Chapter 8: Skeletal Muscle: Structure and Function

OBJECTIVES

By studying this chapter, you should be able to do the following:

1. Draw and label the microstructure of a skeletal muscle fiber.

2. Define satellite cells. What role do satellite cells play in muscle repair from injury?

3. List the chain of events that occur during muscular contraction.

4. Define both dynamic and static exercise. What types of muscle action occur during each form of exercise?

5. Describe the three factors that determine the amount of force produced during muscular contraction.

6. Compare and contrast the major biochemical and mechanical properties of the three primary types of muscle fibers found in human skeletal muscle.

7. Describe how skeletal muscle fiber types influence athletic performance.

8. Graph and describe the relationship between movement velocity and the amount of force exerted during muscular contraction.

OUTLINE

• Structure of Skeletal Muscle 167

• Neuromuscular Junction 170

• Muscular Contraction 171

  • Overview of the Sliding Filament/Swinging Lever-Arm Model 171

  • Energy for Contraction 173

  • Regulation of Excitation-Contraction Coupling 173

• Exercise and Muscle Fatigue 177

• Exercise-Associated Muscle Cramps 177

  • Exercise-Associated Muscle Cramps Are Not Caused by Dehydration or Electrolyte Imbalance 177

  • Exercise-Associated Muscle Cramps Are Likely Due to Changes in the Central Nervous System 178

  • Exercise-Associated Muscle Cramps: Conclusions 178

• Muscle Fiber Types 180

  • Overview of Biochemical and Contractile Characteristics of Skeletal Muscle 180

  • Functional Characteristics of Muscle Fiber Types 181

  • Fiber Types and Performance 183

• Muscle Actions 184

• Speed of Muscle Action and Relaxation 185

• Force Regulation in Muscle 185

• Force-Velocity/Power-Velocity Relationships 187

KEY TERMS

actin

concentric action

dynamic

eccentric action

endomysium

end-plate potential (EPP)

epimysium

extensors

fascicle

fast-twitch fibers

flexors

intermediate fibers

isometric action

lateral sac

motor neurons

motor unit

muscle action

myofibrils

myosin

neuromuscular junction (NMJ)

perimysium

postactivation potentiation (PAP)

sarcolemma

sarcomeres

sarcoplasmic reticulum

satellite cells

sliding filament model

slow-twitch fibers

summation

swinging lever-arm model

terminal cisternae

tetanus

transverse tubules

tropomyosin

troponin

twitch

type I fibers

type IIa fibers

type IIx fibers

INTRODUCTION

The human body contains more than 600 skeletal muscles, which constitute 40% to 50% of the total body weight (61). Skeletal muscle performs three important functions: (1) force generation for locomotion and breathing, (2) ...