Anatomy VI - internal features of the heart

Pectinate muscles -- "true" atrium, horizontal ridges of muscles on anterior atrial wall

Crista terminalis -- border between true atrium and smooth tissue derived from sinus venosum

Posterior wall of right atrium contains SVC, IVC, coronary sinus, and fossa ovalis and limbus fossa ovalis. There are papillary muscles in the ventricles. In the right ventricle, they connect to the three cusps -- anterior, posterior, and septal -- via the chordae tendineae. The anterior papillary muscle is the largest. The posterior is smaller, and the septal is smallest and may be multiple. Each chordae tendineae connects to two cusps. The inner surface of the right ventricle is roughened by trabeculae carneae. The septomarginal trabecula (moderator band) extends from the anterior papillary muscle base to the interventricular septum. It contains part of the right bundle branch, the part that stimulates the papillary muscles. the conus arteriosus (infundibulum) is the smooth, cone-shaped portion of the ventricle leading to the pulmonary trunk. The pulmonary valve has three semilunar valves: left, right, and anterior. Each valve has one fibrous nodule and two lunules, which keep the valve closed to prevent backflow during diastole.

The left atrium is pretty much in the back of the heart. The four great pulmonary veins enter it. The right pulmonary veins are in line with the SVC and PVC. The left atrium is pretty boring: valve of foramen ovale, left auricle, mitral valve. The left ventricle, like the right ventricle, also contains papillary muscles, including anterior papillary muscle and posterior papillary muscle. There is also chordae tendineae as well as trabeculae carneae. As previously mentioned, the aortic valve consists of left, right, and posterior semilunar cusps. The intraventricular septum has a muscular part coming from the apex, and a membranous part connecting just inferior to the right cusp of the aortic valve. The coronary arteries come out of the aortic sinuses. The posterior cusp is the noncoronary cusp.

The AV node is at the superior end of the crista terminalis in the right atrium, right below the SVC. AV impulses pass in AV bundle through membranous septum, then dividing into right and left bundles, which lie on either side of the muscular septum. Again, the right bundle travels through the septomarginal trabecula.