1. Regulation of Contraction I. How do nerves stimulate muscle contraction? II. Factors influencing muscle tension III. How does contraction of smooth/cardiac muscle differ from skeletal?

2. Innervations of Muscle Fiber SR Sarcolemma

3. Neuromuscular Junction AP to synaptic terminal of motor neuron

4. Neuromuscular Junction AP to synaptic terminal of motor neuron Release of Ach

5. Neuromuscular Junction AP to synaptic terminal of motor neuron Release of Ach AP spreads across sarcolemma

6. Neuromuscular Junction AP to synaptic terminal of motor neuron Release of Ach AP spreads across sarcolemma

7. Skeletal Muscle Contraction Sarcolemma

8. Skeletal Muscle Contraction AP passes down T tubules Sarcolemma

9. Skeletal Muscle Contraction AP passes down T tubules Release of Ca + from the ____________

10. Skeletal Muscle Contraction AP passes down T tubules Release of Ca + from the ____________ Ca + binds to Troponin

11. Skeletal Muscle Contraction AP passes down T tubules Release of Ca + from the ____________ Ca + binds to Troponin Sliding Filament Animation

12. Regulation of Contraction I. How do nerves stimulate muscle contraction? II. Factors influencing muscle tension III. How does contraction of smooth/cardiac muscle differ from skeletal?

13. Factors Influencing Muscle Tension 1.Frequency of stimulation 2.Fiber length at onset of contraction 3.Number of muscle fibers contracting 4.Muscle fatigue

14. Frequency of Muscle Fiber Stimulation Incomplete

15. Incomplete

16. Maximum Tension Incomplete

17. Complete Tetanus Sustained maximum muscle tension

18. Tetanus Infection Clostridium tetani Muscles contract severely Respiratory failure

19. Factors Influencing Muscle Tension 1.Frequency of stimulation 2.Fiber length at onset of contraction 3.Number of muscle fibers contracting 4.Muscle fatigue

20. Muscle Tone & L-T Relationship Relaxed muscles are slightly contracted

21. Muscle Tone & L-T Relationship Relaxed muscles are slightly contracted Tension during contraction depends on sarcomere length of optimum length

22. Muscle Tone & L-T Relationship Too much tone yields a weak contraction of optimum length

23. Muscle Tone & L-T Relationship Too much tone yields a weak contraction Too little tone also yields a weak contraction of optimum length

24. Length-Tension Relationship % of resting length Tension (% of maximum) 6080100120140160 100 50 Tension (% of maximum)

25. Northern Leopard Frog

26. Factors Influencing Muscle Tension 1.Frequency of stimulation 2.Fiber length at onset of contraction 3.Number of muscle fibers contracting Each fiber can contract or not (all or none) More fibers means a stronger contraction

27. Factors Influencing Muscle Tension

28. 4. Muscle fatigue Muscle fibers cannot contract strongly until Ca + is sequestered Delay is “fatigue”

29. Regulation of Contraction I. How do nerves stimulate a muscle contraction? II. Factors influencing muscle tension III. How does contraction of smooth/cardiac muscle differ from skeletal?

30. Smooth & Cardiac Muscle Contraction Contain actin & myosin Use ATP to power cross-bridge cycling

31. Smooth & Cardiac Muscle Contraction Contain actin & myosin Use ATP to power cross-bridge cycling Differences in muscle excitation Differences in muscle contraction

32. Smooth Muscle Contraction Myosin and Actin lattice Slow, wavelike contraction Relaxed Contracted

33. Smooth Muscle Contraction Myosin and Actin lattice Slow, wavelike contraction Influx of Ca + from ECF Self-excitable Relaxed Contracted

34. Smooth Muscle Contraction Differs from skeletal and cardiac muscle: –Lacks troponin and tropomyosin –Ca + binds to calmodulin (similar to troponin)

35. Smooth Muscle Contraction Differs from skeletal and cardiac muscle: –Ca + - calmodulin complex phosphorylates Myosin, increases its affinity for Actin –Ca + removal causes Myosin-Actin dissociation Relaxed Contracted

36. Cardiac Muscle

37. Has characteristics of both skeletal and smooth Skeletal Similarity: Troponin & tropomyosin Smooth Similarity: Self-excitable Unique Feature: Long AP’s

38. Skeletal Muscle Cardiac Muscle AP in Cardiac Muscle Long AP prevents tetanus

39. Summary Motor neurons stimulate muscle contraction. The AP then passes along the sarcolemma and down the T tubules, deep into the muscle fiber. This allows all myofilaments within the cell to be stimulated. Release of Ca + from the SR binds to troponin, causing tropomyosin to shift and expose the myosin head binding sites on actin. Sliding filament process then takes over. Muscle fiber length, fatigue, and the number of fibers stimulated can all influence the strength of contraction. Smooth/Cardiac contraction differs from Skeletal contraction.