Cervical Plexus

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Chapter 17 Cervical Plexus

The cervical plexus is formed by the ventral rami of the upper four cervical nerves, and it supplies some neck muscles, the diaphragm and areas of skin on the head, neck and chest (Figs 17.1–17.3; see also Fig. 11.10). It is situated in the neck opposite a line drawn down the side of the neck from the root of the auricle to the level of the upper border of the thyroid cartilage. It is deep to the internal jugular vein, the deep fascia and sternocleidomastoid, and anterior to scalenus medius and levator scapulae. Each ramus, except the first, divides into ascending and descending parts that unite in communicating loops. From the first loop (C2 and C3), superficial branches supply the head and neck; cutaneous nerves of the shoulder and chest arise from the second loop (C3 and C4). Muscular and communicating branches arise from the same nerves. The branches are superficial or deep. The superficial branches perforate the cervical fascia to supply the skin, whereas the deep branches generally supply the muscles. The superficial branches either ascend (lesser occipital, great auricular and transverse cutaneous nerves) or descend (supraclavicular nerves). The deep branches form medial and lateral series.

Fig. 17.1 Plan of the cervical plexus.

Fig. 17.2 Dissection showing the prevertebral region and superior mediastinum. On the right the costal elements of the upper six cervical vertebrae have been removed to expose the cervical part of the vertebral artery. On the left most of the deep relations of the common carotid artery and the internal jugular vein are exposed.

Fig. 17.3 Dissection showing the general distribution of the left hypoglossal and lingual nerves and the position and constitution of some parts of the cervical plexus on the left side.

Lesser Occipital Nerve

The lesser occipital nerve is derived mainly from the second cervical nerve (although fibres from the third cervical nerve sometimes contribute). It curves around the accessory nerve and ascends along the posterior margin of the sternocleidomastoid. Near the cranium it perforates the deep fascia and passes up onto the scalp behind the auricle. It supplies the skin and connects with the great auricular and greater occipital nerves and the auricular branch of the facial nerve. Its auricular branch supplies the skin on the upper third of the medial aspect of the auricle and connects with the posterior branch of the great auricular nerve. The auricular branch is occasionally derived from the greater occipital nerve.

It has been suggested that compression or stretching of the lesser occipital nerve contributes to cervicogenic headache.

Great Auricular Nerve

The great auricular nerve is the largest ascending branch of the cervical plexus. It arises from the second and third cervical rami, encircles the posterior border of the sternocleidomastoid, perforates the deep fascia and ascends on the muscle beneath platysma with the external jugular vein. It passes to the parotid gland, dividing into anterior and posterior branches. The anterior branch is distributed to the facial skin over the parotid gland, connecting in the gland with the facial nerve. The posterior branch supplies the skin over the mastoid process and on the back of the auricle (except its upper part); a filament pierces the auricle to reach the lateral surface, where it is distributed to the lobule and concha. The posterior branch communicates with the lesser occipital nerve, the auricular branch of the vagus nerve and the posterior auricular branch of the facial nerve.

Transverse Cutaneous (Cervical) Nerve of the Neck

The transverse cutaneous nerve arises from the second and third cervical rami, curves around the posterior border of the sternocleidomastoid near its midpoint and runs obliquely forward, deep to the external jugular vein, to the anterior border of the muscle. It perforates the deep cervical fascia and divides under platysma into ascending and descending branches that are distributed to the anterolateral areas of the neck. The ascending branches ascend to the submandibular region, forming a plexus with the cervical branch of the facial nerve beneath platysma. Some branches pierce platysma and are distributed to the skin of the upper anterior areas of the neck. The descending branches pierce platysma and are distributed anterolaterally to the skin of the neck, as low as the sternum.

Supraclavicular Nerves

The supraclavicular nerves arise from a common trunk formed from rami from the third and fourth cervical nerves and emerge at the posterior border of the sternocleidomastoid. Descending under platysma and the deep cervical fascia, the trunk divides into medial, intermediate and lateral (posterior) branches, which diverge to pierce the deep fascia a little above the clavicle. The medial supraclavicular nerves run inferomedially across the external jugular vein and the clavicular and sternal heads of the sternocleidomastoid to supply the skin as far as the midline and as low as the second rib. They supply the sternoclavicular joint. The intermediate supraclavicular nerves cross the clavicle to supply the skin over pectoralis major and deltoid down to the level of the second rib, next to the area of supply of the second thoracic nerve. Overlap between these nerves is minimal. The lateral supraclavicular nerves descend superficially across trapezius and the acromion, supplying the skin of the upper and posterior parts of the shoulder.

Deep Branches—Medial Series

Communicating Branches

Communicating branches pass from the loop between the first and second cervical rami to the vagus and hypoglossal nerves and to the sympathetic trunk. The hypoglossal branch later leaves the hypoglossal nerve as a series of branches—namely, the meningeal, superior root of ansa cervicalis and nerves to thyrohyoid and geniohyoid. A branch also connects the fourth and fifth cervical rami. The first four cervical ventral rami each receive a grey ramus communicans from the superior cervical sympathetic ganglion.

The superior root of the ansa cervicalis (descendens hypoglossi; see Fig. 17.1) leaves the hypoglossal nerve where it curves around the occipital artery and then descends anterior to or in the carotid sheath. It contains only fibres from the first cervical spinal nerve. After giving a branch to the superior belly of omohyoid, it is joined by the inferior root of the ansa from the second and third cervical spinal nerves. The two roots form the ansa cervicalis (ansa hypoglossi), from which branches supply sternohyoid, sternothyroid and the inferior belly of omohyoid. Another branch descends anterior to the vessels into the thorax to join the cardiac and phrenic nerves.

Muscular Branches

Muscular branches supply rectus capitis lateralis (C1), rectus capitis anterior (C1, C2), longus capitis (C1–3) and longus colli (C2–4). The inferior root of the ansa cervicalis and the phrenic nerve are additional muscular branches.

Inferior Root of Ansa Cervicalis

The inferior root of the ansa cervicalis (nervus descendens cervicalis) is formed by the union of branches from the second and third cervical rami (see Fig. 17.1). It descends on the lateral side of the internal jugular vein, crosses it a little below the middle of the neck and continues forward to join the superior root anterior to the common carotid artery, forming the ansa cervicalis (ansa hypoglossi), from which all infrahyoid muscles except the thyrohyoid are supplied. The inferior root comes from the second and third cervical ventral rami in approximately 75% cases, from the second to fourth in 15% and from the third alone in 5%. Occasionally, it may be derived either from the second alone or from the first to third.