**Core Concept**
Strychnine is a competitive antagonist at the inhibitory glycine receptors in the spinal cord, leading to an increase in excitatory neurotransmission and subsequent muscle convulsions.

**Why the Correct Answer is Right**
Strychnine inhibits the action of the neurotransmitter glycine at its receptors, which are located on interneurons in the spinal cord. Normally, glycine acts as an inhibitory neurotransmitter, reducing the excitability of neurons and preventing excessive muscle contraction. By blocking glycine receptors, strychnine effectively removes this inhibitory tone, allowing excitatory neurotransmitters like glutamate to dominate and cause excessive muscle contraction and convulsions.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the mechanism of strychnine poisoning.
* **Option B:** Strychnine does not act as an agonist at GABA receptors; in fact, it can enhance the excitatory effects of glutamate and other excitatory neurotransmitters.
* **Option D:** This option is not related to the mechanism of strychnine poisoning, which is primarily related to the inhibition of glycine receptors.

**Clinical Pearl / High-Yield Fact**
Remember that strychnine poisoning is characterized by the absence of respiratory depression and a normal level of consciousness despite severe muscle convulsions. This is due to the fact that strychnine primarily acts on the spinal cord, causing peripheral muscle convulsions without affecting the central nervous system.

**Correct Answer:** C.