The diaphragm is the principal muscle of inhalation and is innervated by the phrenic nerve. From which spinal cord levels does the phrenic nerve arise?

The diaphragm is the principal muscle of inhalation and is innervated by the phrenic nerve. From which spinal cord levels does the phrenic nerve arise?

• A. C3-C5
• B. T1-T3
• C. C1-C3
• D. C5-C7

Answer: (A)

The phrenic nerve—driving the diaphragm, the main muscle of inhalation—emerges from the cervical spinal cord at levels C3 through C5, with C4 providing the dominant input. This makes C3-C5 the correct root set because it includes all the levels that form the phrenic nerve; T1-T3 are too low to contribute to the diaphragm, while C1-C3 or C5-C7 either miss essential contributors or include levels not involved. A handy reminder is “C3, C4, C5 keeps the diaphragm alive,” which matches the correct roots.

The phrenic nerve—driving the diaphragm, the main muscle of inhalation—emerges from the cervical spinal cord at levels C3 through C5, with C4 providing the dominant input. This makes C3-C5 the correct root set because it includes all the levels that form the phrenic nerve; T1-T3 are too low to contribute to the diaphragm, while C1-C3 or C5-C7 either miss essential contributors or include levels not involved. A handy reminder is “C3, C4, C5 keeps the diaphragm alive,” which matches the correct roots.