Recently, while studying pharmacology, I came to know about the third system of ANS - Enteric nervous system, apart from sympathetic and parasympathetic systems .
Here is some information of ENS:
It consists of highly organized neurons situated in the wall of GI tract.
It mainly includes Auerbach's plexus and Meissner's plexus.
The most interesting point about ENS is this network receives preganglionic fibers from the parasympathetic system and from postganglionic sympathetic neurons.
ENS controls GI motility, secretions, mucosal blood flow.
ENS causes relaxation or stimulation of smooth muscles.
Non-cholinergic excitatory transmitters such as substance - P plays a modulatory role in controlling ENS!