The ansa cervicalis (C1-C3) is a nerve loop which stems from the cervical plexus and innervates the three out of four infrahyoid neck muscles. It is usually located on the anterolateral aspect of the carotid sheath (or inserted into it), deep to the sternocleidomastoid muscle. The term ansa refers to any loop-shaped anatomical structure, as in Latin ansa means the handle of the cup.
The ansa cervicalis is formed by two roots, superior and inferior, which are formed by the fibers from the anterior rami of the cervical spinal nerves.
The superior root is in close anatomical relationship with the hypoglossal nerve (CN XII), which is why it has been thought for a long time that it emerges from the hypoglossal nerve itself. However, even after being confirmed that it does not, some authors still use an outdated synonym for this root “ansa hypoglossi”.
This article will explain the anatomy and function of the ansa cervicalis.
|Superior root (anterior rami of C1-C2)
Inferior root (anterior rami of C2-C3)
|Muscular branches to omohyoid, sternohyoid, sternothyroid
|3 /4 infrahyoid muscles: Omohyoid, sternohyoid, sternothyroid
Roots and location
The ansa cervicalis is formed by two roots which stem from the cervical plexus; superior and inferior.
The superior root is composed of the fibers from the anterior rami of spinal nerves C1 and C2. These fibers travel together with the hypoglossal nerve behind the posterior belly of the digastric muscle, after which they branch off of the hypoglossal nerve and continue as the superior root of the ansa cervicalis. Note that the root does not contain any fibers from the hypoglossal nerve. The superior root then curves downwards and travels along the anterior wall of the carotid sheath. During its path, it gives rise to the muscular branches to the superior belly of the omohyoid muscle, as well as to the upper halves of the sternothyroid and sternohyoid muscles. Then, it joins the inferior root to complete the ansa cervicalis.
The inferior root arises from the fibers of the anterior rami of spinal nerves C2 and C3. It crosses the anterolateral side of the internal jugular vein, giving rise to branches that supply the inferior belly of the omohyoid muscle, as well as the lower halves of the sternothyroid and sternohyoid muscles.
The ansa cervicalis supplies the three out of four infrahyoid muscles: omohyoid, sternothyroid and sternohyoid. The fourth muscle, the thyrohyoid, is instead innervated by the nerve to thyrohyoid which is a branch of the hypoglossal nerve.
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