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2015-­‐04-­‐13 Muscle Tissue Dr. Dinithi Peiris Dept. of Zoology Function of Muscle Tissue
§  Movement §  Maintenance of posture §  Joint stabiliza=on §  Heat genera=on 3 Func=onal Characteris=c Muscle Tissue §  Contrac=lity §  Only one ac=on: to shorten §  Shortening generates pulling force §  Excitability §  Nerve fibers cause electrical impulse to travel §  Extensibility §  Stretch with contrac=on of an opposing muscle §  Elas=city §  Recoils passively aMer being stretched 4 1 2015-­‐04-­‐13 Types of Muscle Tissue §  Skeletal muscle §  Cardiac muscle §  Smooth muscle 5 Types of Muscle Tissue •  Skeletal muscle §  40% of body wt. §  ATach to & move skeleton §  Mul=nucleate fibers §  Long cylindrical bundles §  Cells with obvious stria=ons §  Contrac=ons are voluntary §  Forces for sliding are generated by weak interac=ons between ac=n & myosin 6 Types of Muscle Tissue •  Cardiac muscle •  Only in the wall of the heart •  Cross-­‐stria=ons •  Individual branched elongated cells •  INTERCALATED disks at the end •  Contrac=ons are involuntary, vigorous & rhythmic •  Smooth muscle (walls of hollow organs) •  Lack stria=ons •  Collec=ons of fusiform cells •  Contrac=ons -­‐ involuntary 7 2 2015-­‐04-­‐13 Similari=es •  Their cells are called fibers because they are elongated •  Contrac=on depends on myofilaments •  Ac0n •  Myosin •  Plasma membrane is called sarcolemma •  Sarcos = flesh •  Lemma = sheath 8 Skeletal Muscle Epimysium: surrounds whole muscle Perimysium is around fascicle Endomysium is around each muscle fiber 9 Muscle Fibers or Myofibers § 
Every mature muscle cell developed f• rom 100 myoblasts that fuse together in the fetus. (mul=nucleated) § 
Mature muscle cells cannot divide § 
Muscle growth is a result of cellular enlargement & not cell division § 
Satellite cells retain the ability to regenerate new cells. 10 3 2015-­‐04-­‐13 Muscle Fibers or Myofibers § 
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Muscle cells are long, •  cylindrical & mul=nucleated Sarcolemma = muscle cell membrane Sarcoplasm filled with =ny threads called myofibrils & myoglobin (red-­‐colored, oxygen-­‐binding protein) 11 Transverse (T) Tubules • T (transverse) tubules are invagina=ons •  of the sarcolemma into the center •  filled with extracellular fluid •  carry muscle ac=on poten=als down into cell • Mitochondria lie in rows throughout the cell •  near the muscle proteins that use ATP during contrac=on 12 Myofibrils & Myofilaments •  fibers are filled •  Muscle with threads called myofibrils separated by SR (sarcoplasmic re=culum) •  Myofilaments (thick & thin filaments) are the contrac=le proteins of muscle 13 4 2015-­‐04-­‐13 Sarcoplasmic Re=culum (SR) •  of tubular sacs •  System similar to smooth ER in non-­‐muscle cells •  Stores Ca+2 in a relaxed muscle •  Release of Ca+2 triggers muscle contrac=on 14 Atrophy & Hypertrophy •  What is atrophy ? & hypertrophy? •  • Atrophy •  was=ng away of muscles •  the transi=on to connec=ve =ssue can not be reversed •  Hypertrophy •  increase in the diameter of muscle fibers •  resul=ng from very forceful, repe==ve muscular ac=vity & an increase in myofibrils, SR & mitochondria 15 Muscle Stria=on •  Striated paTern within myofibrills •  Alterna=ng dark thick filaments – A bands and light thin filaments – I bands 16 5 2015-­‐04-­‐13 M Line & Z Line •  M Line •  Center of the A band •  Middle of the sarcomere •  Z Line •  At 2 ends of sarcomere •  H Zone •  Only thick filaments •  Zone of overlap •  Thin & thick filaments overlap •  6 thin filaments surrounds each thick filament. 17 Thick & Thin Myofilaments •  Suppor=ng proteins (M line, & Z disc help anchor the thick & thin filaments in place 18 Thick & Thin Myofilaments 19 6 2015-­‐04-­‐13 Proteins of Muscles § 
Myofibrils are built of 3 kinds of protein §  contrac=le proteins §  myosin and ac=n §  regulatory proteins which turn contrac=on on & off §  troponin and tropomyosin §  structural proteins which provide proper alignment, elas=city and extensibility §  ==n, myomesin, nebulin and dystrophin 20 Proteins of Muscles -­‐ Myosin • 
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Held in place by M line Tail – binds to other myosin molecule Head -­‐ Twisted together §  Reaches the nearest thin filament §  During contrac=on interact with ac=n filament Forming cross bridges 21 Proteins of Muscles -­‐ Ac=n • 
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Made of ac=n, troponin & tropomyosin Relaxed muscle – topomyosin prevents ac=n, myosin interac=on §  Thin filaments are held by Z line, which is the boundary of sarcomere 22 7 2015-­‐04-­‐13 Proteins of Muscles – Ac=n & Myosin 23 8