Fine structure of the conduction system and working myocardium in the little brown bat, Myotis lucifugus.

In the little brown bat, Myotis lucifugus, topography and ultrastructure of the sinus node and the atrioventricular (AV) node resemble those in large mammalian hearts, except that the P cells in the sinus node are smaller than those in the bat AV node or those in the sinus node of slower hearts (e.g., dog, man). Despite rich innervation in the bat nodes, true neuromuscular synapses are rarely formed. Bat working cardiocytes have a well developed sarcoplasmic reticulum, but otherwise resemble working myocytes of larger mammals.