## Innervation of the Diaphragm ### Motor Innervation — Phrenic Nerve The diaphragm receives its primary motor innervation from the **phrenic nerve**, which is derived from the **cervical spinal cord segments C3, C4, and C5**. **Key Point:** The phrenic nerve is the sole motor nerve to the diaphragm. It arises from the cervical plexus and descends through the thorax to innervate the entire diaphragm, including the central tendon, crura, and peripheral muscular portions. **Mnemonic:** **C3, C4, C5 keeps the diaphragm alive** — This classic mnemonic emphasizes that the phrenic nerve originates from these three cervical segments and is essential for diaphragmatic function and respiration. ### Anatomical Course 1. Originates from cervical plexus (C3, C4, C5) 2. Descends anterior to the anterior scalene muscle 3. Passes through the superior thoracic aperture 4. Travels along the mediastinum (right phrenic nerve passes lateral to the right atrium; left phrenic nerve passes lateral to the left ventricle) 5. Pierces the diaphragm at the T8 level (alongside the IVC) 6. Supplies motor innervation to all diaphragmatic muscle fibers **High-Yield:** Injury to the phrenic nerve (e.g., from brachial plexus trauma, thoracic surgery, or birth injury) results in diaphragmatic paralysis and respiratory compromise. This is a clinically important correlation tested in NEET PG. **Clinical Pearl:** Sensory innervation to the diaphragm is dual: - **Phrenic nerve**: sensory to the central portion (visceral peritoneum) - **Intercostal nerves (T5–T12)**: sensory to the peripheral muscular portion (parietal pleura) This dual sensory supply explains referred pain patterns — central diaphragmatic irritation (e.g., from subphrenic abscess) causes shoulder-tip pain via phrenic nerve (C3, C4, C5 dermatome), while peripheral diaphragmatic irritation causes chest wall pain via intercostal nerves. 
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.