Corpus: Deep ansa cervicalis

The deep ansa cervicalis is a nerve loop formed by the superior root (radix superior) of segments C1 and C2 and the inferior root (radix inferior) of segments C2 and C3 of the cerviacal plexus.

The deep ansa cervicalis innervates the entire infrahyoid musculature through its nerve branches, which include:

• thyrohyoid muscle
• sternohyoid muscle
• sternothyroid muscle
• omohyoid muscle

Some fibers of the superior root reach the thyrohyoid muscle via the hypoglossal nerve as the thyrohyoid ramus.

The only suprahyoid muscle supplied by the deep ansa cervicalis is the geniohyoid muscle, which receives its innervation from the superior root.

The deep ansa cervicalis is located beneath the sternocleidomastoid muscle and crosses the internal jugular vein and the anterior scalene muscle during its course.

In the carotid triangle (trigonum caroticum), fibers of the superior root run a short distance with the hypoglossal nerve as the descendent branch of the hypoglossal nerve but do not exchange fibers with it ("ansa hypoglossi").

The fibers of the inferior root run medially along the side of the phrenic nerve as the descending cervical nerve. The superior and inferior roots converge below the intermediate tendon of the omohyoid muscle to form the deep ansa cervicalis.

The superficial ansa cervicalis lies on the sternocleidomastoid muscle and beneath the platysma.