Phrenic nerve fibers originate from which spinal segments?

Phrenic nerve fibers originate from which spinal segments?

• A. C3-C5
• B. T1-T4
• C. T5-T12
• D. T10-L1

Answer: (A)

Phrenic nerve fibers come from the cervical spinal nerves, primarily from C3, C4, and C5. This set of roots is classically remembered by the phrase “C3–C5 keeps the diaphragm alive,” because these ventral rami converge to form the phrenic nerve that travels to the diaphragm to provide motor control and some sensory innervation. The other spinal levels listed (upper thoracic to lumbar) contribute to intercostal or abdominal nerves and do not form the phrenic nerve, so they don’t provide the diaphragmatic innervation.

Phrenic nerve fibers come from the cervical spinal nerves, primarily from C3, C4, and C5. This set of roots is classically remembered by the phrase “C3–C5 keeps the diaphragm alive,” because these ventral rami converge to form the phrenic nerve that travels to the diaphragm to provide motor control and some sensory innervation. The other spinal levels listed (upper thoracic to lumbar) contribute to intercostal or abdominal nerves and do not form the phrenic nerve, so they don’t provide the diaphragmatic innervation.