Which of the following neurotransmitters is released by postganglionic parasympathetic neurons at their target organs?

Explanation

## Parasympathetic Neurotransmission **Key Point:** All postganglionic parasympathetic neurons are cholinergic — they release acetylcholine (ACh) at their target organs, where it binds to muscarinic receptors. **High-Yield:** This is a fundamental distinction in autonomic pharmacology: - **Parasympathetic postganglionic terminals:** ACh → muscarinic receptors (M1–M5) - **Sympathetic postganglionic terminals:** noradrenaline → α and β adrenergic receptors - **Exception:** Sympathetic postganglionic neurons to sweat glands and adrenal medulla are cholinergic (nicotinic) ### Autonomic Neurotransmitter Summary | Pathway | Preganglionic | Postganglionic | Receptor Type | |---------|---------------|----------------|---------------| | **Parasympathetic** | ACh (nicotinic) | ACh (muscarinic) | M1–M5 | | **Sympathetic** | ACh (nicotinic) | Noradrenaline (α, β) | Adrenergic | | **Sympathetic (sweat, adrenal)** | ACh (nicotinic) | ACh (nicotinic) | Nicotinic | **Clinical Pearl:** Muscarinic receptor activation produces the classic parasympathetic effects: miosis, bronchospasm, bradycardia, increased GI motility, and urinary bladder contraction.