In this note, we are going to discuss the anatomy of the cervical plexus (plexus cervicalis), which provides innervation to the head and neck.

This plexus is located in the neck region deep to the sternocleidomastoid muscle, and anterolateral to the levator scapulae.

It is formed by the anterior rami of the four upper cervical spinal nerves (C1-C4).

The C5 is sometimes also considered as part of the plexus, due to its contribution in the formation of one of the deep branches of the cervical plexus, the phrenic nerve.

The cervical nerves within this plexus are intertwined with each other in such a way that each inferior nerve receives fibers from the superior one. For example, C3 receives fibers from C2, C4 receives fibers from C3, and so on. These communicating fibers are branches of the sympathetic trunk (truncus sympathicus)

and are also called gray rami communicantes (rami communicantes grisei).

Each of the cervical nerves, except for the first one (C1), splits into two branches: ascending (r. ascendens) and descending (r. descendens). They subsequently connect with the branches of adjacent cervical nerves, forming loops. These loops contribute to the formation of the cervical plexus.

The cervical plexus has two types of branches:

• Deep or muscular or anterior branches (rr. musculares), which are motor branches that innervate muscles of the neck.
• Superficial or cutaneous or posterior branches (rr. cutanei), which are sensory branches that supply the skin.

Let’s start with the sensory branches.

The loop between C2 and C3 gives off:

• The lesser occipital nerve (n. occipitalis minor), which contains fibers from C2, and innervates the skin of the neck and the skin of the scalp (posterosuperior to the auricle)

• The great auricular nerve (n. auricularis magnus), which contains fibers from C2 and C3, ascends across the sternocleidomastoid muscle, and divides into two branches at the inferior pole of the parotid gland.

These are the posterior (r. posterior) and anterior (r. anterior) branches.

It innervates the skin over the gland, the posteroinferior aspect of the auricle, and the area between the angle of the mandible and the mastoid process.

• The transverse cervical nerve (n. transversus colli) contains fibers from C2 and C3, it curves around the posterior border of the sternocleidomastoid muscle, passing deep to the platysma.

It innervates the skin covering the anterior triangle of the neck (trigonum cervicalis anterius).

• Supraclavicular nerves (nn. supraclaviculares) arise from the loop between C3 and C4,

they contain fibers from C3 and C4, and pass as a common trunk under the sternocleidomastoid muscle. This trunk then divides into medial supraclavicular nerves (nn. supraclaviculares mediales),

intermediate supraclavicular nerves (nn. supraclaviculares intermedii),

and lateral supraclavicular nerves (nn. supraclaviculares laterales).

These branches innervate the skin of the neck region and the skin over the shoulder.

There is a commonly used mnemonic to memorize the sensory branches of the cervical plexus: Let’s Go To Spain!

Muscular branches

Now let’s discuss motor (or muscular) branches of the cervical plexus.

These are the so-called ansa cervicalis (ansa cervicalis), the phrenic nerve (nervus phrenicus), and several smaller muscular branches.

The ansa cervicalis is a loop, formed by two roots: the superior (radix superior) and inferior (radix inferior), which is composed of fibers from nerves C1 to C3.

The ansa cervicalis gives rise to several branches to the corresponding muscles:

• The sternohyoid branch (r. sternohyoideus) – C1 – C3

• The sternothyroid branch (r. sternothyreoideus) – C1 – C3

• The geniohyoid branch (r. geniohyoideus) – C1, passes with the hypoglossal nerve

• The omohyoid branch (r. omohyoideus) – C1 – C3

• The thyrohyoid branch (r. thyrohyoideus) – C1, passes with the hypoglossal nerve

The branches of the ansa cervicalis provide innervation to the mentioned infrahyoid muscles.

You can use the following mnemonic to memorize the nerves, that form the ansa cervicalis: Stephen Stole The Golden Orange

The phrenic nerve receives most of its fibers from C4, with small contributions from C3 and C5 nerves.

The nerve is formed in the area of the lateral part of the anterior scalene muscle at the level of the superior border of the thyroid cartilage. It descends with the internal jugular vein (vena jugularis interna) obliquely along the anterior scalenus muscle.

It passes posteriorly to the subclavian vein (vena subclavia), anteriorly to the internal thoracic artery (a. thoracica interna), and enters the thoracic cavity.

The phrenic nerve contains not only motor but also sensory and sympathetic nerve fibers, which makes it a mixed nerve.

It provides the motor supply to the diaphragm as well as sensation to its central area.

In the thoracic cavity, the nerve innervates the mediastinal pleura and pericardium.

The motor branches of the cervical plexus also include fibers to the levator scapulae muscle, the sternocleidomastoid muscle, and the prevertebral muscles.

Dictionary

Cervical plexus

Cervical plexus

plexus cervicalis

Anterior branch

ramus anterior

Sympathetic trunc

truncus sympathicus

Gray rami communicantes

rami communicantes grisei

Ascending branch

ramus ascendens

Descending branch

ramus descendens

Muscular branches

rr. musculares

Cutaneous branches

rr. cutanei

Lesser occipital nerve

n. occipitalis minor

Great auricular nerve

n. auricularis magnus

Posterior branch

ramus posterior

Transverse cervical nerve

n. transversus colli

Anterior triangle of the neck

trigonum cervicalis anterius

Supraclavicular nerves

nn. supraclaviculares

Medial supraclavicular nerves

nn. supraclaviculares mediales

Intermediate supraclavicular nerves

nn. supraclaviculares intermedii

Lateral supraclavicular nerves

nn. supraclaviculares laterales

Ansa cervicalis

ansa cervicalis

Phrenic nerve

nervus phrenicus

Superior root

radix superior

Inferior root

radix inferior

Sternohyoid branch

r. sternohyoideus

Sternohyoideus muscle

m. sternohyoideus

Sternothyroid branch

r. sternothyroideus

Sternothyroideus muscle

m. sternothyroideus

Geniohyoid branch

r. geniohyoideus

Geniohyoideus muscle

m. geniohyoideus

Omohyoid branch

r. omohyoideus

Omohyoideus muscle

m. omohyoideus

Thyrohyoid branch

r. thyrohyoideus

Thyrohyoideus muscle

m. thyrohyoideus

Internal jugular vein

vena jugularis interna

Subclavian vein

vena subclavia

Internal thoracic artery

a. thoracica interna

Diaphragm

diaphragma

Mediastinal pleura

pleura mediastinalis

Pericardium

pericardium

Levator scapulae muscle

m. levator scapulae

Sternocleidomastideus muscle

m. sternocleidomastoideus