The impulse then proceeds along the right and left ventricular walls to the atrioventricular groove. 7.28), the impulse comes down the septum to the apex of the heart and next portions of myocardium that is activated is the anteroseptal region of the ventricular myocardium (Fig. So the de-polarisation of the ventricular muscle begins at the left side of the interventricular septum because the Purkinje fibres arise more proximally from the left bundle branch than from the right bundle branch and activates the left side of the septum initially.Īfter mid-septal activation from the left to the right direction (Fig. In human beings, the mid-portion of the interventricular septum is activated normally in a left to right direction. The impulse then travels from the endocardium to the epicardium of ventricular muscle perpendicularly. The impulse, after passing through the right and left bundle branches, passes into the Purkinje fibres and also its multiple ramifications within the subendocardial surfaces of both ventricles. Passage of impulse through the bundle of His and its branches is not encountered in the E.C.G. The impulse from the bundle of His passes quickly through the right and left bundle branches and ultimately reaches the Purkinje fibres and ventricular muscle fibres as well. Conduction over Bundle of His and the Right and Left Bundle Branches :īeyond the atrioventricular region, the impulse is transmitted along the bundle branch at a higher velocity (4-5 m per sec.). Because if the ventricle is stimulated, the impulse fails to reach the A.V. node, the impulse is transmitted through this region in one direction only. The delay is however minimised by sympathetic activity and the same is increased by vagal stimulation.īesides nodal delay in the A.V. Because the velocity of conduction is proportional to the diameter of the fibres. The smaller size and the profuse branching of the fibres in the border region as well as in the upper atrioventricular node are presumably the causes of this slow decremental conduction. The size of the border fibres is smaller than that of the atrial fibres and even the size is gradually increased from the atrial-nodal border region onward to the bundle of His.īesides these, the border fibres have numerous interconnections. They have further described that the resting potential of the fibres of atrial-nodal border and of the upper atrioventricular node is lower than that of the atrial or ventricular muscle fibres. Recent observation of Hoffman and Cranefield has claimed that there is a decremental conduction across the atrial- nodal border region. node, (b) a prolonged refractory period within the nodal tissue. node was explained by assuming (a) normal conduction velocity over long pathways in the A.V. The conduction velocity of impulse at this region is approximately 0.05 m per sec. This delay is observed maximally at the junctional region between the atrium and atrioventricular node. nodal delay allows the atrial systole to complete before the ventricle is excited. node before excitation spreads over the ventricle. There is also a considerable delay of 0.07 sec. nodes through the internodal atrial bundle (Fig. node may be transmitted directly to the A.V. and also others, the impulse from the S.A. node is very slow (0.05 m per sec.) but the same through the junctional tissues that connect the node to the atrial musculature or to the A.V. The spread of electrical impulse through the S.A. Conduction over Atrial Muscle :Ĭardiac impulse originated at the S.A node is transmitted over both the atria like concentric waves and thus the P wave is produced in E.C.G. In this article we will discuss about the transmission of cardiac impulse of humans with the help of suitable diagram.
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