ANS PHARMACOLOGY

Description

Here’s a comprehensive, high-yield overview of ANS Pharmacology (Autonomic Nervous System) – extremely important for MBBS exams, Block 5, and Step-style prep:

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🧠 Autonomic Nervous System (ANS) – Basics

Divisions:

Division	Origin	Function	Neurotransmitters
Sympathetic	Thoracolumbar (T1–L2)	Fight or flight	ACh (pre), NE (post)
Parasympathetic	Craniosacral (CN III, VII, IX, X & S2–S4)	Rest & digest	ACh (both pre & post)

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⚙️ Receptors in ANS

🔹 Cholinergic Receptors (respond to ACh)

1. Muscarinic (M1–M5)
   • M1: CNS, gastric glands
   • M2: Heart (↓HR)
   • M3: Smooth muscles, glands (↑secretions, bronchoconstriction, miosis)
2. Nicotinic
   • Nn: autonomic ganglia
   • Nm: neuromuscular junction

🔸 Adrenergic Receptors (respond to NE/E)

Receptor	Main Action
α1	Vasoconstriction, ↑BP, mydriasis
α2	↓NE release (CNS inhibition)
β1	↑HR, ↑contractility, ↑renin
β2	Bronchodilation, vasodilation (skeletal m.), ↓uterine tone
β3	Lipolysis, thermogenesis

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💊 CHOLINERGIC DRUGS

Cholinergic Agonists (Parasympathomimetics)

Drug	Use
Pilocarpine	Glaucoma, dry mouth
Bethanechol	Urinary retention
Neostigmine	Myasthenia gravis
Physostigmine	Atropine overdose
Edrophonium	Diagnosis of MG

Organophosphates: irreversible AChE inhibitors → cause cholinergic crisis
Antidote: Atropine + Pralidoxime

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Cholinergic Antagonists (Antimuscarinics)

Drug	Use
Atropine	Bradycardia, organophosphate poisoning
Scopolamine	Motion sickness
Ipratropium	COPD, asthma
Oxybutynin	Overactive bladder
Tropicamide	Eye exams (mydriasis)

Side effects: dry mouth, urinary retention, tachycardia, confusion

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💊 ADRENERGIC DRUGS

Adrenergic Agonists (Sympathomimetics)

Drug	Receptor	Use
Epinephrine	α1, β1, β2	Anaphylaxis, cardiac arrest
Norepinephrine	α1, β1	Shock (↑BP)
Dopamine	D1, β1, α1 (dose-dependent)	Shock, heart failure
Phenylephrine	α1	Nasal decongestant, ↑BP
Albuterol	β2	Asthma, bronchospasm
Clonidine	α2 agonist	Hypertension

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Adrenergic Antagonists (Sympatholytics)

α-blockers

Drug	Use
Prazosin	Hypertension, BPH
Phenoxybenzamine	Pheochromocytoma
Tamsulosin	BPH (selective for α1A)

β-blockers

Drug	Selectivity	Use
Propranolol	Non-selective	HTN, tremor, migraine
Atenolol, Metoprolol	β1-selective	HTN, angina, heart failure
Labetalol, Carvedilol	α + β blocker	HTN, CHF

Caution: In asthma patients – avoid non-selective β-blockers

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📚 Key Clinical Scenarios

• Mushroom poisoning (muscarine) → cholinergic crisis
  Tx: Atropine
• Organophosphate poisoning → cholinergic excess
  Tx: Atropine + Pralidoxime
• Myasthenia gravis → weakness due to ↓ ACh receptors
  Tx: Neostigmine, Pyridostigmine
• Autonomic drugs in anesthesia: Atropine (to dry secretions), Ephedrine (↑BP)

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🧠 Mnemonics

Cholinergic Toxicity (DUMBBELSS)

• Diarrhea
• Urination
• Miosis
• Bradycardia
• Bronchospasm
• Emesis
• Lacrimation
• Salivation
• Sweating