Origin and spread of cardiac impulse, pacemaker, conducting system of heart, its importance

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Origin and spread of cardiac impulse, pacemaker, conducting system of heart, its importance

  1. 1. RK Goit, Lecturer Department of Physiology Origin & Spread of Cardiac Impulse, Pacemaker, Conducting System of Heart, its Importance
  2. 2. • parts of the heart normally beat in orderly sequence • contraction of the atria (atrial systole) is followed by contraction of the ventricles (ventricular systole) • during diastole all four chambers are relaxed • heartbeat originates in a specialized cardiac conduction system & spreads via this system to all parts of the myocardium
  3. 3. Tissue Conduction rate (m/s) SA node 0.05 Atrial muscle 0.3 Atrial pathways 1 AV node 0.05 Bundle of His 1 Purkinje system 4 Ventricular muscle 0.3-0.5
  4. 4. The Sinus Node as the Pacemaker of the Heart • SA node discharge at an intrinsic rhythmical rate of 70- 80/min (AV nodal fibers 40-60/min, & Purkinje fibers 15- 40/min • each time the SA node discharges, its impulse is conducted into both the A-V node & the Purkinje fibers • SA node discharges again before either the A-V node or the Purkinje fibers can reach their own thresholds for self- excitation • the sinus node controls the beat of the heart
  5. 5. Abnormal Pacemakers—“Ectopic” Pacemaker • occasionally some other part of the heart develops a rhythmical discharge rate that is more rapid than that of the sinus node • a pacemaker elsewhere than the sinus node is called an “ectopic” pacemaker • an ectopic pacemaker causes an abnormal sequence of contraction of the different parts of the heart • another cause of shift of the pacemaker is blockage of transmission of the cardiac impulse from the sinus node to the other parts of the heart
  6. 6. Important functions: • pacemaker – setting the rhythm of electrical excitation that causes contraction of the heart • conduction system – ensures that cardiac chambers become stimulated to contract in a coordinated manner, which makes the heart an effective pump
  7. 7. References • Ganong Review of Medical Physiology, 23/E • Textbook of Medical Physiology, 12/E Guyton & Hall • Understanding Medical Physiology, 4/E Bijlani & Manjunatha
  8. 8. Thank You

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