Organismic Biology Bio 207. Lecture 6. Muscle and movement; sliding filaments; E-C coupling; length-tension relationships; biomechanics. Prof.

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1 Organismic Biology Bio 207 Lecture 6 Muscle and movement; sliding filaments; E-C coupling; length-tension relationships; biomechanics Prof. Simchon Today s Agenda Skeletal muscle Neuro Muscular Junction NMJ, Muscle action potentials EC Coupling Motor units and the length-tension relationship Joint biomechanics 1

2 Today s Agenda Skeletal muscle Neuro Muscular Junction NMJ, Muscle action potentials EC Coupling Motor units and the length-tension relationship Joint biomechanics How does he pick up the glass? 2

3 Skeletal muscle: macro to micro Skeletal muscle: macro to micro Tendon a connective tissue, attaches the muscle to the bone 3

4 Striated muscle Skeletal muscle ultrastructure 4

5 Skeletal muscle ultrastructure Skeletal muscle ultrastructure 5

6 Thick filament organization Skeletal muscle ultrastructure 6

7 Sarcomere organization 7

8 Sliding filament: muscle shortening Relaxed muscle 8

9 Myosin-actin interaction THE CONTRACTION CYCLE Tight Binding in the Rigor State G-actin molecule Myosin binding sites Myosin filament ATP binds to myosin. Myosin releases actin. ADP releases. ATP binds. Myosin releases ADP at the end of the power stroke. The Power Stroke Actin filament moves toward M line. Contractionrelaxation Sliding filament Myosin hydrolyzes ATP. Energy from ATP rotates the myosin head to the cocked position. Myosin binds weakly to actin. Head swivels. Myosin releases P i. Power stroke begins when tropomyosin moves off the binding site. Ca 2 signal ADP and P i remain bound. ADP P i 9

10 Tight Binding in the Rigor State G actin molecule Myosin binding sites Myosin filament 2013 Pearson Education, Inc. Tight Binding in the Rigor State G actin molecule Myosin binding sites Myosin filament ATP binds to myosin. Myosin releases actin. ATP binds Pearson Education, Inc. 10

11 ATP binds to myosin. Myosin releases actin. Myosin hydrolyzes ATP. Energy from ATP rotates the myosin head to the cocked position. Myosin binds weakly to actin. ATP binds. ADP and P i remain bound. ADP P i 2013 Pearson Education, Inc. Myosin hydrolyzes ATP. Energy from ATP rotates the myosin head to the cocked position. Myosin binds weakly to actin. Power stroke begins when tropomyosin moves off the binding site. The Power Stroke Actin filament moves toward M line. Ca 2+ signal ADP and P i remain bound. ADP P i Head swivels. Myosin releases P i Pearson Education, Inc. 11

12 Power stroke begins when tropomyosin moves off the binding site. The Power Stroke Actin filament moves toward M line. Myosin releases ADP at the end of the power stroke. Head swivels. Myosin releases P i. ADP releases Pearson Education, Inc. Tight Binding in the Rigor State G actin molecule Myosin binding sites Myosin filament ATP binds to myosin. Myosin releases actin. ADP releases. NAVIGATOR ATP binds. Myosin releases ADP at the end of the power stroke. The Power Stroke Actin filament moves toward M line. Contractionrelaxation Sliding filament Myosin hydrolyzes ATP. Energy from ATP rotates the myosin head to the cocked position. Myosin binds weakly to actin. Head swivels. Myosin releases P i. Power stroke begins when tropomyosin moves off the binding site. Ca 2+ signal ADP P i ADP and P i remain bound Pearson Education, Inc. 12

13 Sliding filaments produce contraction Which bands and zones are unchanged during contraction and which are changed? Explain why they do what they do. Sliding filaments produce contraction 13

14 Figure 20.5 Molecular interactions that underlie muscle contraction Myosin The ATP Myosin The myosin binding Rigor ATPase attachment head dissociates a hydrolizes transient unbinds moves to actin myosin ADP to ATP state. the to and from ADP triggers cocked remains and actin. rapid position P i. The Energy tightly P i cross-bridge release and from bound binds and the to to the can a now reaction power G-actin (rigor). stroke. through is molecule. transferred Actin the filament cycle to the on a is new cross-bridge. moved G-actin about molecule. ADP 10 nm and toward P i remain the bound center of to the myosin. sarcomere. Myosin-binding sites ATP ADP ADP ADP ADP P ATP-binding i P i P site i Actin-binding site 10nm G-actin Myofibril organization 14

15 Skeletal muscle ultrastructure Today s Agenda Skeletal muscle Neuro Muscular Junction NMJ, Muscle action potentials EC Coupling Motor units and the length-tension relationship Joint biomechanics 15

16 Neuromuscular Junction Action Potential Neuromuscular Junction 16

17 Neuromuscular Junction Vertebrate Neuromuscular Junction (NMJ) 17

18 Events in chemical synaptic transmission Neurotransmitter release is Ca 2+ - dependent NMJ events are similar to other synapses EPP is large enough to depolarize muscle fiber EPP produces a synaptic current that occurs as Na + and K + channels open simultaneously driving V m towards ~0mV Nerve ending Muscle Excitation-contraction coupling KEY DHP = dihydropyridine L-type calcium channel RyR = ryanodine receptor-channel Action potential in t-tubule alters conformation of DHP receptor. DHP receptor opens RyR Ca 2+ release channels in sarcoplasmic reticulum, and Ca 2+ enters cytoplasm. Ca 2+ released Ca 2+ binds to troponin, allowing actin-myosin binding. Myosin thick filament Myosin heads execute power stroke. Distance actin moves Actin filament slides toward center of sarcomere Pearson Education, Inc. 18

19 Relaxation phase KEY DHP = dihydropyridine L-type calcium channel RyR = ryanodine receptor-channel Sarcoplasmic Ca 2+ -ATPase pumps Ca 2+ back into SR. Ca 2+ releases ATP Ca 2+ Decrease in free cytosolic [Ca 2+ ] causes Ca 2+ to unbind from troponin. Myosin thick filament Tropomyosin re-covers binding site. When myosin heads release, elastic elements pull filaments back to their relaxed position. Distance actin moves 2013 Pearson Education, Inc. Muscle fiber AP EC Coupling Relaxation 19

20 Excitation-Contraction Coupling Today s Agenda Skeletal muscle Neuro Muscular Junction NMJ, Muscle action potentials EC Coupling Motor units and the length-tension relationship Joint biomechanics 20

21 One motor neuron may innervate many muscle fibers Each muscle fiber is innervated by only one motor neuron All muscle fiber innervated by a single motor nerve are activated simultaneously The smaller the motor unit, the finer the control e.g. the eye muscles with 3-5 fibers/motor unit vs. the leg gastrocnemius with 2000 fibers/motor unit 21

22 Length Tension relationship Stretching Muscle Tension Muscle length 22

23 Cross-Bridge & Overlapping Overlapping Cross-Bridge No overlapping Cross-Bridge No cross-bridge 23

24 Mechanics of Muscle Contraction: Tension Sarcomere Length Relationship Thin Filaments Thick Filaments Length-tension relationship 24

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26 Length-Tension Relationship in Skeletal Muscle 26

27 Isotonic and Isometric Contractions Isometric Isotonic 27

28 Isometric Contraction Muscle contracts Muscle relaxes Load does 300 kg 300 kg not move. Tension developed (kg) Muscle stimulated Force required to move load Time Muscle relaxes Isotonic Contraction 35 Muscle contracts Muscle relaxes 20 kg Tension developed (kg) Force required to move load Muscle relaxes 20 kg Load moves. Muscle stimulated Time 28

29 Isotonic or Isometric Contractions Isotonic contractions create force and move a load Concentric action is a shortening action Eccentric action is a lengthening action Isometric contractions create force without moving a load Series elastic elements Sarcomeres shorten while elastic elements stretch, resulting in little change in overall length Force-Velocity Relationship 29

30 Today s Agenda Skeletal muscle Neuro Muscular Junction NMJ, Muscle action potentials EC Coupling Motor units and the length-tension relationship Joint biomechanics 30

31 How does he pick up the glass? Human skeletal lever systems 31

32 Human skeletal lever systems Rotation = Torque 1 cm/sec movement of the biceps produces a 5 cm/sec movement of the hand. Biceps force X 5 cm = 7 kg X 25 cm Biceps force = 35 Kg Lever systems A 3 rd class lever has the effort force applied on the same side of the fulcrum as the load The arm is a 3 rd class lever system and it is not very good at lifting heavy weights. The arm s mechanical advantage is far less than 1; it takes 35 kg of effort force to lift 7 kg 5X as much as the lifted load! The ankle joint is a 2nd class lever system and it is force multiplier system, meaning it lifts a greater load than the effort force it applies. A 2 nd class lever system has a mechanical advantage greater than 1; its load is between the fulcrum and the place where the effort force is applied There are also 1 st class lever systems in the body, such as the triceps muscle attachment of the arm Every body joint can be analyzed in this way 32

33 Levers lever is a rigid structure that rotates around a pivot (axis). Forces that cause rotation usually are produced by the pull of muscles or the downward push of gravity on some object. Each force is applied at a specific place on the lever called the point of force application. The effort force (Fe) tends to flex the elbow The resistance force (Fr) tends to extend the elbow A force can be represented by an arrow with its tail starting at the point of application and the head extending in the direction that the force pushes or pulls the distance from the point of force application to the pivot. That distance is called the lever arm of the force: effort (lever) arm (EA) When sufficient force is applied to a lever arm, rotational movement occurs around the pivot Rotational movement around a pivot (or joint) contrasts with linear movement in which an object moves in a straight line between two points. the tendency of a force to cause rotation will change as its point of application this "tendency to rotate is called torque (T) Force x Lever Arm length = Torque When the free arm is raised and supported at 90, two opposing torques are being generated. The first, called the torque of the effort (Te), tends to raise and support the free arm. The second, called the torque of the resistance (Tr), results from the action of gravity and tends to rotate the free arm downward. When the arm is stationary or in equilibrium, the two torques are equal. 33

34 Length from fulcrum to apllied force Length from fulcrum to load Equilibrum (should be) Arm torque = applied force torque Applied force torque = Length x muscle Arm torque = Length x weight Length from fulcrum to load Length from fulcrum to apllied force 34

35 Review Questions on today s lecture In skeletal muscle, the thick filament consists of. A. myosin B. actin C. troponin D. tropomyosin E. titin 35

36 Which of the following structures allows action potentials to move rapidly from the cell surface into the interior? A. terminal cisternae B. fascicles C. t-tubules D. crossbridges E. sarcoplasmic reticulum The lightest color bands of the sarcomere occupied by thin filaments only are the. A. I bands B. A bands C. H zone D. M line 36

37 Which of these statements about sarcomere shortening is FALSE? A. The thick and thin filaments slide past each other. B. The length of the A band remains constant. C. The length of the I band remains constant. D. The H zone almost disappears. Which of the following phases of a muscle twitch requires ATP? A. latent period B. contraction period C. relaxation period D. B and C E. A, B, and C 37

38 The first thing that occurs when the axon terminal releases ACh is. A. calcium ions return to the terminal cisternae of the SR B. the troponin blocks the tropomyosin C. calcium diffuses into the axon terminal of the motor neuron D. diffusion across the synaptic cleft E. the tropomyosin blocks the myosin Acetylcholine receptor-channels allow the passage of when open. A. Na + B. K + C. both Na + and K + D. Cl - E. Ca 2+ 38

39 At the neuromuscular junction, calcium ions act to. A. increase the conduction speed of action potentials B. release the inhibition on Z discs C. remove the blocking action of tropomyosin D. cause ATP binding to actin E. release synaptic vesicles from the axon terminal What type of ion channel opens in response to an action potential arriving at the axon terminal? A. Ligand-gated anion B. Voltage-gated sodium C. Voltage-gated potassium D. Ligand-gated cation E. Voltage-gated calcium 39

40 In skeletal muscle, the Ca 2+ for contraction comes from. A. mitochondria B. extracellular fluid C. sarcoplasmic reticulum D. B and C E. A, B, and C True or false? Skeletal muscle contraction starts when the muscle fiber depolarizes due to the release of calcium into the cytoplasm. A. True B. False 40

41 When a skeletal muscle lengthens, its sarcomeres. A. shorten B. stay the same length C. lengthen The maximal force will be developed by a muscle at its. A. shortest length B. intermediate length C. maximal length 41

42 A skeletal muscle can contract most quickly against a(n). A. minimal load B. intermediate load C. maximum load 42