1. Excitation–Contraction Coupling
Action potential reaches a triad:
releasing Ca2+
triggering contraction
Requires myosin heads to be in “cocked” position:
loaded by ATP energy

2. Exposing the Active Site
Figure 10–11

3. The Contraction Cycle
Figure 10–12 (1 of 4)

4. The Contraction Cycle
Figure 10–12 (2 of 4)

5. The Contraction Cycle
Figure 10–12 (3 of 4)

6. The Contraction Cycle
Figure 10–12 (Navigator) (4 of 4)

7. 5 Steps of the Contraction Cycle
Exposure of active sites
Formation of cross-bridges
Pivoting of myosin heads
Detachment of cross-bridges
Reactivation of myosin

8. Fiber Shortening
As sarcomeres shorten, muscle pulls together, producing tension
Figure 10–13

9. Contraction Duration Depends on: duration of neural stimulus
number of free calcium ions in sarcoplasm
availability of ATP

10. Relaxation Ca2+ concentrations fall Ca2+ detaches from troponin
Active sites are recovered by tropomyosin
Sarcomeres remain contracted

11. A Review of Muscle Contraction
Table 10–1 (1 of 2)

12. KEY CONCEPT (Part 1)
Skeletal muscle fibers shorten as thin filaments slide between thick filaments
Free Ca2+ in the sarcoplasm triggers contraction
SR releases Ca2+ when a motor neuron stimulates the muscle fiber

13. KEY CONCEPT (Part 2) Contraction is an active process
Relaxation and return to resting length is passive

14. Tension Production The all–or–none principal:
as a whole, a muscle fiber is either contracted or relaxed

15. Tension of a Single Muscle Fiber
Depends on:
the number of pivoting cross-bridges
the fiber’s resting length at the time of stimulation
the frequency of stimulation

16. Frequency of Stimulation
A single neural stimulation produces:
a single contraction or twitch
which lasts about 7–100 msec
Sustained muscular contractions:
require many repeated stimuli

17. 3 Phases of Twitch Latent period before contraction:
the action potential moves through sarcolemma
causing Ca2+ release

18. 3 Phases of Twitch Contraction phase: calcium ions bind
tension builds to peak

19. 3 Phases of Twitch Relaxation phase: Ca2+ levels fall
active sites are covered
tension falls to resting levels

20. Treppe Repeated stimulations immediately after relaxation phase:
stimulus frequency < 50/second
Causes a series of contractions with increasing tension

21. Wave Summation Increasing tension or summation of twitches
Figure 10–16b

22. Incomplete Tetanus
Twitches reach maximum tension
Figure 10–16c

23. Complete Tetanus
Figure 10–16d

24. Muscle Tone The normal tension and firmness of a muscle at rest
Muscle units actively maintain body position, without motion
Increasing muscle tone increases metabolic energy used, even at rest

25. 2 Types of Skeletal Muscle Tension
Isotonic contraction
Isometric contraction

26. Isotonic Contraction
Figure 10–18a, b

27. Isometric Contraction
Figure 10–18c, d

28. ATP and Muscle Contraction
Sustained muscle contraction uses a lot of ATP energy
Muscles store enough energy to start contraction
Muscle fibers must manufacture more ATP as needed

29. ATP and CP Reserves Adenosine triphosphate (ATP):
the active energy molecule
Creatine phosphate (CP):
the storage molecule for excess ATP energy in resting muscle

30. ATP Generation Cells produce ATP in 2 ways:
aerobic metabolism of fatty acids in the mitochondria
anaerobic glycolysis in the cytoplasm

31. Aerobic Metabolism Is the primary energy source of resting muscles
Breaks down fatty acids
Produces 34 ATP molecules per glucose molecule

32. Anaerobic Glycolysis
Is the primary energy source for peak muscular activity
Produces 2 ATP molecules per molecule of glucose
Breaks down glucose from glycogen stored in skeletal muscles

33. Energy Use and Muscle Activity
At peak exertion:
muscles lack oxygen to support mitochondria
muscles rely on glycolysis for ATP
pyruvic acid builds up, is converted to lactic acid

34. Results of Muscle Fatigue
Depletion of metabolic reserves
Damage to sarcolemma and sarcoplasmic reticulum
Low pH (lactic acid)
Muscle exhaustion and pain

35. The Recovery Period
The time required after exertion for muscles to return to normal
Oxygen becomes available
Mitochondrial activity resumes

36. Oxygen Debt After exercise:
the body needs more oxygen than usual to normalize metabolic activities
resulting in heavy breathing

37. Hormones and Muscle Metabolism
Growth hormone
Testosterone
Thyroid hormones
Epinephrine

38. Structure of Cardiac Tissue
Cardiac muscle is striated, found only in the heart
Figure 10–22

39. Intercalated Discs Are specialized contact points between cardiocytes
Join cell membranes of adjacent cardiocytes (gap junctions, desmosomes)

40. Functions of Intercalated Discs
Maintain structure
Enhance molecular and electrical connections
Conduct action potentials

41. Smooth Muscle in Body Systems (Part 1)
Forms around other tissues
In blood vessels:
regulates blood pressure and flow
In reproductive and glandular systems:
produces movements

42. Smooth Muscle in Body Systems (Part 2)
In digestive and urinary systems:
forms sphincters
produces contractions
In integumentary system:
arrector pili muscles cause goose bumps

43. Structure of Smooth Muscle
Nonstriated tissue
Figure 10–23

44. Comparing Smooth and Striated Muscle
Different internal organization of actin and myosin
Different functional characteristics

45. 8 Characteristics of Smooth Muscle Cells
Long, slender, and spindle shaped
Have a single, central nucleus
Have no T tubules, myofibrils, or sarcomeres
Have no tendons or aponeuroses

46. 8 Characteristics of Smooth Muscle Cells
Have scattered myosin fibers
Myosin fibers have more heads per thick filament
Have thin filaments attached to dense bodies
Dense bodies transmit contractions from cell to cell

47. Functional Characteristics of Smooth Muscle
Excitation–contraction coupling
Length–tension relationships
Control of contractions
Smooth muscle tone