Editing Autonomic nervous system (section)

===Sensory neurons===
{{Main|Sensory neuron}}
The visceral sensory system - technically not a part of the autonomic nervous system - is composed of primary neurons located in cranial sensory ganglia: the [[geniculate ganglion|geniculate]], [[petrosal ganglion|petrosal]] and [[nodose ganglia]], appended respectively to cranial nerves VII, IX and X. These sensory neurons monitor the levels of [[carbon dioxide]], [[oxygen]] and sugar in the blood, arterial pressure and the chemical composition of the stomach and gut content. They also convey the sense of taste and smell, which, unlike most functions of the ANS, is a conscious perception. Blood oxygen and carbon dioxide are in fact directly sensed by the carotid body, a small collection of chemosensors at the bifurcation of the carotid artery, innervated by the petrosal (IXth) ganglion.
Primary sensory neurons project (synapse) onto "second order" visceral sensory neurons located in the medulla oblongata, forming the [[nucleus of the solitary tract]] (nTS), that integrates all visceral information. The nTS also receives input from a nearby chemosensory center, the area postrema, that detects toxins in the blood and the cerebrospinal fluid and is essential for chemically induced vomiting or conditional taste aversion (the memory that ensures that an animal that has been poisoned by a food never touches it again). All this visceral sensory information constantly and unconsciously modulates the activity of the motor neurons of the ANS.