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Chapter 9 Muscular System
Hole’s Human Anatomy and Physiology Twelfth Edition Shier w Butler w Lewis Chapter 9 Muscular System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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9.1: Introduction Three (3) Types of Muscle Tissues Skeletal Muscle
Usually attached to bones Under conscious control Somatic nervous control Striated Cardiac Muscle Wall of heart Not under conscious control Autonomic nervous control Striated Smooth Muscle Walls of most viscera, blood vessels and skin Not under conscious control Autonomic Not striated
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9.2: Structure of Skeletal Muscle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Skeletal Muscle Organ of the muscular system Skeletal muscle tissue Nervous tissue Blood Connective tissues Fascia Tendons Aponeuroses Aponeuroses Skeletal muscles Tendons
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Connective Tissue Coverings
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Muscle coverings: Epimysium Perimysium Endomysium Muscle Bone Fascicles Tendon Muscle fibers (cells) Fascia (covering muscle) Myofibrils Epimysium Muscle organ Fascicles Muscle cells or fibers Myofibrils Thick and thin myofilaments Actin and myosin proteins Titin is an elastic myofilament Perimysium Thick and thin filaments Endomysium Fascicle Axon of motor neuron Blood vessel Nucleus Sarcoplasmic reticulum Myofibril Filaments Muscle fiber Sarcolemma 5
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Skeletal Muscle Fibers
Sarcolemma Sarcoplasm Sarcoplasmic reticulum (SR) Transverse (‘T’) tubule Triad Cisternae of SR T tubule Myofibril Actin myofilaments Myosin myofilaments Sarcomere Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Myofibrils Cisternae of sarcoplasmic reticulum Triad Nucleus Transverse tubule Sarcoplasmic reticulum Openings into transverse tubules Mitochondria Nucleus Thick and thin filaments Sarcolemma Sarcoplasm
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9.3: Skeletal Muscle Contraction
Movement within the myofilaments I band (thin) A band (thick and thin) H zone (thick) Z line (or disc) M line Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Skeletal muscle fiber Sarcoplasmic reticulum Thick (myosin) filaments Thin (actin) filaments Myofibril Sarcomere Z line H zone Z line M line I band A band I band A band (a) (b)
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Myofilaments Thick myofilaments Composed of myosin protein
Form the cross-bridges Thin myofilaments Composed of actin protein Associated with troponin and tropomyosin proteins Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cross-bridges Thin filament Troponin Tropomyosin Myosin molecule Thick filament Actin molecule
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Neuromuscular Junction
Also known as NMJ or myoneural junction Site where an axon and muscle fiber meet Parts to know: Motor neuron Motor end plate Synapse Synaptic cleft Synaptic vesicles Neurotransmitters Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Synaptic vesicles Mitochondria Motor neuron axon Acetylcholine Synaptic cleft Folded sarcolemma Axon branches Motor end plate Muscle fiber nucleus Myofibril of muscle fiber 9 (a)
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Animation: Function of the Neuromuscular Junction
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Motor Unit Single motor neuron
All muscle fibers controlled by motor neuron As few as four fibers As many as 1000’s of muscle fibers Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Motor neuron of motor unit 2 Motor neuron of motor unit 1 Branches of motor neuron axon Skeletal muscle fibers
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Stimulus for Contraction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acetylcholine (ACh) Nerve impulse causes release of ACh from synaptic vesicles ACh binds to ACh receptors on motor end plate Generates a muscle impulse Muscle impulse eventually reaches the SR and the cisternae Synaptic vesicles Mitochondria Motor neuron axon Acetylcholine Synaptic cleft Folded sarcolemma Axon branches Motor end plate Muscle fiber nucleus Myofibril of muscle fiber (a) 11
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Excitation-Contraction Coupling
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Muscle impulses cause SR to release calcium ions into cytosol Calcium binds to troponin to change its shape The position of tropomyosin is altered Binding sites on actin are now exposed Actin and myosin molecules bind via myosin cross-bridges Tropomyosin Troponin Thin filament Actin monomers ADP + P ADP + P Thick filament 1 Relaxed muscle Ca+2 Ca+2 Muscle contraction Muscle relaxation Release of Ca+2 from sarcoplasmic reticulum exposes binding sites on actin: Active transport of Ca+2 into sarcoplasmic reticulum, which requires ATP, makes myosin binding sites unavailable. Ca+2 binds to troponin ATP Tropomyosin pulled aside Binding sites on actin exposed Ca+2 Ca+2 Ca+2 ADP + P ADP + P 2 Exposed binding sites on actin molecules allow the muscle contraction cycle to occur ADP + P ADP + P Contraction cycle ADP + P ADP + P 6 ATP splits, which provides power to “cock” the myosin cross-bridges 3 Cross-bridges bind actin to myosin ADP ADP ATP ATP ATP P P ATP ADP + P 5 New ATP binds to myosin, releasing linkages 4 Cross-bridges pull thin filament (power stroke), ADP and P released from myosin 13
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Cross Bridge Cycling Myosin cross-bridge attaches to actin binding site Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tropomyosin Troponin Thin filament Actin monomers Myosin cross-bridge pulls thin filament ADP + P ADP + P Thick filament 1 Relaxed muscle Ca+2 Ca+2 Muscle contraction Muscle relaxation Release of Ca+2 from sarcoplasmic reticulum exposes binding sites on actin: Active transport of Ca+2 into sarcoplasmic reticulum, which requires ATP, makes myosin binding sites unavailable. ADP and phosphate released from myosin Ca+2 binds to troponin ATP Tropomyosin pulled aside Binding sites on actin exposed New ATP binds to myosin Ca+2 Ca+2 Ca+2 ADP + P ADP + P 2 Exposed binding sites on actin molecules allow the muscle contraction cycle to occur Linkage between actin and myosin cross-bridge break ADP + P ADP + P Contraction cycle ADP + P ADP + P 6 ATP splits, which provides power to “cock” the myosin cross-bridges 3 Cross-bridges bind actin to myosin ATP splits ADP ADP ATP ATP ATP P P Myosin cross-bridge goes back to original position ATP ADP + P 5 New ATP binds to myosin, releasing linkages 4 Cross-bridges pull thin filament (power stroke), ADP and P released from myosin
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The Sliding Filament Model of Muscle Contraction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. When sarcromeres shorten, thick and thin filaments slide past one another H zones and I bands narrow Z lines move closer together Sarcomere A band Z line Z line 1 Relaxed Thin filaments Thick filaments 2 Contracting 3 Fully contracted (a)
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Animation: The Cross-Bridge Cycle
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Animation: Breakdown of ATP and Cross-Bridge Movement
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Relaxation Acetylcholinesterase – rapidly decomposes Ach remaining in the synapse Muscle impulse stops Stimulus to sarcolemma and muscle fiber membrane ceases Calcium moves back into sarcoplasmic reticulum (SR) Myosin and actin binding prevented Muscle fiber relaxes
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Animation: Action Potentials and Muscle Contraction
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Energy Sources for Contraction
1) Creatine phosphate and 2) Cellular respiration Creatine phosphate – stores energy that quickly converts ADP to ATP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. When cellular ATP is high When cellular ATP is low Creatine P ADP Creatine P ADP Creatine ATP Creatine ATP 17
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Animation: Energy Sources for Prolonged Exercise
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Oxygen Supply and Cellular Respiration
Anaerobic Phase Glycolysis Occurs in cytoplasm Produces little ATP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glucose 2 In the absence of sufficient oxygen, glycolysis leads to lactic acid accumulation. Energy 2 ATP Pyruvic acid Lactic acid Cytosol Aerobic Phase Citric acid cycle Electron transport system Occurs in the mitochondria Produces most ATP Myoglobin stores extra oxygen Mitochondria 1 Oxygen carried from the lungs by hemoglobin in red blood cells is stored in muscle cells by myoglobin and is available to support aerobic respiration. Citric acid cycle Electron transport chain Synthesis of 34 ATP CO2 + H2O + Energy Heat
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Oxygen Debt Oxygen debt – amount of oxygen needed by liver cells to use the accumulated lactic acid to produce glucose Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oxygen not available Glycolysis continues Pyruvic acid converted to lactic acid Liver converts lactic acid to glucose Glycogen Energy to synthesize Glucose Energy from ATP ATP Pyruvic acid Lactic acid Glycolysis and lactic acid formation (in muscle) Synthesis of glucose from lactic acid (in liver)
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Muscle Fatigue Inability to contract muscle Commonly caused from:
Decreased blood flow Ion imbalances across the sarcolemma Accumulation of lactic acid Cramp – sustained, involuntary muscle contraction
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Heat Production By-product of cellular respiration
Muscle cells are major source of body heat Blood transports heat throughout body core
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9.4: Muscular Responses Muscle contraction can be observed by removing a single skeletal muscle fiber and connecting it to a device that senses and records changes in the overall length of the muscle fiber. Threshold Stimulus Minimal strength required to cause contraction
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Recording of a Muscle Contraction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Recording a Muscle Contraction Twitch Latent period Period of contraction Period of relaxation Refractory period All-or-none response Force of contraction Latent period Period of contraction Period of relaxation Time of stimulation Time
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Length-Tension Relationship
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Optimal length (b) Overly shortened (c) Overly stretched Force Muscle fiber length
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Summation Process by which individual twitches combine
Produces sustained contractions Can lead to tetanic contractions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Force of contraction (a) Force of contraction (b) Force of contraction (c) Time
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Recruitment of Motor Units
Recruitment - increase in the number of motor units activated Whole muscle composed of many motor units More precise movements are produced with fewer muscle fibers within a motor unit As intensity of stimulation increases, recruitment of motor units continues until all motor units are activated
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Sustained Contractions
Smaller motor units (smaller diameter axons) - recruited first Larger motor units (larger diameter axons) - recruited later Produce smooth movements Muscle tone – continuous state of partial contraction
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Types of Contractions Isotonic – muscle contracts and changes length
Concentric – shortening contraction Isometric – muscle contracts but does not change length Eccentric – lengthening contraction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Muscle contracts with force greater than resistance and shortens (concentric contraction) (b) Muscle contracts with force less than resistance and lengthens (eccentric contraction) (c) Muscle contracts but does not change length (isometric contraction) No movement Movement Movement 29
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Fast Twitch and Slow Twitch Muscle Fibers
Slow-twitch fibers (Type I) Always oxidative Resistant to fatigue Red fibers Most myoglobin Good blood supply Fast-twitch fatigue-resistant fibers (Type IIb) Intermediate fibers Oxidative Intermediate amount of myoglobin Pink to red in color Resistant to fatigue Fast-twitch glycolytic fibers (Type IIa) White fibers (less myoglobin) Poorer blood supply Susceptible to fatigue
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9.5: Smooth Muscles Compared to skeletal muscle fibers, smooth muscle fibers are: Shorter Single, centrally located nucleus Elongated with tapering ends Myofilaments randomly organized Lack striations Lack transverse tubules Sarcoplasmic reticula (SR) not well developed
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Smooth Muscle Fibers Visceral Smooth Muscle Single-unit smooth muscle
Sheets of muscle fibers Fibers held together by gap junctions Exhibit rhythmicity Exhibit peristalsis Walls of most hollow organs Multi-unit Smooth Muscle Less organized Function as separate units Fibers function separately Iris of eye Walls of blood vessels
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Smooth Muscle Contraction
Resembles skeletal muscle contraction in that: Interaction between actin and myosin Both use calcium and ATP Both are triggered by membrane impulses Different from skeletal muscle contraction in that: Smooth muscle lacks troponin Smooth muscle uses calmodulin Two neurotransmitters affect smooth muscle Acetlycholine (Ach) and norepinephrine (NE) Hormones affect smooth muscle Stretching can trigger smooth muscle contraction Smooth muscle slower to contract and relax Smooth muscle more resistant to fatigue Smooth muscle can change length without changing tautness
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9.6: Cardiac Muscle Located only in the heart
Muscle fibers joined together by intercalated discs Fibers branch Network of fibers contracts as a unit Self-exciting and rhythmic Longer refractory period than skeletal muscle
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Characteristics of Muscle Tissue
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9.7: Skeletal Muscle Actions
Skeletal muscles generate a great variety of body movements. The action of each muscle mostly depends upon the kind of joint it is associated with and the way the muscle is attached on either side of that joint.
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Origin and Insertion Origin – immovable end Insertion – movable end
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Origin – immovable end Insertion – movable end Coracoid process Origins of biceps brachii Tendon of long head Tendon of short head Biceps brachii Radius Insertion of biceps brachii
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Interaction of Skeletal Muscles
Prime mover (agonist) – primarily responsible for movement Synergists – assist prime mover Antagonist – resist prime mover’s action and cause movement in the opposite direction of the prime mover
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9.9: Lifespan Changes Myoglobin, ATP, and creatine phosphate decline
By age 80, half of muscle mass has atrophied Adipose cells and connective tissues replace muscle tissue Exercise helps to maintain muscle mass and function
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Muscles of Facial Expression
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Muscles of Mastication
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Muscles That Move the Head and Vertebral Column
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Muscles That Move the Pectoral Girdle
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Muscles That Move the Arm
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Muscles That Move the Forearm
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Muscles That Move the Hand
Flexors (anterior) and extensors (posterior)
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Muscles of the Abdominal Wall
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Muscles of the Pelvic Outlet
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Muscles That Move the Thigh
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Muscles That Move the Leg
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Muscles That Move the Foot
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Important Points in Chapter 9: Outcomes to be Assessed
9.1: Introduction List various outcomes of muscle action. 9.2: Structure of a Skeletal Muscle Describe how connective tissue is a part of the structure of a skeletal muscle. Name the major parts of a skeletal muscle fiber and describe the functions of each. 9.3: Skeletal Muscle Contraction Describe the neural control of skeletal muscle contraction. Identify the major events that occur during skeletal muscle fiber contraction.
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Important Points in Chapter 9: Outcomes to be Assessed
List the energy sources for skeletal muscle fiber contraction. Describe how a muscle may become fatigued. Describe oxygen debt. 9.4: Muscular Responses Distinguish between fast and slow twitch muscle fibers. Distinguish between a twitch and a sustained contraction. Describe how exercise affects skeletal muscles. Explain how various types of muscular contractions produce body movements and help maintain posture.
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Important Points in Chapter 9: Outcomes to be Assessed
9.5: Smooth Muscle Distinguish between the structures and functions of multiunit smooth muscle and visceral smooth muscle. Compare the contraction mechanisms of skeletal and smooth muscle fibers. 9.6: Cardiac Muscle Compare the contraction mechanisms of skeletal and cardiac muscle fibers. 9.7: Skeletal Muscle Actions Explain how the attachments, locations, and interactions of skeletal muscles make possible certain movements.
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Important Points in Chapter 9: Outcomes to be Assessed
9.8: Major Skeletal Muscles Identify and locate the skeletal muscles of each body region and describe the action (s) of each muscle.
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