- Overview
- Nerves C1 to C3
- Innervates four muscles
- Superior belly of the omohyoid muscle
- Inferior belly of omohyoid muscle
- Sternohyoid
- Sternothyroid
- Two roots
- Superior root (C1)
- Passes in fibers of the Hypoglossal Nerve
- Leaves it in the carotid triangle
- Passes around the occipital artery
- Innervates
- Superior belly of the omohyoid muscle
- Superior portion of the sternothyroid and the sternohyoid muscles
- Then unites with the inferior root of the ansa cervicalis.
- Passes in fibers of the Hypoglossal Nerve
- Inferior root (C2 and C3)
- Courses inferiorly on the outer aspect of the Internal jugular vein
- Then crosses roughly midway down this vessel to pass anterior to this vein.
- Then passes in an anterior direction to unite with the superior root of the ansa cervicalis anterior to the common carotid artery.
- Innervates
- All the infrahyoid (“strap”) muscles
- Except the thyrohyoid which is innervated by the first cervical nerve which accompanies the hypoglossal nerve for a short distance.
- Superior root (C1)
Ansa Cervicalis
- Lies on front of the IJV
- Gives branches to Infrahyoid muscles
- Embedded within anterior wall of Carotid Sheath and classified as one of its contents
- Formed by union of Superior and Inferior Roots
- Superior Root = Branch of Hypoglossal Nerve containing only C1 Fibres hitch-hiked along the Hypoglossal Nerve
- Runs down in front of Internal and Common Carotid Arteries
- Gives branch to Superior Belly of Omohyoid
- Inferior Root = Union of a branch each from C2 and C3 anterior Rami in the Cervical Plexus
- Spirals from behind around the IJV and runs down to join Superior Root in a wide loop over lower part of the IJV
- Gives branches to Infrahyoid muscles (Sternohyoid, Sternothyroid, Inferior Belly of Omohyoid)
- Sometimes inferior root passes forwards between IJV and Internal Carotid Artery
