Extrinsic neural influences on gastrointestinal motility.

The gastrointestinal tract is capable of carrying on all its major functions after all extrinsic nerves have been cut. This automaticity is due to the local nervous mechanisms in the walls of the gastrointestinal tract and the inherent properties of the smooth muscles in its walls, and gastrointestinal hormones. All levels of the central nervous system have been shown, by stimulation and ablation studies, to influence the motility of the entire gastrointestinal tract. Throughout many cerebral areas there are loci which, on stimulation, exert both inhibitory, and less often, excitatory influence on gastrointestinal motility. These influences are mediated by sympathetic and parasympathetic visceral efferent nerves, as well as humoral agents from the neurohypophysis. Thus, they impose an influence of higher control on the automatically efficient intrinsic motility. They are guided by information received from visceral, cranial, and somatic afferents, as well as intracerebral, or psychic inputs. Under normal circumstances they only influence gastrointestinal activity as will best afford the optimal functioning of a performance done automatically with efficiency and finesse.