1. Chapter 9 Muscular System
Hole’s Human Anatomy and Physiology Twelfth Edition Shier w Butler w Lewis
Chapter 9
Muscular System
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2. 9.1: Introduction Three (3) Types of Muscle Tissues Skeletal Muscle
Usually attached to bones
Under conscious control
Somatic
Striated
Cardiac Muscle
Wall of heart
Not under conscious control
Autonomic
Striated
Smooth Muscle
Walls of most viscera, blood vessels and skin
Not under conscious control
Autonomic
Not striated

3. 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

4. Connective Tissue Coverings
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Muscle coverings:
Epimysium
Perimysium
Endomysium
Muscle
Bone
Fascicles
Tendon
Muscle fibers (cells)
Fascia
(covering muscle)
Myofibrils
Epimysium
Muscle organ
Fascicles
Muscle cells or fibers
Myofibrils
Thick and thin myofilaments
Actin and myosin proteins
Titin is an elastic myofilament
Perimysium
Thick and thin filaments
Endomysium
Fascicle
Axon of motor
neuron
Blood vessel
Nucleus
Sarcoplasmic
reticulum
Myofibril
Filaments
Muscle fiber
Sarcolemma 5

5. Skeletal Muscle Fibers
Sarcolemma
Sacroplasm
Sarcoplasmic reticulum (SR)
Transverse (‘T’) tubule
Triad
Cisternae of SR
T tubule
Myofibril
Actin myofilaments
Myosin myofilaments
Sarcomere
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Myofibrils
Cisternae of
sarcoplasmic reticulum
Triad
Nucleus
Transverse tubule
Sarcoplasmic
reticulum
Openings into
transverse tubules
Mitochondria
Nucleus
Thick and thin
filaments
Sarcolemma
Sarcoplasm

6. 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)
filaments
Thin (actin)
filaments
Myofibril
Sarcomere
Z line
H zone
Z line
M line
I band
A band
I band
A band
(a)
(b)

7. 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
Thin filament
Troponin
Tropomyosin
Myosin
molecule
Thick
filament
Actin molecule

8. Neuromuscular Junction
Also known as NMJ or myoneural junction
Site where an axon and muscle fiber meet
Parts to know:
Motor neuron
Motor end plate
Synapse
Synaptic cleft
Synaptic vesicles
Neurotransmitters
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Synaptic
vesicles
Mitochondria
Motor
neuron axon
Acetylcholine
Synaptic
cleft
Folded
sarcolemma
Axon branches
Motor
end plate
Muscle fiber
nucleus
Myofibril of
muscle fiber 9
(a)

9. Animation: Function of the Neuromuscular Junction
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10. Motor Unit Single motor neuron
All muscle fibers controlled by motor neuron
As few as four fibers
As many as 1000’s of
muscle fibers
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Motor neuron
of motor unit 2
Motor neuron
of motor unit 1
Branches of
motor neuron
axon
Skeletal muscle
fibers

11. 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
Motor
end plate
Muscle fiber
nucleus
Myofibril of
muscle fiber
(a) 11

12. 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
Ca+2
Muscle contraction
Muscle relaxation
Release of Ca+2 from sarcoplasmic
reticulum exposes binding sites on
actin:
Active transport of Ca+2 into sarcoplasmic
reticulum, which requires ATP, makes
myosin binding sites unavailable.
Ca+2 binds to troponin
ATP
Tropomyosin pulled aside
Binding sites on
actin exposed
Ca+2
Ca+2
Ca+2
ADP + P
ADP + P 2
Exposed binding sites on actin molecules
allow the muscle contraction cycle to occur
ADP + P
ADP + P
Contraction cycle
ADP + P
ADP + P 6
ATP splits, which
provides power to
“cock” the myosin
cross-bridges 3
Cross-bridges
bind actin to
myosin
ADP
ADP
ATP
ATP
ATP P P
ATP
ADP + P 5
New ATP binds to myosin, releasing linkages 4
Cross-bridges pull thin filament (power stroke),
ADP and P released from myosin 13