Normal Neurophysiology

■ Normal bowel function is under three sets of controls:

■ Intrinsic system of contraction

- Governed by the intrinsic contractility of the intestinal smooth muscles, and the intrinsic system of the nervous system

■ Intrinsic nervous system:

- Submucosal plexus: involved in control of GI secretion and blood flow

- Myenteric plexus: aid coordination of gastrointestinal movement (peristalsis) and process sensory input from the submucosal plexus

- Thus, peristalsis can still occur if the gut is deprived of sympathetic and parasympathetic inputs

- The well-known gastrocolic reflex is also mediated by the intrinsic nervous system of the GI tract

■ The parasympathetic system:

- Originate from cranial and sacral outflows

- Cranial outflow innervates oesophagus to transverse colon

- S2-S4 outflow innervates distal portion of the GI tract from descending colon to rectum

- General action: increased peristalsis, decreased sphincter tone, increased secretion

■ The sympathetic system:

- From T8 to L2 of spinal cord

- Tends to inhibit decreased peristalsis

- Increases sphincter tone

- Decreases secretion, vasoconstriction

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