1. Muscles &Muscle Tissue
Chapter 10

2. Functions of Skeletal Muscles
Produce skeletal movement
Maintain body position
Support soft tissues
Guard body openings
Maintain body temperature

3. Functional Characteristics of Muscle
Excitability (irritability)
Can receive and respond to stimuli.
Stimuli can include nerve impulses, stretch, hormones or changes in the chemical environment.
Contractility – the ability to shorten with increasing tension.
Extensibility – the ability to stretch.
Elasticity – the ability to snap back (recoil) to their resting length after being stretched.

4. Three types of muscle
Skeletal Smooth Cardiac

5. Characteristics of Skeletal Muscle
Striated
Multinucleate (it is a syncytium)
Voluntary
Parallel fibers

6. Organization of Connective Tissues
Figure 10–1

7. Formation of Skeletal Muscle Fibers
Skeletal muscle cells are called fibers
Formation of Skeletal Muscle Fibers

8. Organization of Skeletal Muscle Fibers

9. Anatomy of a myofibril

10. A Triad
Is formed by 1 T tubule and 2 terminal cisternae

11. Sarcomeres
Figure 10–4

12. Muscle Striations A striped or striated pattern within myofibrils:
alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

13. M Lines and Z Lines M line: Z lines: the center of the A band
at midline of sarcomere
Z lines:
the centers of the I bands
at 2 ends of sarcomere

14. Zone of Overlap The densest, darkest area on a light micrograph
Where thick and thin filaments overlap

15. The H Zone The area around the M line
Has thick filaments but no thin filaments

16. Titin Are strands of protein
Reach from tips of thick filaments to the Z line
Stabilize the filaments

17. Sarcomere Structure

18. Summary of skeletal muscle anatomy: muscles are made of fascicles

19. Fascicles are made of fibers, fibers are made of myofibrils

20. Level 1: Skeletal Muscle
Figure 10–6 (1 of 5)

21. Level 2: Muscle Fascicle
Figure 10–6 (2 of 5)

22. Level 3: Muscle Fiber
Figure 10–6 (3 of 5)

23. Level 4: Myofibril
Figure 10–6 (4 of 5)

24. Level 5: Sarcomere
Figure 10–6 (5 of 5)

25. Fibrils are divided into sarcomeres, sarcomeres are made of myofilaments

26. Myofilaments are made of protein molecules

27. A Thin Filament

28. 4 Thin Filament Proteins
F actin:
is 2 twisted rows of globular G actin
the active sites on G actin strands bind to myosin

29. 4 Thin Filament Proteins
Nebulin:
holds F actin strands together

30. 4 Thin Filament Proteins
Tropomyosin:
is a double strand
prevents actin–myosin interaction

31. 4 Thin Filament Proteins
Troponin:
a globular protein
binds tropomyosin to G actin
controlled by Ca2+

32. Troponin and Tropomyosin
Figure 10–7b

33. A Thick Filament
Figure 10–7c

34. Thick Filaments Contain twisted myosin subunits
Contain titin strands that recoil after stretching

35. The Mysosin Molecule
Figure 10–7d

36. Muscle Contraction: the Sliding Filament Theory
Muscle contraction requires:
Stimulus – the generation of an action potential.
Crossbridge formation – interaction between the thick and thin myofilaments. This is triggered by Ca++ ions released from the sarcoplasmic reticulum.
Energy – ATP to energize the myosin molecules.

37. Sliding Filaments

38. Skeletal Muscle Contraction

39. T- tubules supply the stimulus, Sarcoplasmic Reticulum supplies the Ca++, Mitochondria supply the ATP.

40. 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

41. Skeletal Muscle Innervation

42. Skeletal Muscle Innervation
Figure 10–10c

43. The Neuromuscular Junction
Is the location of neural stimulation
Action potential (electrical signal):
travels along nerve axon
ends at synaptic terminal

44. A neuromuscular junction (NMJ).

45. acetylcholine
The actual synapse

46. Synaptic Terminal Releases neurotransmitter (acetylcholine or ACh)
Into the synaptic cleft (gap between synaptic terminal and motor end plate)

47. 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)

48. Action Potential Generated by increase in sodium ions in sarcolemma
Travels along the T tubules
Leads to excitation–contraction coupling

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

50. Exposing the Active Site

51. The Contraction Cycle

52. The Contraction Cycle

53. The Contraction Cycle

54. The Contraction Cycle

55. 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

56. Show the animation

57. A Review of Muscle Contraction

58. Excitation-Contraction coupling
Stimulus or excitation is required for muscles to contract.
In skeletal muscle, the stimulus is from a motor neuron.
The stimulus is in the form of an action potential.
This action potential starts at the neuromuscular junction (NMJ).

59. Excitation-contraction coupling

60. Show NMJ animation

61. Micrograph of an NMJ

62. A Synapse
Synaptic vesicles

63. Tension and Sarcomere Length
Figure 10–14

64. 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

65. Length–Tension Relationship
Normal resting sarcomere length:
is 75% to 130% of optimal length

66. 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

67. Tension in a Twitch
Length of twitch depends on type of muscle

68. Myogram A graph of twitch tension development
Figure 10–15b (Navigator)

69. 3 Phases of Twitch Latent period before contraction:
the action potential moves through sarcolemma
causing Ca2+ release

70. 3 Phases of Twitch Contraction phase: calcium ions bind
tension builds to peak

71. 3 Phases of Twitch Relaxation phase: Ca2+ levels fall
active sites are covered
tension falls to resting levels

72. Treppe
A stair-step increase in twitch tension
Figure 10–16a

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

74. Wave Summation
Increasing tension or summation of twitches

75. Wave Summation
Repeated stimulations before the end of relaxation phase:
stimulus frequency > 50/second
Causes increasing tension or summation of twitches

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

77. Incomplete Tetanus
If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension

78. Complete Tetanus
Figure 10–16d

79. Complete Tetanus
If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction

80. Comparative speed of different muscles

81. 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

82. Motor Units in a Skeletal Muscle
Figure 10–17

83. Motor Units in a Skeletal Muscle
Contain hundreds of muscle fibers
That contract at the same time
Controlled by a single motor neuron

84. Recruitment (Multiple Motor Unit Summation)
In a whole muscle or group of muscles, smooth motion and increasing tension is produced by slowly increasing size or number of motor units stimulated

85. Maximum Tension Achieved when all motor units reach tetanus
Can be sustained only a very short time

86. Sustained Tension Less than maximum tension
Allows motor units to rest in rotation

87. 2 Types of Skeletal Muscle Tension
Isotonic contraction
Isometric contraction

88. Isotonic Contraction
Figure 10–18a, b

89. Isotonic Contraction Skeletal muscle changes length:
resulting in motion
If muscle tension > resistance:
muscle shortens (concentric contraction)
If muscle tension < resistance:
muscle lengthens (eccentric contraction)

90. Isometric Contraction
Figure 10–18c, d

91. Isometric Contraction
Skeletal muscle develops tension, but is prevented from changing length
Note: Iso = same, metric = measure

92. Resistance and Speed of Contraction

93. Resistance and Speed of Contraction
Are inversely related
The heavier the resistance on a muscle:
the longer it takes for shortening to begin
and the less the muscle will shorten

94. 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

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

96. Recharging ATP Energy recharges ADP to ATP:
using the enzyme creatine phosphokinase (CPK)
When CP is used up, other mechanisms generate ATP

97. Energy Storage in Muscle Fiber
Table 10–2

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

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

100. 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

101. Anaerobic Metabolism: a losing proposition

102. 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

103. Muscle Metabolism

104. Muscle Metabolism
Figure 10–20b

105. Muscle Metabolism
Figure 10–20c

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

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

108. 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

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

110. Muscle Performance Power: Endurance: Power and endurance depend on:
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

111. 3 Types of Skeletal Muscle Fibers
Fast fibers
Slow fibers
Intermediate fibers

112. Fast Fibers Contract very quickly
Have large diameter, large glycogen reserves, few mitochondria
Have strong contractions, fatigue quickly

113. Slow Fibers Are slow to contract, slow to fatigue
Have small diameter, more mitochondria
Have high oxygen supply
Contain myoglobin (red pigment, binds oxygen)

114. Intermediate Fibers Are mid-sized Have low myoglobin
Have more capillaries than fast fiber, slower to fatigue

115. Fast versus Slow Fibers
Figure 10–21

116. Comparing Skeletal Muscle Fibers

117. Muscles and Fiber Types
White muscle:
mostly fast fibers
pale (e.g., chicken breast)
Red muscle:
mostly slow fibers
dark (e.g., chicken legs)
Most human muscles:
mixed fibers
pink

118. Muscle Hypertrophy Muscle growth from heavy training:
increases diameter of muscle fibers
increases number of myofibrils
increases mitochondria, glycogen reserves

119. Muscle Atrophy Lack of muscle activity:
reduces muscle size, tone, and power

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

121. 7 Characteristics of Cardiocytes
Unlike skeletal muscle, cardiac muscle cells (cardiocytes):
are small
have a single nucleus
have short, wide T tubules

122. 7 Characteristics of Cardiocytes
have no triads
have SR with no terminal cisternae
are aerobic (high in myoglobin, mitochondria)
have intercalated discs

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

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

125. Coordination of Cardiocytes
Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells

126. 4 Functions of Cardiac Tissue
Automaticity:
contraction without neural stimulation
controlled by pacemaker cells
Variable contraction tension:
controlled by nervous system

127. 4 Functions of Cardiac Tissue
Extended contraction time
Prevention of wave summation and tetanic contractions by cell membranes

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

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

130. 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

131. 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

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

133. Excitation–Contraction Coupling
Free Ca2+ in cytoplasm triggers contraction
Ca2+ binds with calmodulin:
in the sarcoplasm
activates myosin light chain kinase
Enzyme breaks down ATP, initiates contraction

134. Length–Tension Relationships
Thick and thin filaments are scattered
Resting length not related to tension development
Functions over a wide range of lengths (plasticity)

135. Control of Contractions
Subdivisions:
multiunit smooth muscle cells:
connected to motor neurons
visceral smooth muscle cells:
not connected to motor neurons
rhythmic cycles of activity controlled by pacesetter cells

136. Smooth Muscle Tone Maintains normal levels of activity
Modified by neural, hormonal, or chemical factors

137. Smooth Muscle

138. Varicosities

139. Skeletal Smooth Diameter 10 - 100 m 3 - 8 m Connective tissue
Epi-, Peri- & Endomysium
Endomysium only SR
Yes, complex
Barely, simple
T - tubules
yes no
Sarcomeres
Gap Junctions
voluntary
Neurotransmitters
Acetylcholine (Ach)
Ach, epinephrine, norepinephrine, et al
Regeneration
Very little
Lots, for muscle

140. Future governors of Califorina?