Topics

Topic

design image
Cervical spinal nerve 4 (C4)

The cervical spinal nerve 4 (C4) is the fourth pair of cervical nerves emerging from the spinal cord at the C3-C4 intervertebral foramen. It plays a critical role in motor and sensory innervation to the neck, shoulders, and upper thoracic region. C4 is especially significant in the cervical plexus and is involved in the innervation of the diaphragm via the phrenic nerve, making it vital for respiration. Accurate knowledge of the C4 nerve is essential for clinical assessment, radiological interpretation, and understanding cervical spine pathology.

Synonyms

  • C4 nerve

  • Fourth cervical spinal nerve

  • Cervical nerve C4

  • Nerve root C4

Function

  • Provides motor innervation to certain neck and shoulder muscles (e.g., levator scapulae, trapezius via cervical plexus)

  • Supplies sensory fibers to the skin over the lower neck and upper shoulder

  • Major contributor to the phrenic nerve (C3–C5), which innervates the diaphragm and supports breathing

  • Assists in proprioception of cervical musculature

MRI Appearance

  • T1-Weighted Imaging:

    • C4 nerve root appears isointense to slightly hypointense compared to the surrounding muscle

    • Clearly visible in the neural foramen, best appreciated on sagittal and axial planes

  • T2-Weighted Imaging:

    • Nerve root is intermediate relative to muscle

    • Perineural cerebrospinal fluid (CSF) provides contrast, highlighting the nerve root

  • STIR Sequence:

    • C4 nerve root demonstrates low-to-intermediate signal

    • Edematous or inflamed nerve appears hyperintense, indicating pathology (e.g., nerve root compression or neuritis)

CT Appearance

  • C4 nerve root itself is not directly visualized due to limited soft tissue contrast

MRI images

Cervical spinal nerve 4 (C4) MRI axial t2 image