## Core Concept
Non-depolarizing skeletal muscle relaxants are a class of drugs that act as **competitive antagonists** at the **nicotinic acetylcholine receptors** (nAChRs) of the neuromuscular junction. By competing with acetylcholine for receptor sites, they prevent acetylcholine from triggering muscle contraction, leading to muscle relaxation.

## Why the Correct Answer is Right
The correct answer states that one of the options is not true of non-depolarizing skeletal muscle relaxants. To assess this, we need to evaluate each option based on known characteristics of non-depolarizing muscle relaxants.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is not provided, but generally, non-depolarizing muscle relaxants do not cause **initial muscle fasciculations** (a characteristic of depolarizing muscle relaxants like succinylcholine).
- **Option B:** Similarly, without the specific content of Option B, we consider that non-depolarizing agents do not affect **potassium levels** in a way that depolarizing agents do; they can cause a slight increase but not significant hyperkalemia as seen with depolarizing agents.
- **Option C:** Again, specifics are needed, but if it mentions something about **reversed by anticholinesterases** (like neostigmine), this is true. Non-depolarizing block can be reversed by increasing acetylcholine levels with anticholinesterase drugs.
- **Option D:** If this option suggests that non-depolarizing agents **act by blocking nicotinic receptors**, this is accurate and a true statement about their mechanism.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **non-depolarizing muscle relaxants can be reversed** by administering drugs that increase the concentration of acetylcholine in the neuromuscular junction, such as **neostigmine**. This is a critical clinical strategy to terminate neuromuscular blockade at the end of surgery.

## Correct Answer: D.