**Core Concept**
The question is testing the knowledge of the mechanism of action of anesthetic agents, specifically their interaction with NMDA receptors. NMDA (N-methyl-D-aspartate) receptors are a subtype of glutamate receptors involved in excitatory neurotransmission and synaptic plasticity.

**Why the Correct Answer is Right**
Ketamine, an anesthetic agent, acts by blocking NMDA receptors, which are responsible for excitatory neurotransmission in the central nervous system. By blocking NMDA receptors, ketamine reduces the excitatory neurotransmission, leading to a decrease in the activity of neurons and ultimately producing anesthesia. This is in contrast to other anesthetic agents, which may act through other mechanisms such as GABAergic transmission or sodium channel blockade.

**Why Each Wrong Option is Incorrect**
* **Option A:** Propofol does not act through NMDA receptors. It acts by enhancing GABAergic transmission, leading to sedation and hypnosis.
* **Option B:** Etomidate does not act through NMDA receptors. It acts by inhibiting GABA degradation, leading to an increase in GABA levels and subsequently sedation and hypnosis.
* **Option D:** Midazolam does not act through NMDA receptors. It acts by enhancing GABAergic transmission, leading to sedation and anxiolysis.

**Clinical Pearl / High-Yield Fact**
Ketamine has a unique property of producing dissociative anesthesia, where the patient may feel detached from their body and the environment. This is due to its action on NMDA receptors and its ability to alter perception and consciousness.

**Correct Answer:** C. Ketamine.