Autonomic Nervous System Overview

Autonomic Nervous System Subdivisions

• The autonomic nervous system (ANS) regulates involuntary functions like heart rate, digestion, and breathing.
• The sympathetic and parasympathetic nervous systems are its subdivisions.

Sympathetic Nervous System (SNS)

• Function: The "fight-or-flight" response, activated during stress or emergencies.
• Key Neurotransmitters: Norepinephrine (primary), and epinephrine.
• Effects:
  • Increases heart rate and blood pressure.
  • Dilates bronchi (improves airflow).
  • Dilates pupils.
  • Inhibits digestion and urinary activity.
  • Stimulates glucose release for energy.
• Agents Influencing SNS:
  • Sympathomimetics (Adrenergic Agonists): Stimulate adrenergic receptors.
    • Examples: Epinephrine, norepinephrine, albuterol.
    • Uses: Asthma, hypotension, anaphylaxis.
  • Sympatholytics (Adrenergic Antagonists): Block adrenergic receptors.
    • Examples: Beta-blockers (e.g., propranolol), alpha-blockers (e.g., prazosin).
    • Uses: Hypertension, arrhythmias, anxiety.

Parasympathetic Nervous System (PNS)

• Function: The "rest-and-digest" system, active during relaxation.
• Key Neurotransmitter: Acetylcholine.
• Effects:
  • Decreases heart rate.
  • Constrics bronchi.
  • Stimulates digestion and gland secretion.
  • Promotes bladder contraction and urination.
  • Constricts pupils.
• Agents Influencing PNS:
  • Parasympathomimetics (Cholinergic Agonists): Stimulate cholinergic receptors.
    • Examples: Bethanechol, pilocarpine.
    • Uses: Urinary retention, glaucoma.

Receptor Types and Manipulation

• Adrenergic Receptors (SNS):

  • Alpha-1: Vasoconstriction, pupil dilation (blocked by alpha-1 antagonists).
  • Alpha-2: Inhibits norepinephrine release (stimulated by clonidine).
  • Beta-1: Increases heart rate, contractility (blocked by beta-1 blockers like metoprolol).
  • Beta-2: Bronchodilation and vasodilation (stimulated by beta-2 agonists like albuterol).

• Cholinergic Receptors (PNS):

  • Muscarinic: Found in smooth muscles, glands (blocked by atropine).
  • Nicotinic: Found in ganglia and skeletal muscle (blocked by neuromuscular blockers like pancuronium).

Clinical Application

• Drugs manipulate these systems to treat conditions like asthma, hypertension, and more.
• Balancing activation and inhibition is crucial for therapeutic success.

Explore the subdivisions of the autonomic nervous system, focusing on the sympathetic and parasympathetic systems. Learn about their functions, key neurotransmitters, and the effects they have on the body during stress and emergencies.