Sinoatrial node also activates a potassium channel, which allows K to flow out of the cell, making the membrane potential more negative and slowing the pacemaker potential, therefore decreasing the rate of action potential production and therefore decreasing heart rate. A decrease in heart rate is known as negative chronotropy. The first cell to produce the action potential in the SA node isn’t always the same, this is known as pacemaker shift. In certain species of animals, for example, in dogs, a superior shift (i.e. the cell that produces the fastest action potential in the SA node is higher than previously) usually
Longitude of the ascending node it is not possible to tell which node is ascending and which is descending. In this case the orbital parameter which is recorded is the longitude of the node, Ω, which is the longitude of whichever node has a longitude between 0 and 180 degrees. In astrodynamics, the longitude of the ascending node can be calculated from the specific relative angular momentum vector h as follows: Here, n=<"n", "n", "n"> is a vector pointing towards the ascending node. The reference plane is assumed to be the "xy"-plane, and the origin of longitude is taken to be the positive "x"-axis. k