The diaphragm is innervated by which nerve, enabling it to contract?

• A. Vagus
• B. Vestibulocochlear
• C. Hypoglossal
• D. Phrenic

Answer: (D)

The diaphragm’s movement is driven by the phrenic nerve, which provides motor innervation to this primary breathing muscle. The phrenic nerve arises mainly from cervical spinal nerves C3 to C5 and travels down into the chest to reach the diaphragm. When it fires, the diaphragm contracts and moves downward, enlarging the thoracic cavity and drawing air into the lungs.

The other nerves listed do not control the diaphragm. The vagus nerve mainly supplies parasympathetic fibers to thoracic and abdominal organs and also some motor to the larynx; it does not move the diaphragm. The vestibulocochlear nerve handles hearing and balance. The hypoglossal nerve controls tongue muscles.