Innervation of the heart
The first development of the heart takes place independently of its innervation. Later, though, three differing sources for cardiac innervation can be found.
The parasympathetic innervation (cholinergic system) arises from cardiac components of the cranial neural crest cells.
The neurons of the cardiac ganglia, which represent parasympathetic neurons of the second order, migrate directly from the neural crest into the heart. Somewhat later, the axons of the first order nerves obtain access to the heart via the vagus nerve. The parasympathetic innervation slows the heartbeat.
The sympathetic nerve fibers (adrenergic system), which speed up the heartbeat as well as promote the positive inotropism of the cardiac musculature, arise from the thoracic sympathetic ganglia that in their turn come originally from the thoracic neural crest cells.
The third component of the innervation comes directly from the vagus nerve. These are sensory nerves that arise from the ectodermal placode of the nodose ganglion.