THE AUTONOMIC NERVOUS SYSTEM

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• THE AUTONOMIC NERVOUS SYSTEM
• 1. Organization of the Autonomic Nervous System
  (ANS)
• Central components
• hypothalamus
• brain stem
• spinal cord
• Peripheral components
• sympathetic nerves
• parasympathetic nerves

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• 2. The Peripheral Autonomic nervous system
• Sympathetic nervous system
• coordinates the bodys responses to stress
• nerve fibers emerge from the spinal segments
  T1-L2
• preganglionic nerve cells are located in the
  interomedial lateral nuclei (IML)
• postganglionic cells are located in ganglia near
  the spinal cord

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• neurotransmitters
• preganglionic fibers acetylcholine (Ach)
• postganglionic fibers norepinephrine (NE)
• exceptions sweet glands, piloerector muscle and
  a few blood vessels also called adrenergic fibers
• receptors that NE activates
• ? receptors
• ?1, ?2
• ? receptors (greater sensitivity to
  isoproterenol)
• ?1, ?2

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• Parasympathetic nervous system
• coordinates the bodys more vegetative
  activities such as digestion
• nerve fibers exit from the brain stem and sacral
  level of the spinal cord
• preganglionic fibers have long axons
• ganglia are near or in target organs
• neurotransmitters
• preganglionic fibers acetylcholine
• postganglionic fibers acetylcholine
• also called cholinergic fibers

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• Autonomic neurons release their
  neurotransmitter from enlarged areas known as
  varicosities
• The varicosities of autonomic neurons are found
  along the distal end of the postganglionic axon

• Action potential arriving at varicosity opens
  voltage-gated Ca2 channels, causing exocytosis
  of synaptic vesicles
• Any NE transported back into axon can be
  metabolized by monoamine oxidase (MAO) or taken
  back into synaptic vesicles for re-release

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• receptors that Ach activates
• nicotinic receptors located on the
  postganglionic neurons
• muscarinic receptors
• M1, M2
• located on target cells
• Reciprocal regulation of bodily organs by
  sympathetic and parasympathetic systems
• reciprocal regulation at effector organs
• e.g. blood pressure
• heart
• blood vessels

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• 3. Actions of the ANS on organs
• Heart
• Sympathetic fibers increase the overall
  activity of the heart
• by increasing the rate and the force of heart
  contraction
• Parasympathetic fibers the opposite effects
• Lungs
• Bronchial muscles
• Bronchial glands
• Blood vessels

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• effects on target organs

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• Gastrointestinal system
• stomach
• motility and tone
• sphincters
• secretion
• intestine
• motility and tone
• sphincters
• secretion
• Intrinsic eye muscles
• iris muscles
• ciliary muscle
• Blood vessels coronary, skeletal muscle, etc

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• 4. Function of the adrenal Medulla
• Release norepinephrine (20) and epinephrine (EP,
  80) into circulating blood
• Stimulated by sympathetic nerves
• Similar effects as sympathetic stimulation except
  of 5-10 times longer
• Differences of EP from NE
• greater effect on heart (? receptor effects)
• weak constriction of the blood vessels in the
  muscles
• greater metabolic effect (5-10 times)

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• Importance of the adrenal medulla
• supports the sympathetic system and provides a
  safety factor
• can stimulate the structures that are not
  innervated by sympathetic fibers