Download Autonomic Nervous System IV

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