The superficial branches are the lesser (minor) occipital, great auricular, transverse (cutaneous) cervical, and supraclavicular nerves.
The lesser occipital nerve (C2, C3) curves around the accessory (XI) nerve, ascends near the posterior border of the sternocleidomastoid muscle, and divides into branches that supply the skin on the superolateral aspects of the neck, the upper part of the auricle, and the adjacent area of the scalp.
The great auricular nerve (C2, C3) is larger than the lesser occipital and passes obliquely upward over the sternocleidomastoid muscle, lying near the external jugular vein before dividing into anterior and posterior branches. The former passes over or through the parotid gland to supply the skin of the posteroinferior part of the face. The latter supplies the skin over the mastoid process and over the medial and lateral surfaces of the lower part of the auricle.
The transverse cervical nerve (C2, C3) runs forward beneath the external jugular vein to divide into superior and inferior branches, which supply the skin over the anterolateral aspects of the neck from the mandible above to the sternum below.
The supraclavicular nerves (C3, C4) arise from a common trunk, which descends for a variable distance before dividing into medial, intermediate, and lateral supraclavicular nerves. These supply the skin over the lower neck from near the midline to the acromioclavicular region and above the shoulder. They then pass in front of the clavicle to innervate the skin of the anterior chest wall to the level of the sternal angle and the second rib. The medial and lateral nerves, respectively, send twigs to the sternoclavicular and acromioclavicular joints.
The deep branches are mainly motor, but they also carry proprioceptive, osseous, articular, and autonomic fibers to and from muscles, bones, joints, and vessels in their areas of distribution. Some motor branches pass medially to supply the rectus capitis anterior and rectus capitis lateralis (C1, C2), longus capitis (CI, C2, C3), longus colli and intertransverse (C2, C3, C4) muscles, and the diaphragm through the phrenic nerve. Other muscular branches pass laterally to the sternocleidomastoid (C2, C3), trapezius (C3, C4), levator scapulae (C3, C4), and scalenus anterior and scalenus medius (C3, C4) muscles; the branches to the sternocleidomastoid and trapezius muscles are reputedly proprioceptive, but they nevertheless communicate with motor branches of the accessory nerve to these muscles.
A branch from the loop between C1 and C2 joins the hypoglossal (XII) nerve. Some of these fibers continue onward, along with the hypoglossal nerve, to supply the thyrohyoid and geniohyoid muscles, whereas others leave it as a filament running downward, anterolateral to the carotid sheath, the superior root (descendens hypoglossi) of the ansa cervicalis, or ansa hypoglossi. The ansa (“loop”) is completed by the inferior root (descendens cervicalis) derived from C2 and C3. Branches from the ansa supply the sternohyoid, sternothyroid, and omohyoid muscles.