1. Outline I. Types of Muscle II. Anatomy of Skeletal Muscle III. Sliding Filament Theory IV. Role of Ca+ in regulating muscle contraction

2. Muscle 80% of lean mass Responsible for: - locomotion - heart beat - peristalsis

3. Types of Muscle Tissue Smooth Muscle –Involuntary –Visceral organs –Non-striated

4. Types of Muscle Tissue Smooth Muscle –Involuntary –Visceral organs –Non-striated Cardiac Muscle –Involuntary –Striated –Only in heart

5. Types of Muscle Tissue Smooth Muscle –Involuntary –Visceral organs –Non-striated Cardiac Muscle –Involuntary –Striated –Only in heart Skeletal Muscle –Voluntary –Striated –Locomotion

6. Outline I. Types of Muscle II. Anatomy of Skeletal Muscle III. Sliding Filament Theory IV. Role of Ca+ in regulating muscle contraction

7. (fascicle) Skeletal Muscle Anatomy Each muscle has several fascicles

8. (fascicle) Skeletal Muscle Anatomy Each muscle has several fascicles Each fascicle has several muscle fibers

9. Skeletal Muscle Anatomy Each muscle has several fascicles Each fascicle has several muscle fibers Muscle fibers contain myofibrils (fascicle)

10. Skeletal Muscle Anatomy Each muscle has several fascicles Each fascicle has several muscle fibers Muscle fibers contain myofibrils Myofibrils composed of sarcomeres (fascicle)

11. Connective Tissue Sheaths Muscles contain layers of connective tissue

12. Important Cellular Structures Sarcoplasmic Reticulum Transverse “T” Tubules Sarcomere

14. Skeletal Muscle Cell Anatomy Sarcoplasmic Reticulum: Hollow tubules Surround myofibrils Stores Ca + Control Ca + release

16. Skeletal Muscle Cell Anatomy Transverse “T” Tubules: Inward protrusion of Sarcolemma Carry AP from motor neuron into muscle cell Diffusion of the “contract” signal

18. Sarcomere Structure: Myofilaments Composed of 2 filament types Position defines bands Thin filaments attach at “Z” lines Thick filaments attach at “M” lines

19. Microscopic View of a Sacromere I BandA Band H Zone Z LineM Line Sarcomere

20. Remember this from lab? Striations caused by Actin/Myosin overlap

21. Myofilament Anatomy Myosin: Heads act as “cross-bridges” to pull on Actin Head has 2 binding sites

22. Myofilament Anatomy Actin: Contains active sites for Myosin attachment Tropomyosin blocks binding site in resting muscle

23. Outline I. Types of Muscle II. Anatomy of Skeletal Muscle III. Sliding Filament Theory IV. Role of Ca+ in regulating muscle contraction

24. Sliding Filament Theory of Contraction Relaxed Muscle: Slight overlap of Actin and Myosin

25. Sliding Filament Theory of Contraction Relaxed Muscle: Slight overlap of Actin and Myosin Muscle Contraction: Actin slides past Myosin Sarcomere shortens

26. Relaxed Contracted

27. Myosin Actin crossbridges How Does Contraction Occur?

28. Sliding Filament Theory Step 1 – Cross Bridge Formation: Resting state of muscle (a “cocked gun”) Myosin head bound to ADP + P i Myosin weakly attached to Actin binding site

29. Sliding Filament Theory Step 2 - The Power Stroke: Myosin head bends, pulls Actin towards center of sarcomere ~ 10 nm ADP + P i released Tight binding of Actin and Myosin (“rigor state”)

30. Sliding Filament Theory Step 3 - Cross Bridge Detachment: New ATP binds to Myosin head Myosin head detaches from Actin

31. Sliding Filament Theory Step 4 - Cocking the Myosin Head: ATP hydrolyzed to ATP + P i Head returns to “cocked” high-energy form Cycle repeats numerous times

32. 1. 3. 2. 4.

33. Physiology of Sliding Filament Theory Contractions involve cycles of Myosin-Actin attachment & detachment Series of working strokes

34. Physiology of Sliding Filament Theory Contractions involve cycles of Myosin-Actin attachment & detachment Series of working strokes “Centipede walking” of Myosin heads on Actin

35. Myosin Actin crossbridges How is contraction regulated?

36. Outline I. Types of Muscle II. Anatomy of Skeletal Muscle III. Sliding Filament Theory IV. Role of Ca + in regulating muscle contraction

37. No contraction without Ca + Contraction depends on calcium Muscle in resting state (step 1) without Ca +

38. No contraction without Ca + Contraction depends on calcium Muscle in resting state (step 1) without Ca + Ca + allows steps 2-4 to occur

39. 1. 3. 2. 4.

40. No contraction without Ca + Contraction depends on calcium Muscle in resting state (step 1) without Ca + Ca + allows steps 2-4 to occur Ca + shifts tropomyosin out of the way

41. Tropomyosin: muscular “safety switch”

42. Rigor Mortis Ca + diffusion Tropomyosin shift Rigor State

43. Rigor Mortis Ca + diffusion Tropomyosin shift Lack of ATP Myosin head stuck Rigor State Need ATP

44. Rigor Mortis Ca + diffusion Tropomyosin shift Lack of ATP Myosin head stuck Rigor State Need ATP

45. How do Packing Plants Prevent Rigor?

46. Nervous Control of Contraction Sarcoplasmic Reticulum Sequesters Ca + in muscle fibers Membrane densely packed with Ca + pumps

47. Nervous Control of Contraction Neuromuscular Junction Synapse between motor neuron and muscle fiber Motor neuron stimulates AP in membrane of muscle fiber

48. Nervous Control of Contraction Transverse “T” tubule Invagination of muscle fiber’s membrane Enables AP to spread deep within muscle fiber

49. Summary The sarcomere is the functional unit of muscle tissue Sarcomere contains Actin and Myosin Muscle contraction occurs via nervous stimulation and the association/ dissociation of Actin and Myosin filaments Sarcoplasmic reticulum stores Ca+ which allows shift of tropomyosin