Types and Characteristics of Muscle Tissue

Objectives

When you have completed this section, you should be able to

• describe the physiological properties that all muscle types have in common;
• list the defining characteristics of skeletal muscle; and
• state the functions of the series-elastic components of a muscle.

Key Point Review

1. How is skeletal muscle different from any other type of muscle?

2. Define excitability, contractility, extensibility, and elasticity.

3. Why would the skeletal muscles perform poorly if not for their series-elastic components?

Microscopic Anatomy of Skeletal Muscle

Objectives

When you have completed this section, you should be able to

• describe the structural components of a muscle fiber;
• relate the striations of a muscle fiber to the overlapping arrangement of its protein myofilaments; and
• name the proteins that compose the myofilaments and state the function of each.

Key Point Review

4. What special terms are given to the plasma membrane, cytoplasm, and smooth ER in muscle cells?

5. What is the difference between a myofilament and a myofibril?

6. List four proteins that constitute the myofilaments and describe their physical arrangement.

7. Sketch the overlapping pattern of myofilaments to explain how they account for the A bands, I bands, H bands, and Z discs.

Muscle Innervation and Membrane Potentials

Objectives

When you have completed this section, you should be able to

• identify the structures of a neuromuscular junction and explain their functions;
• explain what a motor unit is and how motor units relate to muscle contraction; and
• explain how a cell develops an electrical charge across its plasma membrane, and why this charge is essential to the function of nerve and muscle cells.

Key Point Review

8. Distinguish between acetylcholine, an acetylcholine receptor, and acetylcholinesterase. State where each is found and describe the function it serves.

9. Distinguish between a resting membrane potential and an action potential.

10. What two forces tend to drive potassium ions in opposite directions through a plasma membrane? Why is there a negative charge across the membrane when these forces are in equilibrium?

Contraction and Relaxation of Skeletal Muscle Fibers

Objectives

When you have completed this section, you should be able to

• explain how a nerve fiber stimulates a skeletal muscle fiber;
• explain how stimulation of a muscle fiber activates its contractile mechanism;
• explain the sliding filament mechanism of skeletal muscle contraction;
• explain how a muscle fiber relaxes; and
• explain why the force of a muscular contraction depends on the length of the muscle prior to stimulation.

Think About It

An impulse begins at the middle of a 100-µm-long muscle fiber and travels 5 m/sec. How long would it take to reach the ends of the muscle fiber?

Key Point Review

11. What change does ACh cause in an ACh receptor? How does this electrically affect the muscle fiber?

12. How does an end-plate potential lead to an increase in Ca²⁺ concentration in the sarcoplasm?

13. How do troponin and tropomyosin regulate the interaction between myosin and actin?

14. Describe the roles of ATP in the power and recovery strokes of a myosin head.

15. What steps are necessary for a contracted muscle fiber to return to its resting length?

Behavior of Whole Muscles

Objectives

When you have completed this section, you should be able to

• describe a muscle twitch and explain how it relates to threshold and latency;
• reconcile the fact that muscles contract with variable strength with the fact that individual muscle fibers contract in an all-or-none manner;
• explain how temporal summation produces tetanus and why tetanus is necessary to muscle function;
• distinguish between isometric, isotonic, concentric, and eccentric contractions; and
• describe treppe and explain how it relates to muscle warm-up.

Key Point Review

16. Explain why the all-or-none behavior of muscle fibers does not prevent a whole muscle from exhibiting graded contractions.

17. Explain how warm-up is related to treppe and why it improves athletic performance.

18. Explain the role of tetanus in normal muscle action.

19. Describe an everyday activity in which your muscles would switch from isometric to isotonic contraction.

20. Describe an activity that would involve concentric contraction and one that would involve eccentric contraction. Use examples other than lifting a load or putting it down.

Muscle Metabolism

Objectives

When you have completed this section, you should be able to

• explain how skeletal muscle meets its ATP demands during rest and exercise;
• explain the physiological basis of muscle fatigue and soreness;
• define oxygen debt and list the purposes for which extra oxygen is needed after exercise;
• distinguish between slow- and fast-twitch muscle fibers and explain the functional roles of these two types;
• discuss the factors that affect muscular strength; and
• discuss the effects of resistance and endurance exercises on muscle.

Think About It

Suppose you repeatedly stimulated the sciatic nerve in a frog nerve-muscle preparation until the muscle stopped contracting. What simple test could you do to determine whether this was due to junctional fatigue or to one of the other fatigue mechanisms?

Think About It

Is muscle growth mainly the result of hypertrophy or hyperplasia?

Key Point Review

21. From which two molecules can ADP borrow a phosphate group to become ATP? What is the enzyme that catalyzes each transfer?

22. In a long period of intense exercise, why does muscle generate ATP anaerobically at first, and then switch to aerobic respiration?

23. List four causes of muscle fatigue.

24. List three causes of oxygen debt.

25. What properties of fast- and slow-twitch fibers adapt them for different physiological purposes?

Smooth Muscle

Objectives

When you have completed this section, you should be able to

• describe the ways in which smooth muscle differs structurally and physiologically from skeletal muscle; and
• relate the unique physiological properties of smooth muscle to its locations and functions.

Think About It

How is smooth muscle contraction affected by the drugs called calcium channel blockers? (See p.114)

Key Point Review

26. How do single-unit and multiunit smooth muscle differ in innervation and contractile behavior?

27. How does smooth muscle differ from skeletal muscle with respect to its source of calcium and its calcium receptor?

28. Explain why the same neurotransmitter can cause some smooth muscle cells to contract and others to relax.

29. Explain why the stress-relaxation response is an important factor in smooth muscle function.

Copyright ©1998 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use and Privacy Policy.
McGraw-Hill Higher Education is one of the many fine businesses of The McGraw-Hill Companies.
For further information about this site contact mhhe_webmaster@mcgraw-hill.com.