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Muscles and Muscle
Tissue
Chapter 9
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Overview of Muscle Tissues
• Compare and Contrast the three basic types of muscle
tissue
• List four important functions of muscle tissue
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Muscle Terminology
• Muscle Fibers (skeletal and smooth muscle cells)
• Myo and sarco = muscle
• Sacroplasm, sarcolemma
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Types of Muscle Tissue
• Skeletal Muscle
• Longest muscle cells
• Striated
• Voluntary muscle
• Very powerful, easily
fatigued
• Highly adaptable
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Types of Muscle Tissue
• Cardiac Muscle
• Striated
• Involuntarily controlled
• Connected by intercalated
discs
• Can contract without any
nervous system input
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Types of Muscle Tissue
• Smooth Muscle
• Found in walls of hollow organs
• Elongated cells
• No striations
• Involuntary
• Slow sustained contractions
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Special Characteristics of Muscle
Tissue
• 1. Excitability
• 2. Contractility
• 3. Extensibility
• 4. Elasticity
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Muscle Functions
• Movement Production
• Maintain Posture and Body
Position
• Joint Stabilization
• Heat Generation
• Additional Functions
• Organ Protection
• Valve formation
• Pupil constriction
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Check Your Understanding
• When describing muscle, what does striated mean?
• Andrew is pondering an exam question that asks, Which
muscle type has elongated cells and is found in the walls of
the urinary bladder? How should he respond Reed?
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Skeletal Muscle
• Describe the Gross Structure of a Skeletal Muscle
• Describe the microscopic structure and functional roles of
the myofibrils, sarcoplasmic reticulum, and T tubules of
skeletal muscle fibers
• Describe the sliding filament model of muscle contraction
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Gross Anatomy of a Skeletal
Muscle
• Each muscle is a discrete
organ
• Nerve and Blood supply
• Connective Tissue Sheaths
• Epimysium
• Perimysium and fascicles
• Endomysium
• Attachments
• Direct/Fleshy Attachments
• Indirect Attachments
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Microscopic Anatomy of a Skeletal
Muscle Fiber (Cell)
• Sarcolemma
• Multinucleate
• Sarcoplasm
• Glycosomes
• Myoglobin
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Microscopic Anatomy of a Skeletal
Muscle Fiber
• Myofibrils
• Striations, Sarcomeres, and
Myofilaments.
• Dark A Bands
• H Zone
• M Line
• Light I Bands
• Z Disc
• Sarcomeres
• Myofilaments
• Thick Filaments (myosin)
• Thin Filaments (actin)
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Molecular Composition of Myofilaments
• Thick Filaments
• Myosin
• Elastic Filaments (Titin)
• Thin Filaments
• Actin
• Tropomyosin
• Troponin
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Sarcoplasmic Reticulum and TTubules
• Sarcoplasmic
Reticulum (SR)
• Most tubules run
longitudinully
• Terminal Cistern Pairs
• T-Tubules
• Continuous with the
extracellular fluid
• Form Triads with the
terminal cistern pairs
• Extension of the
sarcolemma
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Sliding Filament Model of
Contraction
• In a relaxed muscle fiber,
thick and thin filaments
overlap only at the ends of
the A band.
• The sliding filament model
states that during
contraction, the thin
filaments slide past the
thick filaments so that the
actin and myosin filaments
overlap to a greater
degree.
• http://www.youtube.com/
watch?v=Ct8AbZn_A8A
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Check Your Understanding
• How does the Term Epimysium relate to the role and
position of this connective tissue sheath?
• Which Myofilaments have binding sites for calcium? What
specific molecule binds calcium?
• Which region or organelle -cytosol, mitochondrion, or SRcontains the highest concentration of calcium ions in a
resting muscle fiber? Which structure provides the ATP
needed for muscle activity?
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Physiology of Skeletal Muscle Fibers
• Explain how muscle fibers are stimulated to contract by
describing events that occur at the neuromuscular junction.
• Describe how an Action Potential is Generated
• Follow the events of excitation-contraction coupling that
lead to cross bridge activity.
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Activation and Excitation-Contraction Coupling
• Activation
• Step 1: The fiber must be activated,
that is, stimulated by a nerve
ending so that a change in
membrane potential occurs.
• Step 2: Next, it must generate an
electrical current, called an action
potential, in its sarcolemma.
• Excitation-Contraction Coupling
• Step 3: The action potential is
automatically propagated along the
sarcolemma.
• Step 4: Then, intracellular calcium
ion levels must rise briefly,
providing the final trigger for
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The Nerve Stimulus and Events at the
NMJ NMJatatheNMJ
• Somatic Motor Neurons
• Neuromuscular Junction
• Synaptic Cleft
• Synaptic Vesicles (ACh)
• How does a motor neuron stimulate a
skeletal muscle fiber?
• Step 1: When a nerve impulse reaches
the end of an axon, the axon terminal
releases ACH into the synaptic cleft
• Step 2: ACh diffuses across the cleft
and attaches to ACh receptors on the
sarcolemma of the muscle fiber.
• Step 3: ACh binding triggers electrical
events that ultimately generate an
action potential
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Generation of an Active Potential Across the
Sarcolemma
• Action Potential: The
predictable sequence of
electrical changes across
a membrane.
• Step 1: Generation of an
end plate potential
• Step 2: Depolarization:
Generation and
Propagation of an action
potential
• Step 3: Repolarization:
Restoring the
Sarcolemma to its original
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Excitation-Contraction Coupling
• Step 1: Action Potential Propagation
• Step 2: Calcium ion release
• Step 3: Calcium binds to Troponin and removes the
blocking action of tropomyosin
• Step 4: Contraction Begins
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Cross Bridge Cycling
• http://www.youtube.com/watch?v=Ct8AbZn_A8A
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Check Your Understanding
• What are the three structural components of a
neuromuscular junction?
• What is the final trigger for contraction? What is the initial
trigger?
• What prevents the filaments from sliding back to their
original position each time a myosin cross bridge detaches
from actin?
• What would happen if a muscle fiber suddenly ran out of
ATP when sarcomeres had only partially contracted?
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Contraction of Skeletal Muscle
• Define motor unit and muscle twitch, and describe the
events occurring during the three phases of muscle twitch.
• Explain how smooth, graded contractions of a skeletal
muscle are produced.
• Differentiate between isometric and isotonic contractions.
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Types of Muscle Contraction
• Muscle tension versus load
• Isometric versus isotonic
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The Motor Unit
• One motor neuron and all of its innervated fibers
• Innervated fibers are spread throughout entire muscle
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The Muscle Twitch
• The motor units response to a single action potential from
its motor neuron
• 3 Phases of a twitch myogram
• Phase 1: Latent Period
• Phase 2: Period of Contraction
• Phase 3: Period of Relaxation
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Graded Muscle Responses
• Can be Graded in two ways
• 1.) By changing the frequency of stimulation
• Temporal summation
• unfused (incomplete) tetanus
• fused (complete) tetanus
• 2.) By changing the strength of stimulation
• Recruitment (multiple motor unit summation)
• Sub threshold stimuli
• threshold stimulus
• maximal stimulus
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Size Principle
• The motor units with the smallest muscle fibers are activated
first
• As motor units with larger and larger muscle fibers begin to
be excited, contractile strength increases.
• The largest motor units are only activated when maximal
contraction is required.
• Prevents fatigue due to asynchronous contraction
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Isotonic and Isometric Contractions
• Isotonic: Muscle length
changes
• Concentric: Muscle
shortens
• Eccentric: Muscle
Lengthens
• Isometric: Muscle length
does not change
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Check your understanding
• What is a motor unit
• What is happening in a muscle during the latent period of a
twitch contraction?
• Matt is competing in a chin up competition, What type of
muscle contractions are occurring in his biceps muscles?
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Muscle Metabolism
• Describe three ways in which ATP is regenerated during
skeletal muscle contraction.
• Define EPOC and muscle fatigue. List possible causes of
muscle fatigue.
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Providing Energy for Muscle Contraction
• ATP is the only energy source used directly for contractile
activities
• Muscles store only 4-6 seconds worth
• Therefore ADP must be converted to ATP as quickly as
ATP is used as energy
• 3 Pathways
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Pathway #1
• Direct Phosphorylation of ADP by Creatine Phosphate
• Creatine Phosphate + ADP -----------> Creatine + ATP
• Pathway is viable for roughly 15 seconds
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Pathway #2
• Anaerobic Pathway: Glycolysis and Lactic Acid Formation
• Glucose is broken down in to two Pyruvic acid molecules releasing 2 ATP
molecules
• Glycolysis occurs both in the presence and absence of oxygen
• Viable as a primary energy source for 30-40 seconds
• Ordinarily the pyruvic acid byproducts enter the mitochondria for further
metabolism
• However At 70% maximal contractile activity blood vessels are compressed
preventing aerobic mitochondrial metabolism.
• Under these circumstances (anaerobic glycolysis) most of the pyruvic acid is
converted to lactic acid
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Pathway #3
• Aerobic Respiration
• During rest, light, and moderate exercise, this
pathway provides 95% of ATP supply.
• Occurs in the mitochondria
• Requires oxygen
• Glucose + Oxygen --------> Carbon Dioxide +
water + 32 ATP
• Slowest of three systems
• Fuel source progression:
• 1. Muscle Glycogen
• 2. Bloodborne glucose, pyruvic acid, free fatty
acids
• 3. After 30 minutes, free fatty acids are the
primary source of fuel
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Energy Systems During Sport
• Aerobic Endurance
• Anaerobic Threshold
• Weightlifting: Direct
Phosphorylation
• On off activities such as
tennis, soccer, 100m swim:
Anaerobic
• Prolonged jogging: Aerobic
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Muscle Fatigue
• Physiological inability to contract in the presence of stimuli
• Caused by ionic disturbances that alter E-C coupling
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Excess Post-exercise Oxygen Consumption
(EPOC)
• Post exercise, muscle tissue must
• replenish its myoglobin bound oxygen reserves
• convert excess lactic acid into pyruvic acid
• replace glycogen stores
• Resynthesize ATP and creatine phosphate reserves
• The increased oxygen demand during this recovery period
is referred to as the EPOC or oxygen debt
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Heat Production
• Only 40% of energy used during muscle contraction is
converted into useful work
• 60% is converted into heat
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Check Your Understanding
• Clayton has just finished jogging and is breathing heavily.
Why is Clayton breathing heavily? What metabolic product
might account for his sore muscles and muscle weakness?
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Forces of Muscle Contraction
• Describe factors that influence the force, velocity, and
duration of skeletal muscle contraction
• Describe three types of skeletal muscle fibers and explain
the relative value of each type
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Muscle Contraction Force
• Influencing Factors
• Number of fibers recruited
• Size of muscle fibers
• Frequency of stimulation
• Degree of muscle stretch
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Velocity and Duration of Contraction
• Influencing factors
• Muscle Fiber Type
• Load
• Recruitment
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Muscle Fiber Type
• Classified based on two criteria
• Speed of contraction
• Slow fibers
• Fast Fibers
• Major pathways for forming ATP
• Glycolytic
• Oxidative
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3 Fiber Types
• Slow Oxidative
• Fast Oxidative
• Fast Glycolytic
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Load
• Greater load results in
• a longer latent period
• a slower contraction
• a shorter duration of muscle contraction
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Recruitment
• The greater number of motor units recruited
• The faster the contraction
• The more prolonged the contraction
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Check Your Understanding
• List two factors that influence contractile force and two that
influence velocity of contraction
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Adaptations to Exercise
• Compare and Contrast the effects of aerobic and
resistance exercise on skeletal muscles and on other body
systems
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Aerobic (endurance) Exercise
• Number of capillaries surrounding the muscle fibers
increases
• Number of mitochondria within the muscle fibers increases
• Concentration of myoglobin increases
• Affects all fiber types, conversion is possible
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Resistance Exercise
• Causes muscle hypertrophy
• Muscle fibers increase in diameter, not number
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Study guide