Anatomy Exam Brachial Plexus Structures 5 — Questions and Answers
Question 1: Which structure separates the anterior and posterior divisions of the brachial plexus trunks?
- First rib (Correct answer)
- Clavicle
- Scalene muscles
- Coracoid process
Correct answer: First rib
The divisions form as the trunks cross over the first rib, passing between the clavicle and the first rib.
Question 2: In thoracic outlet syndrome, which trunk of the brachial plexus is most commonly compressed?
- Lower trunk (Correct answer)
- Upper trunk
- Middle trunk
- All trunks equally
Correct answer: Lower trunk
The lower trunk (C8–T1) is most often compressed in neurogenic thoracic outlet syndrome, causing intrinsic hand weakness.
Question 3: The dorsal scapular nerve innervates the rhomboids and arises from which root?
- C5 (Correct answer)
- C4
- C6
- C7
Correct answer: C5
The dorsal scapular nerve arises from the C5 root (with a small C4 contribution) and innervates the rhomboids and levator scapulae.
Question 4: The medial root of the median nerve arises from which cord?
- Medial cord (Correct answer)
- Lateral cord
- Posterior cord
- Lower trunk directly
Correct answer: Medial cord
The medial cord gives rise to the medial root of the median nerve (C8–T1), which joins the lateral root from the lateral cord.
Question 5: Which statement best describes the relationship of the brachial plexus to the scalene muscles?
- Roots emerge between anterior and middle scalenes (Correct answer)
- Roots emerge anterior to the anterior scalene
- Roots emerge posterior to the middle scalene
- Trunks pass through the anterior scalene
Correct answer: Roots emerge between anterior and middle scalenes
The ventral rami (roots) of the brachial plexus pass between the anterior and middle scalene muscles in the posterior triangle.
Question 6: A patient cannot abduct the arm past 15 degrees and has numbness over the lateral shoulder. Which nerve is injured?
- Axillary nerve (Correct answer)
- Suprascapular nerve
- Long thoracic nerve
- Musculocutaneous nerve
Correct answer: Axillary nerve
Axillary nerve injury paralyzes the deltoid (abduction 15–180°) and causes sensory loss over the regimental badge area of the lateral shoulder.
Question 7: Anterior divisions of the brachial plexus trunks combine to form which cords?
- Lateral and medial cords (Correct answer)
- Posterior cord only
- Lateral cord only
- All three cords
Correct answer: Lateral and medial cords
The anterior divisions of the upper and middle trunks form the lateral cord; the anterior division of the lower trunk forms the medial cord.
Anatomy Exam Brachial Plexus Structures 5
Which structure separates the anterior and posterior divisions of the brachial plexus trunks?