Chapter 9 Lecture PowerPoint Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

9.1: Introduction Three (3) Types of Muscle Tissues Skeletal Muscle Usually attached to bones Under conscious control Somatic Striated Cardiac Muscle Wall of heart Not under conscious control Autonomic Striated Smooth Muscle Walls of most viscera, blood vessels and skin Not under conscious control Autonomic Not striated

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

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

Skeletal Muscle Fibers Sarcolemma Sacroplasm 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

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)

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

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)

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

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

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

The Sliding Filament Model of Muscle Contraction 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)

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

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

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 low When cellular ATP is low Creatine P ADP Creatine P ADP Creatine ATP Creatine ATP 17

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

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)

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 Physiological vs. psychological fatigue

Heat Production By-product of cellular respiration Muscle cells are major source of body heat Blood transports heat throughout body core

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 Threshold Stimulus Minimal strength required to cause contraction

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

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

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

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

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

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

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

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

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

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

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

Characteristics of Muscle Tissue

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.

Body Movement Four Basic Components of Levers: Rigid bar – bones Fulcrum – point on which bar moves; joint Object - moved against resistance; weight Force – supplies energy for movement; muscles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Resistance Resistance Force Resistance Force Resistance Fulcrum Fulcrum Fulcrum Fulcrum Force Force (a) First-class lever (b) Second-class lever Resistance Force Resistance Fulcrum (c) Third-class lever Fulcrum Force

Levers and Movement Movement Movement Forearm movement Biceps brachii Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Forearm movement Movement Biceps brachii contracting muscle Force Radius Relaxed muscle (a) Fulcrum Resistance Relaxed muscle Triceps brachii contracting muscle Ulna Force Movement Fulcrum Resistance (b)

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

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 Fixators