ANATOMY

Detailed explanation-1: -The SA (sinoatrial) node generates an electrical signal that causes the upper heart chambers (atria) to contract. The signal then passes through the AV (atrioventricular) node to the lower heart chambers (ventricles), causing them to contract, or pump. The SA node is considered the pacemaker of the heart.

Detailed explanation-2: -Myocardial conduction cells initiate and propagate the action potential (the electrical impulse) that travels throughout the heart and triggers the contractions that propel the blood.

Detailed explanation-3: -Normal sinus rhythm and sinus arrhythmia-UpToDate. Normal sinus rhythm (NSR) is the rhythm that originates from the sinus node and describes the characteristic rhythm of the healthy human heart. The rate in NSR is generally regular but will vary depending on autonomic inputs into the sinus node.

Detailed explanation-4: -Spontaneous beating of the sinoatrial node is emanated from beating of sinoatrial node pacemaker cells (SANCs), which spontaneously generate action potentials (APs) because of gradual depolarization of the membrane potential during diastole, that is, diastolic depolarization (DD).