1. Muscle
Lecture #10 Ch 10 Muscle
Muse 10/31/12

2. An Introduction to Muscle Tissue
A primary tissue type, divided into
Skeletal muscle
Cardiac muscle
Smooth muscle

3. Functions of Skeletal Muscles
Produce skeletal movement
Maintain body position
Support soft tissues
Guard openings
Maintain body temperature
Store nutrient reserves

4. Skeletal Muscle Structures
Muscle tissue (muscle cells or fibers)
Connective tissues
Nerves
Blood vessels

5. Skeletal Muscle Structures
Organization of Connective Tissues
Muscles have three layers of connective tissues
Epimysium:
exterior collagen layer
connected to deep fascia
Separates muscle from surrounding tissues
Perimysium: (not to be confused with paramecium)
surrounds muscle fiber bundles (fascicles)
contains blood vessel and nerve supply to fascicles
Endomysium:
surrounds individual muscle cells (muscle fibers)
contains capillaries and nerve fibers contacting muscle cells
contains myosatellite cells (stem cells) that repair damage

6. Skeletal Muscle Structures
Figure 10–1 The Organization of Skeletal Muscles.

7. (wrapped by perimysium)
Epimysium
Epimysium
Bone
Perimysium
Tendon
Endomysium
Muscle fiber
in middle of
a fascicle
(b)
Blood vessel
Fascicle
(wrapped by perimysium)
Endomysium
(between individual
muscle fibers)
Perimysium
Fascicle
Muscle fiber
(a)
Figure 9.1

8. Skeletal Muscle Structures
Organization of Connective Tissues
Muscle attachments
Endomysium, perimysium, and epimysium come together:
at ends of muscles
to form connective tissue attachment to bone matrix
i.e., tendon (bundle) or aponeurosis (sheet)

9. Skeletal Muscle Structures
Nerves
Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord)
Blood Vessels
Muscles have extensive vascular systems that
Supply large amounts of oxygen
Supply nutrients
Carry away wastes

10. Skeletal Muscle: Attachments
Muscles attach:
Directly—epimysium of muscle is fused to the periosteum of bone or perichondrium of cartilage
Indirectly—connective tissue wrappings extend beyond the muscle as a ropelike tendon or sheetlike aponeurosis

11. Skeletal Muscle Fibers
Are very long
Develop through fusion of mesodermal cells (myoblasts)
Become very large
Contain hundreds of nuclei

12. Skeletal Muscle Fibers
Figure 10–2 The Formation of a Multinucleate Skeletal Muscle Fiber.

13. Skeletal Muscle Fibers
Figure 10–2a The Formation of a Multinucleate Skeletal Muscle Fiber.

14. Skeletal Muscle Fibers
Figure 10–2b The Formation of a Multinucleate Skeletal Muscle Fiber.

15. Skeletal Muscle Fibers
Internal Organization of Muscle Fibers
The sarcolemma
The cell membrane of a muscle fiber (cell)
Surrounds the sarcoplasm (cytoplasm of muscle fiber)
A change in transmembrane potential begins contractions

16. Sarcolemma
Mitochondrion
Myofibril
Dark A band
Light I band
Nucleus
(b) Diagram of part of a muscle fiber showing the myofibrils. One myofibril is extended afrom the cut end of the fiber.

17. Skeletal Muscle Fibers
Internal Organization of Muscle Fibers
Transverse tubules (T tubules)
Transmit action potential through cell
Allow entire muscle fiber to contract simultaneously
Have same properties as sarcolemma

18. Skeletal Muscle Fibers
Internal Organization of Muscle Fibers
Myofibrils
Lengthwise subdivisions within muscle fiber
Made up of bundles of protein filaments (myofilaments)
Myofilaments are responsible for muscle contraction
Types of myofilaments:
thin filaments:
made of the protein actin
thick filaments:
made of the protein myosin

19. Skeletal Muscle Fibers
Internal Organization of Muscle Fibers
Sarcoplasmic reticulum (SR)
A membranous structure surrounding each myofibril
Helps transmit action potential to myofibril
Similar in structure to smooth endoplasmic reticulum
Forms chambers (terminal cisternae) attached to T tubules

20. Skeletal Muscle Fibers
Internal Organization of Muscle Fibers
Triad
Is formed by one T tubule and two terminal cisternae
Cisternae:
concentrate Ca2+ (via ion pumps)
release Ca2+ into sarcomeres to begin muscle contraction

21. Skeletal Muscle Fibers
Figure 10–3 The Structure of a Skeletal Muscle Fiber.
Show video excitation coupling

22. Skeletal Muscle Fibers
Internal Organization of Muscle Fibers
Sarcomeres
The contractile units of muscle
Structural units of myofibrils
Form visible patterns within myofibrils
Muscle striations
A striped or striated pattern within myofibrils:
alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

23. Sarcomere
Smallest contractile unit (functional unit) of a muscle fiber
The region of a myofibril between two successive Z discs
Composed of thick and thin myofilaments made of contractile proteins

24. Skeletal Muscle Fibers
Internal Organization of Muscle Fibers
Sarcomeres
M Lines and Z Lines:
M line:
the center of the A band
at midline of sarcomere
Z lines:
the centers of the I bands
at two ends of sarcomere

25. Thin (actin)
filament
Z disc
H zone
Z disc
Thick (myosin)
filament
I band
A band
Sarcomere
I band
M line
(c)
Small part of one myofibril enlarged to show the myofilaments
responsible for the banding pattern. Each sarcomere extends from
one Z disc to the next.
Sarcomere
Z disc
M line
Z disc
Thin (actin)
filament
Elastic (titin)
filaments
Thick
(myosin)
filament
(d)
Enlargement of one sarcomere (sectioned lengthwise). Notice the
myosin heads on the thick filaments.

26. Skeletal Muscle Fibers
Internal Organization of Muscle Fibers
Sarcomeres
Zone of overlap:
the densest, darkest area on a light micrograph
where thick and thin filaments overlap
The H Band:
the area around the M line
has thick filaments but no thin filaments

27. Skeletal Muscle Fibers
Internal Organization of Muscle Fibers
Sarcomeres
Titin:
are strands of protein- quite elastic, like springs
reach from tips of thick filaments to the Z line
stabilize the filaments

28. Skeletal Muscle Fibers
Figure 10–4a Sarcomere Structure.

29. Skeletal Muscle Fibers
Figure 10–4b Sarcomere Structure.

30. Skeletal Muscle Fibers
Figure 10–5 Sarcomere Structure.

31. Skeletal Muscle Fibers
Figure 10–6 Levels of Functional Organization in a Skeletal Muscle.

32. Skeletal Muscle Fibers
Figure 10–6 Levels of Functional Organization in a Skeletal Muscle.

33. Skeletal Muscle Fibers
Sarcomere Function
Transverse tubules encircle the sarcomere near zones of overlap
Ca2+ released by SR causes thin and thick filaments to interact

34. Skeletal Muscle Fibers
Muscle Contraction
Is caused by interactions of thick and thin filaments
Structures of protein molecules determine interactions

35. Skeletal Muscle Fibers
Four Thin Filament Proteins
F-actin (Filamentous actin)
Is two twisted rows of globular G-actin
The active sites on G-actin strands bind to myosin
Nebulin
Holds F-actin strands together
Tropomyosin
Is a double strand
Prevents actin–myosin interaction
Troponin
A globular protein
Binds tropomyosin to G-actin
Controlled by Ca2+

36. Skeletal Muscle Fibers
Figure 10–7a, b Thick and Thin Filaments.

37. Skeletal Muscle Fibers
Initiating Contraction
Ca2+ binds to receptor on troponin molecule
Troponin–tropomyosin complex changes
Exposes active site of F-actin

38. Skeletal Muscle Fibers
Thick Filaments
Contain twisted myosin subunits
Contain titin strands that recoil after stretching
The mysosin molecule
Tail:
binds to other myosin molecules
Head:
made of two globular protein subunits
reaches the nearest thin filament

39. Skeletal Muscle Fibers
Figure 10–7c, d Thick and Thin Filaments.

40. Skeletal Muscle Fibers
Myosin Action
During contraction, myosin heads
Interact with actin filaments, forming cross-bridges
Pivot, producing motion

41. Skeletal Muscle Fibers
Skeletal Muscle Contraction
Sliding filament theory
Thin filaments of sarcomere slide toward M line, alongside thick filaments
The width of A zone stays the same
Z lines move closer together

42. Skeletal Muscle Fibers
Figure 10–8a Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber.

43. Skeletal Muscle Fibers
Figure 10–8b Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber.

44. Skeletal Muscle Fibers
Skeletal Muscle Contraction
The process of contraction
Neural stimulation of sarcolemma:
causes excitation–contraction coupling
Cisternae of SR release Ca2+:
which triggers interaction of thick and thin filaments
consuming ATP and producing tension

45. The Neuromuscular Junction
Is the location of neural stimulation
Action potential (electrical signal)
Travels along nerve axon
Ends at synaptic terminal
Synaptic terminal:
releases neurotransmitter (acetylcholine or ACh)
into the synaptic cleft (gap between synaptic terminal and motor end plate)

46. The Neuromuscular Junction
Figure 10–10a, b Skeletal Muscle Innervation.

47. The Neuromuscular Junction
Figure 10–10c Skeletal Muscle Innervation.

48. The Neuromuscular Junction
Figure 10–10c Skeletal Muscle Innervation.

49. The Neuromuscular Junction
The Neurotransmitter
Acetylcholine or ACh
Travels across the synaptic cleft
Binds to membrane receptors on sarcolemma (motor end plate)
Causes sodium–ion rush into sarcoplasm
Is quickly broken down by enzyme (acetylcholinesterase or AChE)

50. The Neuromuscular Junction
Figure 10–10c Skeletal Muscle Innervation.

51. The Neuromuscular Junction
Action Potential
Generated by increase in sodium ions in sarcolemma
Travels along the T tubules
Leads to excitation–contraction coupling
Excitation–contraction coupling:
action potential reaches a triad:
releasing Ca2+
triggering contraction
requires myosin heads to be in “cocked” position:
loaded by ATP energy
Show video neuromuscular junction

52. The Neuromuscular Junction
Figure 10–11 The Exposure of Active Sites.

53. The Contraction Cycle Five Steps of the Contraction Cycle
Exposure of active sites
Formation of cross-bridges
Pivoting of myosin heads
Detachment of cross-bridges
Reactivation of myosin

54. The Contraction Cycle
Figure 10–12 The Contraction Cycle.

55. The Contraction Cycle [INSERT FIG. 10.12, step 1]
Figure 10–12 The Contraction Cycle.

56. The Contraction Cycle
Figure 10–12 The Contraction Cycle.

57. The Contraction Cycle
Figure 10–12 The Contraction Cycle.

58. The Contraction Cycle
Figure 10–12 The Contraction Cycle.

59. The Contraction Cycle
Figure 10–12 The Contraction Cycle.

60. The Contraction Cycle Fiber Shortening Contraction Duration
As sarcomeres shorten, muscle pulls together, producing tension
Contraction Duration
Depends on
Duration of neural stimulus
Number of free calcium ions in sarcoplasm
Availability of ATP

61. The Contraction Cycle
Figure 10–13 Shortening during a Contraction.

62. The Contraction Cycle Relaxation Rigor Mortis Ca2+ concentrations fall
Ca2+ detaches from troponin
Active sites are re-covered by tropomyosin
Sarcomeres remain contracted
Rigor Mortis
A fixed muscular contraction after death
Caused when
Ion pumps cease to function; ran out of ATP
Calcium builds up in the sarcoplasm

63. The Contraction Cycle

64. Tension Production Need more force? Recruit more fibers
The all–or–none principle
As a whole, a muscle fiber is either contracted or relaxed
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
Need more force? Recruit more fibers

65. Tension Production Tension of a Single Muscle Fiber
Length–tension relationship
Number of pivoting cross-bridges depends on:
amount of overlap between thick and thin fibers
Optimum overlap produces greatest amount of tension:
too much or too little reduces efficiency
Normal resting sarcomere length:
is 75% to 130% of optimal length

66. Tension Production
Figure 10–14 The Effect of Sarcomere Length on Active Tension.

67. Tension Production Tension of a Single Muscle Fiber
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

68. Tension Production Three Phases of Twitch
Latent period before contraction
The action potential moves through sarcolemma
Causing Ca2+ release
Contraction phase
Calcium ions bind
Tension builds to peak
Relaxation phase
Ca2+ levels fall
Active sites are covered
Tension falls to resting levels

69. Control of Muscle Tension

70. Tension Production
Figure 10–15 The Development of Tension in a Twitch.

71. Tension Production
Figure 10–15 The Development of Tension in a Twitch.

72. Tension Production Treppe A stair-step increase in twitch tension
Repeated stimulations immediately after relaxation phase
Stimulus frequency <50/second
Causes a series of contractions with increasing tension

73. Tension Production Tension of a Single Muscle Fiber Wave summation
Increasing tension or summation of twitches
Repeated stimulations before the end of relaxation phase:
stimulus frequency >50/second
Causes increasing tension or summation of twitches

74. Tension Production Tension of a Single Muscle Fiber Incomplete tetanus
Twitches reach maximum tension
If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension
Complete Tetanus
If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction

75. Tension Production
Figure 10–16 Effects of Repeated Stimulations.

76. Tension Production
Figure 10–16 Effects of Repeated Stimulations.

77. Tension Production Tension Produced by Whole Skeletal Muscles
Depends on
Internal tension produced by muscle fibers
External tension exerted by muscle fibers on elastic extracellular fibers
Total number of muscle fibers stimulated

78. Tension Production Tension Produced by Whole Skeletal Muscles
Motor units in a skeletal muscle
Contain hundreds of muscle fibers
That contract at the same time
Controlled by a single motor neuron

79. Tension Production Tension Produced by Whole Skeletal Muscles
Recruitment (multiple motor unit summation)
In a whole muscle or group of muscles, smooth motion and increasing tension are produced by slowly increasing the size or number of motor units stimulated
Maximum tension
Achieved when all motor units reach tetanus
Can be sustained only a very short time

80. Tension Production
Figure 10–17 The Arrangement and Activity of Motor Units in a Skeletal Muscle.

81. Tension Production
Figure 10–17 The Arrangement and Activity of Motor Units in a Skeletal Muscle.

82. Tension Production Tension Produced by Whole Skeletal Muscles
Sustained tension
Less than maximum tension
Allows motor units rest in rotation
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

83. Tension Production Two Types of Skeletal Muscle Tension
Isotonic contraction
Isometric contraction

84. Tension Production Two Types of Skeletal Muscle Tension
Isotonic Contraction
Skeletal muscle changes length:
resulting in motion
If muscle tension > load (resistance):
muscle shortens (concentric contraction)
If muscle tension < load (resistance):
muscle lengthens (eccentric contraction)

85. Tension Production Two Types of Skeletal Muscle Tension
Isometric contraction
Skeletal muscle develops tension, but is prevented from changing length
Note: iso- = same, metric = measure

86. Tension Production
Figure 10–18a, b Isotonic and Isometric Contractions.

87. Tension Production
Figure 10–18c, d Isotonic and Isometric Contractions.

88. Tension Production Resistance and Speed of Contraction
Are inversely related
The heavier the load (resistance) on a muscle
The longer it takes for shortening to begin
And the less the muscle will shorten
Muscle Relaxation
After contraction, a muscle fiber returns to resting length by
Elastic forces
Opposing muscle contractions
Gravity

89. Tension Production
Figure 10–19 Load and Speed of Contraction.

90. Tension Production Elastic Forces Opposing Muscle Contractions
The pull of elastic elements (tendons and ligaments)
Expands the sarcomeres to resting length
Opposing Muscle Contractions
Reverse the direction of the original motion
Are the work of opposing skeletal muscle pairs

91. Tension Production Gravity
Can take the place of opposing muscle contraction to return a muscle to its resting state

92. 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

93. ATP and Muscle Contraction
ATP and CP Reserves
Adenosine triphosphate (ATP)
The active energy molecule
Creatine phosphate (CP)
The storage molecule for excess ATP energy in resting muscle
Energy recharges ADP to ATP
Using the enzyme creatine phosphokinase (CPK or CK)
When CP is used up, other mechanisms generate ATP

94. ATP and Muscle Contraction
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

95. ATP and Muscle Contraction
Figure 10–20 Muscle Metabolism.

96. ATP and Muscle Contraction
Figure 10–20a Muscle Metabolism.

97. ATP and Muscle Contraction
Figure 10–20c Muscle Metabolism.

98. ATP and Muscle Contraction
Muscle Fatigue
When muscles can no longer perform a required activity, they are fatigued
Results of Muscle Fatigue
Depletion of metabolic reserves
Damage to sarcolemma and sarcoplasmic reticulum
Low pH (lactic acid)
Muscle exhaustion and pain

99. ATP and Muscle Contraction
The Cori Cycle
The removal and recycling of lactic acid by the liver
Liver converts lactic acid to pyruvic acid
Glucose is released to recharge muscle glycogen reserves
Oxygen Debt
After exercise or other exertion
The body needs more oxygen than usual to normalize metabolic activities
Resulting in heavy breathing

100. ATP and Muscle Contraction
Skeletal muscles at rest metabolize fatty acids and store glycogen
During light activity, muscles generate ATP through anaerobic breakdown of carbohydrates, lipids, or amino acids
At peak activity, energy is provided by anaerobic reactions that generate lactic acid as a byproduct

101. ATP and Muscle Contraction
Muscle Performance
Power
The maximum amount of tension produced
Endurance
The amount of time an activity can be sustained
Power and endurance depend on
The types of muscle fibers
Physical conditioning

102. Muscle Fiber Types Three Types of Skeletal Muscle Fibers Fast fibers
Slow fibers
Intermediate fibers

103. Muscle Fiber Types Three Types of Skeletal Muscle Fibers Fast fibers
Contract very quickly
Have large diameter, large glycogen reserves, few mitochondria
Have strong contractions, fatigue quickly

104. Muscle Fiber Types Three Types of Skeletal Muscle Fibers Slow fibers
Are slow to contract, slow to fatigue
Have small diameter, more mitochondria
Have high oxygen supply
Contain myoglobin (red pigment, binds oxygen)

105. Muscle Fiber Types Three Types of Skeletal Muscle Fibers
Intermediate fibers
Are mid-sized
Have low myoglobin
Have more capillaries than fast fibers, slower to fatigue

106. Muscle Fiber Types
Figure 10–21 Fast versus Slow Fibers.

107. Muscle Fiber Types Muscles and Fiber Types White muscle Red muscle
Mostly fast fibers (aka Fast twitch)
Pale (e.g., chicken breast)
Red muscle
Mostly slow fibers (aka slow twitch)
Dark (e.g., chicken legs)
Most human muscles
Mixed fibers (General proportions determined by genetics)
Pink

108. Muscle Fiber Types Muscle Hypertrophy Muscle Atrophy
Muscle growth from heavy training
Increases diameter of muscle fibers
Increases number of myofibrils
Increases mitochondria, glycogen reserves
Muscle Atrophy
Lack of muscle activity
Reduces muscle size, tone, and power

109. Muscle Fiber Types What you don’t use, you lose
Muscle tone indicates base activity in motor units of skeletal muscles
Muscles become flaccid when inactive for days or weeks
Muscle fibers break down proteins, become smaller and weaker
With prolonged inactivity, fibrous tissue may replace muscle fibers