Ansa cervicalis

The ansa cervicalis (or ansa hypoglossi in older literature) is a loop formed by muscular branches of the cervical plexus formed by branches of cervical spinal nerves C1-C3. The ansa cervicalis has two roots - a superior root (formed by branch of C1) and an inferior root (formed by union of branches of C2 and C3) - that unite distally, forming a loop. It is situated within the carotid sheath.[1]: 334 

Ansa cervicalis
Ansa cervicalis. Superior root labeled as "descending hypoglossal," Inferior root labeled as "descending cervical."
Details
Innervatessternohyoid muscle,
sternothyroid muscle,
omohyoid muscle
Identifiers
Latinansa cervicalis,
ansa hypoglossi
TA98A14.2.02.013
TA26376
FMA55142
Anatomical terms of neuroanatomy

Branches of the ansa cervicalis innervate three of the four infrahyoid muscles: the sternothyroid, sternohyoid, and omohyoid muscles (note that the thyrohyoid muscle is the one infrahyoid muscle not innervated by the ansa cervicalis - it is instead innervated by cervical spinal nerve 1 via a separate thyrohyoid branch[2]: 582, 600 ).

Its name means "handle of the neck" in Latin.

Anatomy

The ansa cervicalis is typically embedded within the anterior wall of the carotid sheath anterior to the internal jugular vein.[1]: 344 

Superior root
Ansa cervicalis

The superior root of the ansa cervicalis (formerly known as descendens hypoglossi[1]: 500 ) is by fibres of the cervical spinal nerve 1 [1]: 344 [3] (and, according to some sources, of cervical spinal nerve 2 as well[3]) that have joined and run with the hypoglossal nerve (CN XII) for some distance before[1]: 344  progressively[1]: 369  branching off the CN XII in the carotid triangle to form the superior root.[1]: 344 

The superior root is situated within the carotid triangle.[1]: 344  It passes anterior-ward between the internal carotid artery and the common carotid artery.[1]: 500  It curves around the occipital artery before descending upon the anterior aspect of the internal carotid artery and the common carotid artery.[1]: 344  on the carotid sheath. It issues a branch to the superior belly of the omohyoid muscle,[1]: 344  and the upper parts of the sternothyroid and sternohyoid muscles before uniting with the inferior root.

Inferior root

The inferior root of the ansa cervicalis (formerly known as descendens cervicalis[1]: 500 ) is formed by the union of fibers of the anterior rami spinal cervical nerves C2-C3 that unite as part of the cervical plexus.[1]: 344 

The inferior root curves posteroanteriorly around[1]: 344  the lateral side of the internal jugular vein[1]: 343  before descending to unite with the superior root upon the (inferior portion of) the internal jugular vein. It may occasionally pass anterior in between the internal jugular vein and the internal carotid artery.[1]: 344 

Branches

Branches to the sternothyroid muscle, sternohyoid muscle, and inferior belly of the omohyoid muscle issue from the loop of the ansa cervicalis, whereas the branch for the superior belly of the omohyoid muscle arises from the superior root.[1]: 344 

Additional images
  • Cervical plexus shown in purple
    Cervical plexus shown in purple
  • Plan of the cervical plexus.
    Plan of the cervical plexus.
  • The right brachial plexus with its short branches, viewed from in front.
    The right brachial plexus with its short branches, viewed from in front.
  • Cervical plexus
    Cervical plexus
  • Muscles, arteries and nerves of neck.Newborn dissection.
    Muscles, arteries and nerves of neck.Newborn dissection.

References
  1. Sinnatamby, Chummy S. (2011). Last's Anatomy (12th ed.). Elsevier Australia. ISBN 978-0-7295-3752-0.
  2. Standring, Susan (2020). Gray's Anatomy: The Anatomical Basis of Clinical Practice (42th ed.). New York. ISBN 978-0-7020-7707-4. OCLC 1201341621.{{cite book}}: CS1 maint: location missing publisher (link)
  3. Moore, Keith L.; Dalley, Arthur F.; Agur, Anne M. R. (2018). Clinically Oriented Anatomy (8th ed.). Wolters Kluwer. p. 1005. ISBN 978-1-4963-4721-3.
  • "Ansa cervicalis." Stedman's Medical Dictionary, 27th ed. (2000). ISBN 0-683-40007-X
  • Gray's Anatomy: The Anatomical Basis of Clinical Practice. (2005). ISBN 0-443-07168-3
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