Parasympathetic nervous system act in a complementary way increasing or slowing the heart rate. In this context, the vagus nerve acts on sinoatrial node slowing its conduction thus actively modulating vagal tone accordingly. This modulation is mediated by the neurotransmitter acetylcholine and downstream changes to ionic currents and calcium of heart cells. The vagus nerve plays a crucial role in heart rate regulation by modulating the response of sinoatrial node, vagal tone can be quantified by investigating heart rate modulation induced by vagal tone changes. As a general consideration, increased vagal tone (and thus vagal action) is associated with a diminished and more
Orbital node moves south through the plane. In the case of objects outside the Solar System, the ascending node is the node where the orbiting secondary passes away from the observer, and the descending node is the node where it moves towards the observer. The position of the node may be used as one of a set of parameters, called "orbital elements", which describe the orbit. This is done by specifying the longitude of the ascending node (or, sometimes, the longitude of the node.) The line of nodes is the intersection of the object's orbital plane with the plane of reference. It