**Core Concept**
The first change occurring in a sharp cut nerve is a series of molecular and cellular events initiated by the disruption of the nerve's structural integrity. This process involves the activation of various ion channels, changes in the concentration of ions, and the subsequent depolarization of the nerve cell.

**Why the Correct Answer is Right**
The correct answer is related to the depolarization of the nerve cell due to the influx of sodium ions. When a nerve is cut, the cell membrane's integrity is compromised, leading to the opening of voltage-gated sodium channels. These channels allow sodium ions to rush into the cell, causing a rapid increase in the intracellular concentration of sodium. This increase in sodium ions triggers the depolarization of the nerve cell, which is the first change occurring in a sharp cut nerve.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the first change occurring in a sharp cut nerve.
* **Option B:** This option refers to a process that occurs later in the injury, not the first change.
* **Option D:** This option is related to a different type of nerve injury, not a sharp cut.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the first change occurring in a sharp cut nerve is depolarization, which is a critical step in the nerve injury process. Understanding this concept is crucial for diagnosing and managing nerve injuries.

**Correct Answer: B. Axonal depolarization.**