Lying somewhat vertically in a groove along each side of the vertebral column, the erector spinae is a set of three long, overlapping muscle groups made up of the longissimus, the iliocostalis, and the spinalis, all interwoven with tendons. Originating close to the sacrum, it extends next to each of the cervical, lumbar, and thoracic spinal areas and goes all the way up into the base of the skull.
Instead of going into detail on each individual muscle of the erector spinae, we can look at the functions of each of its three muscle groups. The spinalis group extends, and together with iliocostalis, rotates the head. Also, longissimus and iliocostalis work together to extend the spine and bend it from side to side. Finally, these muscles get their control from the posterior branches of spinal nerves C2 to L3.