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Cervical spinal nerve 1 (C1)

The Cervical spinal nerve 1 (C1), also known as the first cervical nerve, is the most superior spinal nerve in the human body. Emerging from the spinal cord above the first cervical vertebra (atlas), the C1 nerve plays a critical role in innervating key neck muscles and contributing to the upper cervical plexus. Despite its small size and lack of a significant cutaneous sensory component, C1 is essential for motor control of several muscles in the suboccipital and upper cervical region. Its precise visualization on imaging modalities such as MRI and CT is crucial in assessing upper cervical spine pathologies.

Synonyms:

  • First cervical nerve

  • C1 nerve

  • Suboccipital nerve (motor branch)

  • N. suboccipitalis (Latin)

  • First cervical spinal nerve

Function:

  • Primarily motor innervation; minimal to no sensory component

  • Innervates the following muscles:

    • Rectus capitis anterior and lateralis

    • Rectus capitis posterior major and minor

    • Obliquus capitis superior and inferior

    • Partially contributes to the geniohyoid and thyrohyoid muscles (via hypoglossal nerve fibers)

  • Contributes to the cervical plexus

  • Provides motor control for fine head and neck movements, particularly suboccipital muscles

  • Plays a role in proprioception (awareness of head position)

MRI Appearance:

T1-weighted images:

  • C1 nerve appears as a small, low-to-intermediate signal intensity linear structure

  • Typically difficult to distinguish from surrounding soft tissue

  • Best identified at the lateral margin of the spinal canal above the atlas

T2-weighted images:

  • C1 nerve shows intermediate  signal compared to surrounding muscles

  • Cerebrospinal fluid (CSF) provides a high-signal background for contrast

  • Better visualization than T1, but still subtle

STIR (Short Tau Inversion Recovery):

  • The C1 nerve may be more conspicuous due to fat suppression

  • Appears as a low signal structure against a suppressed fatty background

  • Useful in detecting nerve edema or pathology, though normal C1 nerve is difficult to see unless enlarged or affected

CT Appearance:

  • Direct visualization of the C1 nerve is limited on standard CT

  • CT is primarily useful for bony anatomy and assessing foraminal narrowing or compressive lesions rather than nerve detail

  • C1 nerve root can sometimes be inferred by its relationship to the C1 vertebra and neural foramen

MRI images

Cervical spinal nerve 1 (C1) MRI axial t2 image