© 2013 Pearson Education, Inc. Microscopic Anatomy of Cardiac Muscle Cardiac muscle cells...

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Transcript of © 2013 Pearson Education, Inc. Microscopic Anatomy of Cardiac Muscle Cardiac muscle cells...

  • 2013 Pearson Education, Inc.Microscopic Anatomy of Cardiac MuscleCardiac muscle cells striated, short, branched, fat, interconnected, 1 (perhaps 2) central nucleiConnective tissue matrix (endomysium) connects to cardiac skeletonContains numerous capillariesT tubules wide, less numerous; SR simpler than in skeletal muscleNumerous large mitochondria (2535% of cell volume)

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Figure 18.12a Microscopic anatomy of cardiac muscle.NucleusIntercalated discsCardiac muscle cellGap junctionsDesmosomes

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Microscopic Anatomy of Cardiac MuscleIntercalated discs - junctions between cells - anchor cardiac cells Desmosomes prevent cells from separating during contractionGap junctions allow ions to pass from cell to cell; electrically couple adjacent cellsAllows heart to be functional syncytiumBehaves as single coordinated unit

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Figure 18.12b Microscopic anatomy of cardiac muscle.Cardiac muscle cellIntercalated discMitochondrionNucleusMitochondrionT tubuleSarcoplasmicreticulumZ discI bandA bandI bandNucleusSarcolemma

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  • 2013 Pearson Education, Inc.Cardiac Muscle ContractionThree differences from skeletal muscle:~1% of cells have automaticity (autorhythmicity)Do not need nervous system stimulationCan depolarize entire heartAll cardiomyocytes contract as unit, or none doLong absolute refractory period (250 ms)Prevents tetanic contractions

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Cardiac Muscle ContractionThree similarities with skeletal muscle:Depolarization opens few voltage-gated fast Na+ channels in sarcolemma Reversal of membrane potential from 90 mV to +30 mVBrief; Na channels close rapidlyDepolarization wave down T tubules SR to release Ca2+ Excitation-contraction coupling occursCa2+ binds troponin filaments slide

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  • 2013 Pearson Education, Inc.Cardiac Muscle ContractionMore differencesDepolarization wave also opens slow Ca2+ channels in sarcolemma SR to release its Ca2+ Ca2+ surge prolongs the depolarization phase (plateau)

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Cardiac Muscle ContractionMore differencesAction potential and contractile phase last much longerAllow blood ejection from heartRepolarization result of inactivation of Ca2+ channels and opening of voltage-gated K+ channelsCa2+ pumped back to SR and extracellularly

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Figure 18.13 The action potential of contractile cardiac muscle cells.Slide 1Membrane potential (mV)20020406080AbsoluterefractoryperiodActionpotentialPlateauTensiondevelopment(contraction)0150300Time (ms)Tension (g)123 Depolarization is due to Na+ influx through fast voltage-gated Na+ channels. A positive feedback cycle rapidly opens many Na+ channels, reversing the membrane potential. Channel inactivation ends this phase. Plateau phase is due to Ca2+ influx through slow Ca2+ channels. This keeps the cell depolarized because few K+ channels are open. Repolarization is due to Ca2+ channels inactivating and K+ channels opening. This allows K+ efflux, which brings the membrane potential back to its resting voltage.

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Figure 18.13 The action potential of contractile cardiac muscle cells.Slide 2Membrane potential (mV)20020406080AbsoluterefractoryperiodActionpotentialPlateauTensiondevelopment(contraction)0150300Time (ms)Tension (g)11 Depolarization is due to Na+ influx through fast voltage-gated Na+ channels. A positive feedback cycle rapidly opens many Na+ channels, reversing the membrane potential. Channel inactivation ends this phase.

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Figure 18.13 The action potential of contractile cardiac muscle cells.Slide 3Membrane potential (mV)20020406080AbsoluterefractoryperiodActionpotentialPlateauTensiondevelopment(contraction)0150300Time (ms)Tension (g)1212 Depolarization is due to Na+ influx through fast voltage-gated Na+ channels. A positive feedback cycle rapidly opens many Na+ channels, reversing the membrane potential. Channel inactivation ends this phase. Plateau phase is due to Ca2+ influx through slow Ca2+ channels. This keeps the cell depolarized because few K+ channels are open.

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Figure 18.13 The action potential of contractile cardiac muscle cells.Slide 4Membrane potential (mV)20020406080AbsoluterefractoryperiodActionpotentialPlateauTensiondevelopment(contraction)0150300Time (ms)Tension (g)123 Depolarization is due to Na+ influx through fast voltage-gated Na+ channels. A positive feedback cycle rapidly opens many Na+ channels, reversing the membrane potential. Channel inactivation ends this phase. Plateau phase is due to Ca2+ influx through slow Ca2+ channels. This keeps the cell depolarized because few K+ channels are open. Repolarization is due to Ca2+ channels inactivating and K+ channels opening. This allows K+ efflux, which brings the membrane potential back to its resting voltage.

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Energy RequirementsCardiac muscleHas many mitochondriaGreat dependence on aerobic respirationLittle anaerobic respiration abilityReadily switches fuel source for respirationEven uses lactic acid from skeletal muscles

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Homeostatic ImbalanceIschemic cells anaerobic respiration lactic acid High H+ concentration high Ca2+ concentration Mitochondrial damage decreased ATP production Gap junctions close fatal arrhythmias

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Heart Physiology: Electrical EventsHeart depolarizes and contracts without nervous system stimulationRhythm can be altered by autonomic nervous system

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Heart Physiology: Setting the Basic RhythmCoordinated heartbeat is a function ofPresence of gap junctionsIntrinsic cardiac conduction systemNetwork of noncontractile (autorhythmic) cellsInitiate and distribute impulses coordinated depolarization and contraction of heart

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Autorhythmic CellsHave unstable resting membrane potentials (pacemaker potentials or prepotentials) due to opening of slow Na+ channelsContinuously depolarizeAt threshold, Ca2+ channels open Explosive Ca2+ influx produces the rising phase of the action potentialRepolarization results from inactivation of Ca2+ channels and opening of voltage-gated K+ channels

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Action Potential Initiation by Pacemaker CellsThree parts of action potential:Pacemaker potentialRepolarization closes K+ channels and opens slow Na+ channels ion imbalance DepolarizationCa2+ channels open huge influx rising phase of action potentialRepolarizationK+ channels open efflux of K+

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart.Slide 1123231Membrane potential (mV)+10010203040506070Time (ms)ActionpotentialThresholdPacemakerpotential123 Pacemaker potential This slow depolarization is due to both opening of Na+ channels and closing of K+ channels. Notice that the membrane potential is never a flat line. Depolarization The action potential begins when the pacemaker potential reaches threshold. Depolarization is due to Ca2+ influx through Ca2+ channels. Repolarization is due to Ca2+ channels inactivating and K+ channels opening. This allows K+ efflux, which brings the membrane potential back to its most negative voltage.

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart.Slide 211+10010203040506070Time (ms)ActionpotentialThresholdPacemakerpotential1 Pacemaker potential This slow depolarization is due to both opening of Na+ channels and closing of K+ channels. Notice that the membrane potential is never a flat line.Membrane potential (mV)

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart.Slide 31221+10010203040506070Time (ms)ActionpotentialThresholdPacemakerpotential12 Pacemaker potential This slow depolarization is due to both opening of Na+ channels and closing of K+ channels. Notice that the membrane potential is never a flat line. Depolarization The action potential begins when the pacemaker potential reaches threshold. Depolarization is due to Ca2+ influx through Ca2+ channels.Membrane potential (mV)

    2013 Pearson Education, Inc.

  • 2013 Pearson Education, Inc.Figure 18.14 Pacemaker and action potentials of pacemaker cells in the heart.Slide 4123231Membrane potential (mV)+10010203040506070Time (ms)ActionpotentialThresholdPacemakerpotential123 Pacemaker potential This slow depolarization is due to both opening of Na+ channels and closing of K+ channels. Notice that the membrane potential is never a flat line. Depolarization The action potential begins when the pacemaker potential reaches threshold. Depolarization is due to Ca2+ influx through Ca2+ channels. Repolarization is due to Ca2+ channels inactivating and K+ channels opening. This allows K+ efflux, which brings