## Anatomical & Neurochemical Basis of Autonomic Division ### Parasympathetic Cranial Nerve Distribution **Key Point:** Parasympathetic fibres are distributed via cranial nerves **III, VII, IX, and X** — NOT V or XII. Cranial nerve V (trigeminal) is sensory; cranial nerve XII (hypoglossal) is motor but not parasympathetic. **High-Yield:** The mnemonic for parasympathetic cranial nerves is **"3, 7, 9, 10"** (oculomotor, facial, glossopharyngeal, vagus). The vagus nerve (CN X) carries ~75% of all parasympathetic fibres in the body. ### Correct Statements Verified | Feature | Sympathetic | Parasympathetic | | --- | --- | --- | | **Preganglionic fibre length** | Short | Long | | **Ganglia location** | Paravertebral/prevertebral (near spinal cord) | Near/within target organs | | **Ganglionic neurotransmitter** | ACh (nicotinic) | ACh (nicotinic) | | **Postganglionic neurotransmitter** | NE (mostly α, β-adrenergic) | ACh (muscarinic) | **Key Point:** Both divisions use **acetylcholine at the ganglia** (nicotinic receptors on postganglionic neurons). This is a universal rule — all preganglionic terminals, whether sympathetic or parasympathetic, are cholinergic. ### Why Option 3 Is Wrong Cranial nerve V (trigeminal) carries **sensory fibres** from the face and meninges — not parasympathetic motor fibres. Cranial nerve XII (hypoglossal) innervates tongue muscles but has no parasympathetic component. The correct parasympathetic cranial nerves are **III, VII, IX, and X only**. [cite:Guyton & Hall Ch 60]
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