Learning Objectives

By the end of this section, learners should be able to:

Describe the anatomical location and formation of the cervical plexus.
Identify the spinal nerve roots contributing to the cervical plexus.
Differentiate between the muscular and sensory branches of the cervical plexus.
Explain the functional significance of major branches, including the phrenic nerve and ansa cervicalis.
Apply anatomical knowledge of the cervical plexus to relevant clinical procedures, such as cervical plexus nerve block.

Overview of the Cervical Plexus

The cervical plexus is a network of nerve fibres that provides motor and sensory innervation to structures in the neck, upper thorax, and diaphragm.

It is located within the posterior triangle of the neck, deep to the sternocleidomastoid muscle, approximately at its midpoint, and lies within the prevertebral layer of cervical fascia.

The plexus is formed by the anterior rami of cervical spinal nerves C1–C4, which interconnect to form a series of muscular and cutaneous branches.

Formation from Spinal Nerves

At each cervical vertebral level, paired spinal nerves exit the spinal cord through the intervertebral foramina. Each spinal nerve divides into:

a posterior ramus (supplying deep back muscles and skin), and
an anterior ramus, which contributes to nerve plexuses.

The anterior rami of C1, C2, C3, and C4 unite to form the cervical plexus. These fibres intermingle and reorganise to give rise to its terminal branches.

Branches of the Cervical Plexus

The branches of the cervical plexus are broadly classified into:

Muscular (motor) branches
Cutaneous (sensory) branches

Muscular Branches

The muscular branches lie deep to the sensory branches and primarily supply muscles of the neck and the diaphragm. These branches typically travel in an anteromedial direction, in contrast to the posterior course of cutaneous branches.

Phrenic Nerve

The phrenic nerve arises mainly from C4, with contributions from C3 and C5. It provides motor innervation to the diaphragm, making it essential for respiration.

After originating from the cervical plexus, it descends along the anterior surface of the anterior scalene muscle, enters the thorax, and travels anterior to the lung root to reach the diaphragm.

Mnemonic: “C3, 4, 5 keep the diaphragm alive.”

Nerves to Geniohyoid and Thyrohyoid

Fibres from the C1 spinal nerve supply:

Geniohyoid – moves the hyoid bone anteriorly and superiorly, helping to widen the airway.
Thyrohyoid – depresses the hyoid bone and elevates the larynx.

These fibres travel alongside the hypoglossal nerve to reach their target muscles.

Ansa Cervicalis

The ansa cervicalis is a nerve loop formed by fibres from C1–C3. It supplies the infrahyoid muscles, including:

Sternohyoid
Sternothyroid
Superior belly of the omohyoid
Inferior belly of omohyoid

These muscles function to depress the hyoid bone, an important action during swallowing and speech.

Other Muscular Branches

Additional branches supply muscles of the neck and back:

C1–C2: Rectus capitis anterior and lateralis
C1–C3: Longus capitis
C2–C3: Contributions to prevertebral muscles and sternocleidomastoid
C3–C4: Contributions to levator scapulae, trapezius, and scalenus medius

The anterior and middle scalene muscles also receive direct innervation from the cervical plexus.

Sensory (Cutaneous) Branches

The cutaneous branches provide sensation to the skin of the neck, scalp, upper thorax, and ear. All emerge at the midpoint of the posterior border of the sternocleidomastoid, known as the nerve point of the neck (Erb’s point).

Major Sensory Branches

Greater Auricular Nerve (C2–C3)
Supplies the skin over the parotid gland and external ear. It is the largest ascending branch of the plexus.
Transverse Cervical Nerve (C2–C3)
Supplies sensation to the anterior and anterolateral neck and upper sternum.
Lesser Occipital Nerve (C2 ± C3)
Provides cutaneous sensation to the posterosuperior scalp.
Supraclavicular Nerves (C3–C4)
Supply the skin over the supraclavicular fossa, upper thorax, and sternoclavicular joint.

Clinical Relevance: Cervical Plexus Block

A cervical plexus block provides regional anaesthesia for procedures such as:

Carotid endarterectomy
Thyroidectomy
Cervical lymph node excision

Local anaesthetic is injected at the nerve point of the neck, midway along the posterior border of the sternocleidomastoid, using a fan-shaped injection technique.