**Core Concept**
Acetylcholine is a neurotransmitter that acts on both nicotinic and muscarinic receptors. The muscarinic receptors are further divided into five subtypes (M1 to M5), which are involved in various physiological responses. Atropine is a non-selective muscarinic receptor blocker that can inhibit the action of acetylcholine at these receptors.

**Why the Correct Answer is Right**
The correct answer is C. Bradycardia caused by infusion of acetylcholine. This is because acetylcholine acts on the muscarinic receptors in the heart, specifically the M2 subtype, to decrease heart rate. When atropine blocks these receptors, it prevents the action of acetylcholine, leading to an increase in heart rate. This is known as atropine-induced tachycardia.

**Why Each Wrong Option is Incorrect**
**Option A:** Atropine does not block the nicotinic receptors, which are responsible for the increased blood pressure caused by nicotine. Nicotine acts on nicotinic receptors in the sympathetic nervous system to increase heart rate and blood pressure.

**Option B:** Increased skeletal muscle strength caused by neostigmine is due to its action on nicotinic receptors at the neuromuscular junction. Atropine does not affect this response, as it is not acting on nicotinic receptors.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that atropine can induce tachycardia in patients with bradycardia caused by acetylcholine infusion. This is a critical consideration in the management of patients with heart rate disorders.

**Correct Answer Line**
✓ Correct Answer: C. Bradycardia caused by infusion of acetylcholine.