The cervical plexus is a network of nerve fibers located deep within the neck, nestled against the vertebral column and covered by the sternocleidomastoid muscle. This structure connects the central nervous system—the brain and spinal cord—to many structures in the head, neck, and upper chest. Its function is to distribute both motor signals for muscle movement and sensory information across these regions, playing a role in functions like breathing and head movement.
How the Cervical Plexus Is Formed
The cervical plexus is derived from the anterior rami of the first four cervical spinal nerves, designated C1, C2, C3, and C4. These anterior divisions, or roots, emerge from the spinal cord at each vertebral level. After exiting the spine, these roots immediately branch and connect with one another to form a series of nerve loops.
The plexus lies behind the sternocleidomastoid muscle and anterior to the prevertebral muscles. While the primary structure is formed by C1 through C4, the fifth cervical nerve (C5) often contributes fibers to the phrenic nerve, a major output of the plexus. The reorganization of these nerve fibers allows them to emerge as named branches responsible for specific functions.
Major Nerves Originating from the Plexus
The branches emerging from the cervical plexus are separated into two functional groups: cutaneous (sensory) and muscular (motor). The cutaneous nerves emerge as a group at a point known as the nerve point of the neck, or Erb’s point, near the posterior border of the sternocleidomastoid muscle.
- The Lesser Occipital nerve supplies sensation to the skin of the scalp behind and above the ear.
- The Great Auricular nerve carries sensation from the outer ear, mastoid process, and the area over the parotid gland.
- The Transverse Cervical nerve provides sensation across the front and side of the neck.
- The Supraclavicular nerves supply the skin over the shoulder and upper chest area.
Among the muscular branches, the Phrenic nerve is the most significant, originating primarily from C3 and C4 roots, with a frequent contribution from C5. This nerve is solely responsible for providing motor innervation to the diaphragm, controlling breathing. Another motor structure is the Ansa Cervicalis, a loop formed by fibers from C1 through C3, which innervates the infrahyoid or “strap” muscles in the front of the neck.
Essential Motor and Sensory Functions
The most important motor function of the cervical plexus is respiration. The Phrenic nerve carries the signals necessary for the diaphragm to contract, which expands the chest cavity to draw air into the lungs.
Beyond breathing, the plexus provides motor control to many deep neck muscles, enabling movements like head flexion, rotation, and lateral bending. The Ansa Cervicalis controls the infrahyoid muscles, which depress the hyoid bone and larynx during swallowing and speaking. Direct branches from the plexus also help stabilize and move the head by innervating muscles such as the rectus capitis and longus capitis.
The sensory function of the plexus allows feeling touch, temperature, and pain across specific upper body regions. These cutaneous nerves gather information from the skin of the neck, around the ear, and the upper shoulder. This sensory input is transmitted back to the spinal cord and brain for processing.
Causes and Symptoms of Plexus Damage
Damage to the cervical plexus, known as cervical plexopathy, often results from direct trauma to the neck, such as whiplash injuries sustained in an accident. Other causes include compression from tumors, surgical complications in the neck region, or the formation of scar tissue. Injury can also arise from nerve root compression in the cervical spine, such as from disc disease.
Symptoms of damage vary depending on which specific nerves are affected, but they involve a mix of motor weakness and sensory disturbances. If the Phrenic nerve is compromised, the most serious symptom is difficulty breathing or diaphragmatic weakness. Damage to the motor branches can also lead to a reduced ability to turn the head or control the neck muscles.
Sensory symptoms commonly include pain, numbness, tingling, or a “pins and needles” sensation (paresthesia) in the areas supplied by the cutaneous nerves. The location of these disturbances helps clinicians pinpoint the specific nerve or root level that has been injured.