Figure 1
A schematic representation of the cardiac autonomic nervous system in mammalians including the humans. The diagram demonstrates how preganglionic sympathetic axons arise from the spinal cord, synapse with the second sympathetic neurons in the sympathetic chain or intrinsic cardiac ganglia, and proceed as the postganglionic sympathetic axons innervating the diverse cells in the heart (marked in green). The vagus nerve preganglionic axons primarily arise from the dorsal vagal and ambiguus nuclei and synapse with the second parasympathetic neurons within epicardial ganglionated nerve plexus (in brown). Cardiac sensory neurons localize in the dorsal root and vagus nerve sensory ganglia that involve mostly nitrergic axons spread to the heart, while the first four thoracic dorsal root ganglia give rise to the axons containing substance P (SP) and calcitonin gene related peptide (CGRP). The hilum of heart concentrates all nerves reaching this organ. Epicardial ganglionated nerve plexus encloses numerous nitrergic neuronal somata with neuronal nitric oxide (nNO) synapsing the neurons within the brain stem and spinal trigeminal nuclei (mark in blue). Please notice the noradrenaline (NA) and adrenaline synthetizing small intensively fluorescent (SIF) cells adjacent to ganglia. Despite epicardial localization of ganglionated nerve plexi, there is a highly dense network of sensory and efferent nerve fibers in myocardial and endocardial levels.