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)

L R

L R |

R L CONSENSUAL DIRECT RESPONSE |

X L R

X L R

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

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Page 204 Receptor in stomach Acid receptor in duodenum 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

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