Cervical Plexus
Introduction
The cervical plexus is a network of nerve fibers that supplies innervation to some of the structures in the neck and trunk. The plexus is formed by the anterior rami (divisions) of cervical spinal nerves C1-C4. Each of these rami (except the first) divides into ascending and descending branches that form communicating loops. Location It is located in the posterior triangle of the neck, within the prevertebral layer of cervical fascia. It lies anterior to scalenus medius and levator scapulae, halfway up the sternocleidomastoid (SCM) muscle Opposite C1-C4 vertebrae.
Communication
It receives grey rami communicantes from the superior cervical sympathetic ganglion. Distribution It innervates structures in the head, neck and chest.
Branches Of The Cervical Plexus
These include;
- Ascending superficial branches
- Descending superficial branches
- Deep branches
Lesser occipital nerve (C2)
- Arises from the ventral ramus of C2
- Winds round the accessory nerve and ascends along the posterior border of SCM,
toward the apex of the posterior triangle of the neck - Pierces the deep fascia at the apex of the posterior triangle
- It then ascends to the scalp behind the auricle
- Innervates the cranial aspect of the auricle and adjacent part of the scalp (behind the auricle)
- Communicates with the greater auricular and greater occipital nerves
- Is of variable size and may be duplicated
Greater auricular nerve (C2, C3)
- Arises from the ventral rami of C2 and C3
- Is usually the largest cutaneous branch of the cervical plexus
- Winds round the SCM and pierces the deep fascia to ascend (on that muscle) to the auricle, deep to platysma
- Is intimately related to the external jugular vein (which ascends anterior to it)
- Divides into anterior, intermediate and posterior branches as it ascends
- Anterior branch – Innervates the skin of the parotid area
- Posterior branch – Innervates the skin over the mastoid process
- Intermediate branch – innervates both aspect of the lower part of the auricle
- Communicates with lesser occipital, posterior auricular and facial nerves
Transverse cutaneous nerve of the neck (transverse cervical nerve, C2, C3)
- Arises from the ventral rami of C2 and C3
- Curves forward, round the posterior border of SCM to its anterior border (deep to the external jugular vein)
- It then pierces the deep fascia to reach the deep aspect of platysma, where it divides into ascending and descending branches (to supply the anterolateral skin of the neck and upper sternum)
- Innervates the skin and fascia of the anterior triangle of the neck
- Communicates above with the cervical branch of facial nerve (deep to platysma)
The descending superficial branches of the cervical plexus include the supraclavicular nerves (C3 & C4)
- Arise as a single trunk from the ventral rami of C3 and C4
- This trunk emerges behind the SCM and descends in the posterior triangle of the neck, where it divides into medial, intermediate and lateral branches
- Pierces the deep fascia just above the clavicle to enter the chest, deep to platysma
- Innervates the skin of the shoulder and chest, down to the level of the sternal angle of Louis (2nd costal cartilage)
- Gives articular fibers to the sternoclavicular and acromioclavicular joints (via its medial and lateral branches respectively)
The deep branches of the cervical plexus may be classified as;
- Communicating branches, and
- Muscular branches
Via its communicating branches, the cervical plexus sends fibres to;
- Vagus nerve
- Accessory nerve
- Hypoglossal nerve – communicating fibers leave the hypoglossal nerve as
- Meningeal branch
- Superior root of ansa cervicalis, and
- Nerve to thyrohyoid and geniohyoid
The C1 spinal nerve gives rise to nerves of the geniohyoid, which moves the hyoid bone anteriorly and upwards, expanding the airway. And the thyrohyoid, which depresses the hyoid bone and elevates the larynx. These nerves travel with the hypoglossal nerve to reach their respective muscles. Muscular branches of the cervical plexus innervates the following muscles;
- C1-C2 – Rectus capitis anterior and lateralis
- C1-C3 – Longus capitis
- C2-C6 – Longus colli
- C2-C3 – Prevertebral muscles and SCM
- C3-C4 – Levator scapulae, trapezius and scalenus medius
- C4-C6 – Middle and anterior scalenus
Other muscular branches of the cervical plexus include;
- Phrenic nerve (C3, C4, C5) – innervates the diaphragm
- Inferior root of ansa cervicalis (C2, C3)
Phrenic Nerve
- Arises from the ventral rami of C3-C5 nerves (mainly C4), at the upper part of the lateral border of scalenus anterior
- Descends in the neck, anterior to scalenus anterior and deep to the prevertebral fascia and SCM
- Passes between the subclavian artery and vein to enter the thoracic cavity, through the thoracic inlet
- Descends through the mediastinum, between the fibrous pericardium and mediastinal pleura (anterior to the root of the lung) towards the diaphragm
- Gives motor fibers to the diaphragm
- It also conveys sensory fibres from the diaphragm and pericardium
- Is accompanied in the mediastinum by the pericardiacophrenic vessels
Ansa Cervicalis
- The superior root (C1) branches off the hypoglossal nerve
- It descends anterior to the common carotid artery, in the carotid sheath
- The inferior root is derived from the ventral rami of C2 and C3 nerves
- Having descended on the lateral aspect of internal jugular vein, it turns medially
(anterior to IJV), just below the middle of the neck to join the superior root - Both roots unite anterior to the common carotid artery to form the ansa cervicalis
- The ansa cervicalis innervates all infrahyoid muscles except thyrohyoid
- Thyrohyoid receives motor fibres from the hypoglossal nerve
- These fibres arise from the cervical plexus (C1); and they join the hypoglossal nerve as a communicating branch
Clinical Correlates
Phrenic nerve block
- Could be performed by injecting an anaesthetic around the nerve in the middle 3rd of scalenus anterior (on which this nerve descends)
- This transiently paralyzes the corresponding dome of the diaphragm
- If the phrenic nerve is damaged in the neck, the ipsilateral dome of the diaphragm is paralyzed
- If however, an accessory phrenic nerve is present, partial paralysis occurs
Cervical plexus block
- An anaesthetic is injected at the nerve point of the neck
- At a point along the posterior border of the SCM, at the junction of the upper and middle thirds of this muscle
- This anaesthetizes structures innervated by the main branches of the cervical plexus
- Usually to provide regional anaesthesia for surgery in the neck region (such as carotid endarterectomy, thyroidectomy and cervical lymph node excision)
- As this procedure also affects the phrenic nerve, it is not performed on those with coexisting cardiac or respiratory disease
