1. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings  The predominant extracellular ion is Na +  The predominant intracellular ion is K +  The sarcolemma is relatively impermeable to both ions Action Potential: Electrical Conditions of a Polarized Sarcolemma Figure 9.8a

2. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Action Potential: Depolarization and Generation of the Action Potential  An axonal terminal of a motor neuron releases ACh and causes a patch of the sarcolemma to become permeable to Na + (sodium channels open) Figure 9.8b

3. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Action Potential: Propagation of the Action Potential  Polarity reversal of the initial patch of sarcolemma changes the permeability of the adjacent patch  Voltage-regulated Na + channels now open in the adjacent patch causing it to depolarize Figure 9.8c

4. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Action Potential: Propagation of the Action Potential  Thus, the action potential travels rapidly along the sarcolemma  Once initiated, the action potential is unstoppable, and ultimately results in the contraction of a muscle Figure 9.8c

5. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Action Potential: Repolarization  Immediately after the depolarization wave passes, the sarcolemma permeability changes  Na + channels close and K + channels open  K + diffuses from the cell, restoring the electrical polarity of the sarcolemma Figure 9.8d

6. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Action Potential: Repolarization  Repolarization occurs in the same direction as depolarization, and must occur before the muscle can be stimulated again (refractory period)  The ionic concentration of the resting state is restored by the Na + -K + pump Figure 9.8d

7. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Excitation-Contraction (EC) Coupling 1.Action potential generated and propagated along sarcomere to T-tubules 2.Action potential triggers Ca2+ release 3.Ca++ bind to troponin; blocking action of tropomyosin released 4.contraction via crossbridge formation; ATP hyrdolysis 5.Removal of Ca+2 by active transport 6.tropomyosin blockage restored; contraction ends Figure 9.10

8. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 9.12 ATP ADP ATP hydrolysis ADP ATP PiPi PiPi Myosin head (high-energy configuration) Myosin head attaches to the actin myofilament, forming a cross bridge. Thin filament As ATP is split into ADP and P i, the myosin head is energized (cocked into the high-energy conformation). Inorganic phosphate (P i ) generated in the previous contraction cycle is released, initiating the power (working) stroke. The myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line. Then ADP is released. Myosin head (low-energy configuration) As new ATP attaches to the myosin head, the link between myosin and actin weakens, and the cross bridge detaches. Thick filament 1 4 2 3

9. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Muscle Twitch  A muscle twitch is the response of a muscle to a single, brief threshold stimulus  There are three phases to a muscle twitch  Latent period  Period of contraction  Period of relaxation

10. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Graded Muscle Responses  Required for proper control of skeletal movement  Responses are graded by:  Changing the frequency of stimulation  Changing the strength of the stimulus

11. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Muscle Response to Varying Stimuli refractory period Figure 9.15

12. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Motor Unit: The Nerve-Muscle Functional Unit PLAY InterActive Physiology ®: Contraction of Motor Units, pages 3-9 Figure 9.13a

13. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neuromuscular Junction Figure 9.7 (a-c)

14. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Summation of Motor Units Figure 9.17

15. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Tonus Hypertrophy Atrophy

16. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Treppe: The Staircase Effect  Staircase – increased contraction in response to multiple stimuli of the same strength  Contractions increase because:  There is increasing availability of Ca 2+ in the sarcoplasm  Muscle enzyme systems become more efficient because heat is increased as muscle contracts

17. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Isotonic Contractions Figure 9.19a

18. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Isometric Contractions Figure 9.19b Posture

19. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Muscle Metabolism: Energy for Contraction Figure 9.20

20. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Oxygen Debt  Vigorous exercise causes dramatic changes in muscle chemistry  Oxygen reserves must be replenished  Lactic acid must be converted to pyruvic acid  Glycogen stores must be replaced  ATP and CP reserves must be resynthesized  Oxygen debt – the extra amount of O2 needed for the above restorative processes

21. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Muscle Twitch Comparisons Figure 9.14b

22. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 9.2

23. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Ch 10 Interactions of Skeletal Muscles  Muscles only pull (never push)  As muscles shorten, the insertion generally moves toward the origin  Skeletal muscles work together, Synergists  or in opposition, Antagonists

24. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Lever Systems: First Class Figure 10.3a

25. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Lever Systems: Second Class Figure 10.3b

26. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Lever Systems: Third Class Figure 10.3c