Anatomy
The C1 nerve route is formed by the union of the interior and posterior roots emerging at the first spinal cord segment. The nerve route travels a short distance over the C1 arch before it bifurcates Into the interior and posterior Rami.
C1 exit the vertebral column between C1 and the occiput. Divides into posterior and inferior Rami both of which receive Sensory and motor fibers.
The anterior ramus of the C1 nerve route travels entirely and contributes to the formation of the cervical plexus with other contributions coming from the 2nd to 4th cervical nerves. The anterior ramus of C1 also has communicating branches was the hypoglossal nerve. It innervates the infrahyoid muscles via the ansa cervicalis as well as the prevertebral muscles like the rectus capitalist anterior and the longus capitis muscles.
The posterior ramus is known as the suboccipital nerve it passes posteriorly superior to the posterior arch of the atlas and in the suboccipital region and innervates the muscles of that area (rectus capitis posterior major, rectus capitis posterior minor, obliquus capitis superior, obliquus capitis inferior). It also gives communicating branches to the posterior ramus of C2 the greater and lesser occipital nerves and the accessory nerve.
The posterior ramus also provide sensory innervation from the meninges and the atlantooccipital joint. The posterior ramus has no named branches but multiple anastomotic connections as listed above.
Pathology
Isolated C1 compression is uncommon. These typically presents with headache, particularly occipital neuralgia.