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PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky
Muscles and Muscle Tissue
Part A
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
8
Muscle Overview
 Muscle tissue makes up nearly half the body mass.
 The most distinguishing functional characteristic of
muscles is their ability to transform chemical energy
ATP into directed mechanical energy
 The three types of muscle tissue are skeletal,
cardiac, and smooth
 These types differ in structure, location, function,
and means of activation
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Muscle Similarities
 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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Skeletal Muscle Tissue
 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
 Key words: skeletal, striated and voluntary
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Cardiac Muscle Tissue
 Occurs only in the heart (“blood pump”)
 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
 Key words: cardiac, striated and involuntary
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Smooth Muscle Tissue
 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
 Key words: visceral, non striated and involuntary
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Functional Characteristics of Muscle Tissue
 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
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Muscle Function
 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 Gross Anatomy
• Tissues:
– Blood vessels
– Nerves – branches to each fiber
– Connective Tissue
• Endomysium –wraps each fiber
• Perimysium –wraps fibers into fascicles
• Epimysium –wraps fascicles into a muscle
• All are continuous with each other and the
tendons.
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Skeletal Muscle ( Table 9.1)
Figure 9.2 (a)
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Skeletal Muscle: Nerve and Blood Supply
 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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Structural Organization of
Skeletal Muscle
•
•
•
•
•
Muscle (Organ)
Fascicles (Bundles of fibers)
Fiber (Cell)
Myofibrils (densely packed contractile elements)
Myofilaments (contractile proteins)
– Actin (thin filaments)
– Myosin (thick filaments)
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Myofibrils
Figure 9.3 (b)
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Sarcomeres
 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
Figure 9.3 (c)
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Myofilaments: Banding Pattern
 Thick filaments (composed by myosin) – extend the
entire length of an A band
 Thin filaments (composed by actin) – 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
Figure 9.3 (c, d)
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Ultrastructure of Myofilaments: Thick Filaments
 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
Figure 9.4 (a)(b)
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Ultrastructure of Myofilaments: Thin Filaments
 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
Figure 9.4 (c)
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Arrangement of the Filaments in a Sarcomere
 Longitudinal section within one sarcomere
Figure 9.4 (d)
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Sliding Filament Model of Contraction
 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
 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
 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
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Brain  Spinal Cord  Motor Neuron 
Muscle
Motor =
movement
Neuron = nerve
cell
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Motor Neuron  Muscle Fiber
Motor neuron
releases
neurotransmitter
called acetylcholine
(ACh).
ACh causes muscle
fiber to produce an
electrical signal.
Electrical signal causes actin & myosin
to move, and this causes muscle to
move.
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Destruction of Acetylcholine
 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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A Myofibril at Rest
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A Myofibril at Rest
At rest” = fiber has not received message to move
Actin (thin) attaches to Z-line.
Myosin (thick) does not attach to actin or the Z-line.
Myosin heads are bent back (cocked).
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Contraction

Let’s compare length of sarcomeres:
Relaxed:
Contracted:
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Contraction in the Myofibril

After contraction, muscle relaxes (back to
original length).
– Myosin heads pick up ATP & break it apart.
– This cocks the head, detaching it from actin.
Now ready to contract again.
ATP
Head is Cocked
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Sequential Events of Contraction
 Cross bridge formation – myosin cross bridge
attaches to actin filament
 Working (power) stroke – myosin head pivots and
pulls actin filament toward M line
 Cross bridge detachment – ATP attaches to myosin
head and the cross bridge detaches
 “Cocking” of the myosin head – energy from
hydrolysis of ATP cocks the myosin head into the
high-energy state
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Contraction
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Contraction of Skeletal Muscle (Organ Level)
 Contraction of muscle fibers (cells) and muscles
(organs) is similar
 The two types of muscle contractions are:
 Isometric contraction – increasing muscle tension
(muscle does not shorten during contraction)
 Isotonic contraction – decreasing muscle length
(muscle shortens during contraction)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Types of muscular contraction
• Isometric
–
Muscular contraction where the tension
developed occurs with no change in length
–
Otherwise known as static contraction or
position.
–
Improves muscular strength at fixed joint
angle
–
Does not develop aerobic fitness
–
Can be done anywhere
Examples; rugby scrum, tug of war.
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 publishing as Benjamin Cummings
Types of muscle contraction
Isotonic
Muscles contact at speed controlled by the
performer
Motor unit recruitment is at the speed required for
the specific sports activity.
Develops aerobic and anaerobic fitness
Most physical activities are isotonic
Can occur in two ways: concentric and eccentric.
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Contraction
• Concentric contraction
– Muscle shortens under tension
– Insertion moves towards origin
– Occurs in agonist muscle
– e.g. Chin-ups – use of bicep brachii in
upward phase
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Contraction
Eccentric contraction
Muscle lengthens under tension
Insertion moves away from origin
Occurs in antagonist muscle
Only occurs if the antagonist is acting as a brake
to help control the joint movement
E.g. Chin-ups – use of biceps in downward phase.
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