Fasciculation are caused by
**Core Concept**
Fasciculations are muscle contractions that can be observed in response to certain stimuli, particularly in the context of neuromuscular blockade. They are a result of the depolarization of muscle fibers, leading to an involuntary contraction. This phenomenon is closely related to the mechanism of action of certain neuromuscular blocking agents.
**Why the Correct Answer is Right**
Suxamethonium, a depolarizing neuromuscular blocking agent, causes fasciculations due to its ability to mimic the action of acetylcholine at the motor endplate. When suxamethonium binds to the nicotinic receptors on the muscle fibers, it triggers an initial depolarization, leading to muscle contractions, or fasciculations. This is followed by a rapid desensitization of the receptors, resulting in muscle paralysis. The depolarizing action of suxamethonium is responsible for its characteristic fasciculatory effects.
**Why Each Wrong Option is Incorrect**
**Option B:** Pancuronium is a non-depolarizing neuromuscular blocking agent that works by competitively blocking the action of acetylcholine at the nicotinic receptors on the muscle fibers. It does not cause depolarization and therefore does not induce fasciculations.
**Option C:** D-Tubocurarine (d-TC) is a non-depolarizing neuromuscular blocking agent that also acts by competitively blocking the action of acetylcholine at the nicotinic receptors. Like pancuronium, it does not cause depolarization and therefore does not induce fasciculations.
**Option D:** Vecuronium is another non-depolarizing neuromuscular blocking agent that works by competitively blocking the action of acetylcholine at the nicotinic receptors. It does not cause depolarization and therefore does not induce fasciculations.
**Clinical Pearl / High-Yield Fact**
Fasciculations caused by suxamethonium are often used as a clinical indicator of the onset of neuromuscular blockade. However, it is essential to note that prolonged use of suxamethonium can lead to muscle damage and rhabdomyolysis.
**✓ Correct Answer: A. Suxamethonium**