Anatomy and Physiology I
Muscle Structure and
Contraction
Instructor: Mary Holman
Muscle Functions
• Produce body movements
• Stabilize body position
• Regulate organ volume
• Move fluids and solid food and
wastes in the body
• Produce heat
Properties of Muscle Tissue
•
•
•
•
Electrical excitability
Contractility
Extensibility
Elasticity
Connective Tissue Terms
Related to Muscles
Tendon
Fascia
Aponeurosis
Epimysium
Perimysium
Endomysium
Fig. 9.1
Skeletal Muscle
Aponeuroses
muscle to muscle
Skeletal muscles
Tendons
muscle to bone
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Fig. 9.2d
Muscle
Surrounded by
Fascia
Epimysium
Fascicles
Perimysium
Muscle fibers (cells)
Endomysium
Myofibrils
Thick and thin filaments
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Actin &
Myosin
Fig. 9.2a
Attachment of
Muscle to Bone
Tendon
Fascia
(covering muscle)
Epimysium
Perimysium
Endomysium
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Permission required for reproduction or display.
Fascicle
Fig. 9.2b
Fascicle of Skeletal Muscle
Perimysium
Fascicle
Axon of motor
neuron
Blood vessel
Muscle fiber
(Cell)
Endomysium
Sarcolemma
Nucleus
Sarcoplasmic
reticulum
Fig. 9.2c
Skeletal Muscle Fiber - The Muscle Cell
Nucleus
Sarcoplasmic
reticulum
Myofibril
Filaments
Sarcolemma
Note:This slide does not show SR surrounding each myofibril! Fig 9.4 more accurate.
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Fig. 9.3
SEM of a Fascicle (cross section)
Perimysium
Endomysium
Fascicle
Muscle fiber
Nucleus
Myofibrils
© Ed Reschke
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320X
Fig. 5.28
Skeletal Muscle Tissue 700x
Nuclei
Portion of a
muscle fiber
© The McGraw-Hill Companies, Inc./Al Telser, photographer
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Page 294
Human Striated Muscle Tissue
SEM 3000x
One sarcomere
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© CNRI/SPL/Photo Researchers, Inc.
Fig. 9.5a
Sarcomere
© H.E. Huxley
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16,000x
Fig. 9.4a
Thick and Thin filaments of the Myofibril
Fig. 9.5a
Sarcomere
I band
Z
A band
M
I band
Z
H
zone
© H.E. Huxley
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
16,000x
Fig. 9.5b
Sarcomere
A band
Titin
I band
I band
Z line
Z line
Thin filaments
Actin
Thick filaments
Myosin
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Three Types of Protein Associated with
the Muscle Fiber
• Contractile
– Actin
– Myosin
• Regulatory
– Troponin
– Tropomyosin
• Structural
– Titin
– Dystrophin
– Myomesin
– Nebulin
Fig. 9.6
Thick and Thin Filaments
Myosin heads which form bridges to Actin
Thin filament
Thick
filament
Thin filament
Troponin Tropomyosin
Myosin
molecule
Actin molecule
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Fig. 9.7
Sarcoplasmic Reticulum and Transverse Tubules
Myofibrils
Cisternae of
sarcoplasmic reticulum
Transverse tubule
Nucleus
Sarcoplasmic
reticulum
Openings into
transverse tubules
Mitochondria
Thick and thin
filaments
Sarcoplasm
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Nucleus
Sarcolemma
Triad
Fig. 9.8a
Synaptic
vesicles
The
NeuroMuscular
Junction
( NMJ )
Mitochondria
Motor
neuron axon
Acetylcholine
Synaptic
cleft
Folded
sarcolemma
Axon branches
Muscle fiber
nucleus
Motor
end plate
Myofibril of
muscle fiber
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Fig. 9.8c
Neuromuscular Junction
Synapse
Motor neuron
Synaptic end bulb
Synaptic
vesicles
Muscle cell
Motor end plate
Mitochondria
Acetylcholine
Synaptic
cleft
Folded
sarcolemma
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Fig. 9.8b
Neuromuscular Junction
Motor neuron axon
Muscle fiber
Neuromuscular junction
© McGraw-Hill Higher Education, Inc./Carol D. Jacobson Ph.D., Dept. Veterinary Anatomy, Iowa State University
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500x
Muscle Fibers innervated by Two Motor Neurons
Motor neuron
of motor unit 2
Motor neuron
of motor unit 1
Branches of
motor neuron
axon
Skeletal muscle
fibers
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Muscle Fibers innervated by Two Motor Neurons
Motor neuron
of motor unit 2
Motor neuron
of motor unit 1
Branches of
motor neuron
axon
Skeletal muscle
fibers
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Neuromuscular Junction
SEM 1650x
From: Principles of Anatomy & Physiology Tortora & Grabowsky
Events Leading up to Muscle Contraction
NMJ
Muscle fiber
• Nerve impulse arrives at end
of motor nerve axon causing
• Acetylcholine(ACh) release
into synapse via exocytosis
• ACh floods across synaptic
gap and attaches to receptors
on the sarcolemma
• Permeability of sarcolemma
changes and Na+ enters cell
• A muscle impulse is
triggered
• Muscle impulse travels via the
transverse tubules throughout
the muscle cell
• Ca++ diffuses from SR and
binds to troponin on actin
• Myosin cross bridges link
with actin and muscle
contracts
Fig. 9.9
Sliding Filament Theory
Relaxed muscle
Tropomyosin
Troponin
Actin monomers
ADP + P
Thin filament
Actin
ADP + P
Thick filament - Myosin
1
Muscle contraction begins and continues if
ATP is available and Ca++ level in the
sarcoplasm is high
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Fig. 9.9
Muscle Contraction
Ca++ released from sarcoplasmic reticulum
Ca+2 binds to troponin
Tropomyosin
pulled aside
ATP
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
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Fig. 9.9
ADP + P
3
ADP + P
Myosin heads bind to actin forming cross-bridges
ADP
P
ADP
P
ADP + P
4
Cross-bridges pull thin filament (power stroke),
ADP and P released from myosin
Fig. 9.9
ATP
ATP
ATP
ATP
5 New ATP binds to myosin, releasing linkages
ADP +
6
P
ADP + P
ATP splits, which provides power to“cock” the myosin cross-bridges
Fig. 9.10a
Sarcomere
A band
Z line
Z line
1 Relaxed
Thin
filaments
Thick
filaments
2 Contracting
3 Fully contracted
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Fig. 9.10b
Contracting Sarcomere
A band
Z line
Z line
© H.E. Huxley
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Muscle Fiber Excitation
• Nerve impulse arrives at axon terminal
• Triggers release of Ach by exocytosis
• ACh diffuses across synaptic cleft
• ACh binds to receptors on muscle motor end plate
• Sarcolemma becomes more permeable to Na+
• Na+ triggers release of muscle action potential
• Muscle action potential travels along outside of
sarcolemma and into T tubules
• Action potential triggers Ca++ release from SR
• Ca++ binds to troponin on thin filament
• Tropomyosin is pulled aside, revealing binding
sites
• Myosin links to & pulls actin to contract muscle
Muscle Fiber Relaxation
• Acetylcholinesterase decomposes ACh
in synapse
• Action potential (impulse) ends
• SR actively pumps Ca++ back into SR
• Tropomyosin moves back to cover
binding sites
• Myosin heads detach
• Muscle fiber returns to its longer resting
length