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PowerPoint Lecture Outlines to accompany
Hole’s Human Anatomy and Physiology Eleventh Edition Shier w Butler w Lewis Chapter 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Functions of Muscular System
Movement Posture Maintenance Joint Stability Heat Generation
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Three Types of Muscle Tissue
Skeletal Muscle usually attached to bones under conscious control striated Cardiac Muscle wall of heart not under conscious control striated Smooth Muscle walls of most viscera, blood vessels, skin not under conscious control not striated
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Structure of a Skeletal Muscle
Composed of: skeletal muscle tissue nervous tissue blood connective tissues fascia tendons aponeuroses
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Skeletal Muscle Structure
Muscle cells called muscle fibers wrapped in endomysium Bundles of muscle fibers called fasicles wrapped in perimysium Many fasicles make a muscle and are wrapped in epimysium
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Skeletal Muscle Fiber Structure
Muscle fibers are long, thin cells made of myofibrils Myofibrils composed of 2 types of cytoskeleton Myosin – thick protein filaments Actin – thin protein filaments
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Skeletal Muscle Fibers
sarcolemma - cell membrane sacroplasm – cell cytoplasm sarcoplasmic reticulum – endoplasmic reticulum transverse tubule - channel that is continuous with sarcolemma and extends into sarcoplasm
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Sarcomere: Unit of contraction
I bands – light area = actin only A bands – dark area = overlapping actin and myosin Z lines – dividing line between individual sarcomeres
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Special Features of Myofilaments
Thin Filaments = Actin associated with troponin and tropomyosin Thick Filaments = Myosin cross-bridges
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Neuromuscular Junction
Site where an axon and muscle fiber meet motor neuron motor end plate synapse synaptic cleft synaptic vesicles neurotransmitters
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Motor Unit single motor neuron
all muscle fibers controlled by motor neuron Sliding Filament Model video
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Stimulus for Contraction
acetylcholine (ACh) nerve impulse causes release of ACh from synaptic vesicles ACh binds to ACh receptors on motor end plate generates a muscle impulse
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Excitation Contraction Coupling
muscle impulses cause sarcoplasmic reticulum to release calcium ions into cytosol calcium binds to troponin to change its shape
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Excitation Contraction Coupling
position of tropomyosin is altered binding sites on actin are exposed actin and myosin molecules bind
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Sliding Filament Model of Muscle Contraction
When cross-bridges pull on actin the sarcromeres shorten, thick and thin filaments slide past one another
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Cross-bridge Cycling When myosin is pulling on the actin, ATP is broken down into ADP and phosphate.
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Relaxation acetylcholinesterase – enzyme that rapidly decomposes acetylcholine remaining in the synapse As a result: muscle impulse stops stimulus to sarcolemma and muscle fiber membrane ceases calcium moves back into sarcoplasmic reticulum myosin and actin binding prevented muscle fiber relaxes
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Major Events of Muscle Contraction and Relaxation
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Energy Sources for Contraction
1) Creatine phosphate 2) Cellular respiration creatine phosphate – stores energy that quickly converts ADP to ATP
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Oxygen Supply and Cellular Respiration
Anaerobic Phase glycolysis occurs in cytoplasm produces little ATP Aerobic Phase citric acid cycle electron transport chain occurs in the mitochondria produces most ATP myoglobin stores extra oxygen
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Oxygen Debt Oxygen debt – amount of oxygen needed by liver cells to use the accumulated lactic acid to produce glucose oxygen not available glycolysis continues pyruvic acid converted to lactic acid liver converts lactic acid to glucose
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Muscle Fatigue inability to contract 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
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Muscular Responses Threshold Stimulus
minimal strength required to cause contraction Recording a Muscle Contraction twitch latent period period of contraction period of relaxation refractory period all-or-none response
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Summation process by which individual twitches combine
produces sustained contractions can lead to tetanic contractions
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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
isometric – muscle contracts but does not change length
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Fast and Slow Twitch Muscle Fibers
Fast-twitch glycolytic fibers (type IIa) white fibers (less myoglobin) poorer blood supply susceptible to fatigue “white meat” Slow-twitch fibers (type I) always oxidative resistant to fatigue red fibers most myoglobin good blood supply many mitochodria “dark meat” Fast-twitch fatigue-resistant fibers (type IIb) intermediate fibers oxidative intermediate amount of myoglobin pink to red in color resistant to fatigue
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Smooth Muscle Fibers Compared to skeletal muscle fibers shorter
single, centrally located nucleus elongated with tapering ends myofilaments randomly organized lack striations lack transverse tubules sarcoplasmic reticula not well developed 2 types Visceral – walls of hollow organs Multiunit – iris of eye & blood vessesels
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Smooth Muscle Contraction
Resembles skeletal muscle contraction interaction between actin and myosin both use calcium and ATP both are triggered by membrane impulses Different from skeletal muscle contraction smooth muscle lacks troponin (replaced with calmodulin) two neurotransmitters (acetlycholine and norepinephrine) affect smooth muscle hormones affect smooth muscle stretching can trigger smooth muscle contraction smooth muscle slower to contract and relax smooth muscle more resistant to fatigue
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Cardiac Muscle muscle fibers joined together by intercalated discs
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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Skeletal Muscle Actions
origin – immovable end insertion – movable end prime mover (agonist) – primarily responsible for movement synergists – assist prime mover antagonist – resist prime mover’s action and cause movement in the opposite direction
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Body Movement Four Basic Components of Lever rigid bar – bones
fulcrum – point on which bar moves; joint object - moved against resistance; weight force – supplies energy for movement; muscles
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Levers and Movement
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Life-Span 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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Clinical Application Myasthenia Gravis autoimmune disorder
receptors for ACh on muscle cells are attacked weak and easily fatigued muscles result difficulty swallowing and chewing ventilator needed if respiratory muscles are affected treatments include drugs that boost ACh removing thymus gland immunosuppressant drugs antibodies
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More Clinical Applications
Moebius Syndrome “walking corpse syndrome” or “stone face” Tendinitis Muscular Dystrophy Poliomyelitis Tetanus and Botulism Lou Gehrig's disease amyotrophic lateral sclerosis (ALS)
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Major Skeletal Muscles
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Major Skeletal Muscles
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Muscles of Facial Expression
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Muscles of Mastication
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Muscles of Facial Expression and Mastication
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Muscles That Move the Head and Vertebral Column
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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 Pectoral Girdle
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Muscles That Move the Arm
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Muscles That Move the Arm
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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 Forearm
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Muscles That Move the Forearm
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Cross Section of the Forearm
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Muscles That Move the Hand
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Muscles That Move the Hand
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Muscles of the Abdominal Wall
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Muscles of the Abdominal Wall
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Muscles of the Pelvic Outlet
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Muscles of Pelvic Outlet
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Muscles That Move the Thigh
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Muscles That Move the Thigh
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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 Leg
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Muscles That Move the Leg
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Muscles That Move the Leg
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Muscles That Move the Foot
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Muscles That Move the Foot
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Muscles That Move the Foot
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Cross-bridge Cycling myosin cross-bridge attaches to actin binding site myosin cross-bridge pulls thin filament ADP and phosphate released from myosin new ATP binds to myosin linkage between actin and myosin cross-bridge break ATP splits myosin cross-bridge goes back to original position
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