Autonomic Nervous System (ANS)

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Autonomic Nervous System (ANS)

• Involuntary or visceral nervous system
• Regulates the activity of
• Cardiac Muscle (Heart)
• Smooth Muscle ( In Hollow Organs)
• Blood Vessels
• Digestive System
• Bronchioles
• Sphincters
• Glands
• Adrenal
• Digestive glands

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ANS Divisions

• Parasympathetic
• Rest Digest
• Reduces energy use
• Promotes
• digestion of food
• storage of energy
• elimination of wastes
• homeostasis

• Sympathetic
• Fight or Flight
• Activated during emergencies, exercise or
  vigorous physical activity
• Revs up body to respond to situations that upset
  homeostasis

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Sympathetic - Origin

• Thoracolumbar
• Nerve fibers originate between T1 L2

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Parasympathetic - Origin

• Craniosacral
• Nerve fibers emerge from brain sacrum

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Sympathetic Innervation of Visceral Targets

• Short, lightly myelinated preganglionic neurons

• Long, unmyelinated postganglionic neurons

• Ganglia close to spinal cord

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Sympathetic Neurotransmitters

• Preganglionic neurons -
• Cholinergic ( release acetylcholine )

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Sympathetic Neurotransmitters

• Postganglionic neurons
• release norepinepherine at target organs
• ie. Adrenergic

• Adrenal medulla
• releases epinepherine norepinepherine into
  blood
• ie. Adrenergic

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Adrenergic Receptors

• Located only on sympathetic target organs

• Respond only to norepinepherine released by
  postganglionic neurons (precise effects) or

• Epinepherine norepinepherine released by
  adrenal medulla into blood (general effects)

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Adrenergic Receptor Types

• Alpha 1
• In walls of blood vessels leading to places other
  than skeletal muscles, brain lungs.
• Not on heart (cardiac muscle)
• Alpha 2
• On membranes of platelets.

• Beta 1
• On heart (cardiac muscle) kidneys
• Beta 2
• On coronary arteries, bronchioles on smooth
  muscle walls of digestive urinary systems

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Adrenergic Receptor Effects

• Alpha 1
• Excites (constricts) smooth muscles in certain
  blood vessels in spincters directing blood to
  skeletal muscles
• Dilates pupils.
• Alpha 2
• Promotes blood clotting

• Beta 1
• Cardiac Muscle Increases heart rate strength
• Beta 2
• Depresses (dilates) smooth muscle in bronchioles
  coronary arteries increasing blood flow to
  heart and air flow to lungs.

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Parasympathetic Innervation of Visceral Targets

• Ganglia close to or on target organs

• Preganglionic neurons - long

• Post ganglionic neurons - short

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Parasympathetic Neurotransmitters

• Preganglionic neurons release acetylcholine
  Cholinergic

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Parasympathetic Neurotransmitters

• Postganglionic neurons release acetylcholine
  Cholinergic

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Cholinergic Receptors

• Found on skeletal muscle cells regulated by motor
  neurons.

Motor Neuron
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Cholinergic Receptors

• Found on dendrites cell bodies of
  postganglionic neurons of both sympathetic and
  parasympathetic divisions of ANS.

• Found on parasympathetic target organs.

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Cholinergic Receptor Types

• Nicotinic
• On skeletal muscle cells
• On postganglionic dendrites cell bodies in both
  sympathetic parasympathetic
• Almost always excite

• Muscarinic
• On all target organs of parasympathetic
• May excite or decrease activity depending on
  target

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Muscarinic Receptor Effects

• Cardiac Muscle - Slows heart rate and strength
  of contraction
• Digestive System - Increases digestive activity
  including secretions peristalsis.
• Increases flow of blood to liver, pancreas
  digestive organs by vasodilation of appropriate
  vessels.
• Eye - Causes constriction of Iris

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Blocking Agents

• Interfere with stimulatory or depressing effects
  of neurotransmitters by blocking the receptors on
  target organs.

Normal neurotransmitter cant bind with receptor
because blocker covers the binding site.
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Adrenergic Blockers

• Block receptor binding sites preventing the
  binding of epinepherine or norepinepherine
• Beta 1 blockers on heart
• prevent heart rate increase arrhythmias in
  cardiac patients without interfering with other
  sympathetic effects.
• Examples
• Acebutolol (Sectral), Metoprolol (Lopressor)or
  Inderal.

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Adrenergic Blockers

• Alpha 1 blockers
• Decrease blood pressure in patients with
  hypertension without interfering with other
  sympathetic effects.
• Example
• Phentolamine

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Cholinergic Blockers

• Muscarinic blockers
• Block parasympathetic effects on target organs
• Example
• Atropine
• Used topically during eye exams to dilate pupils
• Sometimes used prior to surgery to reduce
  salivation respiratory secretions

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AcknowledgementsMost of the figures used in this
presentation came from the Benjamin Cummings
Digital Library Version 2.0 for Human Anatomy
Physiology, Fifth Edition. Other figures came
from public domain internet sources and software
in the possession of the author.