The posterior atlantooccipital membrane (posterior atlantooccipital ligament) is a broad but thin membrane extending between the posterior margin of the

foramen magnum The foramen magnum () is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblongata, passes thro ...

above, and

posterior arch In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine and is located in the neck. The bone is named for Atlas of Greek mythology, just as Atlas bore the weight of the heavens, the first cervical vertebra suppor ...

of atlas (first cervical vertebra) below. It forms the floor of the

suboccipital triangle The suboccipital triangle is a region of the neck bounded by the following three muscles of the suboccipital group of muscles: * Rectus capitis posterior major - above and medially * Obliquus capitis superior - above and laterally * Obliquus capit ...

. The membrane helps limit excessive movement of the atlanto-occipital joints.

Anatomy

Attachments

The superior attachment of the membrane at the posterior margin of the

, and its inferior attachment is at the superior margin of the

of atlas (cervical vertebra C1). The membrane additionally attaches posteriorly (by a soft tissue bridge which may contain muscle or tendon fibres) to the recti capitis posteriores minores mucles, and anteriorly to the dura mater.

Innervation

The membrane is innervated by the spinal nerve C1.

Relations

At either lateral extremity, the membrane is pierced by the

vertebral artery The vertebral arteries are major artery, arteries of the neck. Typically, the vertebral arteries originate from the subclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, m ...

and cervical spinal nerve C1. The free border of the membrane arches over the artery and nerve, and is sometimes

ossified Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in t ...

(converting the passage for the vertebral artery into a foramen). Laterally, the membrane blends with the

articular capsules In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint. It is superficial/anterior to the dura mater of the

spinal canal In human anatomy, the spinal canal, vertebral canal or spinal cavity is an elongated body cavity enclosed within the dorsal bony arches of the vertebral column, which contains the spinal cord, spinal roots and dorsal root ganglia. It is a pro ...

(onto which it attaches). The membrane overlies the grooves for vertebral arteries, vertebral venous plexuses, and cervical spinal nerves C1. The membrane forms the floor of the

. It is deep to the recti capitis posteriores minores mucles (which attach onto the membrane), and the obliqui capitis superiores muscles.

Clinical significance

The membrane may be pierced with a needle at the midline superior to the arch of atlas to access the

cisterna magna The cisterna magna (posterior cerebellomedullary cistern, or cerebellomedullary cistern) is the largest of the subarachnoid cisterns. It occupies the space created by the angle between the caudal/inferior surface of the cerebellum, and the dorsa ...

Research

In 2015, Scali et al. revisited the anatomy of the posterior atlantooccipital membrane via

plastination Plastination is a technique or process used in anatomy to preserve bodies or body parts, first developed by Gunther von Hagens in 1977. The water and fat are replaced by certain plastics, yielding specimens that can be touched, do not smell or ...

. Their findings revealed that the PAO membrane superiorly consisted of periosteum of the occiput, whereas inferiorly it formed part of the dura at the cerebrospinal junction, terminating at the level of the third cervical vertebra (rather than attaching to the posterior arch of the atlas). It is believed that this anatomical arrangement permits a superiorly located anchor point for epidural bridging structures and allows dural tensile forces to act in a summated synchronized manner. The author's hypothesize that this complex area assists with outflow of

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless Extracellular fluid#Transcellular fluid, transcellular body fluid found within the meninges, meningeal tissue that surrounds the vertebrate brain and spinal cord, and in the ventricular system, ven ...

Additional images

File:Gray308.png, Median sagittal section through the occipital bone and first three cervical vertebræ.

References

Human head and neck {{musculoskeletal-stub