Nerve · Neck

Phrenic nerve

Nervus phrenicus

The phrenic nerve is the sole motor supply to the diaphragm, and it comes from the neck — the old teaching tag is "C3, 4, 5 keeps the diaphragm alive." It descends the length of the neck and chest to reach the muscle it drives, which explains two clinically important things: a neck injury high enough can stop breathing, and irritation of the diaphragm is felt not in the abdomen but at the tip of the shoulder, because the phrenic nerve and the skin over the shoulder share the same C3–C5 segments. It also carries sensation from the pericardium and the central diaphragm.