Phrenic nerve

The phrenic nerve is a major peripheral nerve arising from the anterior rami of the C3–C5 cervical spinal nerves, primarily C4, and is the sole motor nerve to the diaphragm—the principal muscle of respiration[1][2][3][4]. It is a mixed nerve, conveying motor, sensory, and some sympathetic fibers. The phrenic nerve descends through the neck and thorax on each side to reach and innervate its respective hemidiaphragm. It provides motor stimulation to cause diaphragmatic contraction (essential for inhalation) and sensory fibers to key thoracic and upper abdominal structures, including the central diaphragm, pericardium, mediastinal pleura, and diaphragmatic peritoneum[1][2][3]. Damage to the phrenic nerve results in diaphragmatic paralysis or dysfunction, causing significant breathing difficulties, especially if both nerves are affected[1][2][3]. The phrenic nerve is anatomically a peripheral (somatic) nerve, not a molecular drug target such as a receptor, enzyme, channel, or transporter, and hence is not considered a canonical drug target for small molecules or biologics[2][3].