Lesson 2 | The Muscular System
Name Date Class
LESSON 2
The Muscular System
Directions: Circle the term in parentheses that correctly completes each sentence.
1. Muscles do their work by (contracting/expanding).
2. Muscles that are attached to bones give us movement and (stability/energy).
3. The longest muscle in the body extends from the knee to the (shoulder/hip).
4. Shivering is a way in which the muscles maintain the body’s
(chemical balance/internal temperature).
5. The three types of muscles are skeletal, smooth, and (cardiac/abdominal).
6. Skeletal muscles are also called (voluntary/involuntary) muscles.
7. Smooth muscles are smoother and (longer/shorter) than skeletal muscles.
8. The discs at the ends of heart muscle cells coordinate the heart’s
(pumping action/cell replacement).
9. The energy that muscles need to function comes from (food/sunlight).
10. Without exercise, muscles get smaller and (flatter/weaker).
30 Structure and Movement
Name Date Class
LESSON 2
Word-Meaning Activity
Matching
Directions: On the line before each definition, write the letter of the term that matches it correctly.
1. We are strong tissues made of cells that contract
and relax. We give your body the ability to move.
2. We are also called skeletal muscles. We are
muscles that you can consciously control.
3. We are muscles that move even while you are
asleep.
4. We are muscles that attach to bone. We help you
kick a ball and raise your arm.
5. We are muscles that make up your blood vessels
and your stomach. We are at work even when
you are not aware of it.
6. We are muscles that make up your heart. We are
made of cells that work together to contract at
nearly the same time.
A. cardiac muscles
B. involuntary muscles
C. muscles
D. smooth muscles
E. skeletal muscles
F. voluntary muscles
Structure and Movement 33
Name Date Class
LESSON 2
The Muscular System
Key Concept How do the types of muscle differ?
Directions: Circle the term or phrase that correctly completes each sentence.
skeletal and cardiac.
1. The two kinds of involuntary muscles are smooth and skeletal.
smooth and cardiac.
only push on bones.
2. Skeletal muscles can only pull on bones.
push and pull on bones.
alone.
3. Skeletal muscles operate in pairs.
in triplets.
heart.
4. Cardiac muscles are located only in the blood vessels.
abdomen.
knobs.
5. Cardiac muscle cells have branches ending in points.
discs.
6. Compared with skeletal muscle cells, smooth muscle
cells are
shorter and smoother.
longer and smoother.
wider and smoother.
Structure and Movement 37
Name Date Class
LESSON 2
The Muscular System
When a person dies, the respiratory and
circulatory systems stop delivering oxygen
to the muscles. Muscles use oxygen to
produce ATP, an energy molecule that helps
them relax after contracting. Without ATP,
the muscles stiffen. About 10 to 12 hours
after death, the muscles and joints are
locked into place. This condition is called
rigor mortis.
Rigor Mortis
The term rigor mortis comes from the
Latin words rigor, meaning “stiff,” and
mort, meaning “death.” Rigor mortis
usually affects the facial muscles first,
sometimes within minutes after death.
It then moves to other parts of the upper
body and finally to the lower body. Several
factors affect rates of rigor mortis, including
temperature. Cold temperatures slow
rates of rigor mortis. In contrast, warm
temperatures increase rates of rigor mortis.
A person who exercises shortly before
death will have a warm body temperature,
increasing the rate of rigor mortis.
Fat distribution and age also affect how
quickly rigor mortis sets in.
Rigor mortis usually lasts about one to
two days. A body found outside during the
winter, however, might be locked in rigor
mortis for days. During this period, tissues
in the body begin to decay. This causes
the muscles to relax. The muscles generally
relax in the same order in which they
stiffened—that is, relaxation begins in the
face first and then moves to other parts of
the body.
Forensics
Rigor mortis can provide useful
information in forensic studies. Forensics
is the science of gathering and analyzing
evidence for legal purposes. This work
sometimes involves crime-scene
investigations. Rigor mortis can help
forensic scientists determine the time of
death. Because a body tends to stiffen in
the position it held at the moment of
death, rigor mortis can also help scientists
determine whether a body was moved.
Applying Critical-Thinking Skills
Directions: Answer each question or respond to each statement.
1. Evaluate The upper body of a corpse is stiff, but the lower body is relaxed. When
might death have occurred? Explain your answer.
2. Infer On Friday, police find the body of a person who they know died on Tuesday. The
body exhibits full rigor mortis. What can you infer about the conditions in which the
body was found?
Structure and Movement 39
Name Date Class
LESSON 2
The Muscular System
Multiple Choice
Directions: On the line before each question, write the letter of the correct answer.
1. Which is a function of the muscular system?
A. protects internal organs
B. produces red blood cells
C. creates immovable joints
2. Which system does the muscular system work with when it moves food
through the body?
A. skeletal system
B. immune system
C. digestive system
Matching
Directions: On the line before each definition, write the letter of the term that matches it correctly. Each term is
used only once.
Matching Set 1
3. muscles located in internal organs
4. muscles located only in the heart
5. muscles attached to bones
A. cardiac
B. skeletal
C. smooth
Matching Set 2
6. smooth muscles
7. skeletal muscles
8. the way muscles raise body temperature
9. attach muscles to bones
D. shivering
E. voluntary
F. tendons
G. involuntary
Structure and Movement 43
Name Date Class
LESSON 2
The Muscular System
Key Concept How do the types of muscle differ?
There are two main types of muscles—voluntary and involuntary.
Directions: On the lines, write a V next to each function that is controlled by voluntary muscles. Write an I next
to each function that is controlled by involuntary muscles.
1. smiling
2. digestion
3. walking
4. heartbeat
5. jumping
6. talking
Directions: Answer each question on the lines provided
7. What are voluntary muscles connected to?
8. For that reason, what are these muscles usually called?
9. These muscles are made of long, thin cells that give the muscles a striped appearance.
What are these stripes called?
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Content Practice A
Language Arts Support
Key Concept Builder
Enrichment
Lesson Quiz A
Key Concept Builder
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