Ansa Cervicalis

The ansa cervicalis (or ansa hypoglossi in older literature) is a loop of nerves that are part of the cervical plexus. It lies superficial to the internal jugular vein in the carotid triangle. Branches from the ansa cervicalis innervate most of the infrahyoid muscles, including the sternothyroid muscle, sternohyoid muscle and the omohyoid muscle. Note that the thyrohyoid muscle, which is also an infrahyoid muscle and the geniohyoid muscle which is a suprahyoid muscle are innervated by cervical spinal nerve 1 via the hypoglossal nerve.

The cervical plexus is formed by the ventral rami of the upper four cervical nerves and the upper part of fifth cervical ventral ramus. the network of rami is located deep to the sternocleidomastoid within the neck. the cervical plexus innervates muscles of the neck and areas of skin on the head, neck and chest. the deep branches innervate muscles, while the superficial branches supply areas of skin. a long branch (primarily of fibers of c4 and with contributions of fibers from c3 and c5; nervus phrenicus) innervates muscles of the diaphragm. the cervical plexus also communicates with the cranial nerves vagus nerve and hypoglossal nerve.