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Lecture 23


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Lecture 23

  1. 1. Internal structure of skeletal muscle<br />Nucleus: Contain the genetic material of the cell<br />Sarcolemma: Plasma membrane of muscle cell<br />T Tubule: Invagination of the Sarcolemma project deep into Muscle cells interior<br />Terminal cisternae: Serve as specialized reservoirs for Ca ions<br />Myofibril: Bundle of contractile filaments<br />
  2. 2. The myofibrils composed of individual contractile proteins called myofilaments<br />There are two types of myofilaments:<br />Thin filaments composed mainly of protein Actins<br />The thick filaments is composed mainly of protein myosin<br />Structure of Myofibrils<br />
  3. 3. Organization levels of skeletal muscle <br />Myofilaments: Smallest building blocks. Compose of thick and thin<br />Myofibril: Many myofilaments bundle together making a single myofibril<br />Muscle cell: Many myofibril are contained within the muscle cell<br />Fascicle: Many muscle cells are packed into a fascicle <br />Muscle: Many fascicle make up the muscle <br />
  4. 4. The Sliding Filament<br />Sliding filament occurs as a thin filaments slide past the thick filament. This involve the activity of:<br />Myocin<br />Actin<br />Tropomyosin<br />Troponin<br />ATP<br />Ca ions<br />
  5. 5. The Thick Filament (Myosin)<br />Consists of the protein called myosin.<br />A myosin molecule is shaped a bit like a golf club, but with 2 heads.<br />The heads stick out to form the cross bridge<br />Many of these myosin molecules stick together to form a thick filament<br />Each head contains two binding sites, one for actin and one for ATP. <br />
  6. 6. Thin Filament (Actin)<br />The thin filament consists of a protein called actin. It compose of actin subunit twisted into double helical chain. Actin has specific binding site to which the myosin head binds<br />The thin filament also contains tropomyosin. The position of tropomyosin cover the binding sites on the actin during unstimulated muscle<br />The third component is troponin. Attached along the tropomyosin strand.Which expose the binding site of actin to myosin <br />
  7. 7. Arrangement of Myofilament<br />The arrangement of thick and thin myofilaments forms light and dark alternating bands (striation). <br />In the middle of the light band is the Z-line<br />The repeating unit from one Z-line to the next is called the sarcomere<br />
  8. 8. I Band = actin filaments<br />
  9. 9. Ca Ion<br />After action potential, Ca ions released from the T-Tubules and bind to troponin. This causes change in conformation of the troponin – tropomyosin complex and thus dragging tropomyosin strands off the binding site<br />
  10. 10. Sliding-Filament Mechanism<br />
  11. 11. Sliding-Filament Mechanism<br />
  12. 12. Sliding-Filament Mechanism<br />
  13. 13. Sliding-Filament Mechanism<br />
  14. 14. Sliding-Filament Mechanism<br />
  15. 15. Steps of cross bridge cycle<br />The influx of Ca ion, triggering the exposure of binding sites on actin<br />The binding of myosin to actin<br />The myosin cross bridge pulls the thin filament inward toward the centre of sarcomere<br />The binding of ATP to the myosin head disconnecting from actin<br />The hydrolysis of ATP leads to repositioning of the myosin head<br />The transport of Ca ion to the back into the sarcoplasmic reticulum<br />