Autonomic GI Neural Control
|Parasympathetic Nervous System Innervation|
- Generally speaking, parasympathetic stimulation tends to enhance nearly all functions of the alimentary tract including motility and secretion.
- Preganglionic parasympathetic fibers innervating the alimentary tract travel via the vagus nerve and the pelvic nerve. Those fibers travelling through the vagus innervate the upper GI tract (esophagus, stomach, small intestines, ascending colon) whereas those travelling through the pelvic nerve innervate the lower GI tract (transverse, descending, sigmoid colons, rectum, and anus). Parasympathetic ganglia are located within the actual walls of the GI tract and thus preganglionic neurons are very long whereas postganglionic neurons are very short.
- Most parasympathetic post-ganglionic neurons release acetylcholine. However, some parasympathetic post-ganglionic neurons release non-traditional peptide neurotransmitters, termed "Neurocrines", the major examples of which include VIP, GRP, Neuropeptide Y.
|Sympathetic Nervous System Innervation|
- Generally speaking, sympathetic activity tends to inhibit nearly all functions of the alimentary tract including motility and secretion.
- SNS pre-ganglionic fibers exit throughout the levels of the spinal cord and synapse onto ganglia located outside the alimentary tract such as the celiac ganglia and other mesenteric ganglia. Post-synaptic neurons run from these ganglia to innervate the length of the GI tract.