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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
Contraction of a Skeletal Muscle
Muscle fiber
contraction is
“all or none”
BUT
Not all fibers
in a muscle
are stimulated
at same time
Graded response – different degrees of
skeletal muscle shortening due to different
combinations of muscle fiber contractions.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.19
Types of Graded Responses
 Twitch
 Single, brief contraction
 Not a normal muscle function
Figure 6.9a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.20a
Types of Graded Responses
 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
Types of Graded Responses
 Unfused (incomplete) tetanus
 Some relaxation occurs between
contractions
 The results are summed
Figure 6.9a, b
Figure 6.9c,d
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.21a
Types of Graded Responses
 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.21b
Muscle Tone
 Some fibers are contracted even in a
relaxed muscle
 Different fibers contract at different
times to provide muscle tone
 The process of stimulating various
fibers is under involuntary control
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.29
Types of Muscle Contractions
 Isotonic contractions
 Myofilaments are able to slide past each
other during contractions
 The muscle shortens
 Isometric contractions
 Tension in the muscles increases
 The muscle is unable to shorten
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.28
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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 . . . . . . .
Slide 6.23
Direct
phosphorylation
Muscle cells contain
creatine phosphate
Aerobic
Respiration
Anaerobic
glycolysis
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.27
Effects of Exercise on Muscle
 Results of increased muscle use
 Increase in muscle size (added myofilaments)
 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
The Sliding Filament Theory
Figure 6.8
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.18