Splenius is often divided into two muscles, splenius capitus (those fibres which insert on the skull) and splenius cervicis (those that insert onto the cervical transverse processes of the spine).
Origin : Lower half of the ligamentum nuchae.
Spinous processes of C7-T5.
Insertion : Transverse processes of C3-7 Base of the skull.
Actions : Head and neck extension.
Contraction of one side laterally flexes and rotates the neck to the same side.
Innervation : Posterior rami of the lower cervical spinal nerves.
Lateral branches of the posterior rami of the middle and lower cervical spinal nerves.
Daily uses : Looking up at the ceiling.
Looking over your shoulder.
Example stretches : Lateral neck flexion stretch.