Final answer:
The semispinalis capitis inserts at the mastoid process and the occipital bone, while the longissimus cervicis is responsible for cervical extension.
Step-by-step explanation:
The semispinalis capitis has its insertion at the mastoid process of the temporal bone and the occipital bone. It is a muscle that spans the upper part of the vertebral column to the base of the skull, aiding in extension, rotation, and lateral flexion of the head.
The longissimus cervicis, a muscle of the longissimus group associated with the cervical region of the spine, is responsible for cervical extension action. This function contributes to the erect posture of the head and neck, as well as to the range of motion necessary for these parts of the body.