Question

why their is delay of 0.15s in conduction from S.A. node to AV node? only for genius and experts

Answer 1

The SA node normally discharges most rapidly, spreading depolarization to other regions. Its rate of discharge determines the rate at which the heart beats. Impulses generated in the SA node pass through the atrial pathways to the AV node. There is a delay of about 0.15 s in conduction from the SA node to the AV node, which means that atrial systole is completed before ventricular systole starts. Through the AV node impulses pass to the bundle of His down to the apex of the heart, and then upwards through the Purkinje fibers to the ventricular muscle. This causes the ventricular contractions to start at the apex and push the blood up into the arteries.The electrical activity that spreads through the heart during the cardiac cycle can be detected using electrodes placed on the skin. An electrocardiogram (ECG or EKG) can then be made. Certain heart defects can be detected from studying the ECG.Nerves coming from the medulla and hormones can transmit messages to the pacemaker. Two parasympathetic nerves, the vagus nerves, lead to the SA node and the AV node. Impulses passing along the vagus nerves reduce the heart rate. Other nerves, which are part of the sympathetic nervous system have their endings in the SA node and increase the heart rate. Adrenalin, carried by the blood to the pacemaker speeds up the heart beat.If the SA node does not function properly, it is quite easy to implant an artificial pacemaker to carry out this function. With a well-adjusted pacemaker, a person with a malfunctioning SA node can live a long and active life.