1. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Twitch time course Duration of twitch is largely governed by rate of sequestration of calcium into SR

2. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings X-ray crystal structures In the beginning of the movie, the myosin heads are in the prestroke ADP-Pi state (yellow) and the catalytic cores bind weakly to actin. Once a head docks properly onto an actin subunit (green), phosphate (Pi) is released from the active site. Phosphate release increases the affinity of the myosin head for actin and swings the converter/lever arm to the poststroke, ADP state (transition from yellow to red). The swing of the lever arm moves the actin filament by ~100 Å; the exact distance may vary from cycle to cycle depending upon the initial prestroke binding configuration of the myosin on actin. After completing the stroke, ADP dissociates and ATP binds to the empty active site, which causes the catalytic core to detach from actin. The lever arm then recocks back to its prestroke state (transition from red to yellow).

3. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-13 Phosphocreatine Provides ATP at beginning of exercise needed for contraction

4. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-14 Muscle Fatigue Locations and possible causes of muscle fatigue

5. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-15 Muscle Fiber Types Fast-twitch glycolytic and slow-twitch oxidative muscle fibers

6. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Length-Tension Relationships in Contracting Muscle Figure 12-16

7. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Summation of Contractions Figure 12-17a

8. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Summation of Contractions Figure 12-17b

9. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Summation of Contractions Figure 12-17d

10. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-18 Motor Units

11. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-19 Isotonic and Isometric Contractions

12. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-20 Series Elastic Elements in Muscle

13. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-24 Muscle Contraction Duration of muscle contraction of the three types of muscle

14. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-25a Types of Smooth Muscle

15. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Types of Smooth Muscle Figure 12-25b

16. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Smooth Muscle  Has longer actin and myosin filaments  Myosin ATPase activity much slower  Actin more plentiful  Has less sarcoplasmic reticulum  IP3-receptor channel is the primary calcium channel

17. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-27a–b Anatomy of Smooth Muscle

18. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-28, step 1 Smooth Muscle Contraction ECF Ca 2+ Sarcoplasmic reticulum Intracellular Ca 2+ concentrations increase when Ca 2+ enters cell and is released from sarcoplasmic reticulum. Ca 2+ 1 1

19. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-28, steps 1–2 Smooth Muscle Contraction ECF Ca 2+ Sarcoplasmic reticulum CaM PiPi PiPi Intracellular Ca 2+ concentrations increase when Ca 2+ enters cell and is released from sarcoplasmic reticulum. Ca 2+ binds to calmodulin (CaM). Ca 2+ 1 2 1 2

20. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-28, steps 1–3 Smooth Muscle Contraction ECF Ca 2+ Sarcoplasmic reticulum CaM PiPi PiPi Active MLCK CaM Intracellular Ca 2+ concentrations increase when Ca 2+ enters cell and is released from sarcoplasmic reticulum. Ca 2+ binds to calmodulin (CaM). Ca 2+ –calmodulin activates myosin light chain kinase (MLCK). Ca 2+ Inactive MLCK 1 2 3 1 2 3

21. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-28, steps 1–4 Smooth Muscle Contraction ECF Ca 2+ Sarcoplasmic reticulum CaM PiPi PiPi Active MLCK CaM ADP + Active myosin ATPase P P Intracellular Ca 2+ concentrations increase when Ca 2+ enters cell and is released from sarcoplasmic reticulum. Ca 2+ binds to calmodulin (CaM). Ca 2+ –calmodulin activates myosin light chain kinase (MLCK). MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity. ATP Ca 2+ Inactive myosin Inactive MLCK 1 2 3 4 1 2 3 4

22. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-28, steps 1–5 Smooth Muscle Contraction ECF Ca 2+ Sarcoplasmic reticulum CaM PiPi PiPi Active MLCK CaM ADP + Active myosin ATPase Actin P P Intracellular Ca 2+ concentrations increase when Ca 2+ enters cell and is released from sarcoplasmic reticulum. Ca 2+ binds to calmodulin (CaM). Ca 2+ –calmodulin activates myosin light chain kinase (MLCK). MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity. Active myosin crossbridges slide along actin and create muscle tension. ATP Increased muscle tension Ca 2+ Inactive myosin Inactive MLCK 1 2 3 4 5 1 2 3 4 5

23. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-29, step 1 Relaxation in Smooth Muscle Ca 2+ ECF Ca 2+ Na + Sarcoplasmic reticulum Free Ca 2+ in cytosol decreases when Ca 2+ is pumped out of the cell or back into the sarcoplasmic reticulum. 1 1 ATP

24. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-29, steps 1–2 Relaxation in Smooth Muscle Ca 2+ ECF Ca 2+ Na + CaM Sarcoplasmic reticulum Free Ca 2+ in cytosol decreases when Ca 2+ is pumped out of the cell or back into the sarcoplasmic reticulum. Ca 2+ unbinds from calmodulin (CaM). 1 2 1 2 ATP

25. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-29, steps 1–3 Relaxation in Smooth Muscle Ca 2+ ECF Ca 2+ Na + CaM Inactive myosin Myosin ATPase activity decreases. ADP + Myosin phosphatase P P ATP Sarcoplasmic reticulum Free Ca 2+ in cytosol decreases when Ca 2+ is pumped out of the cell or back into the sarcoplasmic reticulum. Ca 2+ unbinds from calmodulin (CaM). Myosin phosphatase removes phosphate from myosin, which decreases myosin ATPase activity. 1 2 3 1 2 3 ATP

26. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-29, steps 1–4 Relaxation in Smooth Muscle Ca 2+ ECF Ca 2+ Na + CaM Inactive myosin Myosin ATPase activity decreases. ADP + Myosin phosphatase P P ATP Decreased muscle tension Sarcoplasmic reticulum Free Ca 2+ in cytosol decreases when Ca 2+ is pumped out of the cell or back into the sarcoplasmic reticulum. Ca 2+ unbinds from calmodulin (CaM). Myosin phosphatase removes phosphate from myosin, which decreases myosin ATPase activity. Less myosin ATPase results in decreased muscle tension. 1 2 3 4 1 2 3 4 ATP

27. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-30 Control of Smooth Muscle Contraction

28. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Smooth Muscle  Smooth muscle cells contain stretch-activated calcium channels  Open when pressure or other force distorts cell membrane  Known as myogenic contraction

29. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-31a Membrane Potentials Vary in Smooth Muscle

30. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-31b Membrane Potentials Vary in Smooth Muscle

31. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-31c Membrane Potentials Vary in Smooth Muscle

32. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Smooth Muscle Regulation  Many smooth muscles have dual innervation  Controlled by both sympathetic and parasympathetic neurons  Hormones and paracrines also control smooth muscle contraction  Histamine constricts smooth muscle of airways