**Question:** Lower lateral cutaneous nerve of arm is a branch of

A. C5, C6, and C7 roots of the brachial plexus
B. Anterolateral cord of the brachial plexus
C. C6 root of the brachial plexus
D. Posterior cord of the brachial plexus

**Correct Answer:** C. C6 root of the brachial plexus

**Core Concept:** The brachial plexus is a network of nerves formed by the union of spinal nerves C5, C6, C7, C8, and T1. It plays a crucial role in the innervation of the upper limb. The brachial plexus can be divided into different components based on their origin and distribution pattern.

**Why the Correct Answer is Right:** The lower lateral cutaneous nerve of the arm is responsible for supplying sensation to the lateral aspect of the forearm and the skin over the olecranon process of the ulna bone. It arises from the C6 root of the brachial plexus, making option C the correct choice.

**Why Each Wrong Option is Incorrect:**

A. C5, C6, and C7 roots are incorrect because they form the ventral rami of the spinal nerves, supplying motor innervation to the upper limb muscles, not sensory innervation to the skin.

B. Anterolateral cord of the brachial plexus is a term used to describe the formation of the brachial plexus, not a specific nerve responsible for supplying sensory innervation to the arm.

D. Posterior cord of the brachial plexus is a component of the brachial paxus responsible for motor innervation to the upper limb muscles, not sensory innervation to the skin.

**Clinical Pearl:** Understanding the anatomy of the brachial plexus and its divisions is essential for assessing and diagnosing upper limb nerve injuries, performing surgical procedures on the upper limb, and interpreting the results of clinical neurological examinations.

**Explanation of the Brachial Plexus:** The brachial plexus is formed by the union of spinal nerves C5, C6, C7, C8, and T1. It is divided into ventral and dorsal rami. The ventral rami form the musculocutaneous nerve, axillary nerve, and the musculocutaneous artery, while the dorsal rami form the radial, ulnar, and median nerves.

**Why the Correct Answer is Right:** The lower lateral cutaneous nerve of the arm is a specific branch of the ventral rami of the C6, C7, and C8 spinal nerves. It travels through the cubital tunnel alongside the median nerve and the ulnar nerve to supply sensation to the lateral aspect of the forearm and elbow region. This branch is crucial for understanding the distribution of sensory nerves in the upper limb and recognizing potential neuropathies or plexopathies in clinical practice.