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CHAPTER

MUSCULAR SYSTEM

OVERVIEW This chapter presents the muscular system. In conjunction with the skeletal system, the muscular system serves to move the body. The chapter introduces the three types of muscle and their structures (Learning Outcomes 1,2,3, 12) and describes the contraction mechanisms of various muscle types (Learning Outcomes 5, 13, 14). The major focus of this chapter is on the skeletal muscle. The chapter describes the neural control of skeletal muscle contraction, identifies the major events of contraction, identifies the energy sources for contractions, and describes what happens when a muscle overworks (Learning Outcomes 4-8). You will be able to distinguish between a twitch and a sustained contraction, describe how muscles produce movement and sustain posture, and distinguish between fast- and slow-twitch muscles (Learning Outcomes 9-11). You will be able to explain how the attachments, locations, and interactions of skeletal muscles produce movement and will be able to identify and locate the skeletal muscles of each body region and describe their actions (Learning Outcomes 15, 16). Finally, you will be able to describe aging-related changes in the muscular system and discuss how exercise can help maintain a healthy muscular system as the body ages (Learning Outcomes 17, 18). The skeletal system can be thought of as the passive partner in producing movement; the muscular system can be thought of as the active partner. This chapter explains how muscles interact with bones to maintain posture and produce movement. In addition, the chapter tells the characteristics and functions of skeletal, smooth, and cardiac muscles. This knowledge is a foundation for the study of other organ systems, such as the digestive system, the respiratory system, and the cardiovascular system.

LEARNING OUTCOMES After you have studied this chapter you should be able to: 9.1 Introduction (p. 285) I. List various outcomes of muscle actions. 9.2 Structure of a Skeletal Muscle (p. 285) 2. Describe the structure of a skeletal muscle. 3. Name the major parts of a skeletal muscle fiber and describe the functions of each. 9.3 Skeletal Muscle Contraction (p.,289) 4. Describe the neural control of skeletal muscle contraction. 5. Identify the major events of skeletal muscle fiber contraction. 6. List the energy sources for skeletal muscle fiber contraction. 7. Describe oxygen debt. 8. Describe how a muscle may become fatigued. 9.4 Muscular Responses (p. 296) 9. Distinguish between a twitch and a sustained contraction. 10. Explain how various types of muscular contractions produce body movements and help maintain posture. II. Distinguish between fast- and slow-twitch muscle fibers. 9.5 Smooth Muscle (p. 300) 12. Distinguish between the structures and functions of multiunit smooth muscle and visceral smooth muscle. 13. Compare the contraction mechanisms of skeletal and smooth muscle fibers. 9.6 Cardiac Muscle (p. 30 I) 14. Compare the contraction mechanisms of skeletal and cardiac muscle fibers. 9.7 Skeletal Muscle Actions (p. 301) 15. Explain how the attachments, locations, and interactions of skeletal muscles make possible certain movements. 9.8 Major Skeletal Muscles (p. 305) 16. Identify and locate the skeletal muscles of each body region and describe the action(s) of each muscle. 9.9 Life-Span Chan"ges (p. 334) 17. Describe aging-related changes in the muscular system. 18.

Discuss how exercise can help maintain a healthy muscular system as the body ages.

FOCUS QUESTION How do muscle cells utilize energy and interact with bones to accomplish such diverse movements as playing a piano and playing a basketball game?

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MASTERY TEST Now take the mastery test. Do not guess. Some questions may have more than one correct answer. As soon as you complete the test, correct it. Note your successes and failures so that you can read the chapter to meet your learning needs. I.

The kind of energy used by muscles is a. electrical. b. thermal.

c.

chemical.

2.

The kind of muscle under conscious control is _________ muscle.

3.

The functions of muscles are to a. propel body fluids.

c.

provide muscle tone.

b.

d.

all of the above

4.

5.

distribute heat.

A skeletal muscle is separated from adjacent muscles and kept in place by layers of dense connective tissue called a.

fascia.

c.

perimysium.

b.

aponeuroses.

d.

sarcolemma.

c.

aponeuroses.

d.

elastin.

Connective tissue that attaches muscle to the periosteum is called a.

ligaments.

6.

b. tendons. Bundles of muscle fibers are called _ _ _ _ _ _ _.

7.

The layer of connective tissue that closely surrounds a skeletal muscle is the . _ ....~_ _ _ _ _ _.

8.

9.

The connective tissue that penetrates and divides the individual muscles into compartments is the a.

deep fascia.

c.

epimysium.

b.

superficial fascia.

d.

perimysium.

A surgical procedure to relieve pressure within a muscle compartment is a _ _ _ _ _ __

10.

The characteristic striated appearance of skeletal muscle is due to the arrangement of alternating protein filaments composed and

11.

The units that form the repeating pattern along each muscle fiber are called

12.

a.

transverse tubules.

c.

actin filaments.

b.

sarcomeres.

d.

myosin t1Iaments.

The muscle protein found in A bands is (actin/myosin).

13.

Membranous channels formed by invaginations into the sarcolemma are known as ~......._ _ _ _~ ____~ ...._

14.

Tn addition to actin and myosin. two other proteins associated with actin tilaments are _ _ _ _ _ _ _ _ and

15.

When muscle fibers are overstretched, the injury sustained is a _ _ _~ __________

16.

17.

18. 19.

20.

The union between a nerve fiber and a muscle tiber is the a.

motor neuron.

c.

neuromuscular junction.

b.

motor end plate.

d.

neurotransmitter.

The axon of a motor nerve (does/does not) connect physically with the muscle fiber it stimulates. Contraction of skeletal muscle is made possible by ... _ _ _ _ in the synaptic cleft. The substance used by motor neurons to transmit stimuli to skeletal muscle is a.

norepinephrine.

c.

acetylcholine.

b.

dopamine.

d.

serotonin.

When the filaments of actin and myosin slide past each other within the myofibril. the result is a.

shortening of the muscle fiber.

b.

membrane polarization.

c.

release of acetylcholine.

21.

What ion is necessary in relatively high concentrations to allow the formation of cross-bridges between actin and myosin?

22.

When a muscle fiber is at rest. the protein myosin.

23.

Contraction of skeletal muscle after death is _ _ _ _ _.......... _.

prevents the formation of cross-bridges between actin and

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24. 25.

The energy used in muscle contraction is supplied by the decomposition of~~~~~~_~~~~~_ _ The substance that halts stimulation of muscle tissue is a. acetylcholine.

c.

acetylcholinesterase.

b. calcium.

26.

d. sodium. A disease caused by a decreased amount of acetylcholine is _ _ _ _ _ _ _ _ _ _ _ __

27.

The primary source of energy to reconstruct ATP from ADP and phosphate is a substa,nce called _ _ _ _ _ __

28.

The substance stored in large quantities in muscle that can store oxygen is _ _ _ _~~_ _ _ __

29.

A person feels out of breath after vigorous exercise because of oxygen debt. Which of the following statements helps explain this phenomenon? a.

Anaerobic respiration increases during strenuous activity.

c.

b. Lactic acid is metabolized more efficiently when the body is at rest.

d.

Conversion of lactic acid to glycogen occurs in the liver and requires energy.

30.

Priority in energy use is given to A TP synthesis. After prolonged muscle use, muscle fatigue occurs due to an accumulation of _____~_ _ _ _ _ _ __

31.

Muscle tissue is a major source of a.

glycogen.

b. glucose.

c.

water.

d.

heat.

32.

The minimal strength stimulus needed to elicit contraction of a single muscle fiber is called a ...

33.

A record ofa muscle's response to stimulation is called a ~_ _ _ _ _ _.

34.

The period of time following a muscle response to a stimulus when it will not respond to a second stimulus is called the a.

latent period.

c.

refractory period.

c.

the ability of a muscle to maintain contraction against an outside force.

b. contraction. 35.

Muscle tone refers to a.

a state of sustained, partial contraction of muscles that is necessary to maintain posture.

d. the condition athletes attain after intensive training.

b. a feeling of well-being following exercise. 36.

The force generated by muscle contraction in response to different levels of stimulation is determined by the a.

level of stimulation delivered to individual muscle fibers.

c.

number of motor units stimulated.

d. diameter of the muscle fibers.

b. number of fibers that respond in each motor

unit.

37. 38.

39.

A contraction in which muscle shortens is an _ _~~__

When exercise activates primarily the slow, red fibers, the result is a.

increased muscle strength.

b. increased muscle size. 40. 41.

contraction.

A contraction in which tension within the muscle increases without a change in muscle length is an contraction. c.

increased resistance to fatigue.

d.

increased anaerobic tolerance.

c.

many muscle fibers being present for each neuron in a motor unit.

d.

the number of branches in the neuron, many branches being associated with diffuse stimulation.

The muscles that movc the eye are (fast/slow) twitch fibers. The precision of movement produced by a muscle is due to a.

the size of the muscle fiber, small fibers being more precise.

b. the small muscle fiber-to-neuron ratio within a motor unit. 42.

Smooth muscle contracts (more slowly/more rapidly) than skeletal muscle following stimulation.

43. 44.

Two types of smooth muscle are ~~~~~~_muscle and _ _ _ _ _ _ _ muscle. The protein that binds to calcium in smooth muscle is _ _ _ _ _ _ _ __

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45.

Peristalsis is due to which of the following characteristics of smooth muscle? a.

c.

rhythmicity

d.

sympathetic innervation

c.

acetylcholine.

d.

serotonin.

the presence of intercalated disks between muscle cells.

c.

a cell membrane more permeable to sodium ions.

b. a well-developed sarcoplasmic reticulum.

d.

the presence of increased amounts of nonionized calcium.

b. 46.

the capacity of smooth muscle fibers to excite each other

automaticity

The neurotransmitter(s) in smooth muscle islare a.

norepinephrine.

b. dopamine. 47.

The self-exciting property of cardiac muscle is probably due to a.

48.

49.

In the following statements, does statement a explain statement b? a.

Cardiac muscle remains refractory until a contraction is completed.

b.

Sustained tetanic contraction is not possible in heart muscle.

Drugs that stop spasms in cardiac muscle by interfering with the movement of calcium ions across the cardiac muscle cell membranes are called ~_______~_~_ _ _ _ _ _~ _ _ __

50.

In producing movement of body parts, muscles and bones interact in mechanical devices known as _

51.

The attachment of a muscle to a relatively fixed part is called the ~..... movable part is called the ~___.............___.

52.

Smooth body movements depend on . .

53.

The muscle that compresses the cheeks inward when it contracts is the a.

.~_ _ _ __

; the attachment to a relatively

giving way to prime movers.

orbicularis oris.

b. epicranius.

c.

platysma.

d.

buccinator.

54.

Excessive use ofjaw muscles to clench the jaw may lead to _ _ _ _ _ _ _ _.........._ _ _ _ _ syndrome.

55.

The muscle that moves the head so that the face turns to the oppositc side when one side contracts is the a.

sternocleidomastoid.

c.

semispinalis capitis.

b.

splenius capitis.

d.

longissimus capitis.

56.

The large triangular muscle that extends horizontally from the base of the skull and the cervical and thoracic vertebrae to the shoulder is the muscle.

57.

The muscle that abducts the upper arm and can both flex and extend the humerus is the a.

biceps brachii.

b. deltoid. 58.

c.

infraspinatus.

d.

triceps brachii.

The muscle that extends the arm at the elbow is the a.

biceps brachii.

b. brachialis.

c.

supinator.

d.

triceps brachii.

59.

The band of tough connective tissue that extends from the xiphoid process to the symphysis pubis and serves as an attachment for muscles of the abdominal wall is the _ _ _ _ _ _ _ _ _ __

60.

The heaviest muscle in the body, which serves to straighten the leg at the hip during walking, is the a.

61.

psoas major.

c.

adductor longus.

b. gluteus maximus.

d.

gracilis.

The tendon that connects the gastrocnemius muscle with the calcaneus is the _ _ _ _ _ _ _ tendon, or the _ _ _ _ _ _ _ tendon.

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STUDY ACTIVITIES Definition of Word Parts (p. 284) Define the following word parts used in this chapter. calat­ erg­ fasc­ -gram hyperinter­ IS0­

laten­ myo­ reticul­ sarco­ syn­ tetan­ -tonic -troph voluntar­

9.1 Introduction (p. 285) A

What are muscles and what do they do?

B.

What are the three types of muscle?

c.

The muscle type subject to conscious control is _ _ _ _ _ _ _ muscle.

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9.2 Structure of a Skeletal Muscle (p. 285) A.

List the kinds of tissue present in skeletal muscle.

B.

A skeletal muscle is held in position by layers of fibrous connective tissue called ~~~~.~~_. This tissue . When this tissue extends beyond the extends beyond the end of a skeletal muscle to form a cordlike muscle to form a sheetlike structure, it is called a(n) ~~~ _~~~_

C.

What is compartment syndrome?

D.

Label these parts in the following drawings of skeletal muscle: bone, tendon, tascia, epimysium, perimysium, fascicle, endomysium, muscle fiber, sarcolemma, sarcoplasmic reticulum. filaments, nucleus, myofibrils, blood vessels, axon of motor neuron.

Muscle

Fascicles

Muscle fibers (cells)

__ c Myofibrils

Thick and thin filaments

~~~-e

n

E.

Where are deep, subcutaneous, and subserous fascia located?

F.

Answer the following concerning skeletal muscle fibers.

o

1. Describe a muscle fiber. 2. Threadlike parallel structures abundantly present in sarcoplasm are ~~~~~~_. 3. The protein filaments found in the threadlike structures are ~~~~~~_ and ~~~~~~_. Describe their structure. 4. Describe a sarcomere. Be sure to include I bands, A bands, Z lines, H zones, and M lines. 5. List the proteins found in a sarcomere.

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6.

The network of membranous channels in the cytoplasm of muscle fibers is the ____

7.

To what structure in other cells is the structure above analogous?

__ _

G.

Describe the injuries found in a muscle strain.

H.

What is post-polio syndrome?

1.

What is the sliding filament theory and what does it attempt to explain?

J.

Label these structures in the accompanying illustration of a single fiber motor unit: mitochondria, synaptic cleft, synaptic vcsicles, folded sarcolemma, muscle fiber nucleus, myofibril of muscle fiber, motor end plate, axon branches, motor neuron axon.

7

I 6

K.

4

8~

9 10

How is a muscle stimulated to contract?

9.3 Skeletal Muscle Contraction (p. 289) A.

Describe the roles of actin, myosin, tropomyosin, and troponin in muscle contraction.

B.

What is the role of dystrophin in skeletal muscle function?

C.

Answer the following concerning stimulus for contraction. I.

Describe the interaction of acetylcholine and calcium ions in stimulating muscle contraction.

2.

The action of acetylcholine is halted by the enzyme ................~_____.

3.

What is the action of botulinum toxin?

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4. D.

Answer these questions concerning energy sources for contraction. I. How does ATP supply energy for muscle contraction?

2.

E.

F.

What is the result of ingesting this toxin?

How does creatine phosphate supply energy for muscle contraction?

Answer these questions concerning oxygen supply and cellular respiration. 1. What substance in muscle seems able to store oxygen temporarily?

2.

How is oxygen usually brought to muscle cells?

3.

Why is oxygen necessary for muscle contraction?

4.

How does muscle continue to contract in the absence of oxygen?

5.

What is meant by oxygen debt? How is it paid off?

Answer the following concerning muscle fatigue. I.

What is meant by muscle fatigue? What causes it?

2.

About 25% ofthe energy released by cellular respiration is available for metabolic processes. About 75% is lost as

9.4 Muscular Responses (p. 296) A.

Answer the following concerning muscular responses. I. Define threshold stimulus. 2.

Define all-or-none response.

3.

How is all-or-none response related to the strength of a muscle contraction?

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B.

The accompanying illustration shows a myogram of a type of muscle contraction known as a twitch. Label the following: latent period, period of contraction, period of relaxation. Explain the significance of each of these events.

2

stimulation

C.

3

Time

Describe these kinds of muscle contractions. sustained contraction

tetanic contraction

muscle tone

isometric contraction

isotonic contraction

D.

How does the number of fibers in a motor unit affect its function?

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E.

Compare the effects of exercise such as swimming and running with weightlifting. Be sure to note the kinds of muscle fibers involved.

F.

Complete the following chart.

Changes in Muscle Size Conditions Leading to Change

Change

Observable Change in Muscle

Hypertrophy Atrophy

9.5 Smooth :\1uscle (p. 300) A.

B.

Answer the following questions concerning smooth muscle. I.

The contractile mechanisms of smooth muscle are (the same/different) compared to skeletal muscle.

2.

List the structural differences between smooth muscle cells and skeletal muscle cells.

What are the types of smooth muscles and where is each found?

9.6 Cardiac Muscle (p. 301)

Fill in the following chart, which compares skeletal and cardiac muscle.

Types of Muscle Tissue Skeletal

Cardiac

Major location Major function Cellular characteristics striations

nucleus

special features

Mode of control Contraction characteristics

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9.7 Skeletal Muscle Actions (p. 301) A.

Answer the following questions concerning levers. 1.

What are the parts of a lever?

2.

Identify the first- , second- , and third-class levers. Resistance

Force

Force

I Fulcrum (a) Resistance

Resistance

Fulcrum Fulcrum

Force

Force

(b)

Fulcrum

(e)

B.

A skeletal muscle has at least two places of attachment to bone. For instance, the gluteus maximus, which extends the leg at the hip, is attached to the posterior surface of the ilium, the sacrum, and the coccyx at one end and to the posterior surface of the femur and the iliotibial tract at the other. One place of attachment is the origin and the other is the insertion. Explain the difference between the two.

C.

Match the terms in the first column with the statements in the second column that best describe the role of muscle groups in producing smooth muscle movement. a. muscle that returns a part to its original 1. prime mover position 2.

synergist

3.

antagonist

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b.

muscle that makes the action of the prime mover more effective

c.

muscle that has the major responsibility for producing a movement

9.8 Major Skeletal Muscles (p. 305) A.

List and locate the muscles of facial expression.

B.

Answer the following about the muscles of mastication. I.

List and locate the muscles of mastication.

2.

Describe TMJ syndrome.

C.

List and locate the muscles that move the head.

D.

List and locate the muscles that move the upper arm.

E.

List and locate the muscles that move the foreaml.

f.

List and locate the muscles that move the wrist, hand, apd fingers.

G.

List and locate the muscles of the abdominal wall.

H.

List and locate the muscles of the pelvic outlet.

I.

List and locate the muscles that move the thigh.

J.

List and locate the muscles that move the lower leg.

K.

List and locate the muscles that move the ankle, foot, and toes.

9.9 Life-Span Changes (p. 334)

Describe the effects of aging on the muscular system.

Clinical Focus Question Your sister, age 28, is very excited about the opening of a gym in her neighborhood. Many of her friends have joined and she is planning to get in shape. She had her second child three months ago and has been experiencing difficulty losing weight. Your sister is known in the family as a couch potato. What advice will you give her about her plans? Explain your rationale.

When you have completed the study activities to your satisfaction, retake the mastery test and compare your performance with your initial attempt. If there are still areas you do not understand. repeat the appropriate study activities.

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