Cervical Plexus: Motor Innervation of Neck, Shoulder, and Diaphragm

The cervical plexus (C1–C4 ventral rami) is primarily a motor plexus. Key branches:

• Ansa cervicalis (C1–C3) → infrahyoid strap muscles.
• Phrenic nerve (C3–C5) → diaphragm (sole motor supply).
• Segmental branches → prevertebral, lateral vertebral, scalene, levator scapulae, trapezius (C3–C4).
• Cutaneous branches (lesser occipital, great auricular, transverse cervical, supraclavicular) provide sensory innervation to neck, ear, shoulder.

Thus, the plexus controls motor function of neck stabilizers and the diaphragm, while its sensory distribution is limited to the skin of the neck and superior shoulder.