Understanding Autonomic Nervous System and Drugs

Sep 16, 2024

Autonomic Nervous System and Pharmacology

Overview

  • The autonomic nervous system is divided into:
    • Sympathetic Nervous System (SNS): Activates in stress; "fight or flight" response.
    • Parasympathetic Nervous System (PSNS): Activates during rest; "rest and digest" response.
  • SNS works through alpha and beta receptors.
  • PSNS works through muscarinic and nicotinic receptors.
  • These systems work oppositely; when one is activated, the other is inhibited.

Parasympathetic Nervous System

  • Craniosacral outflow: Originates from cranial nerves to sacral nerves.
  • Cranial Nerves with Parasympathetic Activity:
    • Cranial Nerve 3: Paired with Edinger-Westphal nucleus (meiosis, accommodation).
    • Cranial Nerve 7: Paired with Superior Salivary nucleus (salivation in lacrimal gland).
    • Cranial Nerve 9: Paired with Inferior Salivary nucleus (salivation in parotid gland).
    • Cranial Nerve 10: Dorsal Vagal nucleus (secretions in GI tract and lungs).
  • Major neurotransmitter: Acetylcholine.

Muscarinic Receptors

  • Types and effects:
    • M1, M4, M5: Located in CNS, control cognition.
    • M2: Located in the heart, controls heart rate.
    • M3: Located in urinary tract, GI tract, exocrine glands, eye, airway.
      • Agonists cause cholinergic effects (e.g., increased secretions, peristalsis, etc.).
      • Antagonists cause anticholinergic effects (e.g., dry mouth, reduced secretions).

Pharmacology

Parasympathomimetic Drugs (Cholinergic)

  • Direct Muscarinic Agonists:
    • Bethanacol: Used in urinary retention.
    • Carbacol: Decreases intraocular pressure in glaucoma.
    • Methacoline: Used in bronchial challenge tests (asthma diagnosis).
    • Pilocarpine: Treats Sjogren's syndrome, dry eyes, CF diagnosis.
  • Indirect Muscarinic Agonists (Acetylcholine Esterase Inhibitors):
    • Neostigmine, Pyridostigmine, Physostigmine, Rivastigmine, Donepezil, Galantamine, Edrofonium.
    • Physostigmine: Treats atropine overdose.
    • Pyridostigmine: Treats myasthenia gravis.
    • Edrofonium: Diagnoses myasthenia gravis.
    • Donepezil: Treats Alzheimer's disease.

Anticholinergic Drugs

  • Atropine: Treats cholinergic poisoning, unstable bradycardia.
  • Scopolamine: Treats motion sickness.
  • Benztropine, Trihexyphenidyl: Treat extrapyramidal side effects, Parkinson's.
  • Oxybutynin: Treats overactive bladder.
  • Dicyclomine: Treats irritable bowel syndrome.
  • Glycopyrrolate: Treats sialorrhea, used in surgery.
  • Ipratropium, Tiotropium: Used in COPD and asthma.

Study Strategy

  • Focus on understanding the physiology of muscarinic receptors rather than rote memorization.
  • Use understanding of the sympathetic and parasympathetic oppositions to anticipate drug effects.

Conclusion

  • Understanding the interactions between these systems and drugs is crucial for predicting clinical effects.
  • Review and comprehension over memorization leads to dominance in pharmacology.