The nerve that innervates the diaphragm is which?

• A. Phrenic nerve
• B. Intercostal nerves
• C. Vagus nerve
• D. Sciatic nerve

Answer: (A)

The diaphragm’s movement is controlled mainly by the phrenic nerve. This nerve arises from the cervical spinal nerves C3–C5 (with C4 often the dominant contributor) and travels down into the thorax to reach the diaphragmatic muscle. When the phrenic nerve’s motor fibers fire, the diaphragm contracts and flattens, increasing the thoracic volume to draw air into the lungs during inspiration. The phrenic nerve also carries sensory fibers from the diaphragmatic pleura and peritoneum, which helps with reflexes and pain sensation.

Intercostal nerves mostly serve the chest wall muscles and skin and provide only minor or peripheral contributions to diaphragmatic innervation. The vagus nerve carries parasympathetic fibers to thoracic and abdominal organs, not motor to the diaphragm. The sciatic nerve targets the lower limb and has no role in diaphragmatic control.