1. Lecture 7: Chapter 10 Muscle Tissue Pages: 283-325
Lecturer: Dr. Barjis
Room: P313 /P307
Phone: (718)

2. Learning Objectives
Describe the organization of muscle and the unique characteristics of skeletal muscle cells.
Identify the structural components of the sarcomere.
Summarize the events at the neuromuscular junction.
Explain the key concepts involved in skeletal muscle contraction and tension production.

3. Learning Objectives
Describe how muscle fibers obtain energy for contraction.
Distinguish between aerobic and anaerobic contraction, muscle fiber types, and muscle performance.
Identify the differences between skeletal, cardiac and smooth muscle.

4. Skeletal muscle tissue and the Muscular System
Three types of muscle
Skeletal – attached to bone
Cardiac – found in the heart
Smooth – lines hollow organs

5. Skeletal muscle functions
Produce skeletal movement
Maintain posture and body position
Support soft tissues
Guard entrances and exits
Maintain body temperature

6. Anatomy of Skeletal Muscle
Organization of connective tissues
Epimysium surrounds muscle
Perimysium sheathes bundles of muscle fibers
Epimysium and perimysium contain blood vessels and nerves
Endomysium covers individual muscle fibers
Tendons or aponeuroses attach muscle to bone or muscle
Animation: See tutorial

7. The Organization of Skeletal Muscles

8. Skeletal muscle fibers
Sarcolemma (cell membrane)
Sarcoplasm (muscle cell cytoplasm)
Sarcoplasmic reticulum (modified ER)
T-tubules and myofibrils aid in contraction
Sarcomeres – regular arrangement of myofibrils

9. The Structure of a Skeletal Muscle Fiber

10. Sarcomere Structure, Part I

11. Myofibrils
Thick and thin filaments
Organized regularly

12. Sarcomere Structure, Part II

13. Levels of Functional Organization in Skeletal Muscle Fiber

14. Thin filaments F-actin Nebulin Tropomyosin
Covers active sites on G-actin
Troponin
Binds to G-actin and holds tropomyosin in place

15. Thick filaments Bundles of myosin fibers around titan core
Myosin molecules have elongate tail, globular head
Heads form cross-bridges during contraction
Interactions between G-actin and myosin prevented by tropomyosin during rest

16. Thick and Thin Filaments

17. Sliding filament theory
Explains the relationship between thick and thin filaments as contraction proceeds
Cyclic process beginning with calcium release from SR
Calcium binds to troponin
Trponin moves, moving tropomyosin and exposing actin active site
Myosin head forms cross bridge and bends toward H zone
ATP allows release of cross bridge

18. Changes in the appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber

19. The Contraction of Skeletal Muscle
Tension
Created when muscles contract
Series of steps that begin with excitation at the neuromuscular junction
Calcium release
Thick/thin filament interaction
Muscle fiber contraction
Tension

20. An Overview of the Process of Skeletal Muscle

21. Control of skeletal muscle activity occurs at the neuromuscular junction
Action potential arrives at synaptic terminal
ACh released into synaptic cleft
ACh binds to receptors on post-synaptic neuron
Action potential in sarcolemma

22. Skeletal Muscle Innervation

23. Skeletal Muscle Innervation
Animation: See tutorial

24. Excitation/contraction coupling
Action potential along T-tubule causes release of calcium from cisternae of SR
Initiates contraction cycle
Attachment
Pivot
Detachment
Return

25. The Contraction Cycle

26. The Contraction Cycle

27. The Contraction Cycle

28. The Contraction Cycle

29. Relaxation Acetylcholinesterase breaks down ACh
Limits the duration of contraction
Animation: See tutorial

30. Tension production by muscle fibers
All or none principle
Amount of tension depends on number of cross bridges formed
Skeletal muscle contracts most forcefully over a narrow ranges of resting lengths

31. The Effect of Sarcomere Length on Tension

32. Twitch
Cycle of contraction, relaxation produced by a single stimulus
Treppe
Repeated stimulation after relaxation phase has been completed

33. Summation
Repeated stimulation before relaxation phase has been completed
Wave summation = one twitch is added to another
Incomplete tetanus = muscle never relaxes completely
Complete tetanus = relaxation phase is eleminated

34. The Twitch and the Development of Tension

35. Effects of Repeated Stimulations

36. Tension production by skeletal muscles
Internal tension generated inside contracting muscle fibers
External tension generated in extracellular fibers

37. Internal and External Tension

38. Motor units
All the muscle fibers innervated by one neuron
Precise control of movement determined by number and size of motor unit
Muscle tone
Stabilizes bones and joints

39. The Arrangement of Motor Units in a Skeletal Muscle

40. Tension production by skeletal muscles
Internal tension generated inside contracting muscle fibers
External tension generated in extracellular fibers

41. Internal and External Tension

42. Motor units
All the muscle fibers innervated by one neuron
Precise control of movement determined by number and size of motor unit
Muscle tone
Stabilizes bones and joints

43. The Arrangement of Motor Units in a Skeletal Muscle

44. Contractions Isometric
Tension rises, length of muscle remains constant
Isotonic
Tension rises, length of muscle changes
Resistance and speed of contraction inversely related
Return to resting lengths due to elastic components, contraction of opposing muscle groups, gravity
Animation: See tutorial

45. Isotonic and Isometric Contractions
Figure 10.18

46. Resistance and Speed of Contraction
Animation: See tutorial

47. Energy Use and Muscle Contraction
Muscle Contraction requires large amounts
of energy
Creatine phosphate releases stored energy to convert ADP to ATP
Aerobic metabolism provides most ATP needed for contraction
At peak activity, anaerobic glycolysis needed to generate ATP

48. Muscle Metabolism

49. Muscle Metabolism

50. Energy use and level of muscular activity
Energy production and use patterns mirror muscle activity
Fatigued muscle no longer contracts
Build up of lactic acid
Exhaustion of energy resources

51. Recovery period Begins immediately after activity ends
Oxygen debt (excess post-exercise oxygen consumption)
Amount of oxygen required during resting period to restore muscle to normal conditions

52. Types of skeletal muscle fibers
Muscle Performance
Types of skeletal muscle fibers
Fast fibers
Slow fibers
Intermediate fibers

53. Fast versus Slow Fibers

54. Fast fibers Large in diameter Contain densely packed myofibrils
Large glycogen reserves
Relatively few mitochondria
Produce rapid, powerful contractions of short duration

55. Slow fibers Half the diameter of fast fibers
Take three times as long to contract after stimulation
Abundant mitochondria
Extensive capillary supply
High concentrations of myoglobin
Can contract for long periods of time

56. Intermediate fibers Similar to fast fibers
Greater resistance to fatigue

57. Muscle performance and the distribution of muscle fibers
Pale muscles dominated by fast fibers are called white muscles
Dark muscles dominated by slow fibers and myoglobin are called red muscles
Training can lead to hypertrophy of stimulated muscle

58. Physical conditioning
Anaerobic endurance
Time over which muscular contractions are sustained by glycolysis and ATP/CP reserves
Aerobic endurance
Time over which muscle can continue to contract while supported by mitochondrial activities
Animation: See tutorial

59. Structural characteristics of cardiac muscle
Cardiac Muscle Tissue
Structural characteristics of cardiac muscle
Located only in heart
Cardiac muscle cells are small
One centrally located nucleus
Short broad T-tubules
Dependent on aerobic metabolism
Intercalated discs where membranes contact one another

60. Cardiac Muscle Tissue

61. Functional characteristics of cardiac muscle tissue
Automaticity
Contractions last longer than skeletal muscle
Do not exhibit wave summation
No tetanic contractions possible

62. Structural characteristics of smooth muscle
Smooth Muscle Tissue
Structural characteristics of smooth muscle
Nonstriated
Lack sarcomeres
Thin filaments anchored to dense bodies
Involuntary

63. Smooth Muscle Tissue

64. Functional characteristics of smooth muscle
Contract when calcium ions interact with calmodulin
Activates myosin light chain kinase
Functions over a wide range of lengths
Plasticity
Multi-unit smooth muscle cells are innervated by more than one motor neuron
Visceral smooth muscle cells are not always innervated by motor neurons
Neurons that innervate smooth muscle are not under voluntary control

65. You should now be familiar with:
The organization of muscle and the unique characteristics of skeletal muscle cells.
The structural components of the sarcomere.
The events at the neuromuscular junction.
The key concepts involved in skeletal muscle contraction and tension production.
How muscle fibers obtain energy for contraction.
Aerobic and anaerobic contraction, muscle fiber types, and muscle performance.
The differences between skeletal, cardiac and smooth muscle