Which spinal nerve roots primarily innervate the diaphragm via the phrenic nerve?

Which spinal nerve roots primarily innervate the diaphragm via the phrenic nerve?

• A. C1–C4
• B. C3–C5
• C. C4–C6
• D. C2–C4

Answer: (B)

The diaphragm is innervated by the phrenic nerve, which is formed from spinal nerve roots C3, C4, and C5. Among these, C4 provides the main motor input to the diaphragm, with C3 and C5 contributing additional fibers. This is captured by the common saying that “C3, C4, and C5 keep the diaphragm alive.” Clinically, disruption to these roots or the phrenic nerve can impair diaphragmatic movement and breathing.

The diaphragm is innervated by the phrenic nerve, which is formed from spinal nerve roots C3, C4, and C5. Among these, C4 provides the main motor input to the diaphragm, with C3 and C5 contributing additional fibers. This is captured by the common saying that “C3, C4, and C5 keep the diaphragm alive.” Clinically, disruption to these roots or the phrenic nerve can impair diaphragmatic movement and breathing.