Smooth, Skeletal, and Cardiac
Muscles
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
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Printed: September 18, 2014
AUTHORS
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Smooth, Skeletal, and Cardiac Muscles
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Smooth, Skeletal, and
Cardiac Muscles
• Identify the three types of human muscle tissue.
• Compare skeletal muscle to cardiac muscle and to smooth muscle.
What exactly are muscles?
Does the word "muscle" make you think of the biceps of a weightlifter, like the man in pictured above? Muscles
such as biceps that move the body are easy to feel and see, but they aren’t the only muscles in the human body. Many
muscles are deep within the body. They form the walls of internal organs such as the heart and stomach. You can
flex your biceps like a body builder, but you cannot control the muscles inside you. It’s a good thing that they work
on their own without any conscious effort on your part, because movement of these muscles is essential for survival.
What Are Muscles?
The muscular system consists of all the muscles of the body. Muscles are organs composed mainly of muscle cells,
which are also called muscle fibers. Each muscle fiber is a very long, thin cell that can do something no other cell
can do. It can contract, or shorten. Muscle contractions are responsible for virtually all the movements of the body,
both inside and out. There are three types of muscle tissues in the human body: cardiac, smooth, and skeletal muscle
tissues. They are shown in Figure 1.1 and described below.
You can also watch an overview of the three types at this link: http://www.youtube.com/watch?v=TermIXEkavY .
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MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/1727
FIGURE 1.1
Types of Muscle Tissue. Both skeletal and cardiac muscles appear striated, or striped, because their cells are
arranged in bundles. Smooth muscles are not striated because their cells are arranged in sheets instead of
bundles.
Smooth Muscle
Muscle tissue in the walls of internal organs such as the stomach and intestines is smooth muscle. When smooth
muscle contracts, it helps the organs carry out their functions. For example, when smooth muscle in the stomach
contracts, it squeezes the food inside the stomach, which helps break the food into smaller pieces. Contractions of
smooth muscle are involuntary. This means they are not under conscious control.
Skeletal Muscle
Muscle tissue that is attached to bone is skeletal muscle. Whether you are blinking your eyes or running a marathon,
you are using skeletal muscle. Contractions of skeletal muscle are voluntary, or under conscious control. When
skeletal muscle contracts, bones move. Skeletal muscle is the most common type of muscle in the human body.
Cardiac Muscle
Cardiac muscle is found only in the walls of the heart. When cardiac muscle contracts, the heart beats and pumps
blood. Cardiac muscle contains a great many mitochondria, which produce ATP for energy. This helps the heart
resist fatigue. Contractions of cardiac muscle are involuntary, like those of smooth muscle. Cardiac muscle, like
skeletal muscle, is arranged in bundles, so it appears striated, or striped.
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Chapter 1. Smooth, Skeletal, and Cardiac Muscles
Summary
• There are three types of human muscle tissue: smooth muscle (in internal organs), skeletal muscle, and cardiac
muscle (only in the heart).
Explore More I
Explore More II
• Muscles Game at http://www.bbc.co.uk/science/humanbody/body/index_interactivebody.shtml .
Review
1.
2.
3.
4.
5.
Compare and contrast the three types of muscle tissue.
What can muscle cells do that other cells cannot?
Why are skeletal and cardiac muscles striated?
Where is smooth muscle tissue found?
What is the function of skeletal muscle? Give an example.
References
1. Zachary Wilson. Types of muscle tissue. CC BY-NC 3.0
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