Impulse is generated at fastest rate in –
Correct Answer: SA node
Description: Ans. is 'b' i.e., SA node o Impulse generated at fastest rate in SA node.o Impulse conducted fastest in purkinje system.Conduction System of Hearto The depolarization of the various parts of the heart proceeds in an orderly and timely way. This is made possible by the presence of the conductive system of the heart which comprises the sinoatral node (SA node), intermodal atrial pathways, atrioventricular node (AV node), bundle of his and its branches, and Purkinje system. The conduction system is made up of modified cardiac muscles.o Most of cells of the conducting system are specialized for fast conduction though some, like the cells of the AV node, are specialized for slowing down conduction.o The fastest conduction is seen in purkinje system and slowest in AV node and SA node.Cardiac tissueConduction velocity (meter/second)SA node0.05Inteatrial pathways1Atrial muscle0.30AV nixie0 .05 (minimum)Bundle of His1Purkinje system4 (maximum)Ventricular muscle1o Cells of the conductive system also possess automaticity, i.e., the capability of spontaneous excitation.o However, the rate at which different parts of conductive system discharge impulses is not the same.o The SA node discharges impulses at fastest rate, hence the rate at which SA node fires determines the heart rate, therefore, SA node is normal pacemaker of the heart, i.e., it determines the pace of the heart.o The AV node has the next highest automaticity after SA node; therefore, if the SA node stops discharging, the AV node takes over the role of cardiac pacemaker.Conduction of cardiac impulseo The cardiac impulse originates in the SA node.o From SA node it is transmitted to AV node via interatrial pathways (intemodal atrial pathways).o From AV node it is rapidly transmitted to bundle of his and then purkinje system to all parts of ventricles.o In the ventricles, endocardial surface depolarizes before epicardial surface.o Order of spread of impulse (depolarization) in ventricular myocardium is as follow : Depolarization starts at the left side of interventricular septum and then moves to the right across the mid portion of septum.o The wave then spreads down the septum to the apex of heart.o It returns along the ventricular walls to the AV groove, proceeding from the endocardial to epicardial surface.o The last parts of the heart to be depolarized are the posterobasal portion of the left ventricles, the pulmonary conus, and the upper most portion of the septum.o The sequence of repolarization is not exactly the same as that of depolarization.o Although the septum and endocardial surface of ventricles depolarizes first, it is the epicardial surface which repolarizes first, i.e., repolarization spreads from epicardium to endocarium.
Category:
Physiology
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