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Essentials of Human Anatomy & Physiology
Seventh Edition
Elaine N. Marieb
Chapter 6
The Muscular System
Slides 6.18 – 6.31
Lecture Slides in PowerPoint by Jerry L. Cook
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Sliding Filament Theory –
movement is similar to rowing a
boat.
Figure 6.8
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.18
Sliding Filament Animation
• https://docs.google.com/present/view?id=dfh23k6
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Dancing Frogs
• https://docs.google.com/present/view?id=dfh23k6
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Contraction of a Skeletal Muscle
 Muscle fiber contraction is “all or none”
 Within a skeletal muscle, not all fibers
may be stimulated during the same
interval
 Different combinations of muscle fiber
contractions may give differing
responses
 Graded responses – different degrees
of skeletal muscle shortening
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.19
Types of Graded Responses
 1. Twitch
 Single, brief contraction
 Not a normal muscle function
Figure 6.9a, b
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Slide 6.20a
Types of Graded Responses
 2. Tetanus (summing of contractions)
 One contraction is immediately followed by
another
 The muscle does
not completely
return to a
resting state
 The effects
are added
Figure 6.9a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.20b
What is Tetanus?
• Tetanus causes cholinosterase
to not break down the Ach at
the Sarcolemma. This results
in a person’s muscles to
contract and not relax.
• A tetanus shot must be
administered shortly after
exposure to the bacteria.
• Once you develop Tetanus,
there is no cure.
Types of Graded Responses
 3. Unfused (incomplete) tetanus
 Some relaxation occurs between
contractions
 The results are summed
Figure 6.9a, b
Figure 6.9c,d
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Slide 6.21a
Types of Graded Responses
 4. Fused (complete) tetanus
 No evidence of relaxation before the
following contractions
 The result is a sustained muscle contraction
Figure 6.9a, b
Figure 6.9c,d
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Slide 6.21b
Muscle Response to Strong Stimuli
 Muscle force depends upon the number
of fibers stimulated
 More fibers contracting results in
greater muscle tension
 Muscles can continue to contract unless
they run out of energy
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Slide 6.22
Energy for Muscle Contraction
 Initially, muscles used stored ATP for
energy
 Bonds of ATP are broken to release energy
 Only 4-6 seconds worth of ATP is stored by
muscles
 After this initial time, other pathways
must be utilized to produce ATP
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Slide 6.23
Energy for Muscle Contraction
 1. Direct phosphorylation:
 Muscle cells contain creatine
phosphate (CP)
 CP is a high-energy molecule
 After ATP is depleted, ADP is left
 CP transfers energy to ADP, to
regenerate ATP
 CP supplies are exhausted in
about 20 seconds
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Figure 6.10a
Slide 6.24
Energy for Muscle Contraction
 2. Aerobic Respiration:
 Series of metabolic
pathways that occur in the
mitochondria
 Glucose is broken down to
carbon dioxide and water,
releasing energy from food
 about 36 Net ATP
 This is a slower reaction
that requires continuous
oxygen & food supplies
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Figure 6.10c
Slide 6.25
Energy for Muscle Contraction
 3. Anaerobic glycolysis:
 Reaction that breaks down
glucose without oxygen
 Glucose is broken down to
pyruvic acid to produce
some ATP  very little, only
2 net ATP
 Pyruvic acid is converted to
lactic acid
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Figure 6.10b
Slide 6.26a
Energy for Muscle Contraction
 Anaerobic glycolysis
(continued)
 This reaction is not as
efficient, but is fast
 Huge amounts of
glucose are needed
 Lactic acid produces
muscle fatigue and
soreness
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Figure 6.10b
Slide 6.26b
Muscle Fatigue and Oxygen Debt
 When a muscle is fatigued, it is unable to
contract
 The common reason for muscle fatigue is
oxygen debt
 Oxygen must be “repaid” to tissue to remove
oxygen debt
 Oxygen is required to get rid of accumulated
lactic acid
 Increasing acidity (from lactic acid) and lack
of ATP causes the muscle to contract less
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Slide 6.27
Muscle Fatigue Continued . . .
• As mentioned before, muscle soreness will last
until the oxygen debt has been “paid back” and
the accumulated lactic acid has been converted
into ATP and creatine phosphate reserves.
Types of Muscle Contractions
 1. Isotonic contractions
 Myofilaments are able to slide past each
other during contractions
 The muscle shortens (what you know as
normal muscle contractions)
 2. Isometric contractions
 Tension in the muscles increases
 The muscle is unable to shorten  muscle
length stays the same, despite force
applied.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.28
Muscle Tone
 Some fibers are contracted even in a
relaxed muscle
 Different fibers contract at different
times to provide muscle tone
 This process of stimulating various
fibers is under involuntary control
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Slide 6.29
Muscles and Body Movements
 Movement is
attained due to
a muscle
moving an
attached bone
Figure 6.12
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Slide 6.30a
Muscles and Body Movements
 Muscles are
attached to at
least two points:
 1. Origin –
attachment to a
moveable bone
 2. Insertion –
attachment to an
immovable bone
Figure 6.12
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Slide 6.30b
Effects of Exercise on Muscle
 Results of increased muscle use
 Increase in muscle size
 Increase in muscle strength
 Increase in muscle efficiency
 Muscle becomes more fatigue resistant
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.31