It is a closed sac having two layers: the visceral layer (epicardium), immediately surrounding the heart, and the outer parietal layer, forming the sac, composed of strong fibrous tissue, the fibrous pericardium, lined with a serous membrane, the serous pericardium. Synonym(s): heart sac, theca cordis.
The right and left cavernous sinuses are interconnected by the anterior and posterior intercavernous sinuses. Tributaries of the cavernous sinus include the superior ophthalmic, superficial middle cerebral, and inferior cerebral veins and the sphenoparietal sinus.
The sinus node consists of a cluster of cells that are situated in the upper part of the wall of the right atrium (the right upper chamber of the heart). The electrical impulses are generated there. The sinus node is also called the sinoatrial node or, for short, the SA node. The electrical signal generated by the sinus node moves from cell to cell down through the heart until it reaches the atrioventricular node (AV node), a cluster of cells situated in the center of the heart between the atria and ventricles.