The phrenic nerve fibers originate from which spinal levels?

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Multiple Choice

The phrenic nerve fibers originate from which spinal levels?

Explanation:
The phrenic nerve is formed from the ventral rami of the lower cervical spinal nerves, specifically C3 through C5, with C4 typically providing the major contribution. This arrangement explains why diaphragmatic function hinges on these roots, and the common mnemonic “C3, 4, 5 keeps the diaphragm alive.” The other spinal level ranges don’t fit because they miss essential components needed to form the phrenic nerve: C1-C3 omits C4 and C5, C5-C7 misses C3 and C4, and C7-T1 is too low to contribute to the phrenic nerve.

The phrenic nerve is formed from the ventral rami of the lower cervical spinal nerves, specifically C3 through C5, with C4 typically providing the major contribution. This arrangement explains why diaphragmatic function hinges on these roots, and the common mnemonic “C3, 4, 5 keeps the diaphragm alive.” The other spinal level ranges don’t fit because they miss essential components needed to form the phrenic nerve: C1-C3 omits C4 and C5, C5-C7 misses C3 and C4, and C7-T1 is too low to contribute to the phrenic nerve.

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