Ansa cervicalis

The ansa cervicalis is a nerve loop located in the neck, formed by the union of two main roots: the superior root and the inferior root. It is a component of the cervical plexus and is primarily responsible for innervating the infrahyoid muscles, except for the thyrohyoid. This structure is situated superficially to the internal jugular vein within the carotid triangle.

Superior root

The superior root, also known as the descendens hypoglossi, consists of fibers originating from the C1 spinal nerve. These fibers initially travel with the hypoglossal nerve (cranial nerve XII) and later branch off to form the superior root of the ansa cervicalis. This branch innervates the superior belly of the omohyoid muscle as well as the upper portions of the sternohyoid and sternothyroid muscles. The superior root then descends in the neck and unites with the inferior root.

Inferior root

The inferior root, referred to as the descendens cervicalis, is composed of fibers from the C2 and C3 spinal nerves. These fibers descend through the neck to join with the superior root, completing the characteristic loop of the ansa cervicalis. The inferior root provides innervation to the inferior belly of the omohyoid muscle and the lower portions of the sternohyoid and sternothyroid muscles.