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.