Final answer:
The cervical plexus consists of spinal nerves C1-C5, mainly providing muscular branches to the muscles in the posterior neck and head, including the phrenic nerve which innervates the diaphragm.
Step-by-step explanation:
The cervical plexus is composed of axons from spinal nerves C1 through C5 and has muscular branches that mainly innervate the muscles in the posterior neck and head. Notably, it also includes the phrenic nerve, which is crucial for breathing as it innervates the diaphragm. The cervical plexus, along with the brachial, lumbar, and sacral plexuses, constitute the major nerve networks that supply the limbs and other body regions with systemic nerves arising from the spinal cord.
The brachial plexus, associated with lower cervical and upper thoracic spinal nerves, supplies nerves to the arm. The large nerves arising from this plexus include the radial, axillary, ulnar, and median nerves. Conversely, the lumbar plexus gives rise to nerves that enervate the pelvic region and anterior leg, and the sacral plexus predominantly supplies the posterior leg with systemic nerves like the sciatic nerve, which is known to be associated with sciatica.