C3 Cervical Spinal Nerve: Function, Location & Muscle Control

C3 spinal nerve emerges above the C3 vertebra (between C2–C3), contributing to the cervical plexus (C1–C4).

Motor Functions

• Deep neck muscles: Longus capitis, longus colli, rectus capitis anterior/lateral – neck flexion, stabilization.
• Trapezius (accessory nerve CN XI, but C3/C4 proprioceptive input): Shoulder elevation, scapular retraction.
• Diaphragm (phrenic nerve C3–C5): C3 contributes significantly. "C3, 4, 5 keeps the diaphragm alive."

Sensory Functions

• Dermatome: Small area over lower occiput, upper neck, angle of jaw (supraclavicular fossa – C3/C4 overlap).
• Sclerotome: C3 facet joint, intervertebral disc, deep neck structures.

Clinical Correlates

• C3 radiculopathy: Rare. Neck pain radiating to suboccipital/auricular region; possible diaphragmatic weakness (dyspnea).
• Phrenic nerve injury: High cervical trauma, surgery (thyroid, carotid), brachial plexus block → hemidiaphragm paralysis.
• Cervical plexus block: Anesthesia for carotid endarterectomy, superficial neck procedures.

C3 is pivotal for diaphragmatic function and deep neck control.