Final answer:
All deep (medial and lateral) branches of the Cervical Plexus are motor branches that innervate muscles in the neck and head, including the phrenic nerve that serves the diaphragm.
Step-by-step explanation:
The cervical plexus is comprised of axons from spinal nerves C1 through C5, which innervate the posterior neck and the head, and includes the phrenic nerve that connects to the diaphragm at the base of the thoracic cavity. The deep branches of the cervical plexus are motor in function, involved in the movement and support of muscles in those regions. In addition to the cervical plexus, the brachial plexus is associated with the lower cervical spinal nerves and first thoracic spinal nerve (C4 through T1), which innervate the arms. The lumbar and sacral plexuses serve the lower limbs, with the significant systemic nerve from the sacral plexus being the sciatic nerve, which can be associated with sciatica.