Structure and Movement The Muscular System

Structure and Movement
The Muscular System
Key Concepts
What do you think? Read the two statements below and decide
whether you agree or disagree with them. Place an A in the Before column
if you agree with the statement or a D if you disagree. After you’ve read
this lesson, reread the statements to see if you have changed your mind.
Before
Statement
After
3. The same type of muscle that moves bones
• What does the muscular
system do?
• How do types of muscle
differ?
• How does the muscular
system interact with other
body systems?
also pumps blood through the heart.
4. Muscles cannot push bones.
3TUDY#OACH
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Functions of the Muscular System
A muscle is made of strong tissue that can contract in an orderly
way. Your muscular system is made of different types of
muscles and has several functions. Muscles help you move,
help protect your body, help keep your body stable, and help
maintain your body temperature.
All muscle tissues are made of cells that contract. When
the cells of a muscle contract, the muscle tissues become
shorter. The muscle tissues return to their original length
when the cells relax.
Use an Outline As you
read, make an outline to
summarize the information
in the lesson. Use the main
headings in the lesson as the
main headings in the outline.
Complete the outline with
the information under each
heading.
Movement
Many of your muscles help you move. Most of these
muscles attach to bones. These muscles make your skeleton
move. When muscles contract, they move bones. This
movement can be fast, such as when you run. The
movement can also be slow, such as when you stretch.
You have many muscles in your body that are not
attached to bones. Contractions in these muscles cause
blood and food to move through your body. Contractions
also make your heart beat and cause the hair on your arms
to stand on end when you get goose bumps.
1. Identify What is one
major function of the
muscular system?
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Structure and Movement
Key Concept Check
231
Stability
What happens when you start to lose your balance? Your
muscles pull in different directions to help you get your
balance back. Muscles that are attached to your bones
support your body and help you keep your balance.
Reading Check
2. Explain What is the
function of tendons?
Tendons attach muscles to bones. Look at the back of
your hand and move your fingers. Do you see the cordlike
structures moving under your skin? These are tendons.
Tendons work with muscles and keep your joints in place
when your body moves. Tendons also help hold your body
in a correct posture, or shape.
Protection
Muscles protect your body. They cover most of your
skeleton. Muscles also cover most of the organs inside your
body. Muscles are like a layer of padding. They surround
your abdomen, chest, and back, and protect your internal
organs.
Temperature Regulation
Skeletal
muscle
Cardiac
muscle
Types of Muscles
Your body has three different types of muscles—skeletal,
smooth, and cardiac. They are shown in the figures below.
Each type of muscle is specialized for a different function.
Skeletal
Smooth
Cardiac
Smooth
muscle
Visual Check
3. Locate Where is cardiac
tissue? (Circle the correct
answer.)
a. in the stomach
b. in the arm
c. in the heart
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Structure and Movement
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Make the following tri-fold
book to organize your notes
on the three types of
muscles.
Your muscular system helps your body keep your internal
temperature within a certain range. Have you ever felt cold
and then started shivering? Shivering is muscles rapidly
contracting. This changes chemical energy to thermal
energy. The released thermal energy helps maintain your
body’s temperature. This is important because a human’s
body temperature must stay around 37°C in order for the
body to function properly. Muscles also change chemical
energy to thermal energy during exercise. This is why you
feel warm after physical activity.
Skeletal Muscle
Muscle that attaches to bones is skeletal muscle. Skeletal
muscles are also called voluntary muscles. Voluntary muscles
are muscles that you can consciously control. For example, you can
control whether or not you lift your leg. The contractions of
skeletal muscles can be quick and powerful, such as when
you run. However, contracting these muscles for a long time
can tire them or make them cramp.
How Skeletal Muscles Work Skeletal muscles work by
pulling on bones. Muscles cannot push on bones. Instead,
muscles work in pairs and move the body. The figure below
shows how an arm’s biceps (BI seps) and triceps (TRI seps)
muscles work as a pair. The arm on the left shows that as the
biceps muscle contracts, the muscle shortens and pulls the
lower arm up. The arm on the right shows that when biceps
muscle relaxes, the triceps muscle contracts and the lower
arm is pulled down.
Reading Check
4. Describe Why must
skeletal muscles work in
pairs?
Biceps
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Triceps
Visual Check
5. Explain What happens
Changes in Skeletal Muscles Your skeletal muscles can
change throughout your lifetime. If you exercise, your
muscle cells get larger. Then, your entire muscle becomes
larger and stronger.
when the bicep muscle
contracts?
Cardiac Muscle
Your heart is made of cardiac (KAR dee ak) muscles, which
are found only in the heart. A cardiac muscle is a type of
involuntary muscle, which is muscle you cannot consciously control.
As cardiac muscles contract and relax, they pump blood
through your heart and through vessels throughout your
body. Cardiac muscle cells have branches with discs at their
ends. These discs send signals to other cardiac muscle cells.
The signals cause all the cardiac muscle cells to contract at
almost the same time.
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Structure and Movement
233
Smooth Muscle
Key Concept Check
6. Name the three types of
muscles.
7. Evaluate Why is it
important to keep your
muscles healthy?
Smooth muscles line your blood vessels and many of
your organs. Smooth muscles are involuntary muscles named for
their smooth appearance. Contraction of smooth muscles helps
move material through your body, such as food in your
stomach. Smooth muscles also control the movement of
blood through your vessels.
Healthy Muscles
Recall that a good diet helps keep your bones healthy.
Your muscles need a healthful diet, too. All of your muscles
use energy when they contract. This energy comes from the
food you eat. Eating a diet full of nutrients such as protein,
fiber, and potassium can help keep muscles strong.
Exercise also helps keep your muscles healthy. Muscle
cells get smaller and weaker without exercise. Weak muscles
can increase the risk of heart disease. Bone injuries can
happen more often when muscles are not healthy. Joints
might not be as stable when muscles are small and weak.
The Muscular System
and Homeostasis
convert
(verb) to change something
into a different form
Key Concept Check
When you exercise, your cells use more oxygen and release
more waste, such as carbon dioxide. The cardiac muscles in
your heart help maintain homeostasis by contracting more
often. When your heart contracts faster, it pumps more blood
and more oxygen is carried to the cells.
8. Describe How do
muscles help maintain
homeostasis in the body?
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Structure and Movement
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ACADEMIC VOCABULARY
There are many ways the muscular system helps your
body maintain homeostasis. The room where you are sitting
now is probably between 21°C and 27°C. You know that
your body temperature must stay around 37°C to function
well. When your muscles contract, they convert chemical
energy to thermal energy. The thermal energy keeps your
body warm.
Mini Glossary
cardiac (KAR dee ak) muscle: muscle that is only in the
skeletal muscle: the type of muscle that attaches to bones
heart
smooth muscle: involuntary muscle named for its smooth
involuntary muscle: muscle that you cannot consciously
appearance
control
voluntary muscle: muscle that you can consciously control
muscle: strong tissue that can contract in an orderly way
1. Review the terms and their definitions in the Mini Glossary. Write a sentence that
explains the difference between voluntary muscle and involuntary muscle.
2. Complete the table about skeletal, smooth, and cardiac muscles.
Muscle Type
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Skeletal
Description
Cells look like they have
stripes.
Smooth
Cardiac
Function
Location in the Body
help the body move
help move things through
the body
smaller than skeletal
muscles
organs
heart
3. Describe how muscles protect your body.
What do you think
Reread the statements at the beginning of the
lesson. Fill in the After column with an A if you
agree with the statement or a D if you disagree.
Did you change your mind?
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END OF
LESSON
Structure and Movement
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