What anatomical structure is primarily involved in innervating the muscles of the neck?

The cervical plexus is the correct answer because it is a network of nerves formed by the anterior rami of the first four cervical spinal nerves (C1-C4). This plexus primarily innervates the muscles of the neck, including those involved in head movement and stabilization, such as the sternocleidomastoid and trapezius muscles. Additionally, the cervical plexus provides sensory innervation to the skin of the neck and portions of the head, contributing to both motor and sensory functions in that region.

In contrast, the brachial plexus arises from the lower cervical and upper thoracic nerves (C5-T1) and is primarily responsible for the innervation of the upper limb. The lumbar plexus, formed from the anterior rami of lumbar spinal nerves (L1-L4), mainly serves the lower abdominal wall and parts of the leg. The sacral plexus is made up of the anterior rami of the sacral spinal nerves (L4-S4) and primarily innervates the pelvis and the lower limb. Therefore, the cervical plexus is specifically tailored for neck muscle innervation, making it the correct choice in this context.