The shape of the face and the base of the skull are intimately connected and grow together. Each has an equal impact on the development of the other. Together they also affect the shape of the cranial vault, as mentioned above. Consequently, they also affect the tendency to develop cerebellar tonsillar ectopia.
In contrast to the face and base, the cover over the cranial vault of the brain grows from connective tissues that are actually part of the outer membrane of the brain. The cranial vault thus develops along with the brain as the infant brain matures. Nonetheless, the layout of the cranial vault is affected by race as much as the face and the base of the skull. Among other things these factors influence the layout and pitch of the veins inside the brain. The layout of the cranial vault also affects the compartments of the brain and openings in the skull for the passage of nerves and blood vessels.
Although all people have roughly the same number of nerve cells in the brain regardless of whether they have big heads or small heads, how they fit eveything in the cranial vault varies between races, genders and individuals. Some people have large structures and some have smaller compact sizes. Some people have undersized spaces, called hypoplasia. Hypoplasia of the posterior fossa can cause cerebellar tonsillar ectopia.
Asians have the largest cranial capacity of the three races. The base of the skull also inclines upward due to natural head position or inclination, which is affected by upright posture and the face. As a result of the shape of their face and inclined base of the skull, Asians have tall towers that rise straight up over the hole in the base of the skull, called the foramen magnum, making them susceptible to cerebellar tonsillar ectopia. The tall tower also tends to stack the brain up higher in the vault and raises the center of gravity. On the other hand, the design of the in-line face makes Asian skulls more balanced on top of the cervical spine. It has been my experience that Asian males have less bossing at the external occipital protuberance (the knowlege bone). This is probably due to better balance and less strain on the ligamentum nuchae that helps hold the head upright. If anything, Asians tend to tip back slightly.
Europeans have a slightly smaller cranial vault compared to Asians and the face juts out prominently from the rest of the skull. This makes European faces heavy, which increases the strain on the ligamentum nuchae at the back of the skull, which causes bossing commonly called the knowledge bone. The base of the skull tends to incline upward similar to Asians. Thus Europeans tend to have tall towers similar to Asians, which, likewise, raises the center of gravity. The face is somewhat tighter in Europeans compared to Asians and Africans who have comparatively wider cheek bones and rounder nasal openings. More importantly, according to a fairly recent orthodontic study done in the UK, Europeans, also tend to have the shortest length in the base of the skull. The smaller size crams the brainstem and cerebellum in the posterior fossa compared to Asians and Africans. Moreover, the combination of a tall tower, a protruding face and a short base of the skull may further predispose European designs to problems due to whiplash injuries as well as inversion flows in the veins of the brain. It certainly predisposes them to cerebellar tonsillar ectopia. This will discussed further below.
Compared to Asians and Europeans, African skull designs have slightly smaller cranial vaults overall predisposing them to cerebellar tonsillar ectopia. On the other hand, they have a longer base compared to Europeans that is closer to Asian designs. This effectively increases the size of the posterior fossa, compared to European designs. Although on the surface, African faces appear rounder, more like Asians, the design of the African face is technically called brachycephalic. Brachycephalic means the face is more square or similar in height and width. Africans also have deeper faces measuring from the furthest point on the front of the face at the tip of the jaw to the furthest points in the back of the face behind the eyeballs and back of the mouth. The inclination of the base of the skull is also closer to level compared to Asians and Europeans.
The African skull design lowers the forehead and creates wider cheeks and arches for the teeth. Consequently, in contrast to a top heavy, ableit balanced tall tower seen in Asians, or tall tower with an imbalanced protruding face seen in European designs, African cranial vaults are lower and spread out. In contrast to Asian and European designs, this lowers the center of gravity making it more like a sports car in whiplash injuries and other types of truama that cause venous inversion flows into the brain.
Of the three designs the European skull may be more susceptible to inversion flows due to their cranial vault design, especially the posterior fossa and dural sinuses. On the other hand, all the races are susceptible to cerebellar tonsillar ectopia due to the design of the bent base of the skull, and females are more susceptible than males regardless of race. In this regard, cerebellar tonsillar ectopia may also play a role in optic neurtis and transverse myelitis and will be discussed further as this site develops.
In brief, while possibly playing a role buffering the negative impact of inversion flows into the brain during whiplash type injuries the tall tower design of the Asian and the compact design of the African cranial vault may actually increase their susceptibility to optic neuritis and transverse myelitis due to cerebellar tonsillar ectopia and displacement of the brain within the cranial vault.
The design of the cranial vault due to upright posture predisposes humans to neurodegenerative diseases such as Alzheimer’s, Parkinson’s and multiple sclerosis. There are many different types of inherited (genetic) disorders in the design of the cranial vault and of the base of the skull that can cause problems such as craniosynostosis and craniodysostosis and predispose individuals to cerebellar tonsillar ectopia.
The upper cervical spine is closely connected to the base of the skull and parts of it grow from the same primitive musculoskeltal tissue in the embryo. In addition to the cranial vault, there are many types of upper cervical problems that can cause problems with blood and CSF flow and subsequent neurodegenerative diseases. Some are inherited as design problems such Kleppel-Feil and fusion of the upper cervical vertebra of C1 and C2 to each other or to the base of the skull. Other conditons are acquired from aging, injuries and diseases such as rheumatoid arthritis. I refer to them colletively as craniocervical syndromes. Craniocervical syndromes can affect blood and CSF flow in the brain and cord.
The design of the cranial vault affects the spatial orientation of the brain, as well as the length, pitch and layout of the dural sinuses of the brain. It may play a role in optic neuritis and other cranial nerve signs. It may also play a role in the response of the brain to venous backjets and the formation of MS lesions. Upright cine MRI, brain scans, arteriograms (MRA) and venograms (MRV) are starting to show the effects of upright posture and the design of the cranial vault on brain, blood and CSF flow and their role in neurodegenerative condtions and diseases.