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H ., • SA called is a patch of in the right of, node, the and a and left bundles, • AV node pace is of in the lower left corner, • These give rise to and are, -called along with right and left are known as bundle, • A of (AV AV, BIOLOGY-X, ve, the right atrium., of the right atrium, close to the atrio-ventricular septum., These bundles give rise to minute fibres throughout ventricular musculature, •called purkinje fibres; these fibres along with right and left bundles are known as, of His., and, are, bundle, He, Working of the Nodal Tissue, • The nodal musculature has the ability to generate action potentials without any extemal, stimuli (i.e. autoexcitable)., • The SA node can generate the maximum number of action potentials, i.e., 70–75 min-l, (average 72 beats min-1)., • Since SA node is responsible for initiating and rhythmic contractile activity of the heart:, it is called the pace maker., Cardiac cycle, • The sequential event in the heart, which is cyclically repeated is called the cardiac cycle, and it consists of systole and diastole of both the atria and ventricles is called cardiac, cycle., • During a heart beat there is contraction phase called the systole, while the relaxation, phase is called the diastole; when both the atria and ventricles are in diastole or relaxed, phase, it is referred as joint diastole., Joint Diastole, • During joint diastole, the tricuspid and bicuspid valves are open, blood from pulmonary, veins and vena cava flows into the left and the right ventricles respectively, through thne, left and right atria., • The semi-lunar valves remain closed at this stage., Atrial systole, • The SAN now generates an action potential which stimulates both the atria to undergo, simultaneous contraction., • As the atria contract, the flow of blood into ventricles increases to about 30, per cent., Ventricular systole, • The action potential is conducted to the ventricular side by the A.VN and AV ba, from where, the bundle of His transmit it to the entire ventricular musculature., relaxation ( atrial diastole coinciding with the ventricular systole)., орen,, (left side)., pathways.