Largest branch of brachial plexus is?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2021

Applied Anatomy

Easy

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2021

Explanation

The radial nerve is the largest terminal branch of the brachial plexus.
It originates as the direct continuation of the posterior cord, which is itself the largest of the three cords.
The radial nerve receives fibers from all five roots of the brachial plexus (C5, C6, C7, C8, T1), giving it a wide distribution.
It provides motor innervation to all the extensor muscles of the arm and forearm, and sensory innervation to a large area on the posterior aspect of the upper limb.

Option A: The ulnar nerve arises from the medial cord and is significantly smaller than the radial nerve. Its distribution is mainly in the forearm and hand.
Option B: Although the median nerve is a major nerve of the upper limb formed from two cords, the radial nerve is consistently cited as the largest branch due to its greater number of innervated muscles and larger cutaneous territory.
Option D: The axillary nerve is a relatively small branch of the posterior cord that has a limited distribution, primarily to the deltoid and teres minor muscles and the skin over the shoulder.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anatomy of the Brachial Plexus as background academic context rather than a clinical decision trigger.
Understanding the anatomy of the brachial plexus is crucial for nurses to assess and manage patients with upper limb injuries, especially those involving trauma, compression, or surgical procedures.
A key nursing assessment for a suspected radial nerve injury is checking for 'wrist drop'—the inability to extend the wrist and fingers against gravity. This simple test can quickly point to a potential radial nerve palsy.
Nurses should be aware of iatrogenic causes of radial nerve injury, such as prolonged or improper use of crutches ('crutch palsy') or incorrect patient positioning during surgery, which can cause compression in the axilla.

How to Approach the Question

This is a factual recall question based on anatomical knowledge.
First, identify the core concept: the brachial plexus and its branches.
The keyword is 'largest'. This requires you to compare the relative sizes of the terminal branches.
Mentally recall or visualize the five main terminal branches of the brachial plexus: Musculocutaneous, Axillary, Radial, Median, and Ulnar.
Recall that the posterior cord is formed from all three posterior divisions, making it the largest cord. The radial nerve is the main continuation of this large posterior cord.
Compare the options: The radial nerve's extensive supply to all extensor muscles of the arm and forearm makes it the largest branch. The other nerves have a more limited distribution in comparison.

Concept Tested & Keywords

Q767rVF1etO8gFRJG1fz2Y

E6 Anatomy Grays 43e Vol 2 Part 2 pp. 114-116, 64-66