**Question:** Finger by which all three major nerves of the upper limb can be tested -

A. Median nerve
B. Radial nerve
C. Ulnar nerve
D. Brachial plexus

**Core Concept:**

The upper limb has three major nerves that supply motor, sensory, and sympathetic functions:
1. **Median nerve (C8-T1):** This nerve is responsible for sensory innervation to the thumb, index, middle, and half of the ring finger, as well as motor innervation to the muscles in the thumb and index finger.
2. **Radial nerve (C5-C7):** The radial nerve supplies the sensory innervation to the thumb, half of the index finger, and half of the ring finger. Motor innervation is to the muscles in the lateral side of the forearm and the extensor muscles of the hand.
3. **Ulnar nerve (C6-C8):** The ulnar nerve supplies sensory innervation to the little finger, half of the index finger, and half of the ring finger. Motor innervation is to the muscles in the medial side of the forearm, the intrinsic muscles of the hand, and the muscles of the little finger.
4. **Brachial plexus (C5-C8, T1):** The brachial plexus is a complex network of nerves formed by the fusion of the cervical, thoracic, and brachial nerves. It is responsible for innervating the muscles and sensory functions of the upper limb.

**Why the Correct Answer is Right:**

The correct answer is D, **Brachial plexus**, because it is the complex network of nerves formed by the fusion of cervical (C5-C8), thoracic (T1), and upper cervical roots (C8-T1) that innervates the muscles and sensory functions of the upper limb. Each major nerve mentioned (A, B, and C) is a portion of the brachial plexus, specifically the cervical and thoracic roots.

**Why Each Wrong Option is Incorrect:**

A) **Median nerve:** The median nerve is responsible for sensory innervation to the thumb, index, middle, and half of the ring finger, and motor innervation to the muscles in the thumb and index finger. It is not responsible for innervating the entire upper limb.

B) **Radial nerve:** The radial nerve supplies sensory innervation to the thumb, half of the index finger, and half of the ring finger, as well as motor innervation to the muscles in the lateral side of the forearm, the extensor muscles of the hand, and the muscles of the little finger. While it plays a role in sensory and motor innervation of the upper limb, it does not cover the entire limb.

C) **Ulnar nerve:** The ulnar nerve supplies sensory innervation to the little finger, half of the index finger, and half of the ring finger, as well as motor innervation to the muscles in the medial side of the forearm, the intrinsic muscles of the hand, and the muscles of the little finger. While it contributes to sensory and motor innervation of the upper limb, it does not cover