What muscles are involved in cervical extension?

Cervical extension primarily involves the muscles located in the posterior cervical region, which work to extend the neck when the head is tilted back. The splenius cervicis is specifically responsible for extending and rotating the neck. It is positioned in the back of the neck and helps to pull the head backward when it contracts.

Additionally, the iliocostalis, which is part of the erector spinae group, contributes to extension of the neck when its cervical portion is activated. Together, these muscles provide the necessary force and stability to extend the cervical spine efficiently.

The other options listed do not directly relate to cervical extension. The sternocleidomastoid and scalenes, for example, are more engaged during flexion and lateral movement of the neck rather than extension. Muscles like the quadratus lumborum and psoas major are primarily involved in lumbar spine movements and do not play a role in cervical actions. Moreover, the rhomboids and serratus anterior are responsible for the movement of the scapula and have no direct function in cervical spine extension. Thus, the correct choice highlights the key muscles involved in the extension of the cervical spine.