Autonomic Nervous System

• Sympathetic Nervous System (SNS)

  • Originates from the thoracic and lumbar regions of the spinal cord (thoracolumbar outflow)
  • Preganglionic neurons exit the spinal cord and synapse with postganglionic neurons in ganglia located near the spinal cord (paravertebral ganglia) or close to the target organ (prevertebral ganglia)
• Sympathetic Nervous System (SNS)

  • Associated with the "fight or flight" response
  • Increases heart rate, dilates airways, redirects blood flow to muscles, and stimulates the release of glucose for energy
• Parasympathetic Nervous System (PNS)

  • Originates from the brainstem and the sacral region of the spinal cord (craniosacral outflow)
  • Preganglionic neurons exit the brainstem or sacral spinal cord and synapse with postganglionic neurons in ganglia located near or within the target organs
• Parasympathetic Nervous System (PNS)

  • Associated with the "rest and digest" response
  • Conserves energy by slowing heart rate, stimulating digestion, and promoting relaxation
• Functions of the Autonomic Nervous System (ANS)

  • Maintenance of homeostasis
  • Contraction and relaxation of smooth muscle
  • All exocrine and some endocrine secretions
  • Heart rate and contraction
  • Metabolism (in the liver and skeletal muscle)
• Sympathetic Nervous System (SNS)

  Responsible for the "fight or flight" response, which prepares the body for action in response to stress or danger
• Factors that activate the Sympathetic Nervous System (SNS)

  • Environmental changes
  • Emotional stress and anxiety
  • Exercise
  • Dehydration
  • Some disease states
• Parasympathetic Nervous System (PNS)

  The "rest and digest" system, which helps conserve energy and promotes relaxation
• Acetylcholine (ACh)


  Neurotransmitter for both the Sympathetic Nervous System (SNS) and Parasympathetic Nervous System (PNS)
• Muscarinic Receptors


  • ACh binds to muscarinic receptors, which are G protein-coupled receptors
  • Activation of muscarinic receptors can lead to changes in ion flow across the cell membrane, modulation of enzyme activity, and changes in gene expression
• Nicotinic Receptors


  • ACh binds to nicotinic receptors, which are ligand-gated ion channels
  • Activation of nicotinic receptors leads to the influx of ions, such as sodium and potassium, which can depolarize the cell membrane and trigger an action potential
• Adrenergic Receptors


  • Norepinephrine (NE) and Epinephrine (E) bind to adrenergic receptors, which are G protein-coupled receptors
  • Activation of adrenergic receptors can lead to changes in intracellular signaling pathways, resulting in various physiological responses, such as smooth muscle contraction, glycogenolysis, and changes in heart rate
• Physiological responses associated with Sympathetic Nervous System (SNS) activation

  • Increased heart rate and contractility
  • Pupil dilation
  • Relaxation of eye ciliary muscles
  • Decreased salivary gland secretion
  • Bronchodilation
  • Inhibition of gastrointestinal motility and secretion
  • Inhibition of bladder contraction
  • Increased speed of skeletal muscle contraction, increased muscle mass, and glycogenolysis
• Physiological responses associated with Parasympathetic Nervous System (PNS) activation

  • Decreased heart rate, automaticity, and contractility
  • Pupil constriction
  • Accommodation of the eye lens
  • Increased salivary gland secretion
  • Bronchoconstriction
  • Enhanced digestion and absorption of nutrients
  • Increased bladder emptying
• Adrenergic Agonists (Sympathomimetics)


  Drugs that mimic the effects of norepinephrine and epinephrine by activating adrenergic receptors (α and β receptors)
• Adrenergic Agonists (Sympathomimetics)


  • Epinephrine
  • Dobutamine
  • Albuterol
• Adrenergic Antagonists (Sympatholytics)


  Drugs that block the effects of norepinephrine and epinephrine by binding to adrenergic receptors
• Adrenergic Antagonists (Sympatholytics)


  • Propranolol
  • Prazosin
• Muscarinic Agonists (Cholinergic Agonists)


  Drugs that mimic the effects of acetylcholine by activating cholinergic receptors (muscarinic and nicotinic receptors)
• Muscarinic Agonists (Cholinergic Agonists)


  • Bethanechol
  • Pilocarpine
• Muscarinic Antagonists (Anticholinergic Agents)


  Drugs that block the effects of acetylcholine by binding to cholinergic receptors
• Muscarinic Antagonists (Anticholinergic Agents)


  • Atropine
  • Scopolamine
• Ganglionic Blockers


  Drugs that block transmission in autonomic ganglia, leading to widespread autonomic effects