SBA — Single Best Answer · Review
Question 672
Anatomy → Region
Classification
Question
SSBAQuestion Header
Which statement most accurately describes the spinal origin of the phrenic nerve?
Question Stem
Select the single best answer.
Options
A
Anterior primary rami of C1–C3, predominantly C2
B
Anterior primary rami of C3–C5, predominantly C4
C
Posterior primary rami of C3–C5, predominantly C5
D
Anterior primary rami of C5–C7, predominantly C6
E
Thoracic spinal nerves T1–T3
Explanation
Each phrenic nerve arises from the anterior primary rami of C3, C4 and C5, with the greatest contribution arising from C4. The phrenic nerves provide the only motor supply to the diaphragm.
Option Validity
A) The phrenic nerve arises from C3–C5 rather than C1–C3.
C) The phrenic nerve arises from the anterior primary rami, with the greatest contribution from C4.
D) C5–C7 is not the stated segmental origin of the phrenic nerve.
E) The phrenic nerve is derived from cervical rather than thoracic spinal nerves.
Further Reading
Saxena R. Textbook for MRCOG-1. Chapter 2: Anatomy, pp.12–13.