GUT Chapter 6
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Enteric Inhibitory Motor Neurons & Sphincter Gating IAS: Internal anal sphincter of gut Smooth muscle of IAS controlled by ENS and pelvic (sacral) preganglionic excitatory (PEF) and inhibitory (PIF) motor neurons and sympathetic postganglionic efferents of hypogastric nerve that secrete norepinephrine that activates α2-adrenergic (Gq) receptors to maintain constrictive tone of the IAS EAS: External anal sphincter of gut Somatic striated muscle of EAS controlled by pudendal cholinergic efferent fibres from S2-S4 spinal cord
Similar mechanisms occur at ileal orifice & cecocolonic orifice
