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

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 him.

However, its structure is relatively fragile, which requires some type of element that prevents is destroyed or injured by movement or falls and shocks, or is attacked by pathogens and bacteria.

In this sense, our brain has various protection systems, the most prominent of all being the bony covering that surrounds it: the human skull. And it is about this part of the body that we are going to talk about throughout this article.

• Related article: "Parts of the human brain (and functions)"

What is the human skull?

We understand by skull 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 the set of structures of the brain, as a

barrier that prevents blows, injuries and harmful pathogens from directly attacking the brain. It also allows it to maintain a structure and that there can be some buoyancy of it that prevents any blow from crashing against its walls, by acting as a container.

While technically the skull is just the part of the skeleton that surrounds the brain (which would leave out other bones such as the jaw) traditionally when talking about this structure it has been included along with the other bones in the area facial. 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 the viscerocranium, while the skull itself (the part that covers 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 end up ossifying as we grow. Between the viscerocranium and the 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 brain lobes with the exception of ethmoids and sphenoids.: the first of which is the structure from which the eye bones and nostrils depart, while that the second acts as a bone that unites a large part of the bones of the region and protects areas such as the hypophysis.

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

In addition to the aforementioned bones, the so-called cranial sutures are also of great relevance in the skull. These are a type of cartilaginous and elastic tissue that join the different bones of the skull. and that allow the growth and expansion of this as we develop, until they finally end up turning into bone in adulthood. In this sense, there are a total of thirty-seven, among which are, for example, the lambdoid, the sagittal, the squamous, the spheno-ethmoid or the coronal. Synarthrosis or cerebral cartilage are also relevant.

• You may be interested in: "The lobes of the brain and their different functions"

sexual dimorphism

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

But not all skulls are the same. And we are not just 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 between both sexes with regard to their shape and the particularities of their structure.

In general, the male cranial skeleton is more robust and angular, while the feminine 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 a greater or lesser capacity). intellectual, since this will depend on how the brain is configured, on genetic inheritance and on the experiences that the subject is having in his life. life).

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

A fairly easy element to see are the supraorbital arcades, which are usually practically non-existent in women while in men they are usually marked. The orbits tend to be quadrangular and low in men while women have them rounded and higher.

The jaw and teeth are very marked in men, somewhat less common in the case of women. The woman's chin is usually oval and slightly marked, while the man's is very marked and is usually square. It is also observed that the occipital protuberance protrudes and is highly 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 firm and develops throughout our gestation, although this development does not end until many years after birth.

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

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

When we are born we have a total of six cranial bones, instead of the eight that we will have as adults. These bones are separated by spaces of membranous tissue called fontanelles, which will go with time forming the sutures that throughout development will end up configuring the skull adult.

It will be after birth when little by little these fontanelles will close, beginning to take shape just after delivery (in which return to their original position) to grow until reaching final cranial capacity around six years of age, although the skull will continue to grow into 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 growth by expanding to try to counteract the pressure exerted by brain development, which is determined by genetic factors (although it can also be partly influenced by factors environmental).

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 situations that can cause this part of our skeleton to develop abnormally, does not close or even closes too soon (something that prevents the correct growth of the brain).

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

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) produces an inflammation of the bone tissue that can lead to deformations and fractures in the bones.

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 it. And this can imply the appearance of complications and neurological injuries.

Other conditions such as hydrocephalus, macrocephaly, 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 a head injury, such as in a traffic accident or 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 entire 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, difficulties occur for acts such as speaking or sensory problems. Even so, if the problem is only in the skull and has not already generated nerve involvement, it is usually possible to repair it with reconstructive surgery.

Bibliographic references:

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