**Core Concept**
Succinylcholine is a depolarizing neuromuscular blocking agent that acts by mimicking the action of acetylcholine at the neuromuscular junction, leading to sustained depolarization of muscle fibers and subsequent paralysis.

**Why the Correct Answer is Right**
Succinylcholine's mechanism of action involves binding to nicotinic acetylcholine receptors on the muscle endplate, causing an initial contraction (fasciculations) followed by sustained depolarization and muscle paralysis. This is due to the inability of the muscle to repolarize and return to its resting state, leading to muscle fatigue and eventually paralysis. The prolonged depolarization is mediated by the open state of the nicotinic acetylcholine receptor channels, which allows an influx of sodium ions into the muscle fiber.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because succinylcholine does indeed cause initial muscle contraction (fasciculations) due to its depolarizing action.
**Option B:** Incorrect because succinylcholine's mechanism of action involves prolonged depolarization, not desensitization of nicotinic acetylcholine receptors.
**Option C:** Incorrect because succinylcholine's effects are not mediated by the release of acetylcholine from the motor neuron, but rather by its direct action on the nicotinic acetylcholine receptors.

**Clinical Pearl / High-Yield Fact**
It's essential to note that succinylcholine can cause significant hyperkalemia due to the release of potassium ions from muscle fibers during depolarization. This can be particularly problematic in patients with burns, trauma, or other conditions that increase muscle damage.

**Correct Answer: D**