1. Definition
The phrenic nerve originates from the C3, C4, and C5 nerve roots in the cervical spine and travels through the neck and chest to the diaphragm.
2. Course
It then descends vertically through the neck, passing anterior to the scalenus anterior muscle. As it continues, the nerve enters the thoracic cavity, passing between the lungs and heart, and travels along the pericardium before reaching the diaphragm.
3. Function
- Motor function: It sends signals to the diaphragm, causing it to contract, which enables inhalation by pulling air into the lungs.
- Sensory function: It also provides sensory information from parts of the pleura, the pericardium, and the diaphragm itself.
4. Clinical Relevance
- Diaphragmatic Paralysis: Injury to the phrenic nerve, often due to trauma, surgery, or spinal cord issues at C3-C5, can cause diaphragmatic paralysis. This results in difficulty breathing or respiratory failure, particularly if both nerves are affected.
- Hiccups: The phrenic nerve is involved in hiccups, which are involuntary contractions of the diaphragm
- Phrenic Nerve Pacing: In cases where the diaphragm is paralyzed but the phrenic nerve remains intact, phrenic nerve pacing can be used. This involves electrical stimulation of the nerve to help restore breathing.
- Referred Pain: Since the phrenic nerve also provides sensory innervation to the pleura, pericardium, and diaphragm, irritation in these areas (e.g., pleuritis, pericarditis) can cause referred pain to the shoulder or neck (C3-C5 dermatomes).