Transcript PowerPoint to accompany Hole’s Human Anatomy and

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
• Striated
• 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
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
• Sacroplasm
• 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