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Autonomic Nervous System IV

Learn about reflexes and the regulation of the autonomic nervous system, including examples such as the pupillary light reflex and stress activation of the adrenal medulla. Explore the role of the parasympathetic and sympathetic systems in regulating the gastrointestinal tract. Discover how the autonomic nervous system responds to various physiological and psychological stressors. This article also discusses the effects of adrenal medullary catecholamines and the role of the enteric nervous system in GI regulation.

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Autonomic Nervous System IV

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  1. Autonomic Nervous System IV January 20, 2009

  2. Reflexes • Stereotyped responses to specific sensory stimuli • Not under voluntary control --------------- Sensory input over afferent limb  Integrative center  Efferent limb  Response elicited by effectors

  3. 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)

  4. L R

  5. L R |

  6. R L CONSENSUAL DIRECT RESPONSE |

  7. X L R

  8. X L R

  9. 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

  10. Stimuli that release adrenal medullary catecholamines • Physiological stressors • Psychological: emotional states - fear • Metabolic • Hypothermia

  11. 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. Neuronsin the hypothalamus are sensitive to blood glucose or temperature. Activation of the adrenal medulla occurs over brainstem & spinal cord.

  12. Stimuli that release adrenal medullary catecholamines • Physiological stressors • Psychological: emotional states - fear • Metabolic • Hypothermia • Pathological stressors • Severe hemorrhage • Heart attack • Pain

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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)

  19. 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

  20. Page 204

  21. Page 204 COELIAC GANGLION Receptor in stomach Acid receptor in duodenum

  22. 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

  23. 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

  24. NOVEL TRANSMITTERS • PEPTIDES • ATP • NITRIC OXIDE

  25. END

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