CARDIAC CONDUCTION SYSTEM IN THE CHICKEN - GROSS-ANATOMY PLUS LIGHT AND ELECTRON-MICROSCOPY

Twenty-three chicken hearts were used to study the cardiac conduction system by light and electron microscopy. In addition to a sinus node, atrioventricular node (AVN), His bundle, left and right bundle branche s (LBB, RBB), the chicken also has an AV Purkinje ring and a special m iddle bundle branch (MBB). The sinus node lies near the base of the lo wer portion of the right sinoatrial valve. The AV node is just above t he tricuspid valve and anterior to the coronary sinus. The His bundle descends from the anterior and inferior margin of the AV node into the interventricular septum, then dividing into right, left and middle br anches some distance below the septal crest. The middle bundle branch turns posteriorly toward the root of the aorta. The AV Purkinje ring o riginates from the proximal AV node and then encircles the right AV or ifice, joining the MBB to form a figure-of-eight loop. The chicken con duction system contains four types of myocytes: 1) The P cell is small and rounded, with a relatively large nucleus and sparse myofibrils. 2 ) The transitional cell is slender and full of myofibrils. 3) The Purk inje-like cell resembles the typical Purkinje cell, but is smaller and darker. 4) The Purkinje cell is found in the His bundle, its branches , and the periarterial and subendocardial Purkinje network.