The Anatomy of the Cervical Plexus

The cervical plexus is a group of nerves located in the neck. It is one of the most complex structures in the body, providing sensory and motor nerve supply to parts of the neck, upper back, and arms. Branches from the cervical plexus also supply nerve impulses to the diaphragm, a large muscle that powers breathing. 

Made up of divisions of the five uppermost spinal nerves, C1 through C5, the nerves of the cervical plexus divide into smaller nerve branches, each dedicated to its own function. 

Anatomy

The cervical plexus can be described as a web of nerves. A plexus is a combination of nerves. The cervical plexus is formed by the merging of the anterior portion of spinal nerves C1 through C4 and part of C5. 

There is some confusing terminology when it comes to anterior and posterior sections of spinal nerves. All spinal nerves are composed of the merging of anterior (ventral, front, motor) and posterior (dorsal, back, sensory) nerve roots that emerge from the spine.

Once the spinal nerves form from their anterior and posterior components, each spinal nerve then divides again into an anterior and a posterior branch (rami). Anterior and posterior rami of any specific spinal nerve do not necessarily follow the same path.

Anterior and posterior rami can be motor nerves, sensory nerves, or both. The cervical plexus arises from the anterior rami of the corresponding cervical spinal nerves. 

Structure 

The cervical plexus includes six large nerves that divide into smaller branches. The main nerves of the cervical plexus are:

• Ansa cervicalis: Also described as a loop because of its shape, the ansa cervicalis is formed by merged branches from C1, C2, and C3. 
• Lesser occipital nerve: Comprised of branches from C2 and C3, this nerve travels up toward the ear. 
• Great auricular nerve: This nerve travels up towards the ear and is formed by branches from C2 and C3. 
• Transverse cervical nerve: Composed of the merging of branches from C2 and C3, this nerve curves around the neck to receive sensory input from structures in the neck. 
• Supraclavicular nerve: Branches from C3 and C4 combine to form this nerve, which then divides into three sections, the anterior, middle, and posterior. 
• Phrenic nerve: The longest nerve of the cervical plexus, the phrenic nerve is formed by branches of C3, C4, and C5. 

Location 

You have two cervical plexi—one on the left and one on the right. They are located on the left and right side of the neck.

Your cervical plexus is found deep in your neck at the level of the corresponding cervical spinal nerves. The whole nerve plexus structure is behind the sternocleidomastoid muscle, a large muscle that runs along the side of the neck from right below the ear to the sternum (breastbone). This muscle turns your head and flexes your neck. 

The six main nerves of the cervical plexus further divide into smaller branches, all extending in different directions as they reach their destination.

For example, the anterior cervical rami that form the ansa cervicalis loop down in the neck as they merge together before this nerve subdivides into its own smaller nerve branches that extend up towards the jaw. 

The phrenic nerve travels down all the way through the chest, near the heart and lungs, to the diaphragmatic muscle. Since the heart and lungs are not perfectly symmetrical, the phrenic nerve structure and path on the left and right side are not perfectly identical as they each extend down towards the diaphragm.

The lesser occipital nerve and the great auricular nerves have their sensory nerve endings near the ears. The transverse cervical nerve (as the name implies) extends across the neck, while the supraclavicular nerve has sensory fibers down in the upper back and upper chest. 

Anatomic Variations 

The left and right cervical plexi are symmetrical and should be exactly the same, although there may be some slight differences between the two. 

Similarly, there can be some variability in which of the cervical spine rami combine to form the main nerves of the cervical plexus. In particular, the accessory nerve, which is the 12th cranial nerve that emerges from the brainstem, can vary in its path and may be located near the cervical plexus.

Function 

The cervical plexus has numerous nerve branches, some of which supply nerve stimulation to muscles, and many of which bring sensory information from areas of the body. 

Motor 

Motor nerves release neurotransmitters to nearby muscles, which causes the muscles to become activated (contract or shorten). The motor endings of the branches of the cervical plexus activate their corresponding muscles, powering several movements in the body.

Chewing and Swallowing

The ansa cervicalis divides into motor nerve branches that stimulate the omohyoid, sternohyoid, and sternothyroid muscles in the jaw and neck. These movements help in chewing and swallowing. 

Breathing

The phrenic nerve, which activates the diaphragm to power breathing, is one of the main motor components of the cervical plexus.

This nerve travels to the diaphragm, a muscle that separates the chest cavity (where your ribs, heart, and lungs are located) from the abdominal cavity (where your stomach and intestines are located). Each side of the diaphragm is stimulated to contract (shorten) by its corresponding phrenic nerve.

As the diaphragm contracts, the chest expands, allowing the lungs to fill with air. The diaphragm alternately expands and contracts as you inhale and exhale.

Sensory 

The sensory branches of the cervical plexus detect sensory input from areas around the ear, the neck, and the upper chest, bringing this message to the spinal nerves before sending them to the spinal cord, and eventually up to the brain, where they are integrated into the sensory region of the cerebral cortex. 

Sensation around the ear is carried through branches of the lesser occipital nerve and the greater auricular nerve. Sensation from the neck is carried to the transverse cervical nerve, and sensation from the upper back and chest is carried through branches of the supraclavicular nerve. 

The sensory branches of the phrenic nerve bring messages from deep areas of the chest, usually when you have visceral pain from infections or serious medical diseases.

Associated Conditions 

The cervical plexus can be damaged by trauma or disease in the neck. Any of its branches can be damaged as well, causing fewer symptoms and clinical effects than would be expected when the whole structure is damaged. 

The symptoms of cervical plexus damage or disease can vary, depending on which branch is affected.

Some of the most common problems that can affect the cervical plexus include the following.

Neck Trauma

Severe trauma to the neck can cause major damage to portions of the cervical plexus. Injuries such as whiplash can stretch some of the nerve branches. Injuries can cause muscle sprains, strains, and spasms, which may irritate the nerve. Bleeding into the area near the cervical plexus can temporarily compress any of its nerve branches. 

Cancer in the Neck

Cancer arising within the neck or metastasizing from elsewhere in the body can compress or infiltrate (invade) regions of the cervical plexus or its branches. This can cause a variety of sensory and/or motor symptoms, including impairment of breathing. 

Surgical Injury

Cervical plexus injuries may occur during surgical procedures.

Spine Disease

Spine disease can affect the cervical plexus. Any condition that impairs the spinal nerves, such as a herniated spinal disc, a pinched nerve, meningitis, or inflammation, can impair portions of the cervical plexus even without directly damaging it. This is because the proper function of the cervical plexus relies on the corresponding spinal nerves and spinal cord. 

Block For Disease 

A cervical plexus block is a technique used for certain procedures that require anesthesia. You may need a cervical plexus block if you are having a localized procedure for which you do not need to be completely asleep. 

Rehabilitation

The cervical plexus, like most nerves, can gain some improved function after treatment. However, in general, nerves that are transected (cut) cannot easily regain function, even after surgical repair. There are several types of rehabilitation and treatment for conditions that affect the cervical plexus.

Physical Therapy

If you have had a minor injury of the cervical plexus with resulting tingling, sensory loss, or weakness, you could benefit from physical therapy. Exercises can relieve pressure on the nerve and help optimize muscle function. Sometimes physical therapy exercises can help improve sensory symptoms as well. 

Chemotherapy and Radiation

If cancer is the main reason for your cervical plexus impairment, treatment of the cancer with radiation or chemotherapy may shrink the tumor and potentially alleviate the impact of cancer on the cervical plexus.

Surgery

Surgical procedures can be effective when a tumor or another mass lesion compresses a portion of the cervical plexus. Removal of the mass can reduce pressure on regions of the cervical plexus.

Surgical repair of the nerve branches may be effective in some instances, depending on the extent and duration of the damage.