The phrenic nerves control the diaphragm and exit the spinal cord at which levels?

The phrenic nerves control the diaphragm and exit the spinal cord at which levels?

• A. C2-C4
• B. C4-C6
• C. C3-C5
• D. C5-C7

Answer: (C)

The phrenic nerve that innervates the diaphragm comes from the ventral rami of the spinal nerves at levels C3 through C5. The classic mnemonic “C3, 4, 5 keeps the diaphragm alive” helps remember that the main contribution is from C4 with additional input from C3 and C5. So, the phrenic nerve exits the spinal cord at these cervical levels to descend into the chest and reach the diaphragm. Other level ranges would miss part of this nerve’s origin (for example, starting at C2 or ending at C4 omits C5, while C4-C6 or C5-C7 miss the necessary C3 contribution), which is why C3-C5 is the correct range.

The phrenic nerve that innervates the diaphragm comes from the ventral rami of the spinal nerves at levels C3 through C5. The classic mnemonic “C3, 4, 5 keeps the diaphragm alive” helps remember that the main contribution is from C4 with additional input from C3 and C5. So, the phrenic nerve exits the spinal cord at these cervical levels to descend into the chest and reach the diaphragm. Other level ranges would miss part of this nerve’s origin (for example, starting at C2 or ending at C4 omits C5, while C4-C6 or C5-C7 miss the necessary C3 contribution), which is why C3-C5 is the correct range.