Cell signaling of adjacent cells. In cardiac muscle, gap junctions between adjacent cells allows for action potential propagation from the cardiac pacemaker region of the heart to spread and coordinately cause contraction of the heart. The notch signaling mechanism is an example of juxtacrine signaling (also known as contact-dependent signaling) in which two adjacent cells must make physical contact in order to communicate. This requirement for direct contact allows for very precise control of cell differentiation during embryonic development. In the worm "Caenorhabditis elegans", two cells of the developing gonad each have an equal chance of terminally differentiating or becoming a uterine
Cardiac function curve activity of the sympathetic nerves, and a decrease in vagal tone cause the heart to beat more frequently and more forcefully. This alters the cardiac function curve, shifting it upwards. This allows the heart to cope with the required cardiac output at a relatively low right atrial pressure. We get what is known as a family of cardiac function curves, as the heart rate increases before the plateau is reached, and without the RAP having to rise dramatically to stretch the heart more and get the Starling effect. In vivo sympathetic outflow within the myocardium is probably best described by