Which dermatomes innervate the diaphragm?

Which dermatomes innervate the diaphragm?

• A. C3/C4/C5
• B. T4
• C. T10
• D. C5/C6

Answer: (A)

The diaphragm is motorized by the phrenic nerve, which comes from the ventral rami of spinal nerves C3, C4, and C5. This is why the dermatomes corresponding to these cervical levels map to regions of skin around the neck and shoulder—the same nerve roots that feed the phrenic nerve. C4 is often highlighted as the dominant contributor, but all three roots participate, which is why the range C3–C5 is the correct association. Dermatomes from the thoracic levels, like T4 or T10, come from intercostal nerves and do not innervate the diaphragm. Likewise, relying on C5/C6 would miss C3 and C4 and misrepresent the phrenic nerve’s root contributions. The mnemonic “C3-C5 keep the diaphragm alive” captures the essential idea.

The diaphragm is motorized by the phrenic nerve, which comes from the ventral rami of spinal nerves C3, C4, and C5. This is why the dermatomes corresponding to these cervical levels map to regions of skin around the neck and shoulder—the same nerve roots that feed the phrenic nerve. C4 is often highlighted as the dominant contributor, but all three roots participate, which is why the range C3–C5 is the correct association.

Dermatomes from the thoracic levels, like T4 or T10, come from intercostal nerves and do not innervate the diaphragm. Likewise, relying on C5/C6 would miss C3 and C4 and misrepresent the phrenic nerve’s root contributions. The mnemonic “C3-C5 keep the diaphragm alive” captures the essential idea.