**Question:** Common peroneal nerve is related to which of the following structures -

A. Sciatic nerve
B. Femoral nerve
C. Nerve to the long head of the biceps brachii
D. Lateral femoral cutaneous nerve

**Correct Answer:** .

**Core Concept:**
The common peroneal nerve is a division of the sciatic nerve, which is the largest and longest nerve in the body. It arises from the posterior divisions of the ventral rami of the L4, L5, and S1 spinal nerves, and serves as the primary motor and sensory nerve for the lower limb.

**Why the Correct Answer is Right:**
The common peroneal nerve is the motor and sensory nerve responsible for the muscles and sensory functions of the lateral leg and anterior aspect of the ankle and foot. It supplies the following muscles: the extensor digitorum longus, extensor hallucis longus, and the soleus muscles. Furthermore, it innervates the sural nerve, which is responsible for the sensory functions in the lateral aspect of the leg and foot.

**Why Each Wrong Option is Incorrect:**
A. The common peroneal nerve is not related to the femoral nerve (option B). The femoral nerve arises from the ventral rami of the L2, L3, and L4 spinal nerves and is responsible for the motor functions of the thigh.
B. The common peroneal nerve is not related to the lateral femoral cutaneous nerve (option D). The lateral femoral cutaneous nerve arises from the ventral rami of the L2 and L3 spinal nerves and supplies the sensory functions to the lateral thigh and upper leg.
C. The common peroneal nerve is not related to the nerve to the long head of the biceps brachii muscle (option C). The nerve to the long head of the biceps brachii arises from the ventral rami of the C5, C6, and C7 spinal nerves and is responsible for the motor functions of the long head of the biceps brachii muscle, not the common peroneal nerve.

**Clinical Pearl:**
The sciatic nerve is the largest and longest nerve in the body, comprising of the ventral rami of L4, L5, S1, S2, and S3 spinal nerves, and is responsible for the motor and sensory functions of the lower limb. In contrast, the common peroneal nerve is a division of the sciatic nerve and has a more limited function.

**Why Each Wrong Option is Incorrect:**
A. The lateral femoral cutaneous nerve (option D) is a separate entity and arises from the ventral rami of the L2 and L3 spinal nerves and supplies the sensory functions to the lateral thigh and upper leg.
B. The nerve to the long head of the biceps brachii muscle (option C) arises from the ventral rami of C5, C6, and C7 spinal nerves and is responsible for the motor functions of the long head of the biceps brachii muscle.
C. The sciatic nerve (option A) is