GROSS ANATOMY

Detailed explanation-1: -The sinoatrial node (SA node) is a specialized myocardial structure that initiates the electrical impulses to stimulate contraction, and is found in the atrial wall at the junction of superior caval vein and the right atrium (Mikawa and Hurtado, 2007).

Detailed explanation-2: -An electrical stimulus is generated by the sinus node (also called the sinoatrial node, or SA node). This is a small mass of specialized tissue located in the right upper chamber (atria) of the heart.

Detailed explanation-3: -The SA node, also known as the sinus node, represents a crescent-like shaped cluster of myocytes divided by connective tissue, spreading over a few square millimeters. It is located at the junction of the crista terminalis in the upper wall of the right atrium and the opening of the superior vena cava.

Detailed explanation-4: -The sinoatrial node (SAN), located in the right atrium, serves as the primary site for initiation of the normal heartbeat (sinus rhythm) (Figure 1).

Detailed explanation-5: -The septum secundum (the superior and posterior parts of the rim) is mainly the infolded right atrial wall between the base of the superior caval vein and the insertion of the right pulmonary veins to the left atrium (Figure 4B). The wall of the inferior caval vein is continuous with the rim posteroinferiorly.