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skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
skeletal muscle
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skeletal muscle

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Amna inayat medical college …

Amna inayat medical college
UHS
by-dr-roomi
uploaded by class representative,

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  • There are three types of muscle tissue in the body. Skeletal muscle is the type that attaches to our bones and is used for movement and maintaining posture. Cardiac muscle is only found in the heart. It pumps blood. Smooth muscle is found in organs of the body such as the GI tract. Smooth muscle in the GI tract moves food and its digested products.
  • Skeletal muscle attaches to our skeleton. *The muscle cells a long and cylindrical. *Each muscle cell has many nuclei. *Skeletal muscle tissue is striated. It has tiny bands that run across the muscle cells. *Skeletal muscle is voluntary. We can move them when we want to. *Skeletal muscle is capable of rapid contractions. It is the most rapid of the muscle types.
  • Cardiac muscle tissue is only found in the heart. *Cardiac cells are arranged in a branching pattern. * Only one or two nuclei are present each cardiac cell. *Like skeletal muscle, cardiac muscle is striated. *Cardiac muscle is involuntary. *Its speed of contraction is not as fast as skeletal, but faster than that of smooth muscle.
  • Smooth muscle is found in the walls of hollow organs. *Their muscle cells are fusiform in shape. *Smooth muscle cells have just on nucleus per cell. *Smooth muscle is nonstriated. *Smooth muscle is involuntary. *The contractions of smooth muscle are slow and wave-like.
  • SKELETAL MUSCLE
  • A small section of a myofibril is illustrated here. Note the thick myosin filaments are arranged between overlapping actin filaments. *The two Z lines mark the boundary of a sarcomere. The sarcomere is the functional unit of a muscle cell .We will examine how sarcomeres function to help us better understand how muscles work.
  • SKELETAL MUSCLE
  • The actin filaments are moved by the heads of the myosin filaments. In step one the myosin head attaches to an actin filament to create a cross bridge. Step two shows that the attached myosin head bends to move the actin filament. The myosin head as expended energy to create this movement. This is a power stroke or working stroke. Step three shows that energy in the form of ATP will unhook the myosin head. In step 4 the myosin head is cocked and ready to attach to an actin filament to start another power stroke.
  • The string of green circles represents an actin filament. There are binding sites in the filament for the attachment of myosin heads. *In a relaxed muscle the binding sites are covered by tropomyosin. The tropomyosin has molecules of troponin attached to it. *Calcium, shown in yellow, will attach to troponin. *Calcium will change the position of the troponin, tropomyosin complex. *The troponin, tropomyosin complex has now moved so that the binding sites are longer covered by the troponin, tropomyosin complex.
  • The binding sites are now exposed and myosin heads are able to attach to form cross bridges.*
     
  • Here is another diagram of a sarcomere. Note the A band. It is formed by both myosin and actin filaments. The part of the sarcomere with only actin filaments is called the I band. This is a sarcomere that is relaxed.
  • This sarcomere is partially contracted. Notice than the I bands are getting shorter.
  • The sarcomere is completely contracted in this slide. The I and H bands have almost disappeared.
  • Which filament has moved as the sarcomere contracted? Note the thick myosin filaments have not changed, but the thin actin filaments have moved closer together.
  • Transcript

    • 1. By Dr. Mudassar Ali Roomi (MBBS, M. Phil) MECHANISM OF CONTRACTION OF SKELETAL MUSCLE IN THE LIGHT OF ITS STRUCTURE
    • 2. MUSCLE TISSUE • Skeletal Muscle • Cardiac Muscle • Smooth Muscle
    • 3. SKELETAL MUSCLE • Long cylindrical cells • Many nuclei per cell • Striated • Voluntary • Rapid contractions
    • 4. CARDIAC MUSCLE • Branching cells • One or two nuclei per cell • Striated • Involuntary • Medium speed contractions
    • 5. SMOOTH MUSCLE • Fusiform cells • One nucleus per cell • Nonstriated • Involuntary • Slow, wave-like contractions
    • 6. SKELETAL MUSCLE
    • 7. SKELETAL MUSCLE
    • 8. Z line Z line
    • 9. • From surface of thick filaments  projections arise  cross-bridges. • In centre of sarcomere, thick filaments have no projections (H zone). • The thin & thick filaments contain contractile proteins: • The thick filaments contain myosin protein. • The thin filaments contain actin, tropomyosin & troponin proteins. THICK AND THIN FILAMENTS
    • 10. • In 1 thick filament  200 myosin molecules. • Molecular wt. of each myosin molecule = 480,000. • Each myosin molecule has 6 polypeptide chains: 2 heavy chains & 4 light chains. • 2 heavy chains are coiled together  double helix. • At 1 end two heavy chains are folded  head portion. In head portion  4 light chains. MYOSIN PROTEIN: IN THICK FILAMENTS
    • 11. 3 parts of myosin molecule: • Head • Arm / Neck • Body / Tail • There are 2 points in myosin molecule at which molecule is highly flexible  HINGES: i) Between head & arm / neck ii) Between arm & body / tail • Tail/body is present in thick filaments. • Arm & head protrude out from surface of filament as cross bridges. MYOSIN PROTEIN: IN THICK FILAMENTS (CONT…)
    • 12. • Cross bridges are absent in centre. • In the centre of filament is tail only, while cross bridges are formed by arm & head at periphery as cross bridges. In myosin head there are 2 important sites: • Actin binding site. • Catalytic site. MYOSIN PROTEIN: IN THICK FILAMENTS (CONT…)
    • 13. 3 contractile proteins are present here: 1) ACTIN: Consist of 2 F-actin strands. Each strand consist of polymerized G actin molecules. • Attached to each G actin molecule is a molecule of ATP, & point of attachment is  active site on actin strand. • Active sites are present at every 2.7 nm. Each G actin has molecular wt. 42,000. THIN FILAMENTS
    • 14. 2) TROPOMYOSIN:  Consist of 2 strands, with 70,000 molecular wt.  Tropomyosin strands at rest physically cover active sites on actin filaments. 3) TROPONIN:  Attached to tropomyosin at intervals. It has 3 components:  Troponin C, Troponin T, Troponin I.  Molecular wt. 18,000 – 35,000. THIN FILAMENTS (CONT…)
    • 15. • Troponin C  Affinity for calcium ions. • Troponin T  Affinity for tropomyosin. (through which troponin complex is attached to tropomyosin) • Troponin I  Affinity for actin strands. • It is the bond between troponin I & Actin, which keeps tropomyosin strands in such a position that these physically cover active sites of actin filaments. • During muscle contraction  this bond is broken. • Tropomyosin-troponin complex = relaxing protein (keeps muscle relaxed by covering physically the active sites). THIN FILAMENTS (CONT…)
    • 16. COMPONENTS OF TROPONIN (C,T,I)
    • 17. • Muscle is first excited or depolarized and then contratcs (EXCITATION-CONTRACTION COUPLING). • Action potential enters deep into muscle fiber from T-Tubules around which are terminal cisternae. • So depolarization spreads from T Tubules  terminal cisternae. • Membrane of terminal cisternae is depolarized  opening of voltage gated calcium channels  calcium ions move out of the terminal cisternae. MOLECULAR MECHANISM OF SKELETAL MUSCLE CONTRACTION:
    • 18. SKELETAL MUSCLE
    • 19. • When it is in sarcoplasm, calcium is utilized by troponin C to initiate muscle contraction (excitation-contraction coupling). • 4 calcium ions can bind with 1 molecule of troponin C  it breaks the bond between troponin I & Actin  tropomyosin strands become loose  they reach a deeper position  active sites on actin are uncovered.
    • 20. • Muscle contraction involves power strokes. • Before contraction, a molecule of ATP becomes attached to myosin head. • It is hydrolyzed to ADP to liberate energy  stored in myosin head. • When active site is uncovered  myosin head binds with active site on actin. • With stored energy, there is power stroke. • At hinges, myosin molecule moves & carries along actin / thin filaments.
    • 21. • With energy of 2nd molecule of ATP, it detaches & move back to original position  2nd power stroke  a series of power strokes  sliding of actin over myosin so that power stroke is towards centre of sarcomere  shortening of sarcomere or contraction of muscle. • Each cross bridge operates independently. • Greater the number of cross bridges coming in contact with myosin head  greater is force of contraction. • When muscle is stretched  more number of cross bridges attached with actin filaments  increased contraction force.
    • 22. Binding Site Tropomyosin Troponin
    • 23. Myosin
    • 24.  Greater the initial length of muscle, greater is force of contraction up to certain limits.  Cardiac muscle also obeys this law ( increased venous return  increased length of cardiac muscle  increased filling increased emptying by contraction of ventricle. FRANK-STARLING LAW:
    • 25.  Contraction is initiated by calcium ions.  As long as calcium ion is sufficient in sarcoplasm  muscle contraction continues.  Normally in the wall of longitudinal tubule, there is calcium pump.  Calcium is released from terminal cisternae but is pumped back by calcium pump & when calcium is low in sarcoplasm  muscle relaxes.  So, even to produce muscle relaxation, we need ATP because calcium pump needs ATP.
    • 26. SARCOMERE RELAXED
    • 27. SARCOMERE PARTIALLY CONTRACTED
    • 28. SARCOMERE COMPLETELY CONTRACTED
    • 29. SLIDING FILAMENT MODEL OF MUSCLE CONTRACTION
    • 30. • RELAXED MUSCLE: • 2-2.5 µm length of sarcomere. • AFTER CONTRACTION: • 1-1.5 µm length of sarcomere. • Length of A band constant. • Length of I band constant. • Z Membranes become closer. • H zone decreases / disappear • Sliding of thin over thick filaments. • Length of individual filaments remain the same. HISTOLOGICAL CHANGES DURING MUSCLE CONTRACTION:

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