1. Structure of Muscle Tissue and Muscle Contraction Chapter 2

2. Learning Objectives Be able to describe differences among smooth, skeletal, and cardiac muscle. Understand the basic structure of skeletal muscle. Know the characteristics that differentiate fast- twitch from slow-twitch muscle fibers. Be familiar with the sliding filament model of muscle contraction.

3. Your Perspective What happens when you swing a baseball bat or dunk a basketball, do a sit up, or jog a mile?  Have you ever thought about the series of events that your muscles undergo in order to complete these movements? How do you think understanding the processes of muscle contraction will help you later as a physical educator, trainer, or coach?

4. Three Types of Human Muscle Tissue Smooth, nonstriated muscle Skeletal striated muscle Cardiac striated muscle

5. Structure of Smooth Muscle Long, spindle-shaped fibers An external shape that may change to conform to the surrounding elements One nucleus per fiber

6. Structure of Skeletal Muscle Long, cylindrical fibers that make up a large cell Up to several hundred nuclei in each fiber or cell Structural independence from each neighboring fiber or cell Cross-striations of alternating light and dark bands.

7. Structure of Cardiac Muscle A network (syncytium) of interwoven striated muscle fibers Discrete fibers that can contract individually A network of fibers that responds to innervations with a wavelike contraction that passes through the entire muscle

8. Skeletal Muscles Showing Cross-Striations

9. Gross and Microscopic Structure of Skeletal Muscles Gross structure:  Fascia  Epimysium  Fasciculus  Perimysium Microscopic structure:  Endomysium  Vary in diameter from approximately 10 to 100 microns  Vary in length from 1 mm to the length of the whole muscle

10. Muscle Fibers and Connective Tissue Sheaths From J.W. Hole, Jr., Human Anatomy and Physiology, 5th Edition. Copyright © 1990 Wm. C. Brown Communications, Inc., Dubuque, Iowa. Reprinted with permission of The McGraw-Hill Companies.

11. Structure of the Muscle Fiber Sarcolemma:  Cell membrane of the muscle fiber Sarcoplasm:  Fluid part of the cell Myofibrils:  Slender columnlike structures that give the fiber the appearance of lengthwise striations

12. Classification of Muscle Fiber Types Classification is based on... Anatomical appearance Muscle function Biochemical properties Histochemical properties

13. Characteristics of Muscle Fiber Types

14. Three Primary Fiber Types in Human Skeletal Muscle 1. Slow-twitch oxidative 2. Fast-twitch oxidative glycolytic 3. Fast-twitch glycolytic

15. Significance of Fiber Type for Athletics Slow oxidative (SO) fibers:  Contract slowly but are highly fatigue resistant  Good for distance running or other endurance events Fast-twitch (FT) fibers:  Good for power and sprint events

16. A Sarcomere— The Functional Unit of the Myofibril

17. Structure of a Sarcomere Z-line:  The membrane that separates sarcomeres Myofilaments:  Two types of interlocking parallel filaments that run the length of the myofibril  Myosin and actin

18. Myofilaments Myosin:  Its length is equal to the length of the A band.  I band: the area between the ends of the thick filaments. Actin:  A thin filament.  H band: the amount by which its two ends fail to meet (a lighter band within the A band).

19. Actin, Myosin, Troponin, and Tropomyosin

20. Aspects of the Sliding Filament Model of Muscle Contraction At Rest 1.Tropomyosin inhibits actin–myosin binding. 2.Calcium is stored in the sarcoplasmic reticulum. Contraction 1.Neural stimulation causes the sarcoplasmic reticulum to release calcium. 2.Calcium binds to troponin, which removes the inhibitory effect of tropomyosin and actin – myosin bind. 3.Myosin cross-bridges swivel, pulling the actin and Z-lines. 4.Fresh ATP binds to the myosin cross-bridges, leading to cross-bridge recycling. 5.Neural stimulation ceases and relaxation occurs.

21. ATP Breakdown and Muscle Contraction —Theory 1 1. Actin–myosin binding activates myosin ATPase, which breaks down an ATP molecule and liberates energy. 2. Energy causes the myosin cross-bridge to swivel toward the sarcomere, which pulls Z-lines closer together and shortens sarcomeres. 3. A fresh ATP molecule binds to the myosin cross-bridge, causing it to release from the actin molecule. The myosin cross-bridge stands up and binds to a different actin binding site. 4. Binding activates myosin ATPase to break down the new ATP molecule. 5. The process repeats; cross-bridge recycling or cross-bridge recharging.

22. ATP Breakdown and Muscle Contraction —Theory 2 1. The myosin cross-bridge is energized and bound to ADP and inorganic phosphate (Pi). 2. The binding of actin and the myosin cross-bridge releases stored energy, which causes the myosin cross-bridge to swivel, resulting in muscle contraction. 3. During the swiveling, ADP and Pi are released from the myosin cross-bridge 4. After actin and myosin dissociate, fresh ATP is broken down, and liberated energy is used to reenergize the myosin cross- bridge. 5. The cross-bridge recycling process repeats.

23. Where to Learn More Muscles:  http://users.rcn.com/jkimball.ma.ultranet/BiologyPages /M/Muscles.html http://users.rcn.com/jkimball.ma.ultranet/BiologyPages /M/Muscles.html Sliding filament model:  http://users.rcn.com/jkimball.ma.ultranet/BiologyPages /M/Muscles.html#The_Sliding-Filament_Model http://users.rcn.com/jkimball.ma.ultranet/BiologyPages /M/Muscles.html#The_Sliding-Filament_Model

24. NASPE Guideline— D1 Describe the mechanics of muscular contraction from depolarization of the motor neuron through the sliding filament theory.  How would you describe the mechanics of muscular contraction?  How would you describe the mechanics of the sliding filament theory/model?  Does the sliding filament theory seem plausible to you?