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Autonomic Nervous System IV January 20, 2009 Reflexes • Stereotyped responses to specific sensory stimuli • Not under voluntary control --------------Sensory input over afferent limb Integrative center Efferent limb Response elicited by effectors Examples of ANS Reflexes • Pupillary light reflex • Stress activation of the adrenal medulla • Reflex regulation of the GI tract (CNS & LOCAL) – Parasympathetic • Vago-vagal activation of stomach • Gastro-colic reflex – Sympathetic • Global inhibition (stress response) • Selective inhibition (local): Enterogastric reflex • Tonic inhibition (local) R L L R | R CONSENSUAL L DIRECT RESPONSE | R L X R X L • Unilateral MOTOR damage: – pupillary response on the damaged side affected regardless of which eye is illuminated • Unilateral SENSORY damage – pupillary response lost in BOTH eyes when light shone into damaged eye; – pupillary response normal in both eyes when the light is shone into the unaffected eye Stimuli that release adrenal medullary catecholamines • Physiological stressors – Psychological: emotional states - fear – Metabolic – Hypothermia Reflex activation of the adrenal medulla Recognition of a threatening situation involves cognitive processing (forebrain). Autonomic adjustments including activation of the adrenal medulla occur over the brainstem & spinal cord. Neurons in the hypothalamus are sensitive to blood glucose or temperature. Activation of the adrenal medulla occurs over brainstem & spinal cord. Stimuli that release adrenal medullary catecholamines • Physiological stressors – Psychological: emotional states - fear – Metabolic – Hypothermia • Pathological stressors – Severe hemorrhage – Heart attack – Pain Reflex activation of the adrenal medulla SEVERE LOSS OF BLOOD • Reflex activation of adrenal medulla over the splanchnic nerve releases CAs • Circulating ANGIOTENSIN-II becomes high & stimulates adrenal medullary chromaffin cells directly Stimuli that release adrenal medullary catecholamines • Physiological stressors – Psychological: emotional states - fear – Metabolic – Hypothermia • Pathological stressors – Severe hemorrhage – Heart attack – Pain NOTE: Asthmatic attacks do not release CAs Reflex regulation of the GI tract – Parasympathetic (CNS) • Vago-vagal activation of stomach • Gastro-colic reflex – Enteric Nervous System (LOCAL) – Sympathetic • CNS: Global inhibition (stress response) • LOCAL: Selective inhibition: Enterogastric reflex Tonic inhibition Reflex regulation of the GI tract – Parasympathetic - CNS • Vago-vagal activation of stomach • Gastro-colic reflex – Enteric Nervous System - LOCAL – Sympathetic • CNS: Global inhibition (stress response) • LOCAL: Selective inhibition: Enterogastric reflex Tonic inhibition Reflex regulation of the GI tract – Parasympathetic - CNS • Vago-vagal activation of stomach • Gastro-colic reflex – Enteric Nervous System - LOCAL – Sympathetic • occurs at 2 levels • CNS: Global inhibition (stress response) • LOCAL: discrete inhibition (enterogastric reflex) & tonic inhibition Global inhibition of GI function is a normal part of the fight or flight response • Generalized activation of sympathetic outflow to GI tract releases NE and produces: – Inhibition of motility & secretory activity via activation of presynaptic a2 heteroreceptors on postganglionic parasympathetic neurons to inhibit release of Ach. – Reduction in blood flow via a1 receptor activation on smooth muscle of blood vessels – Closure of sphincters (a1 receptor activation) • Adrenal EPI – relaxes GI smooth muscle directly (b2 receptors) Reflex regulation of the GI tract – Parasympathetic (CNS) • Vago-vagal activation of stomach • Gastro-colic reflex – Sympathetic • CNS: Global inhibition (stress response) • LOCAL: Selective inhibition: Enterogastric reflex Tonic inhibition Page 204 Page 204 COELIAC GANGLION Receptor in stomach Acid receptor in duodenum Reflex regulation of the GI tract – Parasympathetic (CNS) • Vago-vagal activation of stomach • Gastro-colic reflex – Enteric Nervous System – Sympathetic • CNS: Global inhibition (stress response) • LOCAL: Selective inhibition: Enterogastric reflex • LOCAL: Tonic inhibition Reflex regulation of the GI tract – Parasympathetic (CNS) • Vago-vagal activation of stomach • Gastro-colic reflex – Enteric Nervous System – Sympathetic • CNS: Global inhibition (stress response) • LOCAL: Selective inhibition: Enterogastric reflex • LOCAL: Tonic inhibition – EVIDENCE: Depletion of NE over-activity of GI tract & diarrhea NOVEL TRANSMITTERS • PEPTIDES • ATP • NITRIC OXIDE END