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

5. 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)

6. L R

7. L R |

8. R L
CONSENSUAL
DIRECT RESPONSE |

9. X L R

10. X L R

11. 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

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

13. 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.

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

15. 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

16. 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

17. 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

19. 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

23. 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

24. 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)

25. 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

26. Page 204

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

28. 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

30. 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

32. NOVEL TRANSMITTERS
PEPTIDES
ATP
NITRIC OXIDE

37. END