Hole’s Human Anatomy
and Physiology
Twelfth Edition
Shier w Butler w Lewis
Chapter
9
Muscular System
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1
9.1: Introduction
Three (3) Types of Muscle Tissues
• Skeletal Muscle
• Cardiac Muscle
• Usually attached to bones
• Under conscious control
• Somatic nervous control
• Striated
• Wall of heart
• Not under conscious control
• Autonomic nervous control
• Striated
• Smooth Muscle
• Walls of most viscera, blood vessels
and skin
• Not under conscious control
• Autonomic
• Not striated
2
9.2: Structure of Skeletal Muscle
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• Skeletal Muscle
• Organ of the muscular system
• Skeletal muscle tissue
• Nervous tissue
• Blood
• Connective tissues
• Fascia
• Tendons
• Aponeuroses
Aponeuroses
Skeletal muscles
Tendons
3
Connective Tissue Coverings
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• Muscle coverings:
• Epimysium
• Perimysium
• Endomysium
Muscle
Bone
Fascicles
Tendon
Muscle fibers (cells)
Fascia
(covering muscle)
• Muscle organ
• Fascicles
• Muscle cells or fibers
• Myofibrils
• Thick and thin myofilaments
• Actin and myosin proteins
• Titin is an elastic myofilament
Epimysium
Perimysium
Myofibrils
Thick and thin filaments
Endomysium
Fascicle
Axon of motor
neuron
Blood vessel
Nucleus
Sarcoplasmic
reticulum
Myofibril
Muscle fiber
Sarcolemma
4
5
Filaments
Skeletal Muscle Fibers
• Sarcolemma
• Sarcoplasm
• Sarcoplasmic reticulum (SR)
• Transverse (‘T’) tubule
• Triad
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Myofibrils
Cisternae of
sarcoplasmic reticulum
Transverse tubule
Nucleus
• Cisternae of SR
• T tubule
• Myofibril
• Actin myofilaments
• Myosin myofilaments
• Sarcomere
Sarcoplasmic
reticulum
Openings into
transverse tubules
Mitochondria
Thick and thin
filaments
Sarcoplasm
Nucleus
Sarcolemma
5
Triad
9.3: Skeletal Muscle Contraction
• Movement within
the myofilaments
• I band (thin)
• A band (thick and
thin)
• H zone (thick)
• Z line (or disc)
• M line
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Skeletal muscle fiber
Sarcoplasmic
reticulum
Thick (myosin) Thin (actin)
filaments
filaments
Myofibril
Sarcomere
Z line
I band
(a)
H zone
Z line
M line
A band
I band
A band
(b)
6
Myofilaments
• Thick myofilaments
• Composed of myosin protein
• Form the cross-bridges
• Thin myofilaments
• Composed of actin protein
• Associated with troponin and
tropomyosin proteins
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Cross-bridges
Troponin
Tropomyosin
Myosin
molecule
Thick
filament
Thin filament
Actin molecule
7
Neuromuscular Junction
• Also known as NMJ or
myoneural junction
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Synaptic
vesicles
Mitochondria
• Site where an axon and
muscle fiber meet
• Parts to know:
• Motor neuron
• Motor end plate
• Synapse
Motor
neuron axon
Acetylcholine
Synaptic
cleft
Folded
sarcolemma
Axon branches
Muscle fiber
nucleus
Motor
end plate
Myofibril of
muscle fiber
• Synaptic cleft
• Synaptic vesicles
• Neurotransmitters
89
(a)
Animation:
Function of the
Neuromuscular Junction
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9
Motor Unit
• Single motor neuron
• All muscle fibers controlled
by motor neuron
Motor neuron
• As few as four fibers
of motor unit 1
• As many as 1000’s of
muscle fibers
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Motor neuron
of motor unit 2
Branches of
motor neuron
axon
Skeletal muscle
fibers
10
Stimulus for Contraction
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• Acetylcholine (ACh)
• Nerve impulse causes release of
ACh from synaptic vesicles
• ACh binds to ACh receptors on
motor end plate
• Generates a muscle impulse
• Muscle impulse eventually
reaches the SR and the cisternae
Synaptic
vesicles
Mitochondria
Motor
neuron axon
Acetylcholine
Synaptic
cleft
Folded
sarcolemma
Axon branches
Muscle fiber
nucleus
Motor
end plate
Myofibril of
muscle fiber
11
(a)
11
Excitation-Contraction
Coupling
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• Muscle impulses cause SR to
release calcium ions into cytosol
• Calcium binds to troponin to
change its shape
• The position of tropomyosin is
altered
• Binding sites on actin are now
exposed
• Actin and myosin molecules bind
via myosin cross-bridges
Tropomyosin
Troponin
Thin filament
Actin monomers
ADP + P
ADP + P
Thick filament
1 Relaxed muscle
Ca+2
Muscle relaxation
Active transport of Ca+2 into sarcoplasmic
reticulum, which requires ATP, makes
myosin binding sites unavailable.
Ca+2
Muscle contraction
Release of Ca+2 from sarcoplasmic
reticulum exposes binding sites on
actin:
Ca+2 binds to troponin
ATP
Tropomyosin pulled aside
Binding sites on
actin exposed
Ca+2
ADP + P
Ca+2
ADP + P
Ca+2
2 Exposed binding sites on actin molecules
allow the muscle contraction cycle to occur
ADP + P
ADP + P
ADP + P
Contraction cycle
6 ATP splits, which
provides power to
“cock” the myosin
cross-bridges
ADP + P
3 Cross-bridges
bind actin to
myosin
ADP
ATP
ATP
ATP
ATP
5 New ATP binds to myosin, releasing linkages
ADP
P
ADP + P
4
P
12
Cross-bridges pull thin filament (power stroke),
ADP and P released from myosin
13
Cross Bridge Cycling
• Myosin cross-bridge attaches
to actin binding site
• Myosin cross-bridge pulls
thin filament
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Tropomyosin
Troponin
ADP + P
Thick filament
Ca+2
Muscle relaxation
Active transport of Ca+2 into sarcoplasmic
reticulum, which requires ATP, makes
myosin binding sites unavailable.
Ca+2
Muscle contraction
Release of Ca+2 from sarcoplasmic
reticulum exposes binding sites on
actin:
Ca+2 binds to troponin
ATP
Tropomyosin pulled aside
Binding sites on
actin exposed
Ca+2
ADP + P
Ca+2
ADP + P
Ca+2
2 Exposed binding sites on actin molecules
allow the muscle contraction cycle to occur
ADP + P
ADP + P
ADP + P
Contraction cycle
6 ATP splits, which
provides power to
“cock” the myosin
cross-bridges
ADP + P
3 Cross-bridges
bind actin to
myosin
ADP
ATP
ATP
ATP
P
ATP
• Myosin cross-bridge goes back
to original position
ADP + P
1 Relaxed muscle
• ADP and phosphate
released from myosin
• New ATP binds to
myosin
• Linkage between actin
and myosin cross-bridge
break
• ATP splits
Thin filament
Actin monomers
5 New ATP binds to myosin, releasing linkages
ADP
P
ADP + P
4
Cross-bridges pull thin filament (power stroke),
ADP and P released from myosin
13
The Sliding Filament Model
of Muscle Contraction
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• When sarcromeres
shorten, thick and thin
filaments slide past one
another
• H zones and I bands
narrow
• Z lines move closer
together
Sarcomere
Z line
Thin
filaments
A band
1 Relaxed
Z line
Thick
filaments
2 Contracting
3 Fully contracted
(a)
14
Animation:
The Cross-Bridge Cycle
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15
Animation:
Breakdown of ATP
and Cross-Bridge Movement
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Relaxation
• Acetylcholinesterase – rapidly decomposes Ach remaining in
the synapse
• Muscle impulse stops
• Stimulus to sarcolemma and muscle fiber membrane ceases
• Calcium moves back into sarcoplasmic reticulum (SR)
• Myosin and actin binding prevented
• Muscle fiber relaxes
17
Animation:
Action Potentials
and Muscle Contraction
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18
Energy Sources for
Contraction
1) Creatine phosphate and 2) Cellular respiration
• Creatine phosphate – stores energy that quickly converts
ADP to ATP
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When cellular ATP is high
Creatine
Creatine
P
When cellular ATP is low
ADP
Creatine
ATP
Creatine
P
ADP
ATP
19
17
Animation:
Energy Sources for
Prolonged Exercise
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20
Oxygen Supply and
Cellular Respiration
• Aerobic Phase
• Citric acid cycle
• Electron transport system
• Occurs in the mitochondria
• Produces most ATP
• Myoglobin stores extra oxygen
Glucose
2 In the absence of
sufficient oxygen,
glycolysis leads to
lactic acid
accumulation.
1 Oxygen carried from
the lungs by
hemoglobin in red
blood cells is stored
in muscle cells by
myoglobin and is
available to support
aerobic respiration.
Energy
Pyruvic acid
2
ATP
Cytosol
• Glycolysis
• Occurs in cytoplasm
• Produces little ATP
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Lactic acid
Mitochondria
• Cellular respiration:
• Anaerobic Phase
Citric acid
cycle
Electron
transport
chain
Synthesis of 34
CO2 + H2O + Energy
Heat
21
ATP
Oxygen Debt
• Oxygen debt – amount of oxygen needed by liver cells to use
the accumulated lactic acid to produce glucose
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• Oxygen not available
• Glycolysis continues
• Pyruvic acid converted to
lactic acid
• Liver converts lactic acid to
glucose
Glycogen
Energy to
synthesize
Glucose
Energy
from
ATP
ATP
Pyruvic acid
Lactic acid
Glycolysis and
lactic acid formation
(in muscle)
Synthesis of glucose
from lactic acid
(in liver)
22
Muscle Fatigue
• Inability to contract muscle
• Commonly caused from:
• Decreased blood flow
• Ion imbalances across the sarcolemma
• Accumulation of lactic acid
• Cramp – sustained, involuntary muscle contraction
23
Heat Production
• By-product of cellular respiration
• Muscle cells are major source of body heat
• Blood transports heat throughout body core
24
9.4: Muscular Responses
• Muscle contraction can be observed by removing a
single skeletal muscle fiber and connecting it to a device
that senses and records changes in the overall length of
the muscle fiber.
•Threshold Stimulus
• Minimal strength required to cause contraction
25
Recording of a Muscle Contraction
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Force of contraction
• Recording a Muscle Contraction
• Twitch
• Latent period
• Period of contraction
• Period of relaxation
• Refractory period
• All-or-none response
Latent
period
Period of
contraction
Time of
stimulation
Period of
relaxation
Time
26
Length-Tension Relationship
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(a) Optimal length
(c) Overly stretched
Force
(b) Overly shortened
Muscle fiber length
27
Summation
• Process by which individual twitches combine
• Produces sustained contractions
• Can lead to tetanic contractions
Force of
contraction
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Force of
contraction
(a)
Force of
contraction
(b)
28
(c)
Time
Recruitment of Motor Units
• Recruitment - increase in the number of motor units
activated
• Whole muscle composed of many motor units
• More precise movements are produced with fewer muscle
fibers within a motor unit
• As intensity of stimulation increases, recruitment of motor
units continues until all motor units are activated
29
Sustained Contractions
• Smaller motor units (smaller diameter axons) - recruited first
• Larger motor units (larger diameter axons) - recruited later
• Produce smooth movements
• Muscle tone – continuous state of partial contraction
30
Types of Contractions
• Isotonic – muscle contracts and
changes length
• Eccentric – lengthening
contraction
• Concentric – shortening contraction
• Isometric – muscle contracts but does
not change length
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(a) Muscle contracts with
force greater than
resistance and
shortens (concentric
contraction)
(b) Muscle contracts
with force less than
resistance and
lengthens (eccentric
contraction)
(c) Muscle contracts but
does not change length
(isometric contraction)
No
movement
Movement
Movement
31
29
Fast Twitch and Slow Twitch
Muscle Fibers
• Slow-twitch fibers (Type I)
• Always oxidative
• Resistant to fatigue
• Red fibers
• Most myoglobin
• Good blood supply
• Fast-twitch glycolytic fibers (Type IIa)
• White fibers (less myoglobin)
• Poorer blood supply
• Susceptible to fatigue
• Fast-twitch fatigue-resistant
fibers (Type IIb)
• Intermediate fibers
• Oxidative
• Intermediate amount of
myoglobin
• Pink to red in color
• Resistant to fatigue
32
9.5: Smooth Muscles
• Compared to skeletal muscle fibers, smooth muscle fibers
are:
• Shorter
• Single, centrally located nucleus
• Elongated with tapering ends
• Myofilaments randomly organized
• Lack striations
• Lack transverse tubules
• Sarcoplasmic reticula (SR) not well developed
33
Smooth Muscle Fibers
• Visceral Smooth Muscle
• Single-unit smooth muscle
• Sheets of muscle fibers
• Fibers held together by gap
junctions
• Exhibit rhythmicity
• Exhibit peristalsis
• Walls of most hollow organs
• Multi-unit Smooth Muscle
• Less organized
• Function as separate units
• Fibers function separately
• Iris of eye
• Walls of blood vessels
34
Smooth Muscle Contraction
• Resembles skeletal muscle contraction in that:
• Interaction between actin and myosin
• Both use calcium and ATP
• Both are triggered by membrane impulses
• Different from skeletal muscle contraction in that:
• Smooth muscle lacks troponin
• Smooth muscle uses calmodulin
• Two neurotransmitters affect smooth muscle
• Acetlycholine (Ach) and norepinephrine (NE)
• Hormones affect smooth muscle
• Stretching can trigger smooth muscle contraction
• Smooth muscle slower to contract and relax
• Smooth muscle more resistant to fatigue
• Smooth muscle can change length without changing tautness
35
9.6: Cardiac Muscle
• Located only in the heart
• Muscle fibers joined together by intercalated discs
• Fibers branch
• Network of fibers contracts as a unit
• Self-exciting and rhythmic
• Longer refractory period than skeletal muscle
36
Characteristics of Muscle Tissue
37
9.7: Skeletal Muscle Actions
• Skeletal muscles generate a great variety of body
movements.
• The action of each muscle mostly depends upon the kind
of joint it is associated with and the way the muscle is
attached on either side of that joint.
38
Origin and Insertion
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Coracoid process
• Origin – immovable end
• Insertion – movable end
Origins of
biceps brachii
Tendon of
long head
Tendon of
short head
Biceps
brachii
Radius
Insertion of
biceps brachii
39
Interaction of Skeletal Muscles
• Prime mover (agonist) – primarily responsible for
movement
• Synergists – assist prime mover
• Antagonist – resist prime mover’s action and cause
movement in the opposite direction of the prime mover
40
9.9: Lifespan Changes
• Myoglobin, ATP, and creatine phosphate decline
• By age 80, half of muscle mass has atrophied
• Adipose cells and connective tissues replace muscle
tissue
• Exercise helps to maintain muscle mass and function
41
Muscles of Facial Expression
42
Muscles of Mastication
43
Muscles That Move the Head
and Vertebral Column
44
Muscles That Move the
Pectoral Girdle
45
Muscles That Move the Arm
46
Muscles That Move the
Forearm
47
Muscles That Move the Hand
• Flexors (anterior) and extensors (posterior)
48
Muscles of the Abdominal Wall
49
Muscles of the Pelvic Outlet
50
Muscles That Move the Thigh
51
Muscles That Move the Leg
52
Muscles That Move the Foot
53
Important Points in Chapter 9:
Outcomes to be Assessed
9.1: Introduction
 List various outcomes of muscle action.
9.2: Structure of a Skeletal Muscle
 Describe how connective tissue is a part of the structure of a skeletal
muscle.
 Name the major parts of a skeletal muscle fiber and describe the
functions of each.
9.3: Skeletal Muscle Contraction
 Describe the neural control of skeletal muscle contraction.
 Identify the major events that occur during skeletal muscle fiber
contraction.
54
Important Points in Chapter 9:
Outcomes to be Assessed
 List the energy sources for skeletal muscle fiber contraction.
 Describe how a muscle may become fatigued.
 Describe oxygen debt.
9.4: Muscular Responses
 Distinguish between fast and slow twitch muscle fibers.
 Distinguish between a twitch and a sustained contraction.
 Describe how exercise affects skeletal muscles.
 Explain how various types of muscular contractions produce body
movements and help maintain posture.
55
Important Points in Chapter 9:
Outcomes to be Assessed
9.5: Smooth Muscle
 Distinguish between the structures and functions of multiunit smooth
muscle and visceral smooth muscle.
 Compare the contraction mechanisms of skeletal and smooth muscle
fibers.
9.6: Cardiac Muscle
 Compare the contraction mechanisms of skeletal and cardiac muscle
fibers.
9.7: Skeletal Muscle Actions
 Explain how the attachments, locations, and interactions of skeletal
muscles make possible certain movements.
56
Important Points in Chapter 9:
Outcomes to be Assessed
9.8: Major Skeletal Muscles
 Identify and locate the skeletal muscles of each body region and
describe the action (s) of each muscle.
57