ABSTRACT
Ions move freely from myocyte to myocyte through gap junctions. Electrical charges carried by ions easily move from cardiac muscle cell to cardiac muscle cell and throughout normal heart muscle tissue. The electrical response of heart muscle is all or none, which means that an adequate stimulus to one healthy atrial myocyte will result in an action potential that is then transmitted to all the other atrial myocytes. Each myocyte is a separate cell with its own cell machinery and bounded by a membrane, the sarcolemma. But the low myocyte-to-myocyte electrical resistance at the gap junctions and easy myocyte-to-myocyte transmission of action potentials result in the heart behaving as if it were a syncytium. Electrical activity is conducted from atrial myocyte to atrial myocyte throughout the right and left atria primarily via gap junctions. The Atrioventricular node is in the right atrium at the bottom of the interatrial septum near the opening of the coronary sinus.
