Anatomy Exam Brachial Plexus Structures 4 — Questions and Answers
Question 1: A 'waiter's tip' deformity results from injury to which brachial plexus component?
- Upper trunk (C5–C6) (Correct answer)
- Lower trunk (C8–T1)
- Posterior cord
- Medial cord
Correct answer: Upper trunk (C5–C6)
Upper trunk injury (Erb's palsy) causes the arm to hang in adduction, medial rotation, and forearm pronation — the waiter's tip position.
Question 2: Injury to the posterior cord of the brachial plexus would spare which movement?
- Elbow flexion (Correct answer)
- Shoulder abduction
- Wrist extension
- Elbow extension
Correct answer: Elbow flexion
Elbow flexion (primarily musculocutaneous nerve) arises from the lateral cord, not the posterior cord.
Question 3: The nerve to the subclavius arises from which part of the brachial plexus?
- Upper trunk (Correct answer)
- Lateral cord
- Posterior cord
- C6 root directly
Correct answer: Upper trunk
The nerve to subclavius (C5–C6) branches from the upper trunk of the brachial plexus.
Question 4: Which cord of the brachial plexus splits into the musculocutaneous nerve and the lateral root of the median nerve?
- Lateral cord (Correct answer)
- Medial cord
- Posterior cord
- Middle trunk
Correct answer: Lateral cord
The lateral cord divides into the musculocutaneous nerve and contributes the lateral root to the median nerve.
Question 5: A crutch placed too high in the axilla compresses which nerve structure, typically injuring which nerve first?
- Posterior cord / Radial nerve (Correct answer)
- Medial cord / Ulnar nerve
- Lateral cord / Musculocutaneous nerve
- Upper trunk / Axillary nerve
Correct answer: Posterior cord / Radial nerve
Crutch palsy most often affects the radial nerve via compression of the posterior cord in the axilla.
Question 6: C7 nerve root contributes most heavily to which terminal nerve of the brachial plexus?
- Radial nerve (Correct answer)
- Ulnar nerve
- Musculocutaneous nerve
- Axillary nerve
Correct answer: Radial nerve
The radial nerve (C5–T1) receives its largest contribution from C7, which forms the middle trunk.
Question 7: Which brachial plexus branch provides motor innervation to the coracobrachialis, biceps brachii, and brachialis?
- Musculocutaneous nerve (Correct answer)
- Median nerve
- Radial nerve
- Axillary nerve
Correct answer: Musculocutaneous nerve
The musculocutaneous nerve (C5–C7) from the lateral cord innervates all three anterior arm muscles.
Anatomy Exam Brachial Plexus Structures 4
A 'waiter's tip' deformity results from injury to which brachial plexus component?