Site of action of ketamine is –
**Core Concept**
Ketamine is a dissociative anesthetic agent that works by blocking the action of glutamate at the N-methyl-D-aspartate (NMDA) receptor, leading to alterations in perception, mood, and consciousness.
**Why the Correct Answer is Right**
The NMDA receptor is a subtype of glutamate receptor that plays a critical role in synaptic plasticity, memory formation, and pain perception. Ketamine binds to the PCP (phencyclidine) site on the NMDA receptor, preventing the influx of calcium ions and thereby blocking the excitatory neurotransmission mediated by glutamate. This action is responsible for the anesthetic, analgesic, and amnesic effects of ketamine.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because ketamine's primary mechanism of action is not related to the GABA receptor, which is the target of benzodiazepines and barbiturates.
**Option B:** This option is incorrect because ketamine does not primarily act on the opioid receptors, which are the targets of morphine and other opioid analgesics.
**Option C:** This option is incorrect because ketamine does not primarily act on the glycine receptor, which is a co-activator of the NMDA receptor but not the primary site of action for ketamine.
**Clinical Pearl / High-Yield Fact**
Ketamine's unique mechanism of action as an NMDA receptor antagonist makes it a useful anesthetic agent for procedures requiring dissociative anesthesia, such as emergency medicine and pediatric anesthesia.
**Correct Answer:** C.