Correct Answer: C. Dorsal scapular nerve
The muscle marked by the arrow in the image is the levator scapulae, a key postural muscle of the back. The levator scapulae originates from the transverse processes of C1–C4 vertebrae and inserts on the medial border of the scapula, functioning to elevate and retract the scapula. Its innervation is the dorsal scapular nerve (DSN), which arises from the ventral ramus of C5 (sometimes with contributions from C4 and C6). The DSN is a branch of the cervical plexus and descends along the medial aspect of the scapula, supplying levator scapulae, rhomboid major, and rhomboid minor. This nerve is clinically significant in India because it can be injured during neck dissections, radical mastectomies, or thoracic outlet syndrome, leading to scapular winging and loss of scapular elevation. The DSN's origin from C5 (a cervical nerve root) and its consistent supply to levator scapulae make it the definitive answer. Understanding this innervation is essential for clinical examination of scapular function and for surgical planning in oncology cases common in Indian practice.
Why the other options are wrong
A. Subscapular nerve — The subscapular nerve (from the posterior cord of the brachial plexus, C5–C6) innervates the subscapularis and teres major muscles on the anterior/posterior aspect of the scapula, not levator scapulae. This is a common trap because both are scapular-region nerves, but subscapular nerve supplies intrinsic scapular muscles, not extrinsic ones like levator scapulae. B. From the dorsal rami of C1 — Dorsal rami of C1 (suboccipital nerve) innervate suboccipital muscles (rectus capitis posterior major/minor, obliquus capitis superior/inferior) for head movement, not scapular muscles. This option confuses cervical segmental innervation with the specific plexus-derived nerve supply; levator scapulae receives ventral ramus contribution via DSN, not dorsal rami. D. Suprascapular nerve — The suprascapular nerve (from the upper trunk of the brachial plexus, C5–C6) innervates supraspinatus and infraspinatus muscles in the supraspinous and infraspinous fossae. Although it is a scapular nerve, it does not supply levator scapulae. NBE pairs this with levator scapulae to test knowledge of specific muscle-nerve relationships in the scapular region.
High-Yield Facts
- Levator scapulae innervation: Dorsal scapular nerve (C5 ventral ramus), not brachial plexus branches.
- Dorsal scapular nerve origin: C5 (sometimes C4–C6), arises from cervical plexus before brachial plexus formation.
- Dorsal scapular nerve supplies: Levator scapulae, rhomboid major, rhomboid minor (extrinsic back muscles).
- Scapular winging differential: DSN injury → medial border winging; long thoracic nerve injury → medial border winging; spinal accessory injury → trapezius paralysis.
- Clinical injury risk: Neck dissection, thoracic outlet syndrome decompression, and radical mastectomy can damage DSN in Indian oncology practice.
Mnemonics
DSN = Dorsal Scapular Nerve supplies LRR = Levator scapulae, Rhomboid major, Rhomboid minor. All three are extrinsic back muscles supplied by C5 ventral ramus via DSN. Scapular nerve memory hook Dorsal Scapular (C5) → extrinsic muscles (Levator, Rhomboids). Suprascapular (C5–C6 upper trunk) → intrinsic muscles (Supraspinatus, Infraspinatus). Subscapular (C5–C6 posterior cord) → subscapularis, teres major.
NBE Trap
NBE pairs levator scapulae with multiple scapular-region nerves (subscapular, suprascapular) to test whether students confuse extrinsic back muscle innervation (cervical plexus via DSN) with intrinsic scapular muscle innervation (brachial plexus branches). The trap is that all four options involve scapular anatomy, but only DSN supplies levator scapulae.
Clinical Pearl
In Indian cancer centres, radical neck dissection and modified radical mastectomy frequently damage the dorsal scapular nerve, presenting as inability to elevate the scapula and medial scapular border winging. Testing scapular elevation (shrug against resistance) is a quick bedside sign of DSN integrity—loss suggests nerve injury during oncologic surgery.
_Reference: Robbins & Cotran Pathologic Basis of Disease (anatomy context); Gray's Anatomy (nerve supply); Clinically, refer to Bailey & Love's Short Practice of Surgery for surgical anatomy of neck dissection and DSN injury risk._