1. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Neuromuscular Junction Figure 9.7 (a-c)

2. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Skeletal Muscle Figure 9.2 (a)

3. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Myofibrils Figure 9.3 (b)

4. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Sarcomeres Figure 9.3 (c)

5. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Myofilaments: Banding Pattern Figure 9.3 (c, d)

6. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Ultrastructure of Myofilaments: Thick Filaments Figure 9.4 (a)(b)

7. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Ultrastructure of Myofilaments: Thin Filaments Figure 9.4 (c)

8. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Arrangement of the Filaments in a Sarcomere  Longitudinal section within one sarcomere Figure 9.4 (d)

9. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Sarcoplasmic Reticulum (SR) Figure 9.5

10. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  At low intracellular Ca 2+ concentration:  Tropomyosin blocks the binding sites on actin  Myosin cross bridges cannot attach to binding sites on actin  The relaxed state of the muscle is enforced Role of Ionic Calcium (Ca 2+ ) in the Contraction Mechanism Figure 9.10 (a)

11. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.10 (b)  At higher intracellular Ca 2+ concentrations:  Additional calcium binds to troponin (inactive troponin binds two Ca 2+ )  Calcium-activated troponin binds an additional two Ca 2+ at a separate regulatory site Role of Ionic Calcium (Ca 2+ ) in the Contraction Mechanism

12. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Calcium-activated troponin undergoes a conformational change  This change moves tropomyosin away from actin’s binding sites Figure 9.10 (c) Role of Ionic Calcium (Ca 2+ ) in the Contraction Mechanism

13. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Myosin head can now bind and cycle  This permits contraction (sliding of the thin filaments by the myosin cross bridges) to begin Figure 9.10 (d) Role of Ionic Calcium (Ca 2+ ) in the Contraction Mechanism

14. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Myosin cross bridge attaches to the actin myofilament 1 2 3 4 Working stroke—the myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line As new ATP attaches to the myosin head, the cross bridge detaches As ATP is split into ADP and P i, cocking of the myosin head occurs Myosin head (high-energy configuration) Thick filament Myosin head (low-energy configuration) ADP and P i (inorganic phosphate) released Sequential Events of Contraction Figure 9.11 Thin filament

15. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Motor Unit: The Nerve-Muscle Functional Unit Figure 9.12 (a)