Gastrointestinal physiology intermediate
Place the following events of parasympathetic (cholinergic) salivary stimulation in the correct chronological order, from first to last.
Answer
Release of acetylcholine from postganglionic parasympathetic fibers, Binding of acetylcholine to muscarinic M3 receptors on salivary acinar cells, Mobilization and increase of intracellular free calcium, Activation of ion transport and fluid secretion
Explanation
The sequence begins with **acetylcholine** release, followed by its binding to **muscarinic M3 receptors**. The lecture then describes an increase in calcium around or within salivary gland cells, which stimulates secretion. Reversing this order would put the cellular response before the receptor interaction that initiates it. **Key takeaway:** ACh binds M3, calcium rises, and secretion is promoted.\n\n**Glossary:**\n- **Cholinergic**: Relating to signaling by acetylcholine.\n- **M3 receptor**: Muscarinic receptor named in the lecture’s salivary secretion pathway.\n- **Cellular calcium**: Calcium involved in signaling within or around gland cells.
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