Sinoatrial node action potentials, so that it can pass throughout the heart and cause contraction. An action potential is a change in voltage (membrane potential) across the membrane of the cell, produced by the movement of charged atoms (ions). Non-pacemaker cells (including the ventricular and atrial cells) have a period, immediately after an action potential, where the membrane potential remains relatively constant; this is known as a resting membrane potential. This resting phase (see cardiac action potential, phase 4) ends when another action potential reaches the cell. This produces a positive change in membrane potential (known as depolarisation), which initiates the start
Longitude of the ascending node Longitude of the ascending node The longitude of the ascending node (☊ or Ω) is one of the orbital elements used to specify the orbit of an object in space. It is the angle from a reference direction, called the "origin of longitude", to the direction of the ascending node, measured in a reference plane. The ascending node is the point where the orbit of the object passes through the plane of reference, as seen in the adjacent image. Commonly used reference planes and origins of longitude include: In the case of a binary star known only from visual observations,