## **Core Concept**
The question tests knowledge of nerve conduction velocities, specifically for A-alpha (Aα) nerve fibers, which are a subtype of **sensory nerve fibers** involved in proprioception and motor functions.

## **Why the Correct Answer is Right**
A-alpha nerve fibers are **large-diameter, myelinated fibers** responsible for transmitting signals related to proprioception (position and movement sense) and are also involved in motor functions. These fibers have a high conduction velocity due to their large diameter and myelination. The conduction velocity of A-alpha fibers typically ranges from **80 to 120 meters per second (m/s)**, making option **C. 90** a reasonable and correct answer within this range.

## **Why Each Wrong Option is Incorrect**
- **Option A: 2**: This velocity is much too slow for A-alpha fibers, as it would be more characteristic of smaller, unmyelinated fibers or certain types of autonomic fibers.
- **Option B: 40**: While faster than many types of nerve fibers, this is still slower than the typical range for A-alpha fibers.
- **Option D: 160**: This velocity is above the typical range for A-alpha fibers and might be considered too high for even the fastest conducting nerve fibers in the human body.

## **Clinical Pearl / High-Yield Fact**
A useful fact to remember is that **nerve conduction velocities** can help in diagnosing and differentiating between various **neuropathies** and nerve injuries. For example, in **demyelinating diseases** like multiple sclerosis, conduction velocities are significantly reduced due to the loss of myelin.

## **Correct Answer: C. 90**