Sympathetic Nervous System
SNS fibers, which originate in the thoracic spine, pass through the stellate ganglion and cervical sympathetic trunks prior to forming the cervical cardiac nerves, which often unite to form one large nerve that eventually parallels the left main. Other thoracic sympathetics unite to form the thoracic cardiac nerves. Both the cervical and thoracic cardiac nerves unite with the PNS nerves in the cardiac plexus before traveling to the heart.
The cardiovascular system is endowed with alpha, beta, cholinergic (muscarinic), adenosite, histamine-2, angiotensin-2, and vasoactive intestinal peptide receptors. Beta and muscarinic (M2) receptors are most important for cardiac functioning. Normally, the ratio of B1 to B2 receptors is 70:30 but in the setting of chronic heart failure, the proportion can decrease to 60:40. M2 receptors are primarily present in the atria although they are present in the ventricles, albeit in lower concentrations.
Parasympathetic Nervous System
Vagal receptors are sensitive to both intracardiac pressures and heart rate.
PNS fibers arise in the dorsal vagal nucleus and nucleus ambiguous, forming the recurrent laryngeal and vagus nerves, which become part of the cervical cardiac nerves and go on to form (with the SNS) the cardiopulmonary plexuses, and eventually the cardiac nerves.
Originate from the stellate ganglion and cervical trunks.