A patient is diagnosed with disc prolapse. Examination reveals paralysis of extensor hallus longus. Which nerve root is affected? (E. REPEAT 2010)

**Core Concept**
The question tests the understanding of the relationship between nerve roots and their corresponding muscle innervations, specifically in the context of disc prolapse and its effects on lower limb muscles. The **extensor hallucis longus** muscle is innervated by the **deep peroneal nerve**, which originates from the **L5 nerve root**.

**Why the Correct Answer is Right**
The **L5 nerve root** is responsible for controlling the muscles of the lower limb, including the **extensor hallucis longus**. When a disc prolapse affects this nerve root, it can lead to paralysis or weakness of the muscles it innervates. The **L5 nerve root** is specifically associated with the **deep peroneal nerve**, which controls foot and toe extension.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not correspond to the nerve root associated with the **extensor hallucis longus**.
**Option B:** Incorrect as it is not related to the specific muscle innervation in question.
**Option C:** Incorrect because, although it might be involved in other neurological deficits, it is not the correct nerve root for **extensor hallucis longus** paralysis.
**Option D:** Incorrect as it does not match the nerve root responsible for the innervation of the **extensor hallucis longus**.

**Clinical Pearl / High-Yield Fact**
Remembering the association between specific nerve roots and their corresponding muscle groups is crucial for diagnosing and managing neurological conditions. The **L5 nerve root** is often implicated in disc prolapse affecting the lower back.

**Correct Answer:** L5. L5 nerve root.