The cervical plexus is a complex network of nerves located in the neck, playing an important role in controlling sensation and movement in several upper body regions. Understanding the cervical plexus offers insight into how our nervous system supports fundamental bodily functions, from feeling a touch on the neck to moving the head.
Location and Formation
The cervical plexus is found deep within the neck, nestled against the cervical vertebrae and partially covered by the sternocleidomastoid muscle. This strategic placement allows it to integrate with various structures in the neck region.
It is formed by the anterior rami of the first four cervical spinal nerves (C1, C2, C3, and C4). While the C5 spinal nerve can contribute to one of its branches, the primary formation involves C1-C4.
These nerve roots emerge from the spinal cord, then divide into anterior and posterior fibers. The anterior rami of C1 through C4 then intertwine, forming loops that constitute the cervical plexus. This interconnected arrangement allows for the distribution of nerve signals to specific areas of the head, neck, and upper torso. The plexus lies laterally to the transverse processes of the prevertebral muscles.
Key Branches and Their Roles
The cervical plexus gives rise to both cutaneous (sensory) and motor branches, each serving distinct functions in the head, neck, and upper chest.
Cutaneous Branches
The cutaneous branches provide sensation to specific skin regions. The lesser occipital nerve, from the C2 spinal nerve, supplies sensation to the scalp behind the ear. The great auricular nerve, from C2 and C3, provides sensory innervation to the skin over the parotid gland, the area behind the ear, and extending towards the angle of the mandible.
The transverse cervical nerve, from C2 and C3, innervates the skin on the front and side of the neck. Lastly, the supraclavicular nerves, from C3 and C4, supply sensation to the skin over the clavicle and the upper part of the chest. These sensory nerves emerge around the middle of the posterior border of the sternocleidomastoid muscle.
Motor Branches
Beyond sensation, the cervical plexus provides motor innervation to several muscles in the neck and diaphragm. Direct muscular branches supply deep neck muscles such as the rectus capitis anterior, rectus capitis lateralis, longus capitis, and longus colli. Other branches contribute to the innervation of the sternocleidomastoid and trapezius muscles. An important motor branch is the phrenic nerve, which receives contributions from C3, C4, and C5 spinal nerves, with C4 providing the main input. The phrenic nerve is the sole motor nerve to the diaphragm, the primary muscle responsible for breathing, and also carries sensory fibers from the diaphragm and surrounding membranes.
Understanding Cervical Plexus Disruption
When the cervical plexus is disrupted, it can lead to various symptoms affecting sensation and movement in the areas it supplies. Such disruptions often stem from physical trauma, including whiplash injuries or direct impacts to the neck. Compression from tumors, swelling, or intervertebral disc issues can also impair the plexus’s function.
Inflammation is another general cause that can affect nerve signaling within this network. Symptoms of a disrupted cervical plexus can include numbness, tingling, or pain in the neck, ear, or shoulder. Individuals might experience weakness or difficulty moving their head or neck. If the phrenic nerve, a major branch of the cervical plexus, is affected, impaired breathing can occur due to compromised diaphragm function.