During a radical neck dissection, the surgeon identifies the ansa cervicalis on the anterior surface of the internal jugular vein. This loop is formed by contributions from which cervical nerve roots?

• A C2–C3 (superior root) and C4 (inferior root)
• B C1–C2 (superior root) and C3–C4 (inferior root)
• C C3–C4 exclusively, with no contribution from C1
• D C1 (superior root) and C2–C3 (inferior root) ✓

Explanation

The ansa cervicalis (cervical loop) is formed by the superior root (descendens hypoglossi) from C1 fibers that hitchhike on CN XII, and the inferior root (descendens cervicalis) from C2–C3 anterior rami. The loop lies on the anterior surface of the internal jugular vein (or the carotid sheath). It innervates the infrahyoid (strap) muscles: omohyoid (both bellies), sternothyroid, and sternohyoid. Thyrohyoid is innervated by the C1 branch that leaves the hypoglossal nerve before the ansa forms.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.