching helps prepare your muscles for exercise or play.
Sometimes, despite taking proper precautions, muscles can become injured. A muscle strain, or pulled
muscle, can occur when muscles are overworked or
overstretched. Tendons can also be overstretched or
partially torn. After a long period of exercise, a skeletal
muscle can cramp. When a muscle cramps, the entire
muscle contracts strongly and stays contracted. If you
injure a muscle or tendon, it is important to follow
medical instructions and to rest the injured area so it
can heal.
Writing Mode Description
Scoring Rubric
4 Includes the function, structure, and
location of smooth and skeletal muscle;
description uses examples and many
supporting details
3 Includes all criteria, but does not include
examples or many details
2 Includes incomplete description
1 Includes inaccurate description
sx05_TE_(NC7-8)302-339.fm Page 327 Thursday, July 14, 2005 3:18 PM
A Look Beneath the Skin
A Look Beneath
the Skin
Problem
Prepare for Inquiry
What are some characteristics of skeletal
muscles? How do skeletal muscles work?
Skills Objectives
After this lab, students will be able to
• observe the structure and function of the
muscles in a chicken wing
• infer how the muscles work together to
move the wing
• classify muscles as smooth, cardiac, or
skeletal
Skills Focus
observing, inferring, classifying
Materials
• water
• paper towels
• scissors
• dissecting tray
• uncooked chicken
wing, treated with
bleach
Procedure
1. Put on goggles, an apron, and protective
gloves. CAUTION: Wear gloves whenever
you handle the chicken.
2. Your teacher will give you a chicken wing.
Rinse it well with water, dry it with paper
towels, and place it in a dissecting tray.
Prep Time 60 minutes
8. Remove the muscles and tendons. Find the
ligaments, which are the whitish ribbonshaped structures between bones. Add them
to your diagram.
9. Dispose of the chicken parts according to
your teacher’s instructions. Wash your hands.
Analyze and Conclude
3. Carefully extend the wing to find out how
many major parts it has. Draw a diagram of
the external structure. Label the upper arm,
elbow, lower arm, and hand (wing tip).
1. Observing How does a chicken wing move
at the elbow? How does the motion compare
to how your elbow moves? What type of
joint is involved?
4. Use scissors to remove the skin. Cut only
through the skin. CAUTION: Cut away from
your body and your classmates.
2. Inferring What happened when you pulled
on one of the arm muscles? What muscle
action does the pulling represent?
5. Examine the muscles, which are the bundles
of pink tissue around the bones. Find the
two groups of muscles in the upper arm.
Hold the arm down at the shoulder, and
alternately pull on each muscle group.
Observe what happens.
3. Classifying Categorize the muscles you
observed as smooth, cardiac, or skeletal.
6. Find the two groups of muscles in the lower
arm. Hold down the arm at the elbow, and
alternately pull on each muscle group. Then,
make a diagram of the wing’s muscles.
7. Find the tendons—shiny white tissue at the
ends of the muscles. Notice what parts the
tendons connect. Add the tendons to your
diagram.
4. Communicating Why is it valuable to record
your observations with accurate diagrams?
Write a paragraph in which you describe
what your diagrams show.
Analyze and Conclude
1. Up and down; similar; hinge
2. If students pulled on the biceps, they bent
the arm at the elbow. If they pulled on the
triceps, the arm straightened. The pulling
represents muscle contraction.
3. Skeletal
Class Time 30 minutes
Advance Planning
• Use only fresh chicken wings. Refrigerate
and use them within 24 hours of purchase.
• Soak wings in a solution of 2 parts
household bleach and 8 parts water for
2 hours before the lab. Rinse with water
to remove the bleach.
• Use disposable latex or vinyl gloves.
Safety
After
students
dispose of the wings, have them remove their
gloves and wash their hands thoroughly with
soap and water. Remind students to cut away
from themselves and others at all times.
Review the safety guidelines in Appendix A.
Teaching Resources
More to Explore
Use the procedures from this lab to examine an
uncooked chicken thigh and leg. Compare how
the chicken leg and a human leg move. Obtain
your teacher's permission before carrying out
your investigation.
Chapter 8 ◆ 327
Expected Outcome
Students will be able to observe skeletal
muscles working in pairs.
L2
4. Paragraphs should describe the structures
and locations of the muscles as shown in
students’ diagrams. Students might note that
diagrams serve as a record of what they
observed and allow comparison of structures
that cannot be seen simultaneously.
• Lab Worksheet: A Look Beneath the Skin
Guide Inquiry
Introduce the Procedure
Direct students’ attention to the photo
showing where to make the cut lines. Tell
them that the skin is relatively thin, and the
muscles lie directly beneath the skin.
Troubleshooting the Experiment
Remind students to work slowly so they do
not damage the wing.
Extend Inquiry
More to Explore Advise students to use
chicken leg quarters with the thighs and legs
attached, and to repeat all safety procedures.
327