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3/15/15 1 1 Muscles and Muscle Tissue Chapter 9 2 Overview of Muscle Tissues Compare and Contrast the three basic types of muscle tissue List four important functions of muscle tissue 3 Muscle Terminology Muscle Fibers (skeletal and smooth muscle cells) Myo and sarco = muscle Sacroplasm, sarcolemma

Muscles and Muscle Tissue - AandPonline.comaandponline.com/wp-content/uploads/2015/03/Muscle-Tissue-Lecture... · 3/15/15 2 4 Types of Muscle Tissue • Skeletal Muscle • Longest

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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 T-Tubules

    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.

    Pg. 285

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    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 SR-

    contains 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 contraction.

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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 state

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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

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