Ch 12 can be done in one        lecture
Chapter 12: MusclesReview muscle anatomy (esp. microanatomyof skeletal muscle)                                      Develo...
Terminology: sarcolemma t-tubules sarcoplasmic reticulum myofibers, myofibrils, myofilaments sarcomere
More Terminology: Tension Contraction Load Excitation-contraction coupling Rigor Relaxation
Anatomy          Fig 12-3
More Anatomy               Fig 12-3
Myofibrils = Contractile Organelles of              Myofiber    Contain 6 types of protein: Actin                        ...
Fig 12-3
Titin and Nebulin   Titin:      biggest protein known (25,000 aa);    elastic!    » Stabilizes position of contractile fi...
Sliding Filament Theory p 403   Sarcomere = unit of contraction   Myosin “walks down” an actin fiber towards Z-    line ...
The Molecular Basis of Contraction  Rigor State                               Compare to Fig 12-9                  myosin ...
Released energy changes                      angle between head & long                      axis of myosinMyosin head acts...
Power stroke begins        ADP released  as Pi released                        Tight binding to actinMyosin crossbridge mo...
Regulation of Contraction by Troponin    and Tropomyosin   Tropomyosin blocks    myosin binding site (weak    binding pos...
Rigor mortis Joint stiffness and muscular rigidity of dead body Begins 2 – 4 h post mortem. Can last up to 4 days dependin...
Initiation of Contraction Excitation-Contraction Coupling explains how you get from AP in axon to contraction in sarcomere...
Details of E/C                             Coupling  Nicotinic cholinergic receptors on motor end  plate = Na+ /K+ channel...
Excitation-    Contraction    CouplingFig 12-11 a
DHP (dihydropyridine) receptors open Ca2+ channels in t-tubulesIntracytosolic [Ca2+] ContractionCa2+ re-uptake into SRRel...
Muscle Contraction Needs Steady Supply of                   ATP    Where / when is ATP needed?    Only enough ATP stored...
Where does all this ATP come from?   Phosphocreatine: backup energy    source                     C(P)Kphosphocreatine + ...
Oxidative onlyMuscle Fiber        Oxidative orClassification      glycolytic
Muscle Adaptation to Exercise         ( not in book)Endurance training: More & bigger                          Resistance...
Muscle Tension is Function of Fiber Length   Sarcomere length reflects    thick, thin filament overlap   Long Sarcomere:...
Force of Contraction (all-or-none)   Increases With     » muscle-twitch summation     » recruitment of motor units    Mec...
Smooth muscle   A few differences    »   Innervation by varicosities    »   Smaller cells    »   Longer myofilaments    »...
muscles
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muscles

  1. 1. Ch 12 can be done in one lecture
  2. 2. Chapter 12: MusclesReview muscle anatomy (esp. microanatomyof skeletal muscle) Developed by John Gallagher, MS, DVM
  3. 3. Terminology: sarcolemma t-tubules sarcoplasmic reticulum myofibers, myofibrils, myofilaments sarcomere
  4. 4. More Terminology: Tension Contraction Load Excitation-contraction coupling Rigor Relaxation
  5. 5. Anatomy Fig 12-3
  6. 6. More Anatomy Fig 12-3
  7. 7. Myofibrils = Contractile Organelles of Myofiber Contain 6 types of protein: Actin Contractile Myosin Tropomyosin Regulatory Troponin Titin Accessory Nebulin Fig 12-3 c-f
  8. 8. Fig 12-3
  9. 9. Titin and Nebulin Titin: biggest protein known (25,000 aa); elastic! » Stabilizes position of contractile filaments » Return to relaxed location Nebulin: inelastic giant protein » Alignment of A & M Fig 12-6
  10. 10. Sliding Filament Theory p 403 Sarcomere = unit of contraction Myosin “walks down” an actin fiber towards Z- line » ? - band shortens » ? - band does not shorten Myosin = motor protein: chemical energy  mechanical energy of motion
  11. 11. The Molecular Basis of Contraction Rigor State Compare to Fig 12-9 myosin affinity changes due to ATP binding ATP ADP + Pi Tight binding between ATP bindsG-actin and myosin  dissociation No nucleotide bound
  12. 12. Released energy changes angle between head & long axis of myosinMyosin head acts as RelaxedATPase Rotation and weak muscle state binding to new G-actin when sufficient ATP
  13. 13. Power stroke begins ADP released as Pi released Tight binding to actinMyosin crossbridge movement pushes actin
  14. 14. Regulation of Contraction by Troponin and Tropomyosin Tropomyosin blocks myosin binding site (weak binding possible but no powerstroke) Troponin controls position of tropomyosin and has Ca2+ binding site  Ca2+ present: binding of A & M Fig 12-10  Ca2+ absent: relaxation
  15. 15. Rigor mortis Joint stiffness and muscular rigidity of dead body Begins 2 – 4 h post mortem. Can last up to 4 days depending on temperature and other conditions Caused by leakage of Ca2+ ions into cell and ATP depletion Maximum stiffness  12-24 h post mortem, then?
  16. 16. Initiation of Contraction Excitation-Contraction Coupling explains how you get from AP in axon to contraction in sarcomereACh released from somatic motor neuron at the Motor End Plate AP in sarcolemma and T-Tubules Ca2+ release from sarcoplasmic reticulum Ca2+ binds to troponin
  17. 17. Details of E/C Coupling Nicotinic cholinergic receptors on motor end plate = Na+ /K+ channels Net Na entry creates EPSP + AP to T-tubules DHP (dihydropyridine) receptors in T- tubules sense depolarization Fig 12-11
  18. 18. Excitation- Contraction CouplingFig 12-11 a
  19. 19. DHP (dihydropyridine) receptors open Ca2+ channels in t-tubulesIntracytosolic [Ca2+] ContractionCa2+ re-uptake into SRRelaxation Fig 12-11 b
  20. 20. Muscle Contraction Needs Steady Supply of ATP  Where / when is ATP needed?  Only enough ATP stored for 8 twitches » Phosphocreatine may substitute for ATP Twitch = single contraction relaxation cycle
  21. 21. Where does all this ATP come from? Phosphocreatine: backup energy source C(P)Kphosphocreatine + ADP creatine + ATP CHO: aerobic and anaerobic resp. Fatty acid breakdown always requires O2 – is too slow for heavy exercise » Some intracellular FA
  22. 22. Oxidative onlyMuscle Fiber Oxidative orClassification glycolytic
  23. 23. Muscle Adaptation to Exercise ( not in book)Endurance training: More & bigger Resistance training: mitochondria  More actin & myosin proteins & more More enzymes for sarcomeres aerobic respiration  More myofibrils More myoglobin muscle hypertrophy no hypertrophy
  24. 24. Muscle Tension is Function of Fiber Length Sarcomere length reflects thick, thin filament overlap Long Sarcomere: little overlap, few crossbridges  weak tension generation Short Sarcomere: Too much overlap limited crossbridge formation  tension decreases rapidly
  25. 25. Force of Contraction (all-or-none) Increases With » muscle-twitch summation » recruitment of motor units Mechanics of body movement covered in lab only Fig 12-17
  26. 26. Smooth muscle A few differences » Innervation by varicosities » Smaller cells » Longer myofilaments » Myofilaments arranged in periphery of cell Cardiac muscle contraction covered later

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