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

1. RK Goit , Lecturer Department of Physiology Origin & Spread of Cardiac Impulse, Pacemaker, Conducting System of Heart, its Importance

2. parts of the heart normally beat in orderly sequence c ontraction 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. 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. 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. Abnormal Pacemakers—“Ectopic” Pacemaker o ccasionally 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 a n ectopic pacemaker causes an abnormal sequence of contraction of the different parts of the heart a nother 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. 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. References Ganong Review of Medical Physiology, 23/E Textbook of Medical Physiology, 12/E Guyton & Hall Understanding Medical Physiology, 4/E Bijlani & Manjunatha

8. Thank You