Phrenic nerve roots.

Phrenic nerve roots.

• A. C5-T1
• B. C1-C4
• C. T2-T5
• D. C3-C5

Answer: (D)

The phrenic nerve is the main motor nerve of the diaphragm, and it is formed from the ventral rami of the cervical spinal nerves C3, C4, and C5. That specific set of roots is why the correct answer is C3-C5. The diaphragm’s function hinges on these roots, which is also remembered by the phrase that “C3, C4, and C5 keep the diaphragm alive.” If the roots or the nerve above or below these levels are involved, diaphragmatic movement can be impaired, with the extent depending on how many sides of the diaphragm are affected. The other root ranges don’t provide all three essential contributions (they miss one or more of C3, C4, or C5, or are in the thoracic region entirely), so they don’t form the phrenic nerve.

The phrenic nerve is the main motor nerve of the diaphragm, and it is formed from the ventral rami of the cervical spinal nerves C3, C4, and C5. That specific set of roots is why the correct answer is C3-C5. The diaphragm’s function hinges on these roots, which is also remembered by the phrase that “C3, C4, and C5 keep the diaphragm alive.” If the roots or the nerve above or below these levels are involved, diaphragmatic movement can be impaired, with the extent depending on how many sides of the diaphragm are affected. The other root ranges don’t provide all three essential contributions (they miss one or more of C3, C4, or C5, or are in the thoracic region entirely), so they don’t form the phrenic nerve.