Our brain is a fundamental organ for survival, since it is the organ in charge of managing and directing the functioning of the rest of the body systems, which allow us, among other things, to breathe, eat, drink, perceive the environment and interact with it.

However, its structure is relatively fragile, so it needs some kind of element to prevent it from being destroyed or injured by movement or by falls and shocks, or from being attacked by pathogens and bacteria.

In this sense, our brain has several protection systems, the most outstanding of which is the bone cover that surrounds it: the human skull . And it is about this part of the organism that we are going to talk throughout this article.

What is the human skull?

We understand the skull as the structure in the form of a bone covering that surrounds and covers our brain, forming only a part of what we come to consider our skull.

Its main function is to protect all the structures of the brain, as a barrier that prevents hits, injuries and harmful pathogens from directly attacking the brain . It also allows the brain to maintain a structure and that there may be a certain buoyancy of the brain that prevents any blow from causing it to hit its walls, by acting as a container.

Although technically the skull is only the part of the skeleton that surrounds the brain (which would leave out other facial bones such as the jaw) traditionally when talking about this structure it has been included along with the other bones of the facial area. In order to integrate both positions, a subdivision has been generated: the facial bones that do not form part of the technical definition of the cranium are called viscerocranium , while the cranium itself (the part that covers the brain) is called neurocranium.

Its main parts

The skull is a structure that does not appear uniformly, but is actually the union of various bones by means of cranial sutures that as we grow end up ossifying. Between viscerocranium and neurocranium, adults have a total of 22 bones.

Among them, eight correspond to and configure the neurocranium: frontal, two parietal, two temporal, sphenoid, ethmoid and occipital. All of them protect the corresponding cerebral lobes with the exception of ethmoids and sphenoids : the first of which is the structure from which the ocular bones and nostrils start, while the second acts as a bone that joins a large part of the region’s bones and protects areas such as the pituitary gland.

The remaining bones of the head are part of the viscerocranium, which includes the nostrils and tear ducts, the jaw and the cheekbones.

In addition to the bones mentioned above, the so-called cranial sutures are also of great importance in the skull. These are a type of cartilaginous and elastic tissue which unite the different bones of the skull and which allow the growth and expansion of this as we develop, until they finally end up becoming bone in adulthood. In this sense, there are a total of thirty-seven, including the lambdoid, sagittal, squamous, spheno-ethmoid and coronal bones. Also relevant are synarthroses or brain cartilages.

Sexual dimorphism

The skull is, as we have said, fundamental for our brain and organism, since it provides protection to our internal organs and contributes to give a structure to the facial physiognomy .

But not all skulls are the same. And we are not only talking about possible injuries or malformations, but there are interindividual differences and it is even possible to find differences derived from sexual dimorphism. In fact, it is possible to recognize whether a skull belongs to a man or a woman based on the differences that exist between both sexes in terms of their shape and the particularities of their structure.

In general, the male skull is more robust and angular , while the female tends to be more delicate and rounded. The male skull tends to have a cranial capacity or size between 150 and 200 cc greater (although this does not imply either greater or lesser intellectual capacity, as this will depend on how the brain is configured, on genetic inheritance and on the experiences the subject will have in his life).

The male has a short, slightly sloping faceplate, while in the female the front of the skull is smoother, more convex and higher. The temporal ridge is also usually very visible in the male case.

A fairly easy element to see are the supra-orbital arches , which are usually practically non-existent in women while in men they are usually marked. The orbits are usually square and low in men while women have rounded and higher.

The jaw and the teeth are very marked in men, something less usual in the case of women. A woman’s chin is usually oval and not very marked, while a man’s chin is very marked and usually square. It is also observed that the occipital protuberance protrudes and is very developed in men, something that does not occur to the same extent in women.

Cranial formation and development

Like the rest of our organs, our skull is signed and develops throughout our gestation, although this development does not end until many years after birth.

Initially the skull develops from the mesenchyme , one of the germinal layers that appear during embryogenesis and which emerges in the fetal period (from three months of age) from the neural crest. The mesenchyme, which is a type of connective tissue, will gradually differentiate into different components, among which the bones will develop (the organs arise from other structures called the endoderm and ectoderm).

As our body develops, these tissues become ossified. Before birth the bones of our skull are not totally formed and fixed , something that is evolutionarily beneficial to us given that the head will be able to deform partially to pass through the birth canal.

When we are born we have a total of six cranial bones, instead of the eight we will have as adults. These bones are separated by spaces of membranous tissue called fontanelles, which over time will form the sutures that will end up shaping the adult skull.

It will be after birth when little by little these fontanelles will close, starting to take shape just after birth (when they return to their original position) to grow until reaching the final cranial capacity around six years of age, although the skull will continue its growth until adulthood .

It can be said that this growth and development of the skull is usually linked to and occurs in relation to that of the brain itself. It is mainly the cartilage and the matrix of soft tissue from the bone that generate the growth by expanding to try to counteract the pressure of brain development, which is determined by genetic factors (although it can also be partially influenced by environmental factors).

Bone diseases and malformations

We have seen throughout the article what the skull is and how it usually forms in most people. However, there are different diseases and situations that can cause this part of our skeleton to develop abnormally , not to close or even to close too soon (something that prevents the correct growth of the brain).

This is the case with diseases such as Crouzon’s or craniosynthesis, in which due to mutations and genetic diseases the sutures that bind the bones close too early.

However, it is not necessary for a congenital problem to exist for the skull to be deformed: in Paget’s disease (the second most common bone disease after osteoporosis) there is an inflammation of the bone tissue that can lead to deformations and fractures in the bones.

Although it is not a specific disease of the skull (it can appear in any bone), one of the possible locations where it can occur and where it is most frequent is precisely in the skull. And this may imply the appearance of complications and neurological injuries.

Other conditions such as hydrocephalus, macrocephalus, spina bifida or some encephalitis or meningitis (especially if they occur in childhood) can also affect the proper development of the human skull.

Finally, it is also worth noting the possibility of this occurring after having suffered some head trauma , such as in a traffic accident or an assault.

An alteration at the level of the skull can have multiple effects, since it can affect the development and functioning of the brain: it can compress and hinder the growth of the whole brain or of specific parts of it, it can alter the level of intracranial pressure, it can generate lesions in the neural tissue or it can even facilitate the arrival of infections by bacteria and viruses.

It is even possible that even without the need for a brain alteration, there may be difficulties with acts such as speech or sensory problems. Even so, if the problem is only in the skull and has not already caused nerve damage, repair with reconstructive surgery is usually possible.

Bibliographic references:

  • Otaño Lugo, R.; Otaño Laffitte, G. and Fernández Ysla, R. (2012). Craniofacial growth and development.
  • Rouviere, H. and Delmas, A. (2005). Anatomía humana: descriptiva, topográfica y funcional; 11ª ed.
  • Sinelnikov, R. D. (1995). Atlas of Human Anatomy. Editorial MIR. Moscow.