The cervical plexus is a collection of nerves arising from the anterior, posterior and lateral roots of C1 – C5, lying deep to the prevertebral fascia. Collectively they provide motor supply to muscles of the neck and cutaneous supply to antero-lateral neck, posterior scalp and lateral face.
· C1 runs in close proximity to the Hypoglossal nerve (CN XII). It provides motor fibres to geniohyoid & thyrohyoid, as well as supplying the superior root of the Ansa Cervicalis. The word ansa cervicalis originates from the Latin for ‘handle of the neck’
· The inferior root of the Ansa Cervicalis arises from C2 and C3 fibres. Once the two roots merge, they provide motor supply to omohyoid, sternohyoid and sternothyroid
· C2 is the sole contributor to the lesser occipital nerve, which pierces prevertebral fascia near the apex of the posterior triangle of the neck and moves superficially to supply sensory fibres to the lateral scalp, posterior to the ear
· C2 and C3 unite to form the great auricular nerve and transverse cervical nerve, deep to sternocleidomastoid. Both nerves exit the posterior triangle, looping around the posterior border of SCM. The great auricular nerve contains sensory fibres to the skin over the angle of the mandible, parotid gland and lower part of the auricle. The transverse cervical supplies the skin over the anterior neck
· Fibres from C3 and C4 form the supraclavicular nerve, which emerges posterior to sternocleidomastoid with the greater auricular and transverse cervical nerves. It soon divides to provide sensory supply to the skin over the lower neck, upper chest and postero-superior aspect of shoulder
· C4 fibres, along with contributions from C3 and C5 descend to become the phrenic nerve
· C1 dorsal root fibres run in close proximity to the vertebral artery as the suboccipital nerve to supply muscles of the suboccipital triangle (obliquus capitis superior and inferior, and rectus capitis posterior major)
· C2, with some minor contribution from C3, forms the greater occipital nerve. This exits through the prevertebral fascia at the apex of the posterior triangle and supplies sensory fibres to the skin over the posterior occiput
· Fibres from C1 – C5 ascend as the spinal accessory nerve within the subarachnoid space lateral to the cord, passing through the foramen magnum posterior to the vertebral artery to join the cranial root
· Although uncommon, insult to the spinal accessory nerve, either traumatic or iatrogenic, results in weakness in turning the head to the opposite side against resistance, and drooping of the shoulder
· Infiltration of local anaesthetic along the posterior border of sternocleidomastoid produces a cervical plexus block, useful in neck surgery. Caution must be taken however, as the block will also affect the phrenic nerve and thus paralysis the ipsilateral hemidiaphragm
The cervical plexus provides sensory fibres to the majority of the neck and posterior head/scalp and motor supply to deep muscles of the neck. It is relatively well protected at its origin, and using the landmark of the posterior border of the sternocleidomastoid, can be blocked to provide regional anaesthesia.