The cervical plexus is a complex network of nerves located in the neck, acting as a major relay station for communications between the brain and structures in the head, neck, and upper chest. This nerve network provides both sensory information, such as touch and pain from the skin, and motor commands to move specific muscles in these regions. It controls fundamental functions, including breathing and head movement.
Anatomy and Formation
The cervical plexus is formed by the anterior rami, or ventral roots, of the first four cervical spinal nerves, designated C1 through C4. These nerve roots emerge from the spinal cord in the neck and immediately begin to communicate with one another. This communication occurs through a series of loops and interconnections, which are the fundamental structural components of the plexus.
These interconnected roots then split into numerous branches that are functionally categorized into two main groups: superficial and deep. The superficial branches primarily carry sensory fibers, providing feeling to the skin. The deep branches, conversely, contain motor fibers that command muscle movement, including a nerve that controls the diaphragm.
Precise Location in the Neck
The cervical plexus is positioned deep within the neck, protected by surrounding muscle and bone. It is situated laterally to the transverse processes of the upper four cervical vertebrae, resting close to the spinal column.
A major landmark for its location is the sternocleidomastoid muscle (SCM). The plexus lies deep to the SCM and rests upon the levator scapulae and scalene muscles. It is encased within the prevertebral fascia, a layer of connective tissue. The cutaneous branches of the plexus emerge from this deep location and wrap around the posterior edge of the SCM at a common point, which is a location often targeted during medical procedures.
Major Nerves and Functional Role
One of its primary motor outputs is the phrenic nerve, which receives contributions primarily from C3, C4, and C5 spinal nerves, though the plexus itself is C1–C4. The phrenic nerve is responsible for the motor innervation of the diaphragm, making it essential for breathing.
Other motor branches supply a group of muscles collectively known as the infrahyoid or strap muscles, which are crucial for swallowing and speaking by depressing the hyoid bone. The sensory role is covered by four main cutaneous branches that emerge near the middle of the SCM’s posterior border:
- The lesser occipital nerve provides sensation to the skin behind the ear and the posterosuperior scalp.
- The great auricular nerve delivers feeling to the skin over the parotid gland and the external ear.
- The transverse cervical nerve extends forward to supply the skin on the front and side of the neck.
- The supraclavicular nerves descend across the collarbone to provide sensation to the skin over the upper chest and shoulder region.
Clinical Significance
The cervical plexus location is important for medical interventions, particularly in regional anesthesia. A common application is the cervical plexus block, where a local anesthetic is injected to numb the area for surgical procedures on the neck, shoulder, or collarbone. This block can be superficial, targeting the sensory branches for less invasive procedures, or deep, targeting the deeper roots for extensive surgery like carotid endarterectomy.
Injury to the cervical plexus can occur from trauma, such as whiplash, or compression. Symptoms often include localized pain, tingling, or numbness in the ear, neck, or shoulder. If the phrenic nerve is affected, difficulty breathing or diaphragmatic paralysis may occur, highlighting the nerve network’s involvement in a life-sustaining function.