Quick Facts
Origin: Formed by the union of anterior and posterior roots emerging from the C1 spinal cord segment.
Course: Travels laterally for a short distance to the bifurcation of anterior and posterior rami.
Branches: Anterior and posterior (suboccipital) rami.
Supply: Motor innervation to the geniohyoid, infrahyoid, and prevertebral muscles and the muscles bordering the suboccipital triangle. Sensory innervation from the meninges and atlantooccipital joint to the spinal cord.
Origin
The first cervical nerve is a mixed nerve, formed by the union of its posterior root (sensory nerve fibers) with its anterior root (which motor nerve fibers). The roots emerge from the posterolateral and anterolateral sulci of the C1 spinal segment and unite to form the first cervical nerve.
Course
The first cervical nerve exits the vertebral column through an opening situated between the first cervical vertebra (atlas) below and the occipital bone above. It travels laterally a short distance until its bifurcation into anterior and posterior (or suboccipital) rami.
Branches
The first cervical nerve divides into posterior (dorsal) and anterior (ventral) rami, both of which receive sensory and motor fibers.
The anterior ramus of the first cervical nerve passes anteriorly and contributes to the formation of the cervical plexus (along with the anterior rami of the second to fourth cervical nerves). It also sends a communicating branch to the hypoglossal nerve.
The posterior ramus, otherwise known as the suboccipital nerve, passes posteriorly to emerge superior to the posterior arch of atlas and enters the suboccipital triangle to innervate the muscles in that region. It also gives several communicating branches to the posterior ramus of the second cervical nerve, greater and lesser occipital nerves, and accessory nerve.
Supplied Structures
The anterior ramus of the first cervical nerve conveys motor fibers to the cervical plexus, thus innervating the infrahyoid muscles (sternohyoid, sternothyroid and superior belly of omohyoid) via the ansa cervicalis, while the thyrohyoid and geniohyoid muscles are innervated through fibers that join the hypoglossal nerve. Other muscles innervated include the anterior prevertebral muscles, including rectus capitis anterior and lateralis and longus capitis muscles.
The posterior ramus, or suboccipital nerve innervates muscles of the suboccipital triangle (rectus capitis posterior major and minor, obliquus capitis superior and inferior) and semispinalis capitis.
Small filaments from the meninges and the atlantooccipital joint join the suboccipital nerve (or the posterior ramus) which conveys sensory information to the first cervical nerve and its posterior root (Ouaknine & Nathan, 1973).
References
Ouaknine, G. & Nathan, H. (1973) Anastomotic connections between the eleventh nerve and the posterior root of the first cervical nerve in humans. J Neurosurg, 38(2), 189-97.
