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The Muscular System

The Muscular System . Muscular System Functions. MOVEMENT Maintain Posture Stabilize Joints Generate HEAT 40% body mass 80% body heat Endothermy!. Muscle Tissue. Tissue Review: Cardiac  Cardiovascular System Involuntary, Striated

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The Muscular System

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  1. The Muscular System

  2. Muscular System Functions • MOVEMENT • Maintain Posture • Stabilize Joints • Generate HEAT • 40% body mass • 80% body heat • Endothermy!

  3. Muscle Tissue • Tissue Review: • Cardiac Cardiovascular System • Involuntary, Striated • Smooth  Cardiovascular, Digestive, Reproductive, etc. • Involuntary, non-striated • Skeletal* MUSCULAR SYSTEM • Voluntary, striated

  4. Muscles are… • Excitable (irritable) • Contractile • Extensible • Elastic • Myo-, Mys, Sarco- (muscle prefixes)

  5. Skeletal Muscle Tissue • MUSCLE CELL STRUCTURE • Arrangement: large, long FIBERS • Fiber = muscle cell • Two major protein filaments present: • Actin • Myosin myofilaments

  6. Skeletal Muscle Structure • Striated • Due to actin/myosin • Elongated • Varied lengths • Multinucleated

  7. TEXT: • Structures / Regions to know: • Muscle • Tendon • Epimysium • Facsicle • Muscle Fiber • Perimysium • Myofibril • Endomysium

  8. Muscle Anatomy

  9. http://www.bmb.psu.edu/courses/bisci004a/muscle/b4muscle.htm

  10. Skeletal Muscle Connections • Direct connection to Bone • Indirect connection via TENDON • ORIGIN: bone that does NOT move when muscle contracts • INSERTION: bone that MOVES when muscle contracts

  11. Microscopic Structure of Muscle Fiber • Cell membrane = Sarcolemma • Cytoplasm = Sarcoplasm • Multiple Mitochondria = High E output • Fiber is filled with long myofibrils • Myofibrils filled with filaments arranged in contractile units called SARCOMERES. • Myosin (thick filament) • Actin (thin filament)

  12. Sarcoplasmic Reticulum • Specialized ER connected to cell surface by T-tubules • Surrounds each myofibril • At rest, filled with Ca++ maintained by a calcium “pump”, uses ATP • When activated, pores open and release calcium, initiating contraction

  13. Actin (thin) filamentComposition • Long chains of actin globules in double spiral arrangement • Each actin contains binding site for myosin • Tropomyosin spiral around chain • blocks active site on actin • Troponin clustered along spiral • Binding site for calcium!

  14. Actin Filament

  15. Myosin (thick) filamentComposition • Contains 2 tails each with globular heads • Heads have ATP binding sites and ATPase for splitting ATP • Heads attracted to active sites on actin molecules • Heads form cross-bridges with actin

  16. Myosin Filament

  17. Multiple Myosin Filaments

  18. Sarcomere structure • Alternating dark and light bands • Central H-zone contains MYOSIN only • Lateral A-bands  contain both ACTIN and MYOSIN filaments • End in I-bands contain ACTIN only (with Z-line in center) Z LINE TO Z LINE = 1 SARCOMERE

  19. SARCOMERE STRUCTURE

  20. Sarcomere

  21. Nerve supplyto Muscle Fiber • Each muscle fiber served by a motor neuron • Motor neuron ends in a pad filled with vacuoles packed with neurotransmitter • Pad sits above specialized piece of sarcolemma called motor end plate

  22. Neuron pad + motor end plate = Neuromuscular junction (Space between called synaptic cleft )

  23. Sliding Filament Theory of Muscle Contraction Sequence of Steps: • Neuron releases neurotransmitter, acetylcholine (ACh) into synaptic cleft • ACh diffuses to motor end plate • ACh binds to receptor on motor end plate • Gated channel protein opens, Na+ rushes into cell interior, upsets RMP!

  24. Generation ofAction Potential • RMP = -70 Mv • Sudden influx of Na+ generates Action Potential • RMP later restored to normal by sodium-potassium pump

  25. 5. Action potential carried along the sarcolemma to transverse (“T”) tubules connected to Sarcoplasmic Reticulum • SR membrane becomes permeable to calcium • Sarcoplasm is flooded with calcium ions

  26. 8. Ca++ binds to troponin 9. Ca/Troponin pulls tropomyosin out of the way, unmasks active site on actin molecules 10. Myosin heads attach to actin 11. Heads rotate, pull actin in to H-zone 12. Z lines get closer…

  27. 13. Myosin splits ATP to recharge 14. Continues until Action Potential is restored and Ca++ is pumped back into SR 15.All sarcomeres shorten, shortening muscle cell

  28. 16. Shortening cell pulls on tendons attached to bones, moving bone at articulation 17. Contraction of opposite muscle required to fully elongate shortened muscle

  29. Reminders: • Refractory Period • All or None Effect • Breakdown of ACh by ACh-esterase

  30. Disorders/Conditions of the Muscular System • Duchenne’s Muscular Dystrophy • Sex linked inheritance • Dystrophin protein deficiency • Tearing of sarcolemma • Accumulation of CT/fat • Muscular ATROPHY

  31. Tetanus

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