Final answer:
The regions innervated via the cervical plexus include the posterior head, neck, and diaphragm.
Step-by-step explanation:
The regions of the body that are innervated via the cervical plexus include the posterior head, neck, and the diaphragm. The cervical plexus is composed of axons from spinal nerves C1 through C5. It also includes the phrenic nerve, which connects to the diaphragm at the base of the thoracic cavity.