The C1-C2 myotome covers the deep muscles that bend and nod the head on the upper neck. The C1 root is mainly motor, supplying the small suboccipital and prevertebral muscles. These levels are tested together as neck flexion.
| Nerve root | C1-C2 |
|---|---|
| Area | Neck flexion (chin toward chest); extension can also be checked |
| How to test | The seated patient tucks the chin and flexes the neck while the examiner resists with a hand on the forehead, and can then extend against a hand behind the head. Strength is graded 0-5 on the Medical Research Council scale and compared side to side. |
| Muscles | |
| Nerve Supply | Cervical plexus (ventral rami of C1-C2); Suboccipital nerve (dorsal ramus of C1); Greater occipital nerve (dorsal ramus of C2) |
Flexes, extends and stabilises the head on the upper cervical spine, producing nodding movements.
Weakness of neck flexion is uncommon in isolated root problems and more often reflects a neuromuscular disease such as myasthenia gravis or myositis. In trauma, any injury at this level is life threatening because the breathing centres and the C3-C5 phrenic outflow lie just below. Myotome charts vary slightly between sources, and most muscles receive more than one root, so a single root lesion usually weakens rather than paralyses.
Injury at C1-C2, such as from a high cervical fracture, can cause loss of all limb function and breathing, needing ventilation.
Abnormal movement between C1 and C2, seen in rheumatoid arthritis and Down syndrome, can compress the cord and upper roots.
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