Three Types of Muscle Tissue
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Three Types of Muscle TissueThree Types of Muscle Tissue
1. Smooth muscle tissue2. Skeletal muscle tissue3. Cardiac muscle tissue
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3 Types of Muscle Tissue3 Types of Muscle Tissue
Skeletal muscleSkeletal muscleattaches to bone, skin or fasciaattaches to bone, skin or fasciastriated with light & dark bands visible striated with light & dark bands visible
with scope with scope voluntary control of contraction & voluntary control of contraction &
relaxationrelaxation
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3 Types of Muscle Tissue3 Types of Muscle Tissue
Cardiac muscleCardiac musclestriated in appearancestriated in appearanceinvoluntary controlinvoluntary controlautorhythmic because of built in autorhythmic because of built in
pacemakerpacemaker
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3 Types of Muscle Tissue3 Types of Muscle Tissue
Smooth muscleSmooth muscleattached to hair follicles in skinattached to hair follicles in skinin walls of hollow organs -- blood vessels in walls of hollow organs -- blood vessels
& GI& GInonstriated in appearancenonstriated in appearanceinvoluntaryinvoluntary
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Functions of Muscle TissueFunctions of Muscle Tissue
Producing body movementsProducing body movementsStabilizing body positionsStabilizing body positionsRegulating organ volumesRegulating organ volumes
bands of smooth muscle called sphinctersbands of smooth muscle called sphinctersMovement of substances within the bodyMovement of substances within the body
blood, lymph, urine, air, food and fluids, spermblood, lymph, urine, air, food and fluids, spermProducing heatProducing heat
involuntary contractions of skeletal muscle involuntary contractions of skeletal muscle (shivering)(shivering)
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Properties of Muscle TissueProperties of Muscle TissueExcitabilityExcitability
respond to chemicals released from nerve cellsrespond to chemicals released from nerve cellsConductivityConductivity
ability to propagate electrical signals over ability to propagate electrical signals over membranemembrane
ContractilityContractilityability to shorten and generate force ability to shorten and generate force
ExtensibilityExtensibilityability to be stretched without damaging the tissueability to be stretched without damaging the tissue
ElasticityElasticityability to return to original shape after being ability to return to original shape after being
stretchedstretched
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Skeletal Muscle -- Skeletal Muscle -- Connective Connective TissueTissue
Superficial fascia is Superficial fascia is loose connective tissue & loose connective tissue & fat underlying the skinfat underlying the skin
Deep fascia = dense irregular connective tissue Deep fascia = dense irregular connective tissue around musclearound muscle
Connective tissue components of the muscle Connective tissue components of the muscle includeincludeepimysium = surrounds the whole muscle epimysium = surrounds the whole muscle perimysium = surrounds bundles (fascicles) of perimysium = surrounds bundles (fascicles) of
10-100 muscle cells10-100 muscle cellsendomysium = separates individual muscle cellsendomysium = separates individual muscle cells
All these connective tissue layers extend All these connective tissue layers extend beyond the muscle belly to form the tendon beyond the muscle belly to form the tendon
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Connective Tissue Connective Tissue ComponentsComponents
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Nerve and Blood Supply Nerve and Blood Supply Each skeletal muscle is supplied by a Each skeletal muscle is supplied by a
nerve, artery and two veins.nerve, artery and two veins.Each motor neuron supplies multiple Each motor neuron supplies multiple
muscle cells (neuromuscular junction)muscle cells (neuromuscular junction)Each muscle cell is supplied by one Each muscle cell is supplied by one
motor neuron terminal branch and is in motor neuron terminal branch and is in contact with one or two capillaries.contact with one or two capillaries.nerve fibers & capillaries are found in the nerve fibers & capillaries are found in the
endomysium between individual cellsendomysium between individual cells
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Fusion of Myoblasts into Muscle Fusion of Myoblasts into Muscle FibersFibers
Every mature muscle cell developed from 100 Every mature muscle cell developed from 100 myoblasts that fuse together in the fetus. myoblasts that fuse together in the fetus. (multinucleated)(multinucleated)
Mature muscle cells can not divideMature muscle cells can not divide Muscle growth is a result of cellular enlargement & Muscle growth is a result of cellular enlargement &
not cell divisionnot cell division Satellite cells retain the ability to regenerate new Satellite cells retain the ability to regenerate new
cells.cells.
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Muscle Fiber or MyofibersMuscle Fiber or Myofibers
Muscle cells are long, cylindrical & multinucleated Muscle cells are long, cylindrical & multinucleated Sarcolemma = muscle cell membraneSarcolemma = muscle cell membrane Sarcoplasm filled with tiny threads called myofibrils & Sarcoplasm filled with tiny threads called myofibrils &
myoglobin (red-colored, oxygen-binding protein) myoglobin (red-colored, oxygen-binding protein)
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Transverse TubulesTransverse Tubules
T (transverse) tubules are invaginations of the T (transverse) tubules are invaginations of the sarcolemma into the center of the cellsarcolemma into the center of the cell filled with extracellular fluidfilled with extracellular fluid carry muscle action potentials down into cellcarry muscle action potentials down into cell
Mitochondria lie in rows throughout the cellMitochondria lie in rows throughout the cell near the muscle proteins that use ATP during near the muscle proteins that use ATP during
contractioncontraction
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Myofibrils & MyofilamentsMyofibrils & Myofilaments
Muscle fibers are filled with threads called Muscle fibers are filled with threads called myofibrils separated by SR (sarcoplasmic myofibrils separated by SR (sarcoplasmic reticulum)reticulum)
Myofilaments (thick & thin filaments) are the Myofilaments (thick & thin filaments) are the contractile proteins of musclecontractile proteins of muscle
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Sarcoplasmic Reticulum Sarcoplasmic Reticulum (SR)(SR)
System of tubular sacs similar to smooth System of tubular sacs similar to smooth ER in nonmuscle cellsER in nonmuscle cells
Stores Ca+2 in a relaxed muscleStores Ca+2 in a relaxed muscle Release of Ca+2 triggers muscle Release of Ca+2 triggers muscle
contractioncontraction
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Atrophy and HypertrophyAtrophy and Hypertrophy
AtrophyAtrophywasting away of muscleswasting away of musclescaused by disuse (disuse atrophy) or severing caused by disuse (disuse atrophy) or severing
of the nerve supply (denervation atrophy)of the nerve supply (denervation atrophy)the transition to connective tissue can not be the transition to connective tissue can not be
reversedreversedHypertrophyHypertrophy
increase in the diameter of muscle fibers increase in the diameter of muscle fibers resulting from very forceful, repetitive muscular resulting from very forceful, repetitive muscular
activity and an increase in myofibrils, SR & activity and an increase in myofibrils, SR & mitochondriamitochondria
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Filaments and the Filaments and the SarcomereSarcomereThick and thin filaments overlap each Thick and thin filaments overlap each
other in a pattern that creates other in a pattern that creates striations (light I bands and dark A striations (light I bands and dark A bands)bands)
The I band region contains only thin The I band region contains only thin filaments.filaments.
They are arranged in compartments They are arranged in compartments called sarcomeres, separated by Z called sarcomeres, separated by Z discs.discs.
In the overlap region, six thin In the overlap region, six thin filaments surround each thick filamentfilaments surround each thick filament
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Thick & Thin MyofilamentsThick & Thin Myofilaments
Supporting proteins (M line, titin and Z disc Supporting proteins (M line, titin and Z disc help anchor the thick and thin filaments in help anchor the thick and thin filaments in place)place)
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Overlap of Thick & Thin Overlap of Thick & Thin Myofilaments within a MyofibrilMyofilaments within a Myofibril
Dark(A) & light(I) bands visible with an electron microscope
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Exercise-Induced Muscle Exercise-Induced Muscle DamageDamage
Intense exercise can cause muscle damageIntense exercise can cause muscle damageelectron micrographs reveal torn sarcolemmas, electron micrographs reveal torn sarcolemmas,
damaged myofibrils an disrupted Z discsdamaged myofibrils an disrupted Z discsincreased blood levels of myoglobin & creatine increased blood levels of myoglobin & creatine
phosphate found only inside muscle cellsphosphate found only inside muscle cellsDelayed onset muscle sorenessDelayed onset muscle soreness
12 to 48 Hours after strenuous exercise12 to 48 Hours after strenuous exercisestiffness, tenderness and swelling due to stiffness, tenderness and swelling due to
microscopic cell damagemicroscopic cell damage
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The Proteins of MuscleThe Proteins of Muscle
Myofibrils are built of 3 kinds of proteinMyofibrils are built of 3 kinds of proteincontractile proteinscontractile proteins
myosin and actinmyosin and actinregulatory proteins which turn contraction regulatory proteins which turn contraction
on & offon & offtroponin and tropomyosintroponin and tropomyosin
structural proteins which provide proper structural proteins which provide proper alignment, elasticity and extensibilityalignment, elasticity and extensibilitytitin, myomesin, nebulin and dystrophintitin, myomesin, nebulin and dystrophin
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The Proteins of Muscle -- MyosinThe Proteins of Muscle -- Myosin
Thick filaments are composed of myosin Thick filaments are composed of myosin each molecule resembles two golf clubs twisted togethereach molecule resembles two golf clubs twisted together myosin heads (cross bridges) extend toward the thin myosin heads (cross bridges) extend toward the thin
filamentsfilaments Held in place by the M line proteins.Held in place by the M line proteins.
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The Proteins of Muscle -- ActinThe Proteins of Muscle -- Actin
Thin filaments are made of actin, troponin, & tropomyosin Thin filaments are made of actin, troponin, & tropomyosin The myosin-binding site on each actin molecule is The myosin-binding site on each actin molecule is
covered by tropomyosin in relaxed musclecovered by tropomyosin in relaxed muscle The thin filaments are held in place by Z lines. From one The thin filaments are held in place by Z lines. From one
Z line to the next is a sarcomere.Z line to the next is a sarcomere.
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Sliding Filament Mechanism Of Sliding Filament Mechanism Of
ContractionContraction Myosin cross bridgesMyosin cross bridgespull on thin filamentspull on thin filaments
Thin filaments slide Thin filaments slide inwardinward
Z Discs come toward Z Discs come toward each othereach other
Sarcomeres Sarcomeres shorten.The muscle shorten.The muscle fiber shortens. The fiber shortens. The muscle shortensmuscle shortens
Notice :Thick & thin Notice :Thick & thin filaments do not filaments do not change in lengthchange in length
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How Does Contraction How Does Contraction Begin?Begin?
Nerve impulse reaches an axon terminal & Nerve impulse reaches an axon terminal & synaptic vesicles release acetylcholine (ACh)synaptic vesicles release acetylcholine (ACh)
ACh diffuses to receptors on the sarcolemma ACh diffuses to receptors on the sarcolemma & Na+ channels open and Na+ rushes into & Na+ channels open and Na+ rushes into the cellthe cell
A muscle action potential spreads over A muscle action potential spreads over sarcolemma and down into the transverse sarcolemma and down into the transverse tubulestubules
SR releases Ca+2 into the sarcoplasmSR releases Ca+2 into the sarcoplasmCa+2 binds to troponin & causes troponin-Ca+2 binds to troponin & causes troponin-
tropomyosin complex to move & reveal tropomyosin complex to move & reveal myosin binding sites on actin--the myosin binding sites on actin--the contraction cycle beginscontraction cycle begins
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Excitation - Contraction CouplingExcitation - Contraction Coupling
All the steps that occur from the muscle action All the steps that occur from the muscle action potential reaching the T tubule to contraction of potential reaching the T tubule to contraction of the muscle fiber.the muscle fiber.
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Contraction CycleContraction CycleRepeating sequence of events that cause the Repeating sequence of events that cause the
thick & thin filaments to move past each thick & thin filaments to move past each other.other.
4 steps to contraction cycle4 steps to contraction cycleATP hydrolysisATP hydrolysisattachment of myosin to actin to form attachment of myosin to actin to form
crossbridgescrossbridgespower strokepower strokedetachment of myosin from actindetachment of myosin from actin
Cycle keeps repeating as long as there is ATP Cycle keeps repeating as long as there is ATP available & high Ca+2 level near thin available & high Ca+2 level near thin filamentfilament
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Steps in the Contraction CycleSteps in the Contraction Cycle
Notice how the myosin head attaches and pulls on Notice how the myosin head attaches and pulls on the thin filament with the energy released from ATPthe thin filament with the energy released from ATP
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ATP and MyosinATP and Myosin
Myosin heads are activated by ATPMyosin heads are activated by ATP Activated heads attach to actin & pull (power Activated heads attach to actin & pull (power
stroke)stroke) ADP is released. (ATP released P & ADP & energy)ADP is released. (ATP released P & ADP & energy) Thin filaments slide past the thick filamentsThin filaments slide past the thick filaments ATP binds to myosin head & detaches it from actinATP binds to myosin head & detaches it from actin All of these steps repeat over and overAll of these steps repeat over and over
if ATP is available &if ATP is available & Ca+ level near the troponin-tropomyosin complex is highCa+ level near the troponin-tropomyosin complex is high
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Overview: From Start to Overview: From Start to FinishFinish
Nerve endingNerve ending NeurotransmittNeurotransmitt
oror Muscle Muscle
membranemembrane Stored Ca+2Stored Ca+2 ATPATP Muscle proteinsMuscle proteins
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RelaxationRelaxationAcetylcholinesterase (AChE) breaks down Acetylcholinesterase (AChE) breaks down
ACh within the synaptic cleftACh within the synaptic cleftMuscle action potential ceasesMuscle action potential ceasesCa+2 release channels closeCa+2 release channels closeActive transport pumps Ca2+ back into Active transport pumps Ca2+ back into
storage in the sarcoplasmic reticulumstorage in the sarcoplasmic reticulumCalcium-binding protein (calsequestrin) Calcium-binding protein (calsequestrin)
helps hold Ca+2 in SR (Ca+2 helps hold Ca+2 in SR (Ca+2 concentration 10,000 times higher than in concentration 10,000 times higher than in cytosol)cytosol)
Tropomyosin-troponin complex recovers Tropomyosin-troponin complex recovers binding site on the actinbinding site on the actin
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Rigor MortisRigor MortisRigor mortis is a state of muscular Rigor mortis is a state of muscular
rigidity that begins 3-4 hours after death rigidity that begins 3-4 hours after death and lasts about 24 hoursand lasts about 24 hours
After death, Ca+2 ions leak out of the SR After death, Ca+2 ions leak out of the SR and allow myosin heads to bind to actinand allow myosin heads to bind to actin
Since ATP synthesis has ceased, Since ATP synthesis has ceased, crossbridges cannot detach from actin crossbridges cannot detach from actin until proteolytic enzymes begin to digest until proteolytic enzymes begin to digest the decomposing cells.the decomposing cells.
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Structures of NMJ RegionStructures of NMJ Region
Synaptic end bulbs are Synaptic end bulbs are swellings of axon terminalsswellings of axon terminals
End bulbs contain synaptic End bulbs contain synaptic vesicles filled with vesicles filled with acetylcholine (ACh)acetylcholine (ACh)
Motor end plate Motor end plate membrane contains 30 membrane contains 30 million ACh receptors.million ACh receptors.
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Events Occurring After a Nerve Events Occurring After a Nerve SignalSignal
Arrival of nerve impulse at nerve terminal causes Arrival of nerve impulse at nerve terminal causes release of ACh from synaptic vesiclesrelease of ACh from synaptic vesicles
ACh binds to receptors on muscle motor end plate ACh binds to receptors on muscle motor end plate opening the gated ion channels so that Na+ can opening the gated ion channels so that Na+ can rush into the muscle cellrush into the muscle cell
Inside of muscle cell becomes more positive, Inside of muscle cell becomes more positive, triggering a muscle action potential that travels triggering a muscle action potential that travels over the cell and down the T tubulesover the cell and down the T tubules
The release of Ca+2 from the SR is triggered and The release of Ca+2 from the SR is triggered and the muscle cell will shorten & generate forcethe muscle cell will shorten & generate force
Acetylcholinesterase breaks down the ACh Acetylcholinesterase breaks down the ACh attached to the receptors on the motor end plate attached to the receptors on the motor end plate so the muscle action potential will cease and the so the muscle action potential will cease and the muscle cell will relax.muscle cell will relax.
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Pharmacology of the NMJPharmacology of the NMJBotulinum toxin blocks release of neurotransmitter at the Botulinum toxin blocks release of neurotransmitter at the
NMJ so muscle contraction can not occurNMJ so muscle contraction can not occurbacteria found in improperly canned foodbacteria found in improperly canned fooddeath occurs from paralysis of the diaphragmdeath occurs from paralysis of the diaphragm
Curare (plant poison from poison arrows)Curare (plant poison from poison arrows)causes muscle paralysis by blocking the ACh receptors causes muscle paralysis by blocking the ACh receptors used to relax muscle during surgeryused to relax muscle during surgery
Neostigmine (anticholinesterase agent)Neostigmine (anticholinesterase agent)blocks removal of ACh from receptors so strengthens weak blocks removal of ACh from receptors so strengthens weak
muscle contractions of myasthenia gravismuscle contractions of myasthenia gravisalso an antidote for curare after surgery is finishedalso an antidote for curare after surgery is finished
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Muscle MetabolismMuscle MetabolismProduction of ATP in Muscle FibersProduction of ATP in Muscle Fibers
Muscle uses ATP at a great rate when Muscle uses ATP at a great rate when activeactive
Sarcoplasmic ATP only lasts for few Sarcoplasmic ATP only lasts for few secondsseconds
3 sources of ATP production within 3 sources of ATP production within musclemusclecreatine phosphatecreatine phosphateanaerobic cellular respirationanaerobic cellular respirationanaerobic cellular respirationanaerobic cellular respiration
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Anaerobic Cellular Anaerobic Cellular RespirationRespiration
ATP produced from ATP produced from glucose breakdown into glucose breakdown into pyruvic acid during pyruvic acid during glycolysis glycolysis if no O2 presentif no O2 present
pyruvic converted to pyruvic converted to lactic acid which diffuses lactic acid which diffuses into the bloodinto the blood
Glycolysis can continue Glycolysis can continue anaerobically to provide anaerobically to provide ATP for 30 to 40 seconds ATP for 30 to 40 seconds of maximal activity (200 of maximal activity (200 meter race)meter race)
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Aerobic Cellular RespirationAerobic Cellular Respiration
ATP for any activity lasting over 30 seconds ATP for any activity lasting over 30 seconds if sufficient oxygen is available, pyruvic acid enters if sufficient oxygen is available, pyruvic acid enters
the mitochondria to generate ATP, water and heatthe mitochondria to generate ATP, water and heat fatty acids and amino acids can also be used by the fatty acids and amino acids can also be used by the
mitochondriamitochondria Provides 90% of ATP energy if activity lasts Provides 90% of ATP energy if activity lasts
more than 10 minutesmore than 10 minutes
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Muscle FatigueMuscle Fatigue Inability to contract after prolonged Inability to contract after prolonged
activityactivitycentral fatigue is feeling of tiredness and a central fatigue is feeling of tiredness and a
desire to stop (protective mechanism)desire to stop (protective mechanism)depletion of creatine phosphatedepletion of creatine phosphatedecline of Ca+2 within the sarcoplasmdecline of Ca+2 within the sarcoplasm
Factors that contribute to muscle Factors that contribute to muscle fatiguefatigueinsufficient oxygen or glycogeninsufficient oxygen or glycogenbuildup of lactic acid and ADPbuildup of lactic acid and ADPinsufficient release of acetylcholine from insufficient release of acetylcholine from
motor neurons motor neurons
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Oxygen Consumption after Oxygen Consumption after ExerciseExercise
Muscle tissue has two sources of oxygen.Muscle tissue has two sources of oxygen.diffuses in from the blooddiffuses in from the bloodreleased by myoglobin inside muscle fibersreleased by myoglobin inside muscle fibers
Aerobic system requires O2 to produce ATP Aerobic system requires O2 to produce ATP needed for prolonged activityneeded for prolonged activityincreased breathing effort during exercise increased breathing effort during exercise
Recovery oxygen uptakeRecovery oxygen uptakeelevated oxygen use after exercise (oxygen elevated oxygen use after exercise (oxygen
debt)debt)lactic acid is converted back to pyruvic acidlactic acid is converted back to pyruvic acidelevated body temperature means all reactions elevated body temperature means all reactions
fasterfaster
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Muscle ToneMuscle Tone Involuntary contraction of a small number Involuntary contraction of a small number
of motor units (alternately active and of motor units (alternately active and inactive in a constantly shifting pattern)inactive in a constantly shifting pattern)keeps muscles firm even though relaxedkeeps muscles firm even though relaxeddoes not produce movement does not produce movement
Essential for maintaining posture (head Essential for maintaining posture (head upright)upright)
Important in maintaining blood pressureImportant in maintaining blood pressuretone of smooth muscles in walls of blood tone of smooth muscles in walls of blood
vesselsvessels
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Classification of Muscle FibersClassification of Muscle Fibers
Slow oxidative (slow-twitch)Slow oxidative (slow-twitch) red in color (lots of mitochondria, myoglobin & blood vessels)red in color (lots of mitochondria, myoglobin & blood vessels) prolonged, sustained contractions for maintaining postureprolonged, sustained contractions for maintaining posture
Fast oxidative-glycolytic (fast-twitch A)Fast oxidative-glycolytic (fast-twitch A) red in color (lots of mitochondria, myoglobin & blood vessels)red in color (lots of mitochondria, myoglobin & blood vessels) split ATP at very fast rate; used for walking and sprintingsplit ATP at very fast rate; used for walking and sprinting
Fast glycolytic (fast-twitch B)Fast glycolytic (fast-twitch B) white in color (few mitochondria & BV, low myoglobin)white in color (few mitochondria & BV, low myoglobin) anaerobic movements for short duration; used for weight-anaerobic movements for short duration; used for weight-
liftinglifting
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Fiber Types within a Whole Fiber Types within a Whole MuscleMuscle
Most muscles contain a mixture of all Most muscles contain a mixture of all three fiber typesthree fiber types
Proportions vary with the usual action of Proportions vary with the usual action of the musclethe muscleneck, back and leg muscles have a higher neck, back and leg muscles have a higher
proportion of postural, slow oxidative fibersproportion of postural, slow oxidative fibersshoulder and arm muscles have a higher shoulder and arm muscles have a higher
proportion of fast glycolytic fibersproportion of fast glycolytic fibersAll fibers of any one motor unit are same.All fibers of any one motor unit are same.Different fibers are recruited as needed.Different fibers are recruited as needed.
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Anabolic SteroidsAnabolic Steroids
Similar to testosteroneSimilar to testosterone Increases muscle size, strength, and Increases muscle size, strength, and
enduranceenduranceMany very serious side effectsMany very serious side effects
liver cancerliver cancerkidney damagekidney damageheart diseaseheart diseasemood swingsmood swingsfacial hair & voice deepening in femalesfacial hair & voice deepening in femalesatrophy of testicles & baldness in malesatrophy of testicles & baldness in males
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Anatomy of Cardiac MuscleAnatomy of Cardiac Muscle
Striated , short, quadrangular-shaped, branching fibers Striated , short, quadrangular-shaped, branching fibers Single centrally located nucleusSingle centrally located nucleus Cells connected by intercalated discs with gap Cells connected by intercalated discs with gap
junctionsjunctions Same arrangement of thick & thin filaments as skeletalSame arrangement of thick & thin filaments as skeletal
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Cardiac versus Skeletal Cardiac versus Skeletal MuscleMuscle
More sarcoplasm and mitochondriaMore sarcoplasm and mitochondriaLarger transverse tubules located at Z Larger transverse tubules located at Z
discs, rather than at A-l band junctionsdiscs, rather than at A-l band junctionsLess well-developed SRLess well-developed SRLimited intracellular Ca+2 reservesLimited intracellular Ca+2 reserves
more Ca+2 enters cell from extracellular more Ca+2 enters cell from extracellular fluid during contractionfluid during contraction
Prolonged delivery of Ca+2 to Prolonged delivery of Ca+2 to sarcoplasm, produces a contraction sarcoplasm, produces a contraction that last 10 -15 times longer than in that last 10 -15 times longer than in skeletal muscleskeletal muscle
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Physiology of Cardiac Physiology of Cardiac MuscleMuscle
Autorhythmic cellsAutorhythmic cellscontract without stimulationcontract without stimulation
Contracts 75 times per min & needs lots O2 Contracts 75 times per min & needs lots O2 Larger mitochondria generate ATP aerobically Larger mitochondria generate ATP aerobically Sustained contraction possible due to slow Sustained contraction possible due to slow
Ca+2 deliveryCa+2 deliveryCa+2 channels to the extracellular fluid stay openCa+2 channels to the extracellular fluid stay open
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Two Types of Smooth Two Types of Smooth MuscleMuscle
Visceral (single-unit)Visceral (single-unit) in the walls of hollow in the walls of hollow
viscera & small BVviscera & small BV autorhythmicautorhythmic gap junctions cause gap junctions cause
fibers to contract in fibers to contract in unisonunison
Multiunit Multiunit individual fibers with individual fibers with
own motor neuron own motor neuron endingending
found in large arteries, found in large arteries, large airways, arrector large airways, arrector pili muscles,iris & pili muscles,iris & ciliary bodyciliary body
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Physiology of Smooth Physiology of Smooth MuscleMuscle
Contraction starts slowly & lasts longerContraction starts slowly & lasts longerno transverse tubules & very little SRno transverse tubules & very little SRCa+2 must flows in from outsideCa+2 must flows in from outside
Calmodulin replaces troponinCalmodulin replaces troponinCa+2 binds to calmodulin turning on an Ca+2 binds to calmodulin turning on an
enzyme (myosin light chain kinase) that enzyme (myosin light chain kinase) that phosphorylates the myosin head so that phosphorylates the myosin head so that contraction can occurcontraction can occur
enzyme works slowly, slowing contractionenzyme works slowly, slowing contraction
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Smooth Muscle ToneSmooth Muscle Tone
Ca+2 moves slowly out of the cellCa+2 moves slowly out of the celldelaying relaxation and providing for delaying relaxation and providing for
state of continued partial contraction state of continued partial contraction sustained long-termsustained long-term
Useful for maintaining blood Useful for maintaining blood pressure or a steady pressure on the pressure or a steady pressure on the contents of GI tract contents of GI tract
5050
Regeneration of MuscleRegeneration of MuscleSkeletal muscle fibers cannot divide after 1st yearSkeletal muscle fibers cannot divide after 1st year
growth is enlargement of existing cellsgrowth is enlargement of existing cellsrepairrepair
satellite cells & bone marrow produce some new cellssatellite cells & bone marrow produce some new cellsif not enough numbers---fibrosis occurs most oftenif not enough numbers---fibrosis occurs most often
Cardiac muscle fibers cannot divide or regenerateCardiac muscle fibers cannot divide or regenerateall healing is done by fibrosis (scar formation)all healing is done by fibrosis (scar formation)
Smooth muscle fibers (regeneration is possible)Smooth muscle fibers (regeneration is possible)cells can grow in size (hypertrophy)cells can grow in size (hypertrophy)some cells (uterus) can divide (hyperplasia)some cells (uterus) can divide (hyperplasia)new fibers can form from stem cells in BV wallsnew fibers can form from stem cells in BV walls
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Aging and Muscle TissueAging and Muscle Tissue
Skeletal muscle starts to be replaced by fat Skeletal muscle starts to be replaced by fat beginning at 30 beginning at 30 ““use it or lose it”use it or lose it”
Slowing of reflexes & decrease in maximal strengthSlowing of reflexes & decrease in maximal strengthChange in fiber type to slow oxidative fibers may Change in fiber type to slow oxidative fibers may
be due to lack of use or may be result of agingbe due to lack of use or may be result of aging
5252
Myasthenia GravisMyasthenia GravisProgressive autoimmune disorder that blocks Progressive autoimmune disorder that blocks
the ACh receptors at the neuromuscular junction the ACh receptors at the neuromuscular junction The more receptors are damaged the weaker The more receptors are damaged the weaker
the muscle. the muscle. More common in women 20 to 40 with possible More common in women 20 to 40 with possible
line to thymus gland tumorsline to thymus gland tumorsBegins with double vision & swallowing Begins with double vision & swallowing
difficulties & progresses to paralysis of difficulties & progresses to paralysis of respiratory muscles respiratory muscles
Treatment includes steroids that reduce Treatment includes steroids that reduce antibodies that bind to ACh receptors and antibodies that bind to ACh receptors and inhibitors of acetylcholinesterase inhibitors of acetylcholinesterase
5353
Muscular Dystrophies Muscular Dystrophies Inherited, muscle-destroying diseases Inherited, muscle-destroying diseases Sarcolemma tears during muscle contractionSarcolemma tears during muscle contractionMutated gene is on X chromosome so problem is Mutated gene is on X chromosome so problem is
with males almost exclusivelywith males almost exclusivelyAppears by age 5 in males and by 12 may be Appears by age 5 in males and by 12 may be
unable to walkunable to walkDegeneration of individual muscle fibers produces Degeneration of individual muscle fibers produces
atrophy of the skeletal muscleatrophy of the skeletal muscleGene therapy is hoped for with the most common Gene therapy is hoped for with the most common
form = Duchenne muscular dystrophyform = Duchenne muscular dystrophy
5454
Abnormal ContractionsAbnormal ContractionsSpasm = involuntary contraction of Spasm = involuntary contraction of
single musclesingle muscleCramp = a painful spasmCramp = a painful spasmTic = involuntary twitching of muscles Tic = involuntary twitching of muscles
normally under voluntary control--normally under voluntary control--eyelid or facial muscleseyelid or facial muscles
Tremor = rhythmic, involuntary Tremor = rhythmic, involuntary contraction of opposing muscle groupscontraction of opposing muscle groups
Fasciculation = involuntary, brief Fasciculation = involuntary, brief twitch of a motor unit visible under twitch of a motor unit visible under the skinthe skin