Obliquus capitis inferior muscle

Origin and insertion

The obliquus capitis inferior muscle is the only muscle of the suboccipital group that does not insert onto the skull. Instead it spans the first and second cervical vertebra. Originating from the lateral surface of the spinous process of the axis (second cervical vertebra), obliquus capitis inferior passes in a superolateral direction to insert onto the posterior aspect of the transverse process of the atlas (first cervical vertebra).

Relations

Obliquus capitis inferior is located in the posterior region of the neck, lying deep to the semispinalis capitis muscle, splenius capitis muscle and the trapezius muscle. Together with rectus capitis posterior major and obliquus capitis superior muscles, it makes up a region in the neck called the suboccipital triangle.

Obliquus capitis inferior muscle forms the inferolateral border of this triangle. 

Innervation

Just like all four muscles of the suboccipital group, obliquus capitis inferior is innervated by the posterior ramus of the spinal nerve C1, the suboccipital nerve. 

Blood supply

Blood supply comes from the vertebral artery and deep descending branches of the occipital artery (a branch of the external carotid artery), while it gets drained by the vertebral vein.

Function

Bilateral contraction of obliquus capitis inferior causes head extension, at the atlantoaxial joint. While unilateral contraction produces rotation of the head towards the ipsilateral side.

Note that due to the oblique angle of its muscle fibers, this muscle is a strong rotator of the neck. Obliquus capitis inferior muscle also plays an important postural role; it works alongside the other suboccipital muscles to stabilize the atlantoaxial joint, and thus the position of the head, during other body movements (such as standing up from a sitting position). 

Expand your knowledge with our learning materials about the muscles of the back.