**Core Concept**
Ion channels are a class of ligand-gated or voltage-gated receptors that directly allow the flow of ions across the cell membrane, thereby altering the electrical properties of the cell. This is in contrast to G-protein coupled receptors (GPCRs), which initiate a second messenger cascade to produce a cellular response.

**Why the Correct Answer is Right**
The nicotinic acetylcholine receptor (nAChR) is a type of ligand-gated ion channel that spans the neuronal cell membrane. Upon binding of acetylcholine to its binding site, the nAChR undergoes a conformational change, resulting in the opening of an ion channel that allows the influx of sodium and calcium ions into the cell. This depolarization of the cell membrane is a crucial step in initiating muscle contraction and neurotransmitter release.

**Why Each Wrong Option is Incorrect**
* **Option A:** The muscarinic acetylcholine receptor, on the other hand, is a G-protein coupled receptor (GPCR) that initiates a second messenger cascade in response to acetylcholine binding.
* **Option B:** The GABA_A receptor is also a type of ligand-gated ion channel, but it is primarily responsible for inhibitory neurotransmission in the brain.
* **Option D:** The dopamine receptor is a G-protein coupled receptor (GPCR) that initiates a second messenger cascade in response to dopamine binding.

**Clinical Pearl / High-Yield Fact**
The nAChR is a prime example of a receptor that can be targeted therapeutically, as seen in the use of nicotinic agonists (e.g., neostigmine) to reverse non-depolarizing neuromuscular blockade.

**Correct Answer:** C.