Cervical nerves are spinal nerves that arise from the cervical region of the spinal cord. These nerves conduct motor and sensory information via efferent and afferent fibers, respectively, to and from the central nervous system. While classified as peripheral nerves, the motor cell body resides in the anterior horn of the spinal cord. There are eight pairs of cervical nerves, denoted C1 to C8, that emerge from the spinal cord superior to their corresponding vertebrae, except for C8 that exits inferiorly to the C7 vertebra. These nerves intertwine through plexuses that give rise to peripheral nerves that maintain a significant motor function in the head, neck, upper limbs, and diaphragm, as well as sensation in the head, neck, shoulders, and upper limbs in a dermatomal pattern.
The cervical nerves arise from the spinal cord in the form of rootlets, or fila radicularia, smaller neuron bundles that coalesce to form roots. For each spinal nerve, an anterior and posterior root join to form the completed nerve. Shortly after branching out of the spinal cord, the cervical nerves form the cervical and brachial plexuses. It is important to note that the inputs and outputs may vary by individual, and therefore, different sources may offer different descriptions.
The cervical plexus forms from the ventral rami of C1 to C4. It is known to anastomose with the facial nerve, hypoglossal nerve, spinal accessory nerve, vagus nerve, and the sympathetic trunk. It lies anteromedial to the scalenes, but is deep to the sternocleidomastoid, and gives rise to the motor and sensory branches:
The brachial plexus forms from the ventral rami of C5 to C8, as well as T1. The plexus projects laterally, anterior to the first rib, but posterior to the clavicle, into the axillary region. The plexus is divided into several sections through its several anastomoses from the five nerve roots into three trunks, six divisions, three cords, and finally, five branches. The final outputs are best described by the location from which they emerge from the plexus, rather than simply based on their motor/sensory function as several nerves carry both types of information :
Spinal nerves originate from the sclerotome, more specifically, the central region of the anterior-half-sclerotome. This portion of the sclerotome is also responsible for the endoneurium and perineurium of the spinal nerves. This origin stands in contrast to the posterior-half-sclerotome that forms the bone and cartilage of the vertebral column. The posterior half also acts to block the outgrowth of neural crest cells and spinal nerve axons, thus leading to the segmentation of the spinal nerves.
The roots of spinal nerves receive vascular supply from the radicular arteries. These arteries pass through the intervertebral foramina with the nerve roots. The first six vessels most commonly arise from the vertebral arteries or the ascending cervical branch of the thyrocervical trunk. In either case, the spinal branches of these two vessels anastomose, so if either source has a blockage, blood flow is maintained. The radicular arteries of the seventh and eighth segments always form from branches of the costocervical trunk.
The Cervical Nerves innervate numerous muscular structures. The C1 spinal nerve gives rise to the nerve to the geniohyoid and the nerve to the thyrohyoid that both function in the oropharynx. Anatomically, these nerves travel closely to the hypoglossal nerve (CN XII). The ansa cervicalis (“handle of the neck” in Latin), is a loop of nerves that lies superficial to the internal jugular vein, composed of the C1 to C3 nerves. More specifically, one end of the loop, the superior root, is derived from C1 (and possibly C2, depending on the literature), while the other, the inferior root, comes from C2 and C3. This structure gives rise to the nerves to the sternohyoid, sternothyroid, and superior and inferior bellies of the omohyoid muscles. All of the muscles supplied by branches of the ansa cervicalis, along with the thyrohyoid, are infrahyoid muscles, and therefore serve to depress the hyoid bone. This function is necessary for proper speech and swallowing. The C3, C4, and C5 roots contribute to form the phrenic nerves. These are responsible for motor and sensory supply to the diaphragm, as well as for sympathetic output. The phrenic nerves run anteriorly to the subclavian arteries, but posterior to the subclavian veins. Outside of the cervical plexus, the several muscles are innervated directly by upper cervical nerve roots: C1 to C2: rectus capitis anterior/lateralis; C1 to C3/4/5: longus capitis; C2/3 to C4: trapezius (sensory)
There are numerous variants of cervical nerves and their derivatives that can present in a patient. Specifically, the cervical nerves that contribute to the cervical and brachial plexuses vary between individuals to a significant degree. Moreover, the terminal nerves that branch off the cervical and brachial plexuses may vary in contribution and location of origin.
Cervical nerve pathologies include radiculopathy, which is caused most commonly by impingement by spondylosis or disk herniation. This topic is covered in depth by the StatPearls article referenced here. Surgery should be a consideration if patients present with any neurological deficit as well as after confirming the ability to approach on MRI, prior surgeries, and any comorbid conditions.
The most common pathology associated with cervical nerves, radiculopathy, is caused most commonly by impingement by spondylosis or disk herniation. This topic is covered in depth by the StatPearls article referenced here. For more information on the specifics of brachial plexus injuries, as well as other cervical nerve-related pathologies, see the associated StatPearls articles.
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