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.
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.
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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