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Chapter 20, part 3

Chapter 20, part 3. The Heart. Contractile Cells. Resting membrane potential of approximately –90mV Action potential Rapid depolarization A plateau phase unique to cardiac muscle Repolarization Refractory period follows the action potential. Calcium Ion and Cardiac contraction.

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Chapter 20, part 3

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  1. Chapter 20, part 3 The Heart

  2. Contractile Cells • Resting membrane potential of approximately –90mV • Action potential • Rapid depolarization • A plateau phase unique to cardiac muscle • Repolarization • Refractory period follows the action potential

  3. Calcium Ion and Cardiac contraction • Cardiac action potentials cause an increase in Ca2+ around myofibrils • Ca2+ enters the cell membranes during the plateau phase • Additional Ca2+ is released from reserves in the sarcoplasmic reticulum

  4. Figure 20.15 The Action Potential in Skeletal and Cardiac Muscle Figure 20.15

  5. Figure 20.15 The Action Potential in Skeletal and Cardiac Muscle Figure 20.15

  6. The cardiac cycle • The period between the start of one heartbeat and the beginning of the next • During a cardiac cycle • Each heart chamber goes through systole and diastole • Correct pressure relationships are dependent on careful timing of contractions PLAY Animation: Intrinsic Conduction System

  7. Figure 20.16 Phases of the Cardiac Cycle Figure 20.16

  8. Figure 20.16 Phases of the Cardiac Cycle Figure 20.16

  9. Pressure and volume changes: atrial systole • rising atrial pressure pushes blood into the ventricle • atrial systole • the end-diastolic volume (EDV) of blood is in the ventricles

  10. Pressure and volume changes: ventricular systole • Isovolumetric contraction of the ventricles: ventricles are contracting but there is no blood flow • Ventricular pressure increases forcing blood through the semilunar valves

  11. Pressure and volume changes: ventricular diastole • The period of isovolumetric relaxation when all heart valves are closed • Atrial pressure forces the AV valves open

  12. Figure 20.17 Pressure and Volume Relationships in the Cardiac Cycle Figure 20.17

  13. Heart sounds • Auscultation – listening to heart sound via stethoscope • Four heart sounds • S1 – “lubb” caused by the closing of the AV valves • S2 – “dupp” caused by the closing of the semilunar valves • S3 – a faint sound associated with blood flowing into the ventricles • S4 – another faint sound associated with atrial contraction

  14. Figure 20.18 Heart Sounds Figure 20.18a, b

  15. SECTION 20-4Cardiodynamics

  16. Stroke Volume and Cardiac Output • Cardiac output – the amount of blood pumped by each ventricle in one minute • Cardiac output equals heart rate times stroke volume

  17. Figure 20.19 A Simple Model of Stroke Volume Figure 20.19a-d

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