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.

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)

Animation: Function of the Neuromuscular Junction Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

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