Figure 14.

A representation of the mammalian autonomic nervous system of the heart in schematic form. The illustration demonstrates how preganglionic axons of the sympathetic system leave the spinal cord, connect with second-order sympathetic neurons in the sympathetic chain or, most likely, within the intrinsic cardiac ganglia, and then continue as postganglionic adrenergic axons to supply signals to the various heart cells (depicted in green). Second-order parasympathetic neurons in the epicardial ganglionated nerve plexus (shown in brown) form synapses with the preganglionic axons of the vagus nerve (in brown). While the first four thoracic dorsal root ganglia give origin to axons containing substance P (SP) and calcitonin gene-related peptide (CGRP), cardiac sensory neurons located in the dorsal root and vagus sensory ganglia mostly have nitrergic axons spread to the heart. The cardiac hilum serves as the conduit for all nerves traveling to the heart. Several nitrergic neuronal somata may be found in the epicardial ganglionated nerve plexus, with neuronal nitric oxide (nNO) connecting the neurons in the brain stem and spinal trigeminal nuclei (indicated in blue). Consider seeing the ganglia-adjacent tiny, intensely fluorescent (SIF) cells that synthesize noradrenaline (NA) and adrenaline. Despite the ganglionated nerve plexus’s epicardial placement, the heart’s muscle tissue and endocardium have an incredibly dense interconnected system of sensory and efferent nerve fibers [adapted from Aksu et al., 2021 [107]].