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

2. An Introduction to Muscle Tissue
Skeletal Muscles
Are attached to the skeletal system
Allow us to move
The muscular system
Includes only skeletal muscles

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:
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. 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)

8. 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

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

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

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

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

13. 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

14. 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

15. 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

16. 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

17. 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

18. Skeletal Muscle Fibers
Figure 10–3 The Structure of a Skeletal Muscle Fiber.

19. 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)

20. 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

21. 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

22. Skeletal Muscle Fibers
Internal Organization of Muscle Fibers
Sarcomeres
Titin:
are strands of protein
reach from tips of thick filaments to the Z line
stabilize the filaments

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

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

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

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

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

28. 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

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

30. 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+

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

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

33. 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

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

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

36. 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

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

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

39. 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

40. Skeletal Muscle Fibers
Figure 10–9 An Overview of Skeletal Muscle Contraction.

41. 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)

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

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

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

45. 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)

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

47. 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

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

49. 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

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

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

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

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

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

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

56. 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

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

58. 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

59. The Contraction Cycle
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
Contraction is an active process
Relaxation and return to resting length are passive

60. The Contraction Cycle

61. 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

62. 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

63. ATP and Muscle Contraction
ATP Generation
Cells produce ATP in two ways
Aerobic metabolism of fatty acids in the mitochondria
Anaerobic glycolysis in the cytoplasm

64. ATP and Muscle Contraction
ATP Generation
Aerobic metabolism
Is the primary energy source of resting muscles
Breaks down fatty acids
Produces 34 ATP molecules per glucose molecule
Anaerobic glycolysis
Is the primary energy source for peak muscular activity
Produces two ATP molecules per molecule of glucose
Breaks down glucose from glycogen stored in skeletal muscles

65. ATP and Muscle Contraction

66. 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

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

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

69. ATP and Muscle Contraction
Figure 10–20b Muscle Metabolism.

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

71. 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

72. ATP and Muscle Contraction
The Recovery Period
The time required after exertion for muscles to return to normal
Oxygen becomes available
Mitochondrial activity resumes

73. 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

74. 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

75. ATP and Muscle Contraction
Heat Production and Loss
Active muscles produce heat
Up to 70% of muscle energy can be lost as heat, raising body temperature
Hormones and Muscle Metabolism
Growth hormone
Testosterone
Thyroid hormones
Epinephrine

76. 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

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

78. 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

79. 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)

80. 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

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

82. 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

83. Muscle Fiber Types Physical Conditioning
Improves both power and endurance
Anaerobic activities (e.g., 50-meter dash, weightlifting):
use fast fibers
fatigue quickly with strenuous activity
Improved by:
frequent, brief, intensive workouts
hypertrophy

84. Muscle Fiber Types Physical Conditioning
Improves both power and endurance
Aerobic activities (prolonged activity):
supported by mitochondria
require oxygen and nutrients
Improved by:
repetitive training (neural responses)
cardiovascular training

85. 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

86. Cardiac Muscle Tissue Structure of Cardiac Tissue
Cardiac muscle is striated, found only in the heart

87. Cardiac Muscle Tissue Seven Characteristics of Cardiocytes
Unlike skeletal muscle, cardiac muscle cells (cardiocytes)
Are small
Have a single nucleus
Have short, wide T tubules
Have no triads
Have SR with no terminal cisternae
Are aerobic (high in myoglobin, mitochondria)
Have intercalated discs

88. Cardiac Muscle Tissue Intercalated Discs
Are specialized contact points between cardiocytes
Join cell membranes of adjacent cardiocytes (gap junctions, desmosomes)
Functions of intercalated discs
Maintain structure
Enhance molecular and electrical connections
Conduct action potentials

89. Cardiac Muscle Tissue
Figure 10–22 Cardiac Muscle Tissue.

90. Cardiac Muscle Tissue
Figure 10–22a Cardiac Muscle Tissue.

91. Cardiac Muscle Tissue
Figure 10–22c Cardiac Muscle Tissue.

92. Cardiac Muscle Tissue Intercalated Discs Coordination of cardiocytes
Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells

93. Cardiac Muscle Tissue Four Functions of Cardiac Tissue Automaticity
Contraction without neural stimulation
Controlled by pacemaker cells
Variable contraction tension
Controlled by nervous system
Extended contraction time
Ten times as long as skeletal muscle
Prevention of wave summation and tetanic contractions by cell membranes
Long refractory period

94. Smooth Muscle Tissue Smooth Muscle in Body Systems
Forms around other tissues
In blood vessels
Regulates blood pressure and flow
In reproductive and glandular systems
Produces movements
In digestive and urinary systems
Forms sphincters
Produces contractions
In integumentary system
Arrector pili muscles cause “goose bumps”

95. Smooth Muscle Tissue Structure of Smooth Muscle Nonstriated tissue
Different internal organization of actin and myosin
Different functional characteristics

96. Smooth Muscle Tissue
Figure 10–23a Smooth Muscle Tissue.

97. Smooth Muscle Tissue
Figure 10–23b Smooth Muscle Tissue.

98. Smooth Muscle Tissue Eight 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
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

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

100. Smooth Muscle Tissue Functional Characteristics of Smooth Muscle
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

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

102. Smooth Muscle Tissue Functional Characteristics of Smooth Muscle
Control of contractions
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

103. Smooth Muscle Tissue Functional Characteristics of Smooth Muscle
Smooth muscle tone
Maintains normal levels of activity
Modified by neural, hormonal, or chemical factors