Muscle contraction

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  • 1. CONTRACTION OF MUSCLE 1
  • 2. MUSCLE TISSUE  Three types of Muscle tissues in our body:  Voluntary: Skeletal muscles  Involuntary: Smooth muscles  Cardiac muscles 2
  • 3. VOLUNTARY: SKELETAL MUSCLES Under voluntary control  Supplied by motor neurons  Functions: Locomotion  3
  • 4. INVOLUNTARY: SMOOTH MUSCLES Under involuntary control  Spontaneous contraction  Under autonomic control  Are found in the wall of blood vessels  Structurally and functionally different from voluntary muscles.  4
  • 5. CARDIAC MUSCLES Forms the heart muscles ( Myocardium)  Are involuntary muscles  Are regulated by Autonomic nervous system  Structurally similar to Voluntary muscles  5
  • 6. SKELETAL MUSCLE 6
  • 7. SKELETAL MUSCLE General Features  EndomysiumConnective tissue (CT) that surrounds individual muscle fibers  Perimysium- CT that surrounds groups (fascicles) of muscle fibers  Epimysium- CT that surrounds the entire muscle 7
  • 8. A GROSS VIEW OF SKELETAL MUSCLE AND THE CONNECTIVE TISSUE (CT) INVESTMENTS 8
  • 9. 9
  • 10. BAND STRUCTURE OF STRIATED MUSCLE A band:  I band:  Z line:Lies in the I band  H band:  M line: 10
  • 11. 11
  • 12. SKELETAL MUSCLE Fibers  Skeletal muscle fibers consist of long cylindrical fibers with multiple ovoid nuclei located peripherally beneath the sarcolemma (plasma membrane) and with striations composed of alternating dark and light bands.  A bands: The dark bands  H band : In the center of the A band a paler region, seen in relaxed muscle.  I bands (isotropic): The light bands  Z line: a dark transverse line, bisects each I band.  M line These bands and the Z lines are well demonstrated in electron micrographs of skeletal muscle. 12
  • 13. 13
  • 14. SKELETAL MUSCLE ELECTRON MMICROSCOPY 14
  • 15. SKELETAL MUSCLE Myofibrils  Skeletal muscle fibers contain 1- to 2-mm myofibrils that lie in the sarcoplasm (cytoplasm) parallel to the long axis of the muscle fiber.  Myofibrils are composed of a series of sarcomeres  Sarcomeres consist of inter-digitating  Thin filaments ( Actin)  Thick filaments ( Myosin)  The sarcomeres are the basic units of contraction of striated muscle 15
  • 16. 16
  • 17. THICK AND THIN FILAMENTS 17
  • 18. 18
  • 19. SARCOMERE STRUCTURE  The banding pattern seen in striated muscle is caused by the arrangement of thin and thick myofilaments.  Thick filaments occupy the central portions of the sarcomere.  Thin filaments attach at one end to the Z line and run parallel to, and between, the thick filaments. bands are composed of thin filaments only.  A bands are composed mostly of thick filaments and the thin filaments between them.  H bands are composed of thick filaments only. 19 I
  • 20. SARCOMERE STRUCTURE BAND PATTERN I bands are composed of thin filaments only.  A bands are composed mostly of thick filaments and the thin filaments between them.  H bands are composed of thick filaments only  20
  • 21. SARCOMERE STRUCTURE: THIN FILAMENTS Thin filaments are composed of the proteins 1. 2. 3. Actin, Tropomyosin, and Troponin. 21
  • 22. 22
  • 23. SARCOMERE STRUCTURE: THIN FILAMENTS  1. Actin:  Long fibrous structure (F-actin) composed of two strands of spherical or globular Gactin monomers twisted in a double helix:  The filament is polar and contains myosinbinding sites on the G-actin monomers. 23
  • 24. 24
  • 25. THIN FILAMENTS Tropomyosin is a polar molecule containing two polypeptide chains in the form of an ahelix. The tropomyosin molecules lie headto-tail to form filaments that lie in the grooves of the actin helix:  2. 25
  • 26. THIN FILAMENTS Troponin (Tn) is composed of three polypeptides: TnT binds to tropomyosin at intervals along the thin filament, TnC binds calcium ions, and Tnl inhibits actin-myosin interaction  3. 26
  • 27. 27
  • 28. THICK AND THIN FILAMENTS 28
  • 29. THICK FILAMENTS Thick filaments are composed of myosin.  Myosin is a molecule that contains a tail and two heads. . The tail fiber is formed from portions of two heavy chains, which are wound in a coil.  29
  • 30. THICK FILAMENTS  The heads are globular regions formed by the association of part of one heavy chain with two light chains.  Myosin heads function as active sites for ATPase activity and as actin-binding sites 30
  • 31. THICK FILAMENTS: PARTS of the myosin molecule  myosin head  an arm that extends the head outward from the body,  tail 31
  • 32. THICK FILAMENTS: PARTS  The protruding arms and heads together are called cross-bridges.  Each cross-bridge is flexible at two points called hinges—one where the arm leaves the body of the myosin filament, and the other where the head attaches to the arm  The hinged arms allow the heads either to be extended far outward from the body of the myosin filament or to be brought close to the body. 32
  • 33. THICK FILAMENTS: PARTS  ATPase Activity of the Myosin Head.  the myosin head that is essential for muscle contraction  is that it functions as an ATPase enzyme.  As explained later, this property allows the head to cleave ATP and to use the energy derived from the ATP’s high-energy phosphate bond to energize the contraction process. 33
  • 34. THICK FILAMENTS: PARTS 34
  • 35. THICK AND THIN FILAMENTS 35
  • 36. 36
  • 37. 37
  • 38. SARCOMERE STRUCTURE 38
  • 39. TRANSVERSE TUBULAR SYSTEM 39
  • 40. SARCOMERE STRUCTURE TRANSVERSE TUBULAR SYSTEM 40
  • 41. SARCOMERE STRUCTURE TRANSVERSE TUBULAR SYSTEM Skeletal muscle fibers contain fingerlike invaginations of the sarcolemma that surround each myofibril.  These invaginations constitute the transverse (T) tubule system .  Note the following:   Each T tubule lies between the two cisternae of the sarcoplasmic reticulum (SR) to form a triad 41
  • 42. SARCOMERE STRUCTURE TRANSVERSE TUBULAR SYSTEM There are two triads in each sarcomere, which are present at the junction between the A and I bands.  These units serve to couple excitation of muscle cells to their contraction (excitation-contraction coupling).  42
  • 43. SARCOMERE STRUCTURE TRANSVERSE TUBULAR SYSTEM  Function of ER:  Acts as a store of calcium and release Ca++ after action potential reaches the adjacent T tubule. 43
  • 44. SARCOMERE STRUCTURE TRANSVERSE TUBULAR SYSTEM 44
  • 45. CARDIAC MUSCLE 45
  • 46. CARDIAC MUSCLE  Cardiac muscle has an arrangement of sarcomeres similar to that in skeletal muscle as well as a T tubule system associated with the SR (near the Z line).  However, unlike skeletal muscle fibers, the fibers are electrically coupled through gap junctions.  Cardiac muscle fibers are joined together by junctional complexes called intercalated discs.. 46
  • 47. 47
  • 48. CARDIAC MUSCLE Striated pattern  Fibres divide and join at intercalated discs  There are many gap junctions between fibres   Provides easy spread of impulses Large T tubules are present  SR is present, but less than in skeletal muscle  48
  • 49. 49
  • 50. CARDIAC MUSCLE ACTION POTENTIAL Action potentials are prolonged in the heart, 0.2 to 0.3 seconds  i.e. there is a ‘plateau’ in the AP  This is due to an additional slow Ca ++ channel  Much of the Ca++ entry comes from the T tubules  50
  • 51. 51
  • 52. Top: Phases of the action potential of a cardiac muscle fiber. 0, depolarization; 1, initial rapid repolarization; 2, plateau phase; 3, late rapid repolarization; 4, baseline. Bottom: Diagrammatic summary of Na+, Ca2+, and cumulative K+ currents during the action potential. Inward current down, outward current up. 52
  • 53. •Transient outward (ph 1; early incomplete repolarization) – ITO •Inward rectifying ( ph 2; plateau influx of K)- IKr •Delayed rectifying(ph 3; repolarization, slowly outflux of K)IKs IKr + IKs = repolarization 53
  • 54. SMOOTH MUSCLE Smooth muscle is found in the walls of blood vessels and hollow viscera.  Bands of smooth muscle cells can be found in the erector pili muscles of the skin  54
  • 55. SMOOTHMUSCLE Gap Junctions  Gap junctions electrically couple smooth muscle cells.  55
  • 56. SMOOTHMUSCLE  Filaments  Smooth muscles contain actin and myosin filaments, but the filaments are not arranged in orderly arrays as in skeletal muscle. 56
  • 57. 57
  • 58. SMOOTH MUSCLE  Contraction  Smooth muscle contraction may be triggered by various stimuli such as autonomic nerves or hormones. 58
  • 59. SMOOTH MUSCLE. DIFFERENCES Does not show striations  Does contain actin and myosin, but in a different arrangement  Does not have troponin  59
  • 60. SMOOTH MUSCLE. DIFFERENCES 2 No sarcoplasmic reticulum (or very little)  Ca++ enters from ECF, not from SR  60
  • 61. CONTROL OF SMOOTH MUSCLE CONTRACTION Spontaneous contraction occurs  Contraction may be due to release of local chemicals  Stretching leads to contraction  Autonomic system modifies contraction  Parasympathetic and sympathetic stimulation generally have opposite effects  61