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The Muscular SystemThe Muscular SystemThe Muscular SystemThe Muscular System

Chapter 8

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Types of muscle & Types of muscle & functionfunction

Types of muscle & Types of muscle & functionfunction

• Skeletal- 40-50% of total body weight- voluntarymostly movement of bone & body partsStabilizing body positions

• Cardiac- only in heart- involuntaryHeart onlyDevelops pressure for arterial blood flow

• Smooth- grouped in walls of hollow organsSphincters regulate flow in tubesMaintain diameter of tubesMove material in GI tract and reproductive organs

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Muscle FunctionsMuscle FunctionsMuscle FunctionsMuscle Functions

•Produce body movements•Stabilize body positions•Regulate organ volume• Moving substances internally• Producing heat

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Skeletal Muscle TissueSkeletal Muscle TissueSkeletal Muscle TissueSkeletal Muscle Tissue

• Muscle includes: muscle fibers, connective tissue, nerves & blood vessels

• Wrapped in Epimysium•Perimysium surrounds fiber

bundles called fascicles•Endomysium surrounds each

individual fiber

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Skeletal Muscle TissueSkeletal Muscle TissueSkeletal Muscle TissueSkeletal Muscle Tissue

• Well-supplied with blood vessels and nerves

• Terminal of a neuron on each muscle fiber

Figure 8.1Figure 8.1

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Muscle HistologyMuscle HistologyMuscle HistologyMuscle Histology

• elongated cylindrical cells = muscle fibers

• plasma membrane = sarcolemma• Transverse (T- tubules) tunnel

from surface to center of each fiber• Multiple nuclei lie near surface• Cytoplasm = sarcoplasm

Figure 8.2aFigure 8.2a

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Muscle histology (cont.)Muscle histology (cont.)Muscle histology (cont.)Muscle histology (cont.)

• Throughout sarcoplasm is sarcoplasmic reticulumStores Calcium ions

• Sarcoplasm contains myoglobinRed pigmented protein related to Hemoglobin that carries oxygen

• Along entire length are myofibrils• Myofibrils made of protein

filamentsCome in thick and thin filaments

Figure 8.2bFigure 8.2b

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SarcomereSarcomereSarcomereSarcomere

• Filaments overlap in repeating patterns

• Unit structure is called sarcomere• Separated by Z-discs• Darker area = A-band associated with

thick filaments• H-zone has no thin filaments• I-band has thin filaments no thick

filaments

Figure 8.2cFigure 8.2c

Figure 8.3aFigure 8.3a

Figure 8.3bFigure 8.3b

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Functional StructureFunctional StructureFunctional StructureFunctional Structure

• Thick filament (myosin) has moveable heads

• Thin filaments (actin) are anchored to Z-discsContain myosin binding sites for

myosin headAlso contain tropomyosin & troponin

• Tropomyosin blocks myosin binding site at rest

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Sliding Filament Sliding Filament MechanismMechanism

Sliding Filament Sliding Filament MechanismMechanism

• During contraction myosin heads bind actin sites

• Pull and slide actin molecules (and Z-discs) toward H-zone

• I-bands and H-zones narrow• Sliding generates force and

shortens sarcomeres and thus fibers.

Figure 8.4Figure 8.4

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Neuromuscular Neuromuscular InteractionInteraction

Neuromuscular Neuromuscular InteractionInteraction

• Nerve signal triggers muscle action potential

• Delivered by motor neuron• One neuron can trigger 1 or

more fibers at the same time• Neuron plus triggered fibers =

motor unit

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Neuromuscular JunctionNeuromuscular JunctionNeuromuscular JunctionNeuromuscular Junction

• neuronal ending to muscle fiber = Neuromuscular junction

•Synaptic end bulbs (at neuron terminal)Release neurotransmitter

• Muscular area = Motor end plate

• Between is synaptic cleft

Figure 8.5Figure 8.5

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Action at NMJAction at NMJAction at NMJAction at NMJ

1. Release of acetylcholine (ACh)Diffuses across cleft

2. Activation of ACh receptors3. Generation of Muscle Action

PotentialRepeats with each neuronal action

potential4. Breakdown of ACh

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Contraction TriggerContraction TriggerContraction TriggerContraction Trigger

• Muscle action potential=> Ca2+ release from Sacroplasmic Reticulum (SR)

• Ca2+ binds to troponin =>• Moves tropomyosin off actin

sites =>• Myosin binds & starts cycle

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Contraction CycleContraction CycleContraction CycleContraction Cycle

• Myosin binds to actin & releases phosphate group (Forming crossbridges)

• Crossbridge swivels releasing ADP & shortening sarcomere (Power stroke)

• ATP binds to Myosin => release of myosin from actin

• ATP broken down to ADP & Pi => activates myosin head to bind and start again

• Repeats as long as Ca2+ concentration is high

Figure 8.6Figure 8.6

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RelaxationRelaxationRelaxationRelaxation

• Breakdown of Ach to stop muscle Action potentials

• Ca2+ ions transported back into SR lowering concentration=>This takes ATP

• tropomyosin covers actin binding sites

Figure 8.7Figure 8.7

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Muscle ToneMuscle ToneMuscle ToneMuscle Tone

• Even at rest some motor neuron activity occurs = Muscle Tone

• If nerves are cut fiber becomes flaccid (very limp)

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MetabolismMetabolismMetabolismMetabolism

• Rapid changes from very low ATP consumption to high levels of consumption

• Creatine phosphate (high energy store)

•Fast & good for ~ 15 sec

Figure 8.8aFigure 8.8a

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GlycolysisGlycolysisGlycolysisGlycolysis

• Break down glucose to 2 pyruvates getting 2 ATPs

• If insufficient mitochondria or oxygen pyruvate => lactic acid

• Get about 30-40 seconds more at max.

Figure 8.8bFigure 8.8b

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Aerobic Cellular Aerobic Cellular RespirationRespiration

Aerobic Cellular Aerobic Cellular RespirationRespiration

• Production of ATP in mitochondria

• Requires oxygen and carbon substrate

• Produces CO2 and H2O and heat.

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FatigueFatigueFatigueFatigue

• Inability to contract forcefully after prolonged activity

• Limiting factors can include:Ca2+

Creatine Phosphate

Oxygen

Build up of acid

Neuronal failure

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Oxygen Use After Oxygen Use After ExerciseExercise

Oxygen Use After Oxygen Use After ExerciseExercise

• Convert lactic acid back to glucose in liver

• Resynthesize Creatine Phosphate and ATP

• Replace oxygen removed from myoglobin

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Control of Muscle Control of Muscle ContractionContraction

Control of Muscle Control of Muscle ContractionContraction

• Single Action Potential(AP) =>twitchSmaller than maximum muscle force

• Total tension of fiber depends on frequency of APs (number/second)Require wave summationMaximum = tetanus

• Total tension of muscle depends on number of fibers contracting in unisonIncreasing numbers = Motor unit

recruitment

Figure 8.9Figure 8.9

Figure 8.10Figure 8.10

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Fiber typesFiber typesFiber typesFiber types

• Slow oxidative (SO)- small diameter & redlarge amounts of myoglobin and mitochondriaATP production primarily oxidativeFatigue resistant-

• Fast oxidative- glycolytic (FOG)Large diameter = many myofibrilsMany mitochondria and high glycolytic

capacity• Fast glycolytic fibers (FG)

white, fast & powerful and fast fatiguingFor strong, short term use

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RecruitmentRecruitmentRecruitmentRecruitment

• Muscle contractions only use the fibers required for the work

• Recruited in order: SO=>FOG=>FG• if force is constant and the muscle

shortens = Isotonic Contraction• If length is constant and the force

varies = Isometric ContractionThe latter is often a postural muscle

activity

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Effects of ExerciseEffects of ExerciseEffects of ExerciseEffects of Exercise

• SO/FG fiber ratio genetically determinedHigh FG => sprintersHigh SO=> marathoners

• Endurance exercise gives FG=> FOGIncreased diameter and numbers of

mitochondria

• Strength exercise increases size & strength of FG fibers

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Cardiac MuscleCardiac MuscleCardiac MuscleCardiac Muscle

• Striated, short fibers and branched• Single central nucleus; Cells joined

by gap junctions & desmosomes • Thickened joint area called

intercalated discs• Some cardiac muscles generate

own AP- autorhythmicity• Involuntary

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Cardiac muscleCardiac muscleCardiac muscleCardiac muscle

• No nerve- internal pacemaker• Ca2+- from S.R. and extracellular

space• separate cells with gap junctions ->

electrical connections

Figure 15.2bFigure 15.2b

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Smooth muscleSmooth muscleSmooth muscleSmooth muscle

• Involuntary• In internal organs• Filaments not regular so not

striated• Visceral (single unit) type or

Form sheets and are autorhythmicContract as a unit

• Multi-unit type- each has own nerve and can contract

independently

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Smooth MuscleSmooth MuscleSmooth MuscleSmooth Muscle

• Graded contractions and slow responses

• Often sustain long term tone• Often triggered by autonomic

nerves• modulated chemically, nerves,

by mechanical events (stretching)

Figure 8.11Figure 8.11

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AgingAgingAgingAging

• Like bone there is a slow progressive loss of skeletal muscle mass

• Relative number of SO fibers tends to increase

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MovementMovementMovementMovement

• Move one bone relative to another•Origin => most stationary end

Location where the tendon attaches• Insertion => the most mobile end

Location where tendon inserts• Action => the motion or function of

the muscle

Figure 8.12Figure 8.12

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Movement (cont.)Movement (cont.)Movement (cont.)Movement (cont.)

• Generally arranged in opposing pairsFlexors- extensors; abductors- adductors

• The major actor = Prime mover or agonist

• The one with opposite effect = antagonist

• Synergists- help prime mover• Fixators- stabilize origin of prime mover• Role of muscle varies with motion

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Naming Terms-Table 8.2Naming Terms-Table 8.2Naming Terms-Table 8.2Naming Terms-Table 8.2

• Direction relative to body axese.g. Lateralis, medialis (medius),

intermedius, rectus• Specific regions

e.g. abdominus, Brachialis, cleido, oculo-, uro-,

• Origin e.g. biceps, triceps, quadriceps

• Shapee.g. deltoid, orbicularis, serratus, trapezius

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Names (Cont.)Names (Cont.)Names (Cont.)Names (Cont.)

• Other featurese.g. alba, brevis, longus, magnus,

vastus

• Actionse.g. abductor, adductor, flexor,

extensor

• Specific referencese.g. Buccinator (trumpeter), Sartorius

(like a tailor)

Figure 8-13aFigure 8-13a

Figure 8-13bFigure 8-13b

Figure 8.14Figure 8.14

Figure 8.15Figure 8.15

Figure 8.16Figure 8.16

Figure 8.17Figure 8.17

Figure 8.18Figure 8.18

Figure 8.19Figure 8.19

Figure 8.20Figure 8.20

Figure 8.21abFigure 8.21ab

Figure 8.21cFigure 8.21c

Figure 8.22Figure 8.22

Figure 8.23aFigure 8.23a

Figure 8.23bFigure 8.23b

Figure 8.24abFigure 8.24ab

Figure 8.24cdFigure 8.24cd