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![Page 1: © 2012 Pearson Education, Inc. An Introduction to Muscle Tissue Muscle Tissue A primary tissue type, divided into: Skeletal muscle tissue Cardiac muscle.](https://reader035.fdocuments.net/reader035/viewer/2022081420/56649f2b5503460f94c45c4a/html5/thumbnails/1.jpg)
© 2012 Pearson Education, Inc.
An Introduction to Muscle Tissue
• Muscle Tissue
• A primary tissue type, divided into:
• Skeletal muscle tissue
• Cardiac muscle tissue
• Smooth muscle tissue
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© 2012 Pearson Education, Inc.
10-1 Functions of Skeletal Muscle Tissue
• Skeletal Muscles
• Are attached to the skeletal system
• Allow us to move
• The muscular system
• Includes only skeletal muscles
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© 2012 Pearson Education, Inc.
10-1 Functions of Skeletal Muscle Tissue
• Six Functions of Skeletal Muscle Tissue
1. Produce skeletal movement
2. Maintain posture and body position
3. Support soft tissues
4. Guard entrances and exits
5. Maintain body temperature
6. Store nutrient reserves
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© 2012 Pearson Education, Inc.
10-2 Organization of Muscle
• Organization of Connective Tissues
• Muscles have three layers of connective tissues
1. Epimysium
2. Perimysium
3. Endomysium
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© 2012 Pearson Education, Inc.
10-2 Organization of Muscle
• Epimysium
• Exterior collagen layer
• Connected to deep fascia
• Separates muscle from surrounding tissues
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© 2012 Pearson Education, Inc.
10-2 Organization of Muscle
• Perimysium
• Surrounds muscle fiber bundles (fascicles)
• Contains blood vessel and nerve supply to
fascicles
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10-2 Organization of Muscle
• Endomysium
• Surrounds individual muscle cells (muscle fibers)
• Contains capillaries and nerve fibers contacting
muscle cells
• Contains myosatellite cells (stem cells) that repair
damage
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© 2012 Pearson Education, Inc.
Figure 10-1 The Organization of Skeletal Muscles
Skeletal Muscle (organ)
Musclefascicle
Musclefibers
Bloodvessels
Epimysium Perimysium Endomysium
Nerve
Epimysium
Blood vesselsand nerves
Endomysium
Perimysium
Tendon
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© 2012 Pearson Education, Inc.
Figure 10-1 The Organization of Skeletal Muscles
Epimysium
Blood vesselsand nerves
Endomysium
Perimysium
Tendon
Muscle Fascicle (bundle of fibers)
Perimysium
Muscle fiber
Endomysium
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© 2012 Pearson Education, Inc.
Figure 10-1 The Organization of Skeletal Muscles
Epimysium
Blood vesselsand nerves
Endomysium
Perimysium
Tendon
Muscle Fiber (cell)Endomysium
Sarcoplasm
Mitochondrion
MyosatellitecellSarcolemmaNucleus
Capillary Myofibril
Axon of neuron
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© 2012 Pearson Education, Inc.
10-2 Organization of Muscle
• Organization of Connective Tissues
• Muscle Attachments
• Endomysium, perimysium, and epimysium come
together:
• At ends of muscles
• To form connective tissue attachment to bone
matrix
• I.e., tendon (bundle) or aponeurosis (sheet)
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10-2 Organization of Muscle
• Blood Vessels and Nerves
• Muscles have extensive vascular systems that:
• Supply large amounts of oxygen
• Supply nutrients
• Carry away wastes
• Skeletal muscles are voluntary muscles, controlled
by nerves of the central nervous system (brain and
spinal cord)
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10-3 Characteristics of Skeletal Muscle Fibers
• Skeletal Muscle Cells
• Are very long
• Develop through fusion of mesodermal cells
(myoblasts)
• Become very large
• Contain hundreds of nuclei
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Figure 10-2 The Formation of a Multinucleate Skeletal Muscle Fiber
Muscle fibers developthrough the fusion ofmesodermal cellscalled myoblasts.
Myoblasts
A muscle fiber formsby thefusion ofmyoblasts.
A diagrammatic view and amicrograph of one muscle fiber.
Up to 30 cmin length
Myosatellite cell
Nuclei
Immaturemuscle fiber
Myofibrils
Mitochondria
Myosatellite cell
Mature muscle fiber
SarcolemmaNuclei
Muscle fiber LM 612
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Figure 10-2a The Formation of a Multinucleate Skeletal Muscle Fiber
Muscle fibers developthrough the fusion ofmesodermal cellscalled myoblasts.
Myoblasts
A muscle fiber formsby thefusion ofmyoblasts.
Up to 30 cmin length
Myosatellite cell
Nuclei
Immaturemuscle fiber
Myosatellite cell
Mature muscle fiber
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Figure 10-2b The Formation of a Multinucleate Skeletal Muscle Fiber
A diagrammatic view and amicrograph of one muscle fiber.
Myofibrils
Mitochondria
SarcolemmaNuclei
Muscle fiber LM 612
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10-3 Characteristics of Skeletal Muscle Fibers
• The Sarcolemma and Transverse Tubules
• The sarcolemma
• The cell membrane of a muscle fiber (cell)
• Surrounds the sarcoplasm (cytoplasm of muscle
fiber)
• A change in transmembrane potential begins
contractions
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10-3 Characteristics of Skeletal Muscle Fibers
• The Sarcolemma and Transverse Tubules
• Transverse tubules (T tubules)
• Transmit action potential through cell
• Allow entire muscle fiber to contract
simultaneously
• Have same properties as sarcolemma
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10-3 Characteristics of Skeletal Muscle Fibers
• Myofibrils
• Lengthwise subdivisions within muscle fiber
• Made up of bundles of protein filaments (myofilaments)
• Myofilaments are responsible for muscle contraction
• Types of myofilaments:
• Thin filaments
• Made of the protein actin
• Thick filaments
• Made of the protein myosin
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10-3 Characteristics of Skeletal Muscle Fibers
• The Sarcoplasmic Reticulum (SR)
• A membranous structure surrounding each myofibril
• Helps transmit action potential to myofibril
• Similar in structure to smooth endoplasmic reticulum
• Forms chambers (terminal cisternae) attached to T
tubules
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10-3 Characteristics of Skeletal Muscle Fibers
• The Sarcoplasmic Reticulum (SR)
• Triad
• Is formed by one T tubule and two terminal
cisternae
• Cisternae
• Concentrate Ca2+ (via ion pumps)
• Release Ca2+ into sarcomeres to begin muscle
contraction
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Figure 10-3 The Structure of a Skeletal Muscle Fiber
Myofibril
Sarcolemma
Sarcoplasm
Nuclei
MUSCLE FIBER
Mitochondria
Sarcolemma
Myofibril
Thin filament
Thick filamentTriad Sarcoplasmic
reticulumT tubules
Myofibrils
Sarcoplasm
Sarcolemma
Terminal cisterna
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Figure 10-3 The Structure of a Skeletal Muscle Fiber
Triad Sarcoplasmicreticulum
T tubules
Myofibrils
Sarcoplasm
Sarcolemma
Terminal cisterna
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10-3 Structural Components of a Sarcomere
• Sarcomeres
• The contractile units of muscle
• Structural units of myofibrils
• Form visible patterns within myofibrils
• A striped or striated pattern within myofibrils
• Alternating dark, thick filaments (A bands) and light,
thin filaments (I bands)
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Figure 10-4a Sarcomere Structure, Part I
A longitudinalsection of asarcomere,showing bands
I band A band
H band Z line Titin
Zone of overlap M line
Sarcomere
Thinfilament
Thickfilament
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Figure 10-4b Sarcomere Structure, Part I
A correspondingview of a sarcomere in a myofibril from amuscle fiber in thegastrocnemiusmuscle of the calf
I band A band
H band Z line
Zone of overlap M line
Sarcomere
Z line
Myofibril TEM 64,000
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Figure 10-5 Sarcomere Structure, Part II
Myofibril
Sarcomere
Thinfilament
Thickfilament
Titinfilament
Actininfilaments
Attachmentof titin
Z line I band M line H band Zone of overlap
A superficial viewof a sarcomere
Cross-sectional views of differentportions of a sarcomere
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Figure 10-6 Levels of Functional Organization in a Skeletal Muscle
Skeletal Muscle
Muscle Fascicle
Muscle Fiber
Myofibril
Sarcomere
Epimysium
Surrounded by:Epimysium
Contains:Muscle fascicles
Perimysium
Surrounded by:Perimysium
Contains:Muscle fibers
Endomysium Surrounded by:Endomysium
Contains:Myofibrils
Surrounded by:Sarcoplasmicreticulum
Consists of:Sarcomeres(Z line to Z line)
Contains:Thick filaments
Thin filaments
Z lineTitinM lineZ line
H band
I band A band
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Figure 10-7ab Thick and Thin Filaments
Z line M line
Myofibril
H band
Sarcomere
Troponin Active site Nebulin Tropomyosin G-actinmolecules
F-actinstrand
Actinin Z line Titin
The gross structure of a thinfilament, showing theattachment at the Z line
The organization of G-actin subunitsin an F-actin strand, and the positionof the troponin–tropomyosin complex
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10-3 Structural Components of a Sarcomere
• Initiating Contraction
• Ca2+ binds to receptor on troponin molecule
• Troponin–tropomyosin complex changes
• Exposes active site of F-actin
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10-3 Structural Components of a Sarcomere
• Thick Filaments
• Contain about 300 twisted myosin subunits
• Contain titin strands that recoil after stretching
• The mysosin molecule
• Tail
• Binds to other myosin molecules
• Head
• Made of two globular protein subunits
• Reaches the nearest thin filament
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Figure 10-7cd Thick and Thin Filaments
Titin
Myosinhead
HingeMyosin tail
The structure of a myosin molecule
M lineThe structure of thick filaments, showing the orientation of themyosin molecules
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10-3 Structural Components of a Sarcomere
• Myosin Action
• During contraction, myosin heads:
• Interact with actin filaments, forming cross-
bridges
• Pivot, producing motion
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10-3 Structural Components of a Sarcomere
• Sliding Filaments and Muscle Contraction
• Sliding filament theory
• Thin filaments of sarcomere slide toward M line,
alongside thick filaments
• The width of A zone stays the same
• Z lines move closer together
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Figure 10-8a Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber
A bandI band
Z line H band Z line
A relaxed sarcomere showing location of the A band, Z lines, and I band.
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Figure 10-8b Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber
Z line Z line
A bandI band
H band
During a contraction, the A band stays thesame width, but the Z lines move closertogether and the I band gets smaller. Whenthe ends of a myofibril are free to move,the sarcomeres shorten simultaneouslyand the ends of the myofibril are pulledtoward its center.
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10-3 Structural Components of a Sarcomere
• Skeletal Muscle Contraction
• The process of contraction
• Neural stimulation of sarcolemma
• Causes excitation–contraction coupling
• Muscle fiber contraction
• Interaction of thick and thin filaments
• Tension production
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Figure 10-9 An Overview of Skeletal Muscle Contraction
Neural control
Excitation–contraction coupling
Excitation
ATP
Calciumrelease
Thick-thinfilament interaction
triggers
Muscle fibercontraction
Tensionproduction
leads to
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10-4 Components of the Neuromuscular Junction
• The Control of Skeletal Muscle Activity
• The neuromuscular junction (NMJ)
• Special intercellular connection between the
nervous system and skeletal muscle fiber
• Controls calcium ion release into the sarcoplasm
A&P FLIX Events at the Neuromuscular Junction
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Figure 10-11 Skeletal Muscle Innervation
Synapticterminal
Neuromuscularjunction
Sarcoplasmicreticulum
Motorend plate
Myofibril
SEE BELOW
Motor end plate
Path of electrical impulse(action potential)
Motor neuron
Axon
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Figure 10-11 Skeletal Muscle Innervation
The synaptic cleft, anarrow space, separatesthe synaptic terminal of
the neuron from theopposing motor end
plate.Junctional
fold ofmotor end plate
AChE
Vesicles ACh
The cytoplasm of the synapticterminal contains vesiclesfilled with molecules ofacetylcholine, or ACh.Acetylcholine is aneurotransmitter, a chemicalreleased by a neuron to changethe permeability or otherproperties of another cell’s plasma membrane. The synaptic cleft and themotor end plate containmolecules of the enzymeacetylcholinesterase (AChE),which breaks down ACh.
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Figure 10-11 Skeletal Muscle Innervation
Arriving actionpotential
The stimulus for ACh releaseis the arrival of an electricalimpulse, or action potential,at the synaptic terminal. Anaction potential is a suddenchange in the transmembranepotential that travels alongthe length of the axon.
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Figure 10-11 Skeletal Muscle Innervation
When the action potentialreaches the neuron’s synapticterminal, permeabilitychanges in the membranetrigger the exocytosis of AChinto the synaptic cleft.Exocytosis occurs as vesiclesfuse with the neuron’s plasmamembrane.
Motorend plate
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Figure 10-11 Skeletal Muscle Innervation
AChreceptor site
ACh molecules diffuseacross the synatpic cleft andbind to ACh receptors on thesurface of the motor endplate. ACh binding alters themembrane’s permeability tosodium ions. Because theextracellular fluid contains ahigh concentration ofsodium ions, and sodium ion concentration inside thecell is very low, sodium ionsrush into the sarcoplasm.
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Figure 10-11 Skeletal Muscle Innervation
The sudden inrush ofsodium ions results in thegeneration of an actionpotential in thesarcolemma. AChE quicklybreaks down the ACh onthe motor end plate and inthe synaptic cleft, thusinactivating the AChreceptor sites.
Actionpotential
AChE
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10-4 Components of the Neuromuscular Junction
• Excitation–Contraction Coupling
• Action potential reaches a triad
• Releasing Ca2+
• Triggering contraction
• Requires myosin heads to be in “cocked” position
• Loaded by ATP energy
A&P FLIX Excitation-Contraction Coupling
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Figure 10-10 The Exposure of Active Sites
In a resting sarcomere, thetropomyosin strands coverthe active sites on the thinfilaments, preventingcross-bridge formation.
When calcium ions enterthe sarcomere, they bindto troponin, whichrotates and swings thetropomyosin away fromthe active sites.
Cross-bridgeformation then occurs,and the contractioncycle begins.
SARCOPLASMIC RETICULUM
Calcium channelsopen
Troponin
NebulinActive site
G-actin(thin filament)
Tropomyosinstrand
Myosin tail(thick filament)
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10-4 Skeletal Muscle Contraction
• The Contraction Cycle
1. Contraction Cycle Begins
2. Active-Site Exposure
3. Cross-Bridge Formation
4. Myosin Head Pivoting
5. Cross-Bridge Detachment
6. Myosin Reactivation
A&P FLIX The Cross Bridge Cycle
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Figure 10-12 The Contraction Cycle
Myosin head
Troponin
Tropomyosin Actin
The contraction cycle, whichinvolves a series of interrelatedsteps, begins with the arrival ofcalcium ions within the zone ofoverlap.
Contraction Cycle Begins
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Figure 10-12 The Contraction Cycle
Calcium ions bind to troponin,weakening the bond betweenactin and the troponin–tropomyosin complex. Thetroponin molecule then changesposition, rolling the tropomyosinmolecule away from the activesites on actin and allowinginteraction with the energizedmyosin heads.
Active-Site Exposure
Sarcoplasm
Activesite
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Figure 10-12 The Contraction Cycle
Once the active sites areexposed, the energizedmyosin heads bind to them,forming cross-bridges.
Cross-Bridge Formation
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Figure 10-12 The Contraction Cycle
After cross-bridge formation,the energy that was stored inthe resting state is releasedas the myosin head pivotstoward the M line. This actionis called the power stroke;when it occurs, the boundADP and phosphate groupare released.
Myosin Head Pivoting
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Figure 10-12 The Contraction Cycle
When another ATP binds tothe myosin head, the linkbetween the myosin head andthe active site on the actinmolecule is broken. Theactive site is now exposedand able to form anothercross-bridge.
Cross-Bridge Detachment
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Figure 10-12 The Contraction Cycle
Myosin reactivationoccurs when the freemyosin head splits ATPinto ADP and P. Theenergy released is used torecock the myosin head.
Myosin Reactivation
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10-4 Skeletal Muscle Contraction
• Fiber Shortening
• As sarcomeres shorten, muscle pulls together,
producing tension
• Muscle shortening can occur at both ends of the
muscle, or at only one end of the muscle
• This depends on the way the muscle is attached at
the ends
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Figure 10-13 Shortening during a Contraction
When both ends are free to move, the ends of acontracting muscle fiber move toward the center ofthe muscle fiber.
When one end of a myofibril is fixed in position, andthe other end free to move, the free end is pulledtoward the fixed end.
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10-4 Skeletal Muscle Relaxation
• Relaxation
• Contraction Duration
• Depends on:
• Duration of neural stimulus
• Number of free calcium ions in sarcoplasm
• Availability of ATP
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10-4 Skeletal Muscle Relaxation
• Relaxation
• Ca2+ concentrations fall
• Ca2+ detaches from troponin
• Active sites are re-covered by tropomyosin
• Rigor Mortis
• A fixed muscular contraction after death
• Caused when:
• Ion pumps cease to function; ran out of ATP
• Calcium builds up in the sarcoplasm
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10-4 Skeletal Muscle Contraction and Relaxation
• Summary
• Skeletal muscle fibers shorten as thin filaments slide between thick filaments
• Free Ca2+ in the sarcoplasm triggers contraction
• SR releases Ca2+ when a motor neuron stimulates the muscle fiber
• Contraction is an active process
• Relaxation and return to resting length are passive
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Table 10-1 Steps Involved in Skeletal Muscle Contraction and Relaxation
Steps in Initiating Muscle Contraction
ACh released, bindingto receptors
Synapticterminal
Motorend plate T tubule Sarcolemma
ActionpotentialreachesT tubule
Sarcoplasmicreticulumreleases Ca2
Ca2
Actin
Myosin
Active siteexposure,cross-bridge formation
Contractionbegins
Steps in Muscle Relaxation
ACh broken down by AChE
Sarcoplasmicreticulumrecaptures Ca2
Active sites covered, nocross-bridgeinteraction
Contractionends
Relaxation occurs,passive return toresting length
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10-5 Tension Production and Contraction Types
• Tension Production by Muscles Fibers
• As a whole, a muscle fiber is either contracted or
relaxed
• Depends on:
• The number of pivoting cross-bridges
• The fiber’s resting length at the time of stimulation
• The frequency of stimulation
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Figure 10-14 The Effect of Sarcomere Length on Active Tension
Normalrange
Decreased length Increased sarcomere length
Ten
sio
n (
per
cen
t o
f m
axim
um
)
Optimal resting length:The normal range of
sarcomere lengths in thebody is 75 to 130 percent of
the optimal length.
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10-5 Tension Production and Contraction Types
• Tension Production by Muscles Fibers
• The Frequency of Stimulation
• A single neural stimulation produces:
• A single contraction or twitch
• Which lasts about 7–100 msec.
• Sustained muscular contractions
• Require many repeated stimuli
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10-5 Tension Production and Contraction Types
• Tension Production by Muscles Fibers
• Twitches
1. Latent period
• The action potential moves through sarcolemma
• Causing Ca2+ release
2. Contraction phase
• Calcium ions bind
• Tension builds to peak
3. Relaxation phase
• Ca2+ levels fall
• Active sites are covered and tension falls to resting levels
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Figure 10-15a The Development of Tension in a Twitch
Eye muscle
Soleus
GastrocnemiusT
ensi
on
Time (msec)Stimulus
A myogram showing differences intension over time for a twitch in different skeletal muscles.
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Figure 10-15b The Development of Tension in a Twitch
Te
ns
ion
The details of tension over time for a single twitch in the gastrocnemius muscle. Notice the presence of a latent period, which corresponds to the time needed for the conduction of an action potential and the subsequent release of calcium ions by the sarcoplasmic reticulum.
Stimulus
Maximum tensiondevelopment
Restingphase
Latentperiod
Contractionphase
Relaxationphase
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10-5 Tension Production and Contraction Types
• Tension Production by Muscles Fibers
• Treppe
• A stair-step increase in twitch tension
• Repeated stimulations immediately after relaxation
phase
• Stimulus frequency <50/second
• Causes a series of contractions with increasing
tension
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10-5 Tension Production and Contraction Types
• Tension Production by Muscles Fibers
• Wave summation
• Increasing tension or summation of twitches
• Repeated stimulations before the end of relaxation
phase
• Stimulus frequency >50/second
• Causes increasing tension or summation of
twitches
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Figure 10-16ab Effects of Repeated Stimulations
Maximum tension (in tetanus)
Maximum tension (in treppe)
Ten
sio
n
Time
Treppe. Treppe is an increase inpeak tension with each successive stimulus delivered shortly after the completion of the relaxation phase of the preceding twitch.
Stimulus
Time
Wave summation. Wavesummation occurs whensuccessive stimuli arrivebefore the relaxation phasehas been completed.
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10-5 Tension Production and Contraction Types
• Tension Production by Muscles Fibers
• Incomplete tetanus
• Twitches reach maximum tension
• If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension
• Complete tetanus
• If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction
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Figure 10-16cd Effects of Repeated Stimulations
Ten
sio
n
Maximum tension (in tetanus)
Time Time
Complete tetanus. Duringcomplete tetanus, the stimulusfrequency is so high that therelaxation phase is eliminated;tension plateaus at maximallevels.
Incomplete tetanus. Incomplete tetanus occurs if the stimulus frequency increases further. Tension production rises to a peak, and the periods of relaxation are very brief.
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10-5 Tension Production and Contraction Types
• Tension Production by Skeletal Muscles
• Depends on:
• Internal tension produced by muscle fibers
• External tension exerted by muscle fibers on
elastic extracellular fibers
• Total number of muscle fibers stimulated
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10-5 Tension Production and Contraction Types
• Motor Units and Tension Production
• Motor units in a skeletal muscle:
• Contain hundreds of muscle fibers
• That contract at the same time
• Controlled by a single motor neuron
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10-5 Tension Production and Contraction Types
• Motor Units and Tension Production
• Recruitment (multiple motor unit summation)
• In a whole muscle or group of muscles, smooth motion and increasing tension are produced by slowly increasing the size or number of motor units stimulated
• Maximum tension
• Achieved when all motor units reach tetanus
• Can be sustained only a very short time
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Figure 10-17a The Arrangement and Activity of Motor Units in a Skeletal Muscle
SPINAL CORD
Axons ofmotor neurons
Motornerve
Muscle fibersKEY
Motor unit 1
Motor unit 2
Motor unit 3
Muscle fibers of different motor units areintermingled, so the forces applied to thetendon remain roughly balanced regardless ofwhich motor units are stimulated.
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Figure 10-17b The Arrangement and Activity of Motor Units in a Skeletal Muscle
Motorunit 1
Motorunit 2
Motorunit 3
Tension in tendon
Ten
sio
n
Time
The tension applied to thetendon remains relativelyconstant, even thoughindividual motor units cyclebetween contraction andrelaxation.
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10-5 Tension Production and Contraction Types
• Motor Units and Tension Production
• Sustained tension
• Less than maximum tension
• Allows motor units rest in rotation
• Muscle tone
• The normal tension and firmness of a muscle at rest
• Muscle units actively maintain body position, without motion
• Increasing muscle tone increases metabolic energy used, even at rest
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10-5 Tension Production and Contraction Types
• Motor Units and Tension Production
• Contraction are classified based on pattern of
tension production
• Isotonic contraction
• Isometric contraction
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10-5 Tension Production and Contraction Types
• Isotonic Contraction
• Skeletal muscle changes length
• Resulting in motion
• If muscle tension > load (resistance):
• Muscle shortens (concentric contraction)
• If muscle tension < load (resistance):
• Muscle lengthens (eccentric contraction)
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Figure 10-18a Concentric, Eccentric, and Isometric Contractions
Tendon
Musclecontracts
(concentriccontraction)
2 kg
2 kg
Musclelength(percentof restinglength)
Time
Muscletension
(kg)
Amount ofload
Musclerelaxes
Contractionbegins Resting length
Peak tensionproduction
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Figure 10-18b Concentric, Eccentric, and Isometric Contractions
Support removedwhen contraction
begins(eccentric contraction)
Musclelength(percentof restinglength)
Muscletension
(kg)
Peak tensionproduction
Resting length
Time
Support removed,contraction begins
6 kg
6 kg
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10-5 Tension Production and Contraction Types
• Isometric Contraction
• Skeletal muscle develops tension, but is
prevented from changing length
• iso- = same, metric = measure
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Figure 10-18c Concentric, Eccentric, and Isometric Contractions
Musclecontracts(isometric
contraction)
6 kg 6 kg
Muscletension
(kg)
Musclelength(percentof restinglength)
Amount of load
Length unchanged
Peak tensionproduction
Contractionbegins
Musclerelaxes
Time
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10-5 Tension Production and Contraction Types
• Muscle Relaxation and the Return to Resting Length
• Elastic Forces
• The pull of elastic elements (tendons and ligaments)
• Expands the sarcomeres to resting length
• Opposing Muscle Contractions
• Reverse the direction of the original motion
• Are the work of opposing skeletal muscle pairs
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10-5 Tension Production and Contraction Types
• Muscle Relaxation and the Return to Resting
Length
• Gravity
• Can take the place of opposing muscle contraction
to return a muscle to its resting state
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10-6 Energy to Power Contractions
• ATP Provides Energy For Muscle Contraction
• Sustained muscle contraction uses a lot of ATP
energy
• Muscles store enough energy to start contraction
• Muscle fibers must manufacture more ATP as
needed
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10-6 Energy to Power Contractions
• ATP and CP Reserves
• Adenosine triphosphate (ATP)
• The active energy molecule
• Creatine phosphate (CP)
• The storage molecule for excess ATP energy in resting muscle
• Energy recharges ADP to ATP
• Using the enzyme creatine kinase (CK)
• When CP is used up, other mechanisms generate ATP
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10-6 Energy to Power Contractions
• ATP Generation
• Cells produce ATP in two ways
1. Aerobic metabolism of fatty acids in the
mitochondria
2. Anaerobic glycolysis in the cytoplasm
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10-6 Energy to Power Contractions
• Aerobic Metabolism
• Is the primary energy source of resting muscles
• Breaks down fatty acids
• Produces 34 ATP molecules per glucose molecule
• Glycolysis
• Is the primary energy source for peak muscular activity
• Produces two ATP molecules per molecule of glucose
• Breaks down glucose from glycogen stored in skeletal muscles
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Table 10-2 Sources of Energy in a Typical Muscle Fiber
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10-6 Energy to Power Contractions
• Energy Use and the Level of Muscular Activity
• Skeletal muscles at rest metabolize fatty acids and store glycogen
• During light activity, muscles generate ATP through anaerobic breakdown of carbohydrates, lipids, or amino acids
• At peak activity, energy is provided by anaerobic reactions that generate lactic acid as a byproduct
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Figure 10-20 Muscle Metabolism
Fatty acids Blood vessels
Glucose Glycogen
MitochondriaCreatine
Resting muscle: Fatty acids are catabolized; theATP produced is used to build energy reserves of ATP,CP, and glycogen.
Moderate activity: Glucose and fatty acids arecatabolized; the ATP produced is used to powercontraction.
Glycogen
Fatty acids
Glucose
Pyruvate
To myofibrils to support muscle contraction
GlycogenGlucose
PyruvateCreatine
Lactate
Lactate
To myofibrils to support muscle contraction
Peak activity: Most ATP is produced through glycolysis,with lactate as a by-product. Mitochondrial activity(not shown) now provides only about one-third of the ATP consumed.
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10-6 Energy to Power Contractions
• Muscle Fatigue
• When muscles can no longer perform a required activity, they are fatigued
• Results of Muscle Fatigue
• Depletion of metabolic reserves
• Damage to sarcolemma and sarcoplasmic reticulum
• Low pH (lactic acid)
• Muscle exhaustion and pain
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10-6 Energy to Power Contractions
• The Recovery Period
• The time required after exertion for muscles to
return to normal
• Oxygen becomes available
• Mitochondrial activity resumes
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10-6 Energy to Power Contractions
• Lactic Acid Removal and Recycling
• The Cori Cycle
• The removal and recycling of lactic acid by the liver
• Liver converts lactate to pyruvate
• Glucose is released to recharge muscle glycogen
reserves
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10-6 Energy to Power Contractions
• The Oxygen Debt
• After exercise or other exertion:
• The body needs more oxygen than usual to normalize
metabolic activities
• Resulting in heavy breathing
• Also called excess postexercise oxygen
consumption (EPOC)
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10-6 Energy to Power Contractions
• Heat Production and Loss
• Active muscles produce heat
• Up to 70% of muscle energy can be lost as heat,
raising body temperature
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10-6 Energy to Power Contractions
• Hormones and Muscle Metabolism
• Growth hormone
• Testosterone
• Thyroid hormones
• Epinephrine
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10-7 Types of Muscles Fibers and Endurance
• Muscle Performance
• Force
• The maximum amount of tension produced
• Endurance
• The amount of time an activity can be sustained
• Force and endurance depend on:
• The types of muscle fibers
• Physical conditioning
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10-7 Types of Muscles Fibers and Endurance
• Three Major Types of Skeletal Muscle Fibers
1. Fast fibers
2. Slow fibers
3. Intermediate fibers
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10-7 Types of Muscles Fibers and Endurance
• Fast Fibers
• Contract very quickly
• Have large diameter, large glycogen reserves,
few mitochondria
• Have strong contractions, fatigue quickly
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10-7 Types of Muscles Fibers and Endurance
• Slow Fibers
• Are slow to contract, slow to fatigue
• Have small diameter, more mitochondria
• Have high oxygen supply
• Contain myoglobin (red pigment, binds oxygen)
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10-7 Types of Muscles Fibers and Endurance
• Intermediate Fibers
• Are mid-sized
• Have low myoglobin
• Have more capillaries than fast fibers, slower to
fatigue
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Figure 10-21 Fast versus Slow Fibers
Slow fibersSmaller diameter,
darker color due tomyoglobin; fatigue
resistant
Fast fibersLarger diameter,
paler color;easily fatigued
LM 170
LM 170 LM 783
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Table 10-3 Properties of Skeletal Muscle Fiber Types
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10-7 Types of Muscles Fibers and Endurance
• Muscle Performance and the Distribution of Muscle Fibers
• White muscles
• Mostly fast fibers
• Pale (e.g., chicken breast)
• Red muscles
• Mostly slow fibers
• Dark (e.g., chicken legs)
• Most human muscles
• Mixed fibers
• Pink
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10-7 Types of Muscles Fibers and Endurance
• Muscle Hypertrophy
• Muscle growth from heavy training
• Increases diameter of muscle fibers
• Increases number of myofibrils
• Increases mitochondria, glycogen reserves
• Muscle Atrophy
• Lack of muscle activity
• Reduces muscle size, tone, and power
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10-7 Types of Muscles Fibers and Endurance
• Physical Conditioning
• Improves both power and endurance
• Anaerobic activities (e.g., 50-meter dash,
weightlifting)
• Use fast fibers
• Fatigue quickly with strenuous activity
• Improved by:
• Frequent, brief, intensive workouts
• Causes hypertrophy
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10-7 Types of Muscles Fibers and Endurance
• Physical Conditioning
• Improves both power and endurance
• Aerobic activities (prolonged activity)
• Supported by mitochondria
• Require oxygen and nutrients
• Improves:
• Endurance by training fast fibers to be more like
intermediate fibers
• Cardiovascular performance
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10-7 Types of Muscles Fibers and Endurance
• Importance of Exercise
• What you don’t use, you lose
• Muscle tone indicates base activity in motor units of skeletal muscles
• Muscles become flaccid when inactive for days or weeks
• Muscle fibers break down proteins, become smaller and weaker
• With prolonged inactivity, fibrous tissue may replace muscle fibers