What does the human skull look like and how does it develop?

This is how the skull (with all its bones and parts) develops in men and women.

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 falls and shocks, or from being attacked by pathogens and bacteria.

In this sense, our encephalon has several protection systems, the most outstanding of them all being the bony covering that surrounds it: the human skull.. And it is this part of the organism that we are going to talk about in this article.

What is the human skull?

We understand by skull to the structure in the form of bony covering that surrounds and covers our encephalon, 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 blows, lesions and barrier that prevents blows, injuries and harmful pathogenic agents from directly attacking the brain.. It also allows the brain to maintain a structure and to maintain a certain buoyancy that prevents any blow from causing it to collide against its walls, as it acts 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 speaking of 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 are not part of the technical definition of the skull are collectively called viscerocraniumwhile the skull itself (the part covering the brain) is called the 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, eventually ossify. Between viscerocranium and neurocranium, adults have a total of 22 bones.

Of these, eight correspond to and make up the neurocranium: frontal, two parietal, two temporal, sphenoid, ethmoid and occipital bones. All of them protect the corresponding cerebral lobes with the exception of the ethmoid and sphenoid.The viscerocranium is the structure from which the eye bones and nostrils arise, while the second acts as the bone that joins most of the bones of the region and protects areas such as the pituitary gland.

The rest of the bones of the head form part of the viscerocranium, which includes everything from the nostrils and tear ducts to the jaw and cheekbones.

In addition to the aforementioned bones, the cranial sutures are also of great importance in the skull. These are a type of cartilaginous and elastic tissue that join the different bones of the skull and allow the growth and expansion of the skull. and that allow the growth and expansion of the skull as we develop, until they finally become bone in adulthood. In this sense, there are a total of thirty-seven, among which we find, for example, the lambdoid, sagittal, squamous, spheno-ethmoidal or coronal. Also relevant are the synarthroses or cerebral cartilages.

Sexual dimorphism

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

But not all skulls are the same. And we are not only talking about possible lesions 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 according to the differences between the two sexes in terms of shape and the particularities of its structure.

In general, the male cranial skeleton is more robust and angular, while the female one tends to bewhile 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 larger (although this does not imply either greater or lesser intellectual capacity, as this will depend on how the brain is configured, genetic inheritance and the experiences that the subject will have in his life).

The male has a short and slightly sloping frontal plate, while in the female the frontal part of the skull is smoother, convex and high. Also, the temporal crest is usually very visible in the male.

One element that is quite easy to see are the supraorbital arches, which tend to be practically nonexistent in males.They tend to be practically nonexistent in women, while in men they are usually marked. The orbits are usually quadrangular and low in men, while in women they are rounded and higher.

The jaw and teeth are very marked in men, which is less common in women. The female chin is usually oval and not very marked, while the male chin is very marked and usually square. It is also observed that the occipital protuberance protrudes and is very developed in males, something that does not occur to the same extent in females.

Cranial formation and development

Like the rest of our organs, our skull signs 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 germ layersone of the germinal layers that appear during embryogenesis and which arises in the fetal period (from three months of age) from the neural crest. The mesenchyme, which is a type of connective tissue, differentiates into different components, among which bones will develop (organs arise from other structures called endoderm and ectoderm).

As our organism develops, these tissues ossify. Before we are born, the bones of our skull are not fully formed and fixed, something that is evolutionarily beneficial for us.This is evolutionarily beneficial for us, since the head will be able to deform partially in order 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 will eventually form the sutures that will eventually shape the adult skull during development.

It will be after birth when these fontanelles will gradually close, starting to take shape just after birth (when they return to their original position) to grow until reaching the final cranial capacity at around six years of age, although the skull will continue to grow until adulthood. will continue to grow 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 soft tissue matrix from the bone that generate the growth by expanding to try to counteract the pressure exerted by brain development, which is determined by genetic factors (although it may also be partially influenced by environmental factors).

Bone diseases and malformations

We have seen throughout the article what the skull is and how it is usually formed in most people. However, there are different diseases and diseases and situations that can cause this part of our skeleton to develop abnormally, not to close or even to close too early (something that prevents the brain from growing properly).This is what happens with diseases such as Crouzon's disease or craniosyntosis, in which the skeleton does not close or even closes too early (something that prevents the correct growth of the brain).

This is what happens with diseases such as Crouzon's disease or craniosynthosis, in which, due to mutations and genetic diseases, the sutures that join the bones close too early.

However, it is not necessary that there is a congenital problem 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 bone deformities and fractures.

Although it is not a disease specifically 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 can involve the appearance of complications and neurological lesions.

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

Finally, it is also worth noting the possibility of this occurring after having suffered some cranioencephalic traumatismsuch 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 existence of a brain alteration, difficulties in acts such as speaking or sensory problems may occur. Even so, if the problem is only in the skull and has not already generated nerve involvement it is usually possible to repair with reconstructive surgery.

Bibliographic references:

• Otaño Lugo, R.; Otaño Laffitte, G. and Fernández Ysla, R. (2012). Craniofacial growth and development.
• Rouviere, H. and Delmas, A. (2005). Human anatomy: descriptive, topographic and functional; 11th ed.
• Sinelnikov, R. D. (1995). Atlas of Human Anatomy. Editorial MIR. Moscow.