**Core Concept**
The question tests the knowledge of nicotinic receptors, a type of acetylcholine receptor found in the nervous system. These receptors are ligand-gated ion channels that play a crucial role in neurotransmission and neuromuscular transmission.

**Why the Correct Answer is Right**
Nicotinic receptors are primarily found in the neuromuscular junction (NMJ), autonomic ganglia, and the central nervous system (CNS). They are composed of five subunits (α2-α7, β2-β4) and are responsible for the transmission of signals from neurons to muscles and other neurons. The activation of nicotinic receptors by acetylcholine leads to an influx of sodium and calcium ions, which depolarizes the muscle or neuron.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect, as nicotinic receptors are indeed found in the neuromuscular junction (NMJ), where they play a crucial role in transmitting signals from motor neurons to skeletal muscles.
**Option B:** Incorrect, as nicotinic receptors are found in autonomic ganglia, where they regulate the transmission of signals from preganglionic to postganglionic neurons.
**Option C:** Incorrect, as nicotinic receptors are found in the central nervous system (CNS), where they are involved in various functions, including learning and memory.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that nicotinic receptors are the primary target for non-depolarizing neuromuscular blockers, such as vecuronium and rocuronium, which are commonly used in anesthesia to facilitate tracheal intubation.

**Correct Answer:** A. Muscarinic receptors, not nicotinic receptors, are found in the heart.