Chapter 1 - Evolution of the cardiovascular autonomic nervous system in vertebrates

Abstract

The foundations of the autonomic nervous system evolved prior to the appearance of vertebrates and, while rudimentary, there is a division between the parasympathetic and sympathetic systems even in the earliest diverging vertebrates. The dual autonomic innervation of the heart and vasculature, however, did not appear until the evolution of cartilaginous fishes. Within tetrapods, the autonomic innervation of the cardiovascular system is well conserved, but most ectothermic air-breathing vertebrates differ from mammals by having an undivided ventricle and exhibit cardiac shunts that are largely regulated by the parasympathetic nervous system.