The Anatomy of the Occipital Bone

The occipital bone is the trapezoid-shaped bone at the lower-back of the cranium (skull). The occipital bone houses the back part of the brain and is one of seven bones that come together to form the skull. It is located next to five of the cranium bones. 

As a person ages, their occipital bones will fuse to the other bones of their skull. Your sphenoid bone, which is located in the middle of your skull, will fuse with the occipital bone between the ages of 18 and 25. Then, between the ages of 26 and 40, the parietal bones at the top of your head and occipital bone will fuse together.

At the base of your skull there is a large oval opening in the occipital bone that is called the foramen magnum. This opening allows for passage of the spinal cord. The occipital bone is the only cranial bone to connect to the cervical spine. It has many important functions, but its most important role is in protecting your brain.

Anatomy

Like other bones in your skull, the occipital bone is flat, and it has many attachments and features, which is why it is often described in parts.

Foramen Magnum 

The foramen magnum is curved externally and hollow inside. It is the passageway of the central nervous system through the skull that connects the brain to the spinal cord.

The structures that pass through the foramen magnum are: 

• Brainstem, also called the medulla oblongata
• Spinal branch of your accessory nerve, the nerve that provides motor function to your neck, shoulders, and back
• Anterior and posterior spinal arteries
• Vertebral artery
• Spinal nerves

The foramen magnum is divided into four parts: one basilar part, two condylar parts, and a squamous part. All these four are part of the opening of the foramen magnum.  

Basilar Part

The basilar part is at the front of the foramen magnum and sits next to the dense area of the temporal bone of your skull surrounding the inner ear. Towards the front, the basilar part fuses to the sphenoid bone to form the tribasilar bone during puberty. The pharyngeal tubercle leading to the pharynx (airway) is found on the lower surface of the basilar part. 

Condylar Parts 

The two condylar parts are located adjacent to the foramen magnum. They are oval-shaped and connect to the first cervical vertebra. Next to them are the condylar canals where the condylar emissary veins connect the external vertebral venous plexuses to the sigmoid sinuses. The hypoglossal nerve (the 12th cranial nerve) spears through the condylar part of the occipital bone. 

Squamous Part 

The squamous part of the largest part of the occipital bone. It is situated above and behind the foramen magnum and curved downward on each side. There are two curved lines on each side: the highest nuchal line and the superior nuchal line. There is also a middle line running through the nuchal plane called the inferior nuchal line. The nuchal plane is rough and irregular to attach to several muscles, including the muscles of the head and neck. 

The internal surface of the squamous part is bowl-shaped and divided into four depressions of the cruciform eminence. The two upper depressions are triangular-shaped and embed the occipital lobes of the cerebrum, the largest part of the brain. The lower two depressions are rectangular and contain the hemispheres of the cerebellum, the part of the brain that receives information. 

Along this internal surface of the occipital bone, there is a point of intersection of the four divisions of the cruciform eminence. This point is called the internal occipital protuberance and runs from the superior angle of the bone to a deep grove, called the sagittal sulcus, which hides part of the superior sagittal sinus and is attached to the falx cerebri. The superior sagittal sinus allows blood to drain from the adjacent parts of the anterior hemisphere to the sinuses. At the upper part is the internal occipital crest, which houses the transverse sinuses. 

Function

The occipital bone has a variety of functions. The most important role it plays is in protecting your brain. Specifically, it protects the brain’s visual processing center. It also acts as the connecting pathway from the brain to the spine.

As the occipital bone connects with the first vertebra—the area called the atlas­—it forms the atlantooccipital joint. This junction helps you to nod and shake your head throughout the day. The atlas is also the direct link between the spine and skull.

Associated Conditions

When a person is born, their occipital bone is not completely hardened, and it takes up to six years for the hardening to fully complete. Any problems with the development of occipital bone can lead to health issues.  

For example, if the occipital bone is misaligned, this also causes misalignment of the spine, causing pain. 

When the occipital bone is functioning or moving incorrectly, a number of mental and physical health problems may develop. This may include: 

• Headaches, especially migraines
• Neck, shoulder, and back pain
• Balance and coordination problems
• Vision difficulties
• Lowered immune functioning
• Sensory processing disorders
• Nervous system problems

Treatment

As your brain’s protector, your occipital bone plays an important role in your overall health and life quality.  It is therefore important to investigate the cause of head and spine symptoms you may be experiencing, especially pain and problems with function and movement. Your doctor can recommend a variety of treatments, from medications to physical therapy and surgery.

Physical therapy can correct misalignment and help manage pain. It may also restore function and correct body movement.