Course
The anterior rami of C1 to C4 leave the intervertebral foramina, pass behind the vertebral artery, and join one another in a series of loops. The plexus lies on levator scapulae and scalenus medius, deep to the prevertebral fascia, and is covered by the internal jugular vein and sternocleidomastoid.
Each ramus receives a grey ramus communicans from the superior cervical sympathetic ganglion. The plexus also communicates with the vagus, hypoglossal and accessory nerves. The C1 fibres that join the hypoglossal nerve later leave it to form the superior root of the ansa cervicalis and the nerves to thyrohyoid and geniohyoid.
The nerve point
The four cutaneous branches pierce the prevertebral fascia and emerge together around the midpoint of the posterior border of sternocleidomastoid, a spot called the nerve point of the neck (sometimes called Erb's point, a name also used for a site on the upper trunk of the brachial plexus). From here they fan out upwards, forwards and downwards. The accessory nerve emerges from behind sternocleidomastoid just above this point.
Branches
The branches of the cervical plexus fall into cutaneous, motor and communicating groups.
| Branch | Roots | Course | Supply |
|---|---|---|---|
| Lesser occipital | C2 | Hooks round the accessory nerve and ascends along the posterior border of sternocleidomastoid | Skin of the scalp behind the ear |
| Great auricular | C2, C3 | Ascends obliquely across sternocleidomastoid towards the ear lobe, behind the external jugular vein | Skin over the parotid, angle of mandible, mastoid and both surfaces of the lower ear; parotid capsule |
| Transverse cervical | C2, C3 | Runs horizontally forwards across sternocleidomastoid, deep to the external jugular vein | Skin of the anterior triangle |
| Supraclavicular (medial, intermediate, lateral) | C3, C4 | Descend through the posterior triangle and cross the clavicle | Skin over the clavicle, shoulder and upper chest to about the second rib |
| Ansa cervicalis | C1–C3 | Loop on the carotid sheath | Sternohyoid, sternothyroid, omohyoid |
| Nerves to thyrohyoid and geniohyoid | C1 | Travel with the hypoglossal nerve | Thyrohyoid, geniohyoid |
| Phrenic nerve | C3–C5 | Descends on scalenus anterior into the thorax | Diaphragm (sole motor supply) |
Short segmental branches supply the prevertebral muscles (longus capitis, longus colli, rectus capitis anterior and lateralis), scalenus medius and levator scapulae. Branches from C2 to C4 also reach sternocleidomastoid and trapezius; these are thought to be mainly proprioceptive, with the accessory nerve providing the motor supply.
Relations
The cervical plexus sits in a layered position that matters for neck surgery and blocks. Superficial to it lie sternocleidomastoid, the internal jugular vein and the carotid sheath. Deep to it lie levator scapulae and scalenus medius. The prevertebral fascia covers it, so the cutaneous branches must pierce this fascia to reach the posterior triangle, while the plexus itself stays deep.
In the posterior triangle the accessory nerve runs superficial to the prevertebral fascia, within the loose tissue under the investing layer, whereas the phrenic nerve and the brachial plexus roots lie deep to it. The supraclavicular nerves cross the triangle superficially, just under the investing fascia.
Clinical relevance
A superficial cervical plexus block anaesthetises the skin of the neck by injecting local anaesthetic along the midpoint of the posterior border of sternocleidomastoid, where the cutaneous branches emerge. It is used for carotid endarterectomy under regional anaesthesia, clavicle fixation and some thyroid procedures. A deep cervical plexus block targets the roots near the transverse processes and more often blocks the phrenic nerve, causing temporary hemidiaphragm paralysis.
The great auricular nerve is the branch most often injured. It crosses the operative field in parotidectomy and facelift surgery, leaving numbness of the ear lobe and skin over the angle of the mandible. It is also a convenient donor for nerve grafting, including facial nerve repair.
Pain from the diaphragm is referred to the shoulder tip because the phrenic nerve and the supraclavicular nerves share the C4 segment. The lesser occipital nerve is one of the targets in occipital neuralgia and in blocks for occipital headache.