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Essentials of Anatomy and Physiology
Fifth edition
Seeley, Stephens and Tate
Chapter 7: Muscular System
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 2.1
Contraction of a Skeletal Muscle
 Individual muscle fiber contraction is “all
or none”
Within a skeletal muscle, not all fibers
may be stimulated
Different combinations of muscle fiber
contraction give variations in response
“Strength” of response
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.19
Types of Graded Responses
 Twitch
Fig. 7.9
 Involves a
single muscle
fiber
 Single, brief
contraction
 Not a normal
muscle
function
Phases of a Muscle Twitch
Figure 6.9a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.20a
Types of Graded Responses
 Twitch has three
phases
Fig. 7.9
Lag phase
Contraction
Relaxation
Phases of a Muscle Twitch
Figure 6.9a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.20a
Types of Graded Responses
 Summation
Fig. 7.10
 Increasing
force of
contraction of
muscle fiber
 Recruitment
 Increasing the
number of
muscle fibers
contracting
Figure 6.9a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.20b
Types of Graded Responses
 Tetanus (sustained contraction)
 One contraction is immediately followed by
another
Fig. 7.10
 The muscle does
not return to a
resting state
 Due to increased
frequency of stimuli
 The effects
are added
Figure 6.9a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.20b
Types of Graded Responses
Fig. 7.10
 Fatigue:
 Muscle
eventually runs
out of ATP
 Fibers cannot
contract
Types of Graded Responses:
Tetanus and Fatigue
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 result is summation
Figure 6.9a, b
Figure 6.9c,d
Summation
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.21a
Muscle Response to Strong Stimuli
 Muscle force depends upon number of
fibers stimulated
 More fibers contracting results in
greater muscle tension
 Muscles continue to contract until 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
After this, other pathways must be
used
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.23
Energy for Muscle Contraction
 Aerobic Respiration
 Metabolic pathways in
the mitochondria
 Glucose is broken down,
releasing energy
 This is a slow reaction
requiring oxygen
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.10c
Slide 6.25
Energy for Muscle Contraction
 Anaerobic respiration
 Breaks down glucose
without oxygen
 Glucose is broken down
to pyruvic acid
 produces some ATP
 Pyruvic acid is
converted to lactic acid
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.10b
Slide 6.26a
Energy for Muscle Contraction
 Anaerobic respiration
(continued)
 This reaction is not as
efficient, but is fast
 Huge amounts of
glucose are needed
 Lactic acid produces
muscle fatigue
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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”
 Oxygen is required to get rid of lactic acid
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.27
Types of Muscle Contractions
 Isotonic (equal tension) contractions
 Myofilaments slide past each other during
contractions
 The muscle shortens
 Isometric (equal weight) 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 Tone (tonus)
 Some fibers are contracted even in a
“relaxed” muscle
 Different fibers contract at different
times to provide muscle tone
 Maintains posture
 The process is involuntary
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.29
Muscles and Body Movements
 Movement is
produced when
a muscle moves
an attached
bone
Figure 6.12
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Slide 6.30a
Muscles and Body Movements
 Bones serve as
levers
 Lever: a rigid
rod
 Fulcrum: point
of rotation
Figure 6.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.30a
Muscles and Body Movements
Movement requires force or energy
Object to be moved provides resistance
“System” consists of a fulcrum, resistance,
and energy for movement
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.27
Muscles and Body Movements
 Joints serve as
fulcra
 Classes of
levers:
 First class
 Second class
 Third class
Figure 6.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.30a
Muscles and Body Movements
 First class lever: fulcrum lies between
resistance and energy
 Example: hyperextending neck
tilt face upward, look at the ceiling
Trapezius and splenius muscles
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.27
Muscles and Body Movements
 Second class lever: resistance lies
between “energy” and fulcrum
Example: standing on “tip toes”
Gastrocnemius muscle
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.27
Muscles and Body Movements
 Third class:
“energy’ is
applied between
resistance and
fulcrum
flexing elbow
Biceps brachii
Figure 6.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.30a
Muscles and Body Movements
 Third class
lever: most
common in a
human body
Figure 6.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.30a
Muscles and Body Movements
 Muscles are
attached at two
points
Fig. 7.12
 Origin – fixed
attachment
 Insertion –
movable
attachment
Figure 6.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.30b
Muscles and Body Movements
 Muscle
attachments must
cross a joint
(fulcrum)
Fig. 7.12
 If it doesn’t, no
movement!
Figure 6.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.30b
Effects of Exercise on Muscle
 Results of increased muscle use
 Increase in size of muscle fibers
(hypertrophy), NOT in number of fibers
 Increase in actin and myosin
 Increase in blood supply, mitochondria
 Muscle becomes resistant to fatigue
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.31
Types of Ordinary Body Movements
 Flexion
 Extension
 Rotation
 Abduction
 Circumduction
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Slide 6.32
Body Movements
Figure 6.13
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Slide 6.33
Special Movements
 Dorsiflexion: toes point “up”
 Plantar flexion: toes point “down”
 Inversion: soles of feet “in”
 Eversion: soles of feet “out”
 Supination: face or palm “up”
 Pronation: face or palm “down”
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.34
Functions of Muscles
 Prime mover – muscle with the major
responsibility for a certain movement
 Antagonist – muscle that opposes or
reverses a prime mover
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.35
Functions of Muscles
 Synergist – muscle that aids a prime
mover in a movement and helps prevent
rotation
 Fixator – stabilizes the origin of a prime
mover
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.35
Naming of Skeletal Muscles
 Direction of muscle fibers
 Example: rectus (straight)
 Relative size of the muscle
 Example: maximus (largest)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.36a
Naming of Skeletal Muscles
 Location of the muscle
Example: many muscles are named
for bones (e.g., temporalis)
 Number of origins
Example: triceps (three heads)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.36b
Naming of Skeletal Muscles
 Attachments of muscle
 Example: sterno (origin on the sternum)
 Shape of the muscle
 Example: deltoid (triangular)
 Action of the muscle
 Example: flexor and extensor (flexes or
extends a bone)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.37