Risus-sardonicus term used in:
**Core Concept**
Risus sardonicus is a characteristic facial grimace seen in patients with tetanus infection, characterized by a sustained, spasmodic smile. This occurs due to the tetanus toxin's effect on the nervous system, which causes intense muscle spasms and rigidity.
**Why the Correct Answer is Right**
The tetanus toxin, produced by Clostridium tetani, binds to nicotinic acetylcholine receptors at the neuromuscular junction, blocking the release of acetylcholine. This results in hyperexcitability of motor neurons and muscle rigidity, leading to the characteristic spasmodic smile of risus sardonicus.
**Why Each Wrong Option is Incorrect**
* **Option A:** Not applicable, as risus sardonicus is a specific clinical sign associated with tetanus.
* **Option B:** Not related to risus sardonicus, which is a distinct clinical entity from other facial grimaces or spasms.
* **Option C:** Not directly associated with risus sardonicus, although other tetanus symptoms like rigidity and spasms may be present.
**Clinical Pearl / High-Yield Fact**
Risus sardonicus is a classic sign of tetanus infection, but it can also occur in other conditions like strychnine poisoning, which has a similar mechanism of action on the nervous system.
**Correct Answer:** C. Tetanus.