Erector Spinae

(iliocostalis, longissimus, and spinalis)

Origin = Ligamentum nuchae; posterior portions of cervical, thoracic, and lumbar spine; lower nine ribs; iliac crest; and posterior sacrum.

Insertion = mastoid process of temporal bone; posterior portions of cervical, thoracic, and lumbar vertebrae; angles and adjacent portions of the twelve ribs.

Action =

One side - Lateral flexion of spine and rotation to the same side.

Both Sides - Extension and hyperextension of atlantooccipital joint and entire spine.