Autonomic Nervous System

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Autonomic Nervous System
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• Main input from autonomic sensory neurons (most
  associated with interoceptors)
• monitor internal environment- not conscious
• example- chemoreceptors for CO2 level

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• Autonomic motor neurons regulate visceral
  activities
• (increase or decrease)
• function somewhat even if nerve supply damaged
• example- heart beat
• difficult to consciously control
• (i.e. lie detector test, yoga)

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See figure 15.1

• Most autonomic motor pathways consist of two
  motor neurons
• in series through autonomic ganglion (second not
  myelinated)
• preganglionic (CNS) and postganglionic (PNS)
• some extend to adrenal medullae- hormones
  released

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The preganglionic motor neurons of the
sympathetic system arise in the spinal cord.
They pass into sympathetic ganglia which are
organized into two chains that run parallel to
and on either side of the spinal cord.
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The main nerves of the parasympathetic system is
the tenth cranial nerve, the vagus nerve. It
originates in the medulla oblongata. Other
preganglionic parasympathetic neurons also extend
from the brain as well as from the lower tip of
the spinal cord.
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• Anatomy of autonomic motor pathways
• Three types of autonomic ganglia
• sympathetic trunk ganglia- vertical row on
  either side of vertebral canal
• sympathetic division
• innervate organs above diaphragm
• prevertebral ganglia- anterior to vertebral
  canal
• sympathetic division
• innervate organs below diaphragm
• terminal ganglia- close to or actually in wall of
  organ (longer)
• parasympathetic division
• Postganglionic neurons- one sympathetic ganglia
  can synapse with 20 postganglionic neurons
  (effect much of body simultaneously)

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• Autonomic plexuses
• tangled networks of axons from sympathetic and
  parasympathetic neurons
• cardiac (heart), pulmonary (lungs), celiac or
  solar (liver, gallbladder, stomach, pancreas,
  spleen, kidneys, testes, ovaries), superior
  mesenteric (small and large intestines), inferior
  mesenteric (large intestine), renal (kidneys and
  ureters)

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• ANS neurotransmitters and Receptors
• cholinergic- release acetylcholine (Ach)
• all preganglionic neurons, parasympathetic
  postganglionic neurons, some sympathetic
  postganglionic (sweat glands)
• nicotinic and muscarinic receptors- effects
  brief
• adrenergic (release norepinephrine/ NE)
• most sympathetic postganglionic
• alpha and beta receptors- longer lasting
• agonists can activate receptors, antagonists
  block receptors

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• Physiological effects of ANS- tables 15.3 and
  15.4
• autonomic tone- balance between sym. and
  parasym.- regulated by hypothalamus
• Sympathetic dominates during physical or
  emotional stress (rapid ATP production)--- flight
  or fight response--- E situations (exercise,
  emergency, excitement, embarassment)
• Parasympathetic dominates rest and digest
  activities- conserve and restore energy --- SLUDD
  (salivation, lacrimation, urination, digestion,
  defecation)

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• Autonomic reflexes- controlled conditions (i.e.
  blood pressure)
• reflex arc receptor- sensory neuron-
  integrating center- motor neuron- effector
• hypothalamus major control center