1. `

2. The microstructure of muscle

3. myofiber (muscle fiber)- a single muscle cell
Muscle Terminology
myofiber (muscle fiber)- a single muscle cell
sarcolemma- muscle cell membrane
sarcoplasm- muscle cell cytoplasm
myofibril- long contractile protein structure
actin and myosin
sarcomere- the contractile unit between two z-lines

4. Connective tissue surrounding muscle

5. The sarcoplasm with sarcoplasmic reticulum and transverse tubules

6. More Terms
sarcoplasmic reticulum- storage and release site of calcium
transverse tubule- also involved in calcium flux

7. The Neuromuscular Junction

8. Neuromuscular Junction
1) Impulse travels down motor neuron
2) at end of neuron, acetylcholine released
3) Acetylcholine diffuses across synaptic cleft
4) acetylcholine binds to receptors on sarcolemma causing permeabilty
5) sodium enters cell causing depolarization and muscle contraction

9. Muscular Contraction functions to produce force for locomotion
force for breathing
force for postural support
heat production in cold (no force)

10. How do skeletal muscles contract?
Sliding filament model of contraction
the interaction of actin and myosin

11. The sliding filament theory of contraction

12. Sliding Filament Animation
-- sliding filament animation.htm

13. How do the Actin and Myosin Interact?
The myosin head binds to the actin filament in a weak state initially (or unbound)
the signal to contract initiates a strong binding state
Binding of calcium to troponin regulates this strong-weak state

14. The Contraction Itself
during the strong binding the myosin pulls the actin past
this effectively shortens or contracts the muscle

15. Relationship between myosin cross-bridges and Ca++ binding

16. Where does the energy for contraction come from?
ATP is necessary for each contraction cycle to occur
each contraction cycle results in a shortening of the muscle by 1%
some muscles can shorten by up to 60 % of their resting length
therefore many shortening cycles must occur for a single contraction

17. Sources of ATP for Muscle Contraction
Fig 8.7

18. Excitation-Contraction Coupling
Fig 8.9

19. Crossbridge Animation
Quicktime - Actin Myosin Crossbridge 3D Animation.htm

20. Summary of excitation contraction-coupling

21. Steps in Excitation - Contraction coupling
at rest actin and myosin are weakly bound (or unbound)
an excitation impulse from the a motor nerve causes an end-plate potential
the potential depolarizes the muscle cell beginning at the sarcolemma

22. The Neuromuscular Junction

23. Excitation- Contraction cont’d
depolarization travels down the T-tubules to the sarcoplasmic reticulum
the impulse reaches the SR and calcium is released
calcium binds to troponin and causes the strong binding state

24. Excitation- Contraction (one more)
during strong binding, myosin head cocks
this action moves actin filament along myosin
Binding of ATP causes the weak binding (or release) again enabling another contraction

25. Summary of excitation contraction-coupling

26. Important Points
depolarization causes release of calcium by SR
calcium enables the strong binding state
ATP provides energy for cocking of myosin head, BUT
binding of ATP causes the weak binding state (or release) of actin and myosin

27. A couple more important points
contraction can continue as long as calcium is available to enable strong binding AND
ATP is available for energy of cocking and release of strong binding
the signal to stop contraction is the loss of an impulse and uptake of calcium

28. Muscle fatigue is characterized by a reduced ability to generate force

29. Properties of Muscle Fiber Types
Biochemical properties
Oxidative capacity
Type of ATPase
Contractile properties
Maximal force production
Speed of contraction
Muscle fiber efficiency

30. Individual Fiber Types
Fast fibers
Type IIx fibers
Fast-twitch fibers
Fast-glycolytic fibers
Type IIa fibers
Intermediate fibers
Fast-oxidative glycolytic fibers
Slow fibers
Type I fibers
Slow-twitch fibers
Slow-oxidative fibers

31. Muscle Fiber Types Fast Fibers Slow fibers
Characteristic Type IIx Type IIa Type I
Number of mitochondria Low High/mod High
Resistance to fatigue Low High/mod High
Predominant energy system Anaerobic Combination Aerobic
ATPase Highest High Low
Vmax (speed of shortening) Highest Intermediate Low
Efficiency Low Moderate High
Specific tension High High Moderate

32. Comparison of maximal shortening velocities between fiber types

33. Type I vs Type II (velocity)
type II are fast twitch muscles
type IIa are sort of like slow twitch but faster
type I are slow twitch muscles
therefore IIb will have the fastest shortening velocity and type I will have the slowest

34. Endurance exercise training induced changes in fiber type in skeletal muscle

35. Training-Induced Changes in Muscle Fiber Type
Fig 8.13

36. Isotonic vs. Isometric Actions

37. Isometric Muscle Action
an isometric contraction is occurs when there is no change in muscle length when force is being produced
trying to push a car out of the snow
holding up a table so it can be leveled

38. Isotonic Muscle Action
an isotonic contraction occurs when there is a change in muscle length
concentric when muscle shortens
bicep curl, lifting
eccentric when muscle lengthens
tug o war, negatives in weights, putting down a beer

39. Recording of a simple twitch

40. Relationship between stimulus strength and force of contraction

41. Stimulus Strength vs Force of Contraction
Weak stimulus does not recruit many motor units
Stronger stimulus recruits more motor units
When all motor units are recruited, no more force can be applied regardless of stimulus strength

42. Length-tension relationship in skeletal muscle

43. Length Tension Relationship
There exists an optimal length of muscle at which it produces the greatest force
Typically between % resting length
Maximal tensions at lengths longer or shorter than the optimal length will be less

44. Progression of simple twitches, summation and tetanus

45. Tetanus
If twitches become more frequent, greater force can be developed during summation than for a single twitch
If twitches become to frequent, tetanus will develop and the muscle will not relax
Typically results only from electrical stimulation

46. Muscle force-velocity relationships

47. Muscle power-velocity relationships

48. The Golgi tendon organ

49. GTO Provides info to the CNS about tension development in the muscle
Acts like a governor to prevent damaging tension from being generated
Can be overridden to a certain extent by training
Supraphysiological strength in crisis

50. Muscle spindles structure and location

51. Spindle Provides info to the CNS about muscle length or stretch
Excessive muscle stretch, especially during contraction is damaging
Helps prevent damaging stretch during contraction