1. Muscles & Skeleton Locomotion Chapter 50

2. Muscle structure  Muscle fibers  Single cell with many nuclei  Each fiber has a bundle of myofibrils  Each myofibril contains myofilaments  Thick(myosin) or thin (actin)

3. Muscle structure  Myosin (thick) proteins with a head region  Several actin (thin) form a double helix  Cross-bridges  Head region from myosin  Extends to actin

5. Cross-bridge Cross-bridge ADP P i ATP Actin Myosin Myosin binding sites

6. Muscle Bundle of muscle fibers Muscle Single muscle fiber (cell) Nuclei Z lines Plasma membrane Myofibril Sarcomere

7. Muscle structure  Sacromere  Z-lines borders of the unit  Thin filaments attached to Z-line  I-bands thin filaments alone  A-bands length of thick filaments  H-zone center of the A-band only thick filaments

10. Muscle

13. Muscle structure

16. Muscle contraction  Myosin head binds an ATP  Spits ATP  Forms cross-bridge  Binds actin  Pulls the actin  Cross-bridge broken when binds new ATP  Continues muscle is stimulated to contract  Myofilaments move by sliding mechanism

17. Muscle structure

18. Control of contraction  Calcium  Tropomyosin:  Protein found on actin  Troponin:  Regulatory protein  Transverse tubules (T tubules):  Tube in the muscle fiber  Sarcoplasmic reticulum (SR):  Stores calcium in muscle

19. Mechanism of contraction  Relaxed muscle  Myosin heads are ready (split ATP)  Not attached to actin  Cross-bridges cannot form  Tropomyosin is on the actin  Blocking binding site on actin

20. Mechanism of contraction  Contracting muscle  Calcium binds the troponin  Removes tropomysin off actin binding sites  Cross-bridges form  Muscles contract

21. Contraction Myosin- binding site Tropomyosin (a) Myosin-binding sites blocked (b) Myosin-binding sites exposed Ca 2+ Ca 2+ -binding sites Troponin complex Actin

22. Mechanism of contraction  Relaxed muscle low calcium levels  Contracting muscle high calcium levels  Electric impulse (nerve)  Stimulates calcium release from SR  Travels down T tubules  Binds troponin  Contraction happens

24. Mechanism  Impulses stop  Calcium is pumped back into SR  Troponin no longer attached to calcium  Tropomysin returns to actin

26. Cardiac muscle  Shorter, branched cells  Each with own nucleus  Form a lattice  Gap junctions electrical impulses

27. Smooth muscle  Internal organs  Myosin/actin not organized into sacromeres  No sacroplasmic reticulum  Need calcium to contract  Capable of contracting when stretched

28. Skeleton  Axial skeleton  Supports  Protects

29. Skeleton  Appendicular skeleton  Attach to axial skeleton

30. Skeleton  Articulations  Joints, where movement happens

32. Lou-Gehrig’s disease