Corpus: Deep cervical ansa

The deep cervical ansa is a nerve loop formed by a superior root originating from the C1 and C2 segments, and an inferior root originating from the C2 and C3 segments of the cervical plexus.

The deep cervical ansa provides motor innervation to the entire infrahyoid musculature through its nerve branches, which include:

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

Some fibers from the superior root (radix superior) reach the thyrohyoid muscle via the hypoglossal nerve, forming the thyrohyoid branch (ramus thyrohyoideus). Additionally, the superior root is the only pathway that supplies the geniohyoid muscle, a suprahyoid muscle.

The deep cervical ansa is located beneath the sternocleidomastoid muscle, crossing both the internal jugular vein and the anterior scalene muscle along its course.

In the carotid triangle (trigonum caroticum), fibers from the superior root run a short distance with the hypoglossal nerve as the "ramus descendens nervi hypoglossi," although they do not exchange fibers with it, despite being referred to as the "ansa hypoglossi."

The fibers of the inferior root (radix inferior) run medially alongside the phrenic nerve as the descending cervical nerve. The superior and inferior roots join together below the intermediate tendon of the omohyoid muscle to form the cervical loop (ansa cervicalis).

The superficial cervical ansa, in contrast, lies on the sternocleidomastoid muscle, just beneath the platysma.