Cervical Plexus In Situ Anatomy
1. Hypoglossal nerve (CN XII)
2. Ansa cervicalis (Superior root; Inferior root)
3. Vagus nerve (CN X)
4. Phrenic nerve
5. Accessory nerve (CN XI)
6. Lesser occipital nerve
7. Great auricular nerve
Comment: The cervical plexus arises from ventral rami of C1-4. It provides motor innervation for many of the muscles of the anterior and lateral compartments of the neck. This plexus also provides cutaneous innervation to the skin of the neck.
Most of the motor contributions to the infrahyoid muscles arise from a nerve loop called the ansa cervicalis (C1-3).
The cervical plexus also gives rise to the first 2 of 3 roots contributing to the phrenic nerve (C3, C4, and C5). The phrenic nerve innervates the abdominal diaphragm.
Clinical: Unilateral trauma to the posterior cervical triangle of the neck may injure the accessory nerve (CN XI) (ipsilateral innervation of the sternocleidomastoid and trapezius muscles), the phrenic nerve (C3-5) (innervates the ipsilateral hemi- diaphragm), or the trunks or cords of the brachial plexus. The integrity of each of these nerves should be assessed when trauma is evident.