**Question:** Which is not a branch of posterior cord of Brachial plexus-

A. C5
B. C6
C. C7
D. C8

**Correct Answer:** **D.** C8

**Core Concept:**
The brachial plexus is a network of nerves that results from the union of spinal nerves from cervical segments C5-C8 and T1. The posterior cord of the brachial plexus consists of motor neurons that innervate the muscles of the posterior compartment of the upper limb. The posterior cord branches are:

1. C5-C6: Ulnar nerve (innervates the muscles of the medial arm and forearm)
2. C7: Radial nerve (innervates the posterior and lateral arm, forearm, and hand muscles)
3. C8: Ulnar nerve (innervates the posterior arm and forearm muscles)
4. T1: Ansa cervicalis (innervates the posterior and lateral chest wall and upper limb muscles)

**Why the Correct Answer is Right:**
C8 belongs to the posterior cord of the brachial plexus and innervates the muscles of the medial forearm and the ulnar nerve in the hand.

**Why Each Wrong Option is Incorrect:**
A. C5 and C6: Both of these belong to the posterior cord and are not included in the correct answer. C5 innervates the radial nerve, and C6 innervates the ulnar nerve and posterior forearm muscles.
B. C7: This belongs to the posterior cord and innervates the posterior arm, forearm, and hand muscles, making it incorrect in this context.
C. T1: Ansa cervicalis is a branch of the T1 spinal nerve, not a posterior cord branch of the brachial plexus. It innervates the posterior and lateral chest wall and upper limb muscles.

**Clinical Pearl:**
Understanding the anatomy of the brachial plexus and its branches is essential for evaluating the upper limb motor function and diagnosing nerve injuries or plexopathies. This knowledge aids in formulating an accurate differential diagnosis and selecting the appropriate diagnostic tests and treatment options.