Muscle Time with Hans and Franz

1. Muscle Time with Hans and Franz Today’s goal: learn types, characteristics, functions, attachments, organization of muscles http://www.hulu.com/watch/4184/saturday-night-live-pumping-up-with-hans-and-franz

2. Post it Time • First muscle test will be general: • Focus on • Types • Characteristics • Functions • The Tough stuff is organization!

3. 2.0 test questions • What are the characteristics of muscle? • What are the types of muscle? • What are the characteristics of cardiac muscle? • What are the functions of muscles?

4. 3 Muscle Types • Skeletal (our major focus over the next ~2 weeks) • Smooth – surrounds hollow organ • Cardiac – Bachelor Rejects have broken these

5. Three Types of Muscle Tissue • Skeletal muscle tissue: • Attached to bones and skin • Striated • Voluntary • Powerful

6. Three Types of Muscle Tissue • Cardiac muscle tissue: • Only in the heart • Striated • Involuntary

7. Three Types of Muscle Tissue • Smooth muscle tissue: • In the walls of hollow organs, e.g., stomach, urinary bladder, and airways • Not striated • Involuntary

8. Special Characteristics of Muscle Tissue • Excitability (responsiveness or “irritability”): receive and respond to stimuli • Contractility: ability to shorten when stimulated • Stretchable • Elasticity: recoils to resting length

9. Muscle Functions • Movement of bones or fluids (e.g., blood) • Maintaining posture and body position • Stabilizing joints • Heat generation

10. Skeletal Muscle: Attachments • Muscles attach: • Directly—epimysium of muscle fuses to outer membrane of bone • tendon or sheetlikeaponeurosis

12. Skeletal Muscle • Each muscle is served by one artery, one nerve, and one or more veins • But just what is a muscle???

13. Muscle organization • Muscles made up of tons (100s to 1000s) muscle fibers • Muscle fiber is a sophisticated way of saying muscle cell! • Muscle cell is bourgeois to say muscle fiber • Blood vessels and nerve fibers also found throughout muscle

14. Fibers are wrapped by CT

15. Russian Dolls • Muscle • Fascicle • Fiber • Myofibrils • Myofilaments • Above: Your next week, somewhat simplified though not a perfect analogy

16. Connective tissue sheaths of skeletal muscle • Epimysium: dense regular CT surrounding entire muscle • Perimysium: fibrous CT surrounding fascicles (groups of muscle fibers) • Endomysium: fine areolarCT surrounding each muscle fiber

17. Epimysium Epimysium Bone Perimysium Endomysium Tendon Muscle fiber in middle of a fascicle (b) Blood vessel Fascicle (wrapped by perimysium) Endomysium (between individual muscle fibers) Perimysium Fascicle Muscle fiber (a) Figure 9.1

18. Fiber is an individual cells • Fibers are bundled into fascicles • Fascicles bundled into muscle

19. Today: • Review yesterday • Muscle “cells” • Organelles of the muscle fiber

20. What is a muscle cel… you mean fiber like? 1 muscle cell • Cylindrical up to 1 foot long! • Multiple nuclei • Many mitochondria

21. Muscle fibers • Glycosomes for glycogen storage, myoglobin for O2 storage • Modified organelles: myofibrils, sarcoplasmic reticulum, sarcolemma and T tubules

22. Myofibrils • Densely packed, rodlike elements • ~80% of cell volume • These are where we will see striations • A and I bands alternate

23. Myofibrils are made of myofilaments! • Forest is a fiber • Tree is a myofibril • 1 branch is myofilament

24. Sarcolemma Mitochondrion Myofibril Dark A band Light I band Nucleus (b) Diagram of part of a muscle fiber showing the myofibrils. Onemyofibril is extended afrom the cut end of the fiber.

25. Sarcomere • Smallest contractile unit (functional unit) of a muscle fiber • region of a myofibril • between two successive Z discs • Composed of thick and thin myofilaments made of contractile proteins Poorly comparble to an osteon And bone

26. Features of a Sarcomere • Thick filaments: run the entire length of an A band • Thin filaments: run the length of the I band and partway into the A band

27. Z disc: sheet of proteins that anchors the thin filaments • connects myofibrils to one another • H zone: lighter midregion where filaments do not overlap • M line: line of protein myomesin that holds adjacent thick filaments together

28. Thin (actin) filament Z disc H zone Z disc Thick (myosin) filament I band A band Sarcomere I band M line (c) Small part of one myofibril enlarged to show the myofilaments responsible for the banding pattern. Each sarcomereextends from one Z disc to the next. Sarcomere Z disc Z disc M line Thin (actin) filament Elastic (titin) filaments Thick (myosin) filament (d) Enlargement of one sarcomere (sectioned lengthwise). Notice the myosin heads on the thick filaments. Figure 9.2c, d

29. Structure of Thick Filament • Composed of the protein myosin (tail and head) • Myosin tails contain: • 2 interwoven, protein chains • Myosin heads contain: • 2 smaller, light chains that act as cross bridges during contraction • Binding sites for actin(thin filaments) • Binding sites for ATP • ATPase enzymes

30. Structure of Thin Filament • Twisted double strand of fibrous protein F actin • F actin consists of G (globular) actin subunits • G actin bears active sites for myosin head attachment during contraction • Tropomyosin and troponin: regulatory proteins bound to actin

31. Longitudinal section of filaments within one sarcomere of a myofibril Thick filament Thin filament In the center of the sarcomere, the thick filaments lack myosin heads. Myosin heads are present only in areas of myosin-actin overlap. Thick filament Thin filament Each thick filament consists of many myosin molecules whose heads protrude at opposite ends of the filament. A thin filament consists of two strands of actin subunits twisted into a helix plus two types of regulatory proteins (troponin and tropomyosin). Portion of a thick filament Portion of a thin filament Myosin head Tropomyosin Troponin Actin Actin-binding sites Active sites for myosin attachment Tail Heads Actin subunits ATP- binding site Flexible hinge region Myosin molecule Actin subunits Figure 9.3

32. Sarcoplasmic Reticulum (SR) • Network of smooth endoplasmic reticulum surrounding each myofibril • Pairs of terminal cisternae form perpendicular cross channels • Regulates intracellular Ca2+ levels

33. T Tubules • Continuous with the sarcolemma • Sarcolemma = cell membrane of muscle fiber • Penetrate the cell’s interior at each A band–I band junction • Associate with the paired terminal cisternae to form triads that encircle each sarcomere

34. Organelles

35. Part of a skeletal muscle fiber (cell) I band A band I band Z disc H zone Z disc Myofibril M line Sarcolemma Triad: T tubule • • Terminal cisternae of the SR (2) Sarcolemma Tubules of the SR Myofibrils Mitochondria Figure 9.5

36. Triad Relationships • T tubules conduct impulses deep into muscle fiber • Integral proteins protrude from T tubule and SR cisternae membranes • T tubule proteins: voltage sensors • SR has gated channels that regulate Ca2+ release from the SR cisternae

37. Contraction • The generation of force • Does not necessarily cause shortening of the fiber • Shortening occurs when tension generated by cross bridges on the thin filaments exceeds forces opposing shortening

38. Sliding Filament Model of Contraction • In the relaxed state, thin and thick filaments overlap only slightly • During contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments toward the M line

39. As H zones shorten and disappear, sarcomeres shorten, muscle cells shorten, and the whole muscle shortens

40. Role of Calcium (Ca2+) in Contraction • At low intracellular Ca2+ concentration: • Tropomyosin blocks the active sites on actin • Myosin heads cannot attach to actin • Muscle fiber relaxes

41. Role of Calcium (Ca2+) in Contraction • At higher intracellular Ca2+ concentrations: • Ca2+ binds to troponin • Troponin changes shape and moves tropomyosin away from active sites • Events of the cross bridge cycle occur • When nervous stimulation ceases, Ca2+ is pumped back into the SR and contraction ends

42. Cross Bridge Cycle • Continues as long as the Ca2+ signal and adequate ATP are present • Cross bridge formation—high-energy myosin head attaches to thin filament • Working (power) stroke—myosin head pivots and pulls thin filament toward M line

43. Cross Bridge Cycle • Cross bridge detachment—ATP attaches to myosin head and the cross bridge detaches • “Cocking” of the myosin head—energy from hydrolysis of ATP cocks the myosin head into the high-energy state

44. Thin filament Ca2+ Actin ADP Myosin cross bridge Pi Thick filament Myosin Cross bridge formation. 1 ADP ADP Pi ATP hydrolysis Pi The power (working) stroke. 4 2 Cocking of myosin head. ATP ATP Cross bridge detachment. 3 Figure 9.12

45. Actin Thin filament Ca2+ ADP Myosin cross bridge Pi Thick filament Myosin Cross bridge formation. 1 Figure 9.12, step 1

46. ADP Pi The power (working) stroke. 2 Figure 9.12, step 3

47. ATP Cross bridge detachment. 3 Figure 9.12, step 4

48. ADP ATP hydrolysis Pi Cocking of myosin head. 4 Figure 9.12, step 5

49. Actin Thin filament Ca2+ ADP Myosin cross bridge Pi Thick filament Myosin Cross bridge formation. 1 Figure 9.12, step 1

50. ADP Pi The power (working) stroke. 2 Figure 9.12, step 3