1 Hole’s Human Anatomy and Physiology Twelfth Edition Shier Butler Lewis Chapter 9 Muscular...

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Hole’s Human Anatomyand Physiology

Twelfth Edition

Shier Butler 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• Striated

• Smooth Muscle• Walls of most viscera, blood vessels and skin• Not under conscious control• Autonomic• Not striated

• Cardiac Muscle• Wall of heart• Not under conscious control• Autonomic• Striated

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9.2: Structure of Skeletal Muscle

• 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

• Muscle coverings:• Epimysium• Perimysium• Endomysium

Bone

Muscle

EpimysiumPerimysium

Endomysium

Fascicle

Fascicles

Muscle fibers (cells)

Myofibrils

Thick and thin filaments

Blood vessel

Muscle fiber

Myofibril

Sarcolemma

Nucleus Filaments

Tendon

Fascia(covering muscle)

Axon of motorneuron

Sarcoplasmicreticulum


• Muscle organ• Fascicles• Muscle cells or fibers• Myofibrils• Thick and thin myofilaments

• Actin and myosin proteins• Titin is an elastic myofilament

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Skeletal Muscle Fibers

• Sarcolemma• Sacroplasm• Sarcoplasmic reticulum (SR)• Transverse (‘T’) tubule• Triad

• Cisternae of SR• T tubule

• Myofibril• Actin myofilaments• Myosin myofilaments• Sarcomere


Nucleus

Mitochondria

SarcolemmaSarcoplasm

Nucleus

Myofibrils


Openings intotransverse tubules

Thick and thinfilaments

Cisternae ofsarcoplasmic reticulum

Transverse tubule

Triad

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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


Myofibril

Sarcomere

(a)

Skeletal muscle fiber

Z lineH zone M line

I band I band

(b)

Z line


Thick (myosin)filaments

Thin (actin)filaments

A bandA band

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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


Cross-bridges

Actin molecule

Thin filament

Myosinmolecule

Thickfilament

Troponin Tropomyosin

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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


Axon branches

Mitochondria

Acetylcholine

(a)

Synapticvesicles

Synapticcleft

Foldedsarcolemma

Motorend plate

Myofibril ofmuscle fiber

Muscle fibernucleus

Motorneuron axon

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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


Motor neuronof motor unit 2

Motor neuronof motor unit 1

Skeletal musclefibers

Branches ofmotor neuronaxon

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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• Muscle impulse eventually reaches the SR and the cisternae


Axon branches

Mitochondria

Acetylcholine

(a)

Synapticvesicles

Synapticcleft

Foldedsarcolemma

Motorend plate

Myofibril ofmuscle fiber

Muscle fibernucleus

Motorneuron axon

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Excitation-Contraction Coupling

• 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


Actin monomers

Release of Ca+2 from sarcoplasmicreticulum exposes binding sites onactin:

Muscle contraction Muscle relaxationActive transport of Ca+2 into sarcoplasmicreticulum, which requires ATP, makesmyosin binding sites unavailable.

Ca+2 binds to troponin

Tropomyosin pulled aside

ATP

Contraction cycle

PADP +

PADP + PADP +

Ca+2

Ca+2

PADP +

PADP + PADP +

PADP

P

ADPATP ATP ATP

PADP + PADP +

ATP

Tropomyosin

Troponin Thin filament

Thick filament

Ca+2

Binding sites onactin exposed

1 Relaxed muscle

Ca+2

PADP +Ca+2

2 Exposed binding sites on actin moleculesallow the muscle contraction cycle to occur

6 ATP splits, whichprovides power to“cock” the myosincross-bridges

3 Cross-bridgesbind actin tomyosin

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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