ANSA CERVICALIS:
Netter Plate Number: 27 (and 26)

Ansa cervicalis innervates 3 out of 4 of the strap muscles, including the omohyoid, the sternohyoid, and the sternothyroid muscles. This nerve arises from a small loop between C1 and C2 to join fibers of the hypoglossal nerve for a few centimeters to descend in front of the internal and common carotid arteries as the superior root. This nerve loops to the inferior root of the ansa (formed by C2 and C3) which descends posterior to the carotid sheath, winding laterally to join the superior root either lateral to the internal jugular vein or between it and the common carotid artery.
Of note, some nerve fibers from C2, also travelling with the hypoglossal nerve continue to travel with this nerve after the superior root branches off to innervate the thyrohyoid and geniohyoid muscles.
This nerve is not generally considered clinically significant and is commonly taken during surgical procedures for access purposes.

The transverse cervical nerve as shown here winds around the lateral border of the SCM to divide into the superior and inferior branches to travel through the platysma (but does not innervate it) to supply the subcutaneous tissue and skin of the anterior triangle of the neck from the mandible to the sternum.

The great auricular nerve appears in the posterior triangle at the lateral border of the SCM to cross toward the angle of the mandible. This nerve divides into the mastoid branch supplying skin over mastoid process, the auricular branch which supply the inferior portion of the auricle and the facial branch to supply the skin over the parotid gland and angle of the mandible.

The lesser occipital nerve also found at Erb's point travels superiorly along the posterior border to supply the skin and subcutaneous tissue of the scalp behind and above the ear.