Purkinje fibres are -

Ans. is 'c' i.e., Modified cardiac muscle Conducting system of hearto The conducting system is made of specialized myocardium (cardiac muscle), that is capable for initation and conduction of cardiac impulse. It has following parts : -SA node SA node is located in the upper part of crista terminalis at the junction of SVC and the right atrium. It is the pacemaker of the heart and generates impulse at a rate of 70-100/min. SA node is suplied by nodal artery, a branch of RCA in 65% cases and a branch of circumflex branch of LCA in 35% cases. SA node is supplied by right vagus/parasympathetic (inhibitory) and right Sympathetic (excitatory') system as it develops from structures on the right side of embryo.AV nodeIt lies in the right atrial floor near the interatrial septum in the 'triangle of koch' It is supplied by AV nodal artery, a branch of RCA. AV node develops from left side of heart, thus is supplied by left vagus and left sympathetic fibers.Atrioventricular bundle or bundle of HisIt arises from AV node and crosses the AV ring (annulus fibrosus). In the muscular septum it divides into right and left branches. It has a dual blood supply from AV nodal artery (branch of RCA) and anterior descending (interventricular) branch ofLCA.4) Right bundle branch (RBB) and left bundle branch (LBB)These bundle branches consist of modified muscle fibers (Purkinie fibers). Both RBB and L BB are supplied by LCA, except a small part of the LBB which is supplied by RCA.