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PowerPoint® Lecture Slides prepared by Vince Austin, University of Texas
Muscles and Muscle Tissue
Part A
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
6
Muscle Overview - know
The three types of muscle tissue are:
 skeletal, cardiac, and smooth
 These types differ in structure, location, function,
and means of activation
 http://www.youtube.com/watch?v=WFQLFHbMMaM
 http://www.youtube.com/watch?v=PJDrR3sZPZU
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Muscle Similarities - know
 Skeletal and smooth muscle cells are elongated and are
called muscle fibers
 Muscle contraction depends on two kinds of myofilaments –
actin and myosin
 Muscle terminology is similar
 Sarcolemma – muscle plasma membrane
 Sarcoplasm – cytoplasm of a muscle cell
 Prefixes – myo, mys, and sarco all refer to muscle
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1. Skeletal Muscle Tissue - know
 Packaged in skeletal muscles that attach to and cover the
bony skeleton
 Has obvious stripes called striations
 Is controlled voluntarily (i.e., by conscious control)
 Contracts rapidly but tires easily
 Is responsible for overall body motility
 Is extremely adaptable and can exert forces ranging from a
fraction of an ounce to over 70 pounds
 http://www.youtube.com/watch?v=pbTah5NVOtU&feature=related
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2. Cardiac Muscle Tissue - know
 Occurs only in the heart
 Is striated like skeletal muscle but is not voluntary
 Contracts at a fairly steady rate set by the heart’s
pacemaker
 Neural controls allow the heart to respond to
changes in bodily needs
 http://www.youtube.com/watch?v=wqEY-gb4jCI&feature=related
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3. Smooth Muscle Tissue - know
 Found in the walls of hollow visceral organs, such
as the stomach, urinary bladder, and respiratory
passages
 Forces food and other substances through internal
body channels
 It is not striated and is involuntary
 http://www.youtube.com/watch?v=nf47ZO4_HUs
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Functional Characteristics of Muscle Tissue - know
 Excitability, or irritability – the ability to receive
and respond to stimuli
 Contractility – the ability to shorten forcibly
 Extensibility – the ability to be stretched or extended
 Elasticity – the ability to recoil and resume the
original resting length
 http://www.youtube.com/watch?v=Ry9IcQMFiz8&f
eature=fvw
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Ms. Muscles
 http://www.youtube.com/watch?v=_cpZVyyD_c&feature=related
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Muscle Function - understand
 Skeletal muscles are responsible for all locomotion
 Cardiac muscle is responsible for coursing the
blood through the body
 Smooth muscle helps maintain blood pressure, and
squeezes or propels substances (i.e., food, feces)
through organs
 Muscles also maintain posture, stabilize joints, and
generate heat
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Skeletal Muscle - know
 Each muscle is a discrete organ composed of muscle tissue,
blood vessels, nerve fibers, and connective tissue
 The three connective tissue sheaths are:
 Endomysium – fine sheath of connective tissue composed
of reticular fibers surrounding each muscle fiber
 Perimysium – fibrous connective tissue that surrounds
groups of muscle fibers called fascicles
 Epimysium – an overcoat of dense regular connective tissue
that surrounds the entire muscle
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Skeletal Muscle – be
able to label all parts
http://www.yo
utube.com/wat
ch?v=2NydxMgpIo
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Skeletal Muscle: Nerve and Blood Supply - understand
 Each muscle is served by one nerve, an artery, and
one or more veins
 Each skeletal muscle fiber is supplied with a nerve
ending that controls contraction
 Contracting fibers require continuous delivery of
oxygen and nutrients via arteries
 Wastes must be removed via veins
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Skeletal Muscle: Attachments - know
 Most skeletal muscles span joints and are attached to bone in
at least two places
 When muscles contract the movable bone, the muscle’s
insertion moves toward the immovable bone, the muscle’s
origin
 Muscles attach:
 Directly – epimysium of the muscle is fused to the
periosteum of a bone
 Indirectly – connective tissue wrappings extend beyond the
muscle as a tendon or aponeurosis
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Microscopic Anatomy of a Skeletal Muscle Fiber - know
 Each fiber is a long, cylindrical cell with multiple nuclei just beneath the
sarcolemma
 Fibers are 10 to 100 m in diameter, and up to hundreds of centimeters
long
 Each cell is a syncytium produced by fusion of embryonic cells
 Sarcoplasm has numerous glycosomes and a unique oxygen-binding
protein called myoglobin
 Fibers contain the usual organelles, myofibrils, sarcoplasmic reticulum,
and T tubules
 http://www.youtube.com/watch?v=IZjZAutXzbw&feature=related
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Myofibrils - know
 Myofibrils are densely packed, rodlike contractile
elements
 They make up most of the muscle volume
 The arrangement of myofibrils within a fiber is such
that a perfectly aligned repeating series of dark A
bands and light I bands is evident
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Myofibrils – be able to label
Figure 9.3 (b)
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Sarcomeres - know
 The smallest contractile unit of a muscle
 The region of a myofibril between two successive Z
discs
 Composed of myofilaments made up of contractile
proteins
 Myofilaments are of two types – thick and thin
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Sarcomeres – be able to label
http://www.youtube.com/watch?v=
U2TSaz8-yNQ;
http://www.youtube.com/watch?v=
7V-zFVnFkWg&feature=related
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Myofilaments: Banding Pattern - understand
 Thick filaments – extend the entire length of an A
band
 Thin filaments – extend across the I band and
partway into the A band
 Z-disc – coin-shaped sheet of proteins (connectins)
that anchors the thin filaments and connects
myofibrils to one another
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Myofilaments: Banding Pattern - understand
 Thin filaments do not overlap thick filaments in the
lighter H zone; appear thin due to the presence of
thin filaments of actin
 M lines appear darker due to the presence of thick
bundles of the proteins myosin and desmin
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Myofilaments: Banding Pattern – know, important slide!
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Ultrastructure of Myofilaments: Thick Filaments - know
 Thick filaments are composed of the protein myosin
 Each myosin molecule has a rodlike tail and two
globular heads
 Tails – two interwoven, heavy polypeptide chains
 Heads – two smaller, light polypeptide chains
called cross bridges
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Ultrastructure of Myofilaments: Thick Filaments
- understand
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Ultrastructure of Myofilaments: Thin Filaments understand
 Thin filaments are chiefly composed of the protein
actin
 Each actin molecule is a helical polymer of globular
subunits called G actin
 The subunits contain the active sites to which myosin
heads attach during contraction
 Tropomyosin and troponin are regulatory subunits
bound to actin
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Ultrastructure of Myofilaments: Thin Filaments – be
able to label
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Arrangement of the Filaments in a Sarcomere - know
 Longitudinal section within one sarcomere
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Sarcoplasmic Reticulum (SR) - know
 SR is an elaborate, smooth endoplasmic reticulum that mostly runs
longitudinally and surrounds each myofibril
 Paired terminal cisternae form perpendicular cross channels
 Functions in the regulation of intracellular calcium levels
 Elongated tubes called T tubules penetrate into the cell’s interior
at each A band–I band junction
 T tubules associate with the paired terminal cisternae to form
triads
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Sarcoplasmic Reticulum (SR) - understand
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T Tubules - know
 T tubules are continuous with the sarcolemma
 They conduct impulses to the deepest regions of the
muscle
 These impulses signal for the release of Ca2+ from
adjacent terminal cisternae
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Triad Relationships - understand
 T tubules and SR provide tightly linked signals for
muscle contraction
 A double zipper of integral membrane proteins
protrudes into the intermembrane space
 T tubule proteins act as voltage sensors
 SR foot proteins are receptors that regulate Ca2+
release from the SR cisternae
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Sliding Filament Model of Contraction – know
important concept!
 Thin filaments slide past the thick ones so that the
actin and myosin filaments overlap to a greater
degree
 In the relaxed state, thin and thick filaments overlap
only slightly
 Upon stimulation, myosin heads bind to actin and
sliding begins
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Sliding Filament Model of Contraction – know
important concept!
 Each myosin head binds and detaches several times
during contraction, acting like a ratchet to generate
tension and propel the thin filaments to the center of
the sarcomere
 As this event occurs throughout the sarcomeres, the
muscle shortens
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Skeletal Muscle Contraction - understand
 In order to contract, a skeletal muscle must:
 Be stimulated by a nerve ending
 Propagate an electrical current, or action potential,
along its sarcolemma
 Have a rise in intracellular Ca2+ levels, the final
trigger for contraction
 Linking the electrical signal to the contraction is
excitation-contraction coupling
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Nerve Stimulus of Skeletal Muscle - know
 Skeletal muscles are stimulated by motor neurons of
the somatic nervous system
 Axons of these neurons travel in nerves to muscle
cells
 Axons of motor neurons branch profusely as they
enter muscles
 Each axonal branch forms a neuromuscular junction
with a single muscle fiber
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Neuromuscular Junction - know
The neuromuscular junction is formed from:
 Axonal endings, which have small membranous sacs
(synaptic vesicles) that contain the neurotransmitter
acetylcholine (ACh)
 The motor end plate of a muscle, which is a specific part of
the sarcolemma that contains ACh receptors and helps form
the neuromuscular junction
Though exceedingly close, axonal ends and muscle fibers are
always separated by a space called the synaptic cleft
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Neuromuscular
Junction understand
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Neuromuscular Junction - know
 When a nerve impulse reaches the end of an axon at
the neuromuscular junction:
 Voltage-regulated calcium channels open and allow
Ca2+ to enter the axon
 Ca2+ inside the axon terminal causes axonal
vesicles to fuse with the axonal membrane
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Neuromuscular Junction - know
 This fusion releases ACh into the synaptic cleft via
exocytosis
 ACh diffuses across the synaptic cleft to ACh
receptors on the sarcolemma
 Binding of ACh to its receptors initiates an action
potential in the muscle
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Destruction of Acetylcholine - know
 ACh bound to ACh receptors is quickly destroyed
by the enzyme acetylcholinesterase
 This destruction prevents continued muscle fiber
contraction in the absence of additional stimuli
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Action Potential – know, understand definition!
 A transient depolarization event that includes
polarity reversal of a sarcolemma (or nerve cell
membrane) and the propagation of an action
potential along the membrane
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Role of Acetylcholine (Ach) - know
 ACh binds its receptors at the motor end plate
 Binding opens chemically (ligand) gated channels
 Na+ and K+ diffuse out and the interior of the
sarcolemma becomes less negative
 This event is called depolarization
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Animations
 http://www.youtube.com/watch?v=WRxsOMenNQM&featu
re=related
 http://www.youtube.com/watch?v=70DyJwwFnkU&feature
=related
 http://www.youtube.com/watch?v=VQ4OMSi6qAg&feature
=related
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What to Know About Skeletal
Muscle Physiology
1. Diagram the chemical and mechanical steps
in the cross-bridge cycle and explain the
effect on the muscle fiber length.
2. Describe the end of contraction mechanisms.
3. Muscle excitation and energy sources.

Three roles of ATP in muscle function.

Three sources of ATP for muscle function.
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Sliding myofilaments shorten sarcomeres
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http://www.sci.sdsu.edu/movies/actin_myosin_gif.html
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1.
2.
3.
4.
Excitation - contraction coupling
ACh binds to, opens Na+/K+channels
Muscle depolarizes
Ca2+ released from sarcoplasmic reticulum
Ca2+ binds to troponin, cross-bridge cycling
between actin & myosin begins, filaments slide
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5.
6.
7.
8.
End of contraction
ACh destroyed by ACh-esterase in synapse
Muscle repolarizes
Ca2+ returned to SR by Ca2+ active transporter
ATP hydrolysis (+Mg) re-extends myosin head
9. Muscle elastic
elements recoil,
muscle returns to
resting length.
Titin is the largest polypeptide known
(34,350 amino acids in length). It spans
from the M to Z lines.
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Be able to:
Draw and label a diagram to show the following
stage of the cross-bridge cycle:
1. At rest, when the muscle is not stimulated.
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Be able to:
Draw and label a diagram to show the following
stage of the cross-bridge cycle:
2. At death when the muscle has depleted ATP.
(rigor)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Genetic mutation
turns tot into superboy
4-year-old is first documented
human case, scientists say
A German boy, seen here at sevenmonths old, has a genetic mutation
that boosts muscle growth.
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At age 14?
Excitation-Contraction Coupling
 action potentials, generated at neuromuscular
junction travel around sarcolemma and through Ttubules
 T-tubules signal SR to release Ca2+ into
sarcoplasm (cytosol)
 Ca2+ saturates troponin (in non-fatigued state)
 troponin undergoes conformational change that
lifts tropomyosin away from actin filament
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E-C Coupling (cont.)
 myosin head attaches to active site on actin
filament forming cross-bridge
 after forming cross-bridge, myosin head moves
actin-myosin complex forward and ADP and Pi are
released
 ATP binds with myosin head, which releases actin,
and returns to original position
 in resting state, myosin head contains partially
hydrolyzed ATP (ADP and Pi)
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E-C Coupling (cont.)
 entire cycle takes ~50 ms although myosin heads
are attached for ~2 ms
 a single cross-bridge shortens 10 nm
 as long as action potentials continue, Ca2+ will
continue to be released
 when action potentials cease, SR Ca2+ pumps
return Ca2+, ceasing contractions
 skeletal motor units follow “all or nothing” principle
– contracts maximally or not at all
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