Nervous Regulation of the Gastrointestinal Functions
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Cranial and sacral parasympathetic outflow is generally excitatory to the GI smooth muscle.
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Thoracolumbar sympathetic outflow is generally inhibitory to non-sphincteric areas and excitatory to sphincters.
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Acetylcholine is the neurotransmitter of the parasympathetic system and of the prevertebral sympathetic ganglia; norepinephrine is the neurotransmitter of the postganglionic sympathetic fibers.
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The interneurons of the ENS elaborate signals, arriving from the ANS, the mucosa, and blood circulating hormones, to coordinate sterotyped response regulating regional gastrointestinal muscular, secretory and blood flow activity, as well as biliary and pancreatic motor-secretory activities. –
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Visceral afferents:
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activate viscero-visceral reflexes in the prevertebral ganglia
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convey gastrointestinal sensations such as hunger, feeling of fulness and distention via vagal fibers and, in part, via fibers of the intermediomedial columns of the spinal cord
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convey sensation of pain with fibers associated with the sympathetic nervous system to the dorsal root ganglia of the spinal cord.
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Nervous fibers arising in the cortex and brain stem, pontine locus ceruleus, periacqueductal grey in the midbrain, raphe nuclei, lateral nuclei of the reticular formation, can modulate the peripheral viscero-visceral reflexes and the sensations arising in the gastrointestinal tract.
