<P> BMP (Bone morphogenetic protein) cell signaling plays a key role in diverse aspects of cardiac differentiation and morphogenesis . (BMPs) are multifunctional signaling molecules critical for the development of AV node . BMP influences AV node development through Alk3 receptor (Activin receptor - like kinase 3). Abnormalities seen in BMP and Alk3 are associated with some cardiovascular diseases like Ebstein's anomaly and AV conduction disease . </P> <P> The AV node receives two inputs from the right atrium: posteriorly, via the crista terminalis, and anteriorly, via the interatrial septum . </P> <P> Contraction of heart muscle cells requires depolarization and repolarization of their cell membranes . Movement of ions across cell membranes causes these events . The cardiac conduction system (and AV node part of it) coordinates myocyte mechanical activity . A wave of excitation spreads out from the sinoatrial node through the atria along specialized conduction channels . This activates the AV node . The atrioventricular node delays impulses by approximately 0.09 s . This delay in the cardiac pulse is extremely important: It ensures that the atria have ejected their blood into the ventricles first before the ventricles contract . </P> <P> This also protects the ventricles from excessively fast rate response to atrial arrhythmias (see below). </P>

Why is action potential delayed at av node
find me the text answering this question