The Muscular System

28 Pages·2014·8.335 MB·English

by  Susan H. Gray

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THE
M
uscular
systeM
by SuSan H. Gray
Published by The Child’s World® about the author
1980 Lookout Drive • Mankato, MN 56003-1705
Susan H. Gray has a
800-599-READ • www.childsworld.com
bachelor’s and a master’s
Acknowledgments
The Child’s World®: Mary Berendes, Publishing Director degree in zoology. In her
Red Line Editorial: Editorial direction
The Design Lab: Design 25 years as an author, she
Amnet: Production
has written many medical
Content Consultant: R. John Solaro, Ph.D., Distinguished
articles, grant proposals, and
University Professor and Head, Department of Physiology and
Biophysics, University of Illinois Chicago
children’s books. Ms. Gray
Photographs ©: Shutterstock Images, cover (background), and her husband, Michael,
1 (background), 14; Sanjay Deva/Shutterstock Images, cover
(foreground), 1 (foreground); Nate Allred/Shutterstock Images, live in Cabot, Arkansas.
4; BlueRingMedia/Shutterstock Images, 7; Jupiterimages/
Thinkstock, 8; iStockphoto/Thinkstock, 11, 12; Monkey Business
Images/Thinkstock, 17; Wong Sze Yuen/Shutterstock Images,
19; Wavebreak Media/Shutterstock Images, 20
Copyright © 2015 by The Child’s World®
All rights reserved. No part of this book may be reproduced or
utilized in any form or by any means without written permission
from the publisher.
ISBN 9781626873360
LCCN 2014930673
Printed in the United States of America
Mankato, MN
July, 2014
PA02221
TAblE of
ConTEnTS
Chapter 1
Jeremy Proves Himself . . . . . . . . . . . . . . . . . . . . 4
Chapter 2
What Is the Muscular System? . . . . . . . . . . . . 6
Chapter 3
What Are the Parts of a Muscle? . . . . . . . . . . . 10
Chapter 4
How Can Muscles Make You Move? . . . . . . . . . 14
Chapter 5
What Makes a Muscle Contract? . . . . . . . . . . . 16
Chapter 6
Healthy and Unhealthy Muscles . . . . . . . . . . . 18
Glossary . . . . . . . . . .22
Learn More . . . . . . .23
Index . . . . . . . . . . . .24
Chapter 1
Jeremy Proves
Himself
“
H
ey, Jeremy! Show us your muscles!” Jeremy’s
big brothers were trying to prove how strong
they were . one brother did six push-ups . The other
brother grabbed a tree limb and did a pull-up .
Your muscles help you move and play. They even help
you pull yourself up to hang from a tree branch!
4
DiD You Know?
Jeremy shouted back,
Some people believe
“Watch this!” He ran over
exercise turns fat cells
to a concrete block and
into muscle cells.
dug his fingertips under
This is not true. With
it . Jeremy tried to stand
exercise, you can
up . His body grew tense . build up your muscle
Electrical signals shot cells while fat cells
shrink in size.
through his nerves .
A special chemical flowed
out of the nerves going
to his muscle cells . The chemical made thousands of
Jeremy’s muscle cells try to shorten .
Jeremy slowly rose with the block in his hands .
More muscle cells shortened . Jeremy stood up straight
and lifted the block to his chest . His arm muscles were
bulging . And his legs were trembling . Jeremy dropped
the block on the ground .
Jeremy’s brothers were impressed . Jeremy’s legs and
arms were hurting . He had no energy left . Jeremy had
certainly shown his muscles .
5
Chapter 2
What Is the
Muscular System?
T here are three kinds of muscle tissue in the body .
Smooth muscle lies inside the walls of blood
vessels and some of the organs . The heart is made
of cardiac muscle . Skeletal muscles are the ones we
usually think of as muscles . They are in the arms,
legs, back, neck, face, chest, and abdomen . These
muscles help us move . They also help us sit and stand
without falling over .
Sometimes skeletal muscles go by other names .
They are often called striated muscles . Striations
are little stripes . Under a microscope, skeletal
muscles appear to have many striations . Skeletal
muscles are also called voluntary muscles . If
something is voluntary, that means we have control .
We can control the movements of voluntary muscles .
Involuntary muscles work without us telling them to .
6
The heart is a special kind of involuntary muscle .
other involuntary muscles are found in the lungs
and blood vessels .
The cardiac muscle is only found in the heart.
7
8