Axial skeleton: what it is, parts and characteristics.

A summary of the characteristics of the axial skeleton, a basic component of the skeletal system.

The skeleton or skeletal system is a biological system that provides support, support and protection to soft tissues and muscles in living organisms.

Vertebrates have an internal skeletal system (endoskeleton) composed of bones, while arthropods have opted for the exoskeleton as an evolutionary adaptation, a complex layer composed mainly of chitin, which gives these animals protection, support and the ability to breathe.

The functions of the skeleton in humans are multiple: mechanical support, production of movement, protection, metabolic storage of substances such as calcium and formation of Blood cells. The bone marrow (which is located inside many bones) contains hematopoietic stem cells, which, when differentiated, give rise to all circulating blood bodies. This includes lymphocytes, platelets and red blood cells, among others.

Thus, the functionality of the skeleton in vertebrates goes far beyond postural maintenance. Today we tell you everything about the axial skeletonThe axial skeleton, the one that makes up the central axis of the human body and allows us to remain upright in three-dimensional space.

What is the axial skeleton?

The skeleton of the human being is composed of a total of 206 bones, each and every one of them with a different morphology, from the femur of the thigh (the longest in the body) to the stapes (the smallest), which forms the middle ear. In an adult human being, the skeletal system accounts for 15% of body weight: if a man has a mass of 75 kilos, 9 of these will correspond to bone matter alone.

Bones are 98% composed of extracellular matter (mainly based on hydroxyapatite and collagen) and only 2% of their tissues are cells themselves, i.e. osteoblasts, osteoclasts and osteocytes (responsible for renewing the bone matrix). Due to their percentage of eminently mineral matter, bone structures store 99% of the body's calcium..

On the other hand, there are 2 parts in the human skeleton:

• Axial skeleton: formed by the skull, the vertebral column, the ribs and the sternum. It consists of 80 bones.
• Appendicular skeleton: it is formed by the bones of the upper and lower limbs, together with the shoulder girdle and pelvic girdle. It includes 126 bones.

Thus, following this small list, we could define the axial skeleton as the set of bones that make up the central axis of the human body.. The term "axial" comes from the Latin word axis, which refers to a central point from which the rest of the structures and formations are distributed in a stable way. Without this main axis, the limbs would have no points to anchor to, so the name comes to this skeletal system like a glove.

Parts of the axial skeleton

The axial skeleton consists of the skull, the spine, the ribs and the sternum.. We show you the particularities of each of these subsystems in the following lines.

1. Skull

The bones of the skull make up a bony box that protects the brain and the sternum. gives us the facial structure, which in turn makes it possible to see, breathe, swallow, emit sounds and basically perform all the functions that define us as living beings.. In zoology, we really speak of osteocranium and not just skull, since other animals have cranial structures analogous to ours that are not completely ossified.

In turn, the cranial bones are divided into two large groups based on their functionality: the neurocranium and the splacnocranium. The neurocranium contains the brain and the cranial meninges, and is composed of the occipital, sphenoid, squamosal, mastoid, parietal and frontal bones. Perhaps the frontal bone is the most famous of all, because, as its name indicates, it occupies our forehead and on it is inserted the occipitofrontal muscle, which allows the elevation of the eyebrows and the expression of many emotions.

On the other hand, splacnocranium refers to the part of the skull that contains the anterior part of the digestive and respiratory systems.. Also known as viscerocranium, it contains the following bones: ethmoid, lacrimal, vomer, maxilla, zygomatic, tympanic portion, styloid of the temporals and mandible.

2. Thoracic cage

The rib cage is composed of a total of 24 ribs (12 on each side of the body plane) and the sternum, for a total of 25 total bony bodies.. Also included in this ultrastructure are the costal cartilages, although they are not materials made from bone.

The thoracic cage has an eminently protective function, since it safeguards the most important organs of the entire human body: the heart and the lungs. It also provides an anchor point for the shoulder bones (and therefore the upper limbs), serves as an attachment point for the diaphragm and the muscles of the chest, back, neck and arms. Undoubtedly, the physiology of the human being could not be conceived as it is today without the rib cage.

Also worthy of special mention is the sternum, a long, flat, pointed bone that serves as an insertion site for almost all of the ribs (except for the last 2 pairs, which are therefore known as floating). In humans, this bone is made up of 3 sections: the shaft or manubrium, the body and the xiphoid process or process, which has a very variable shape.

3. Vertebral column

At birth, most human beings come into the world with 33 vertebrae, but during development some of these fuse, giving a total of 24 in almost all cases.

Broadly speaking, the spinal column can be differentiated into several sectionsThe cervical (7 vertebrae forming the neck), thoracic (12 vertebrae) and lumbar (5 vertebrae). Finally, the sacrum and the coccyx are present, the latter being a "vestigial" remnant of the tail of ancestral mammals.

The vertebral column provides protection for the spinal cord and nerve roots, which allow communication between all parts of our body and the brain.. In addition, it is also the support base for ligaments, tendons and muscles. On the other hand, the spine is a structural support, allows flexibility and mobility at the level of the trunk and is an excellent storage center for minerals and the production of red blood cells.

The axial skeleton summarized in 6 points

If the information previously provided has seemed a bit confusing, do not worry: it is normal, because the skeletal apparatus stands out for its anatomical complexity. As long as you remember these 6 essential points, you will know the basics of the axial skeleton:

• The skull is the first section of the axial skeleton. It is composed of 8 bones of the neurocranium and 14 of the splacnocranium, for a total of 22.
• 6 ear ossicles (3 on each side) are also involved in the axial skeleton. These are the malleus, incus and stapes.
• 1 hyoid bone in the neck, which rises and falls in movements such as swallowing or breathing, is also part of the central axis.
• The vertebral column is the next ultrastructure of the axial skeleton, composed of 24 vertebrae, the sacrum and the coccyx (a total of 26 bones).
• In last place we have the rib cage, with a total of 24 ribs and the sternum (25 bones).

Thus, the axial skeleton totals 80 bones, as we have indicated at the beginning. Although we have focused on the bony elements that form the skull, the vertebral column and the thoracic cage, you should not forget that the ossicles of the ear and the hyoid also form part of this central axis.

If there is one thing that can be made clear about the human skeleton, it is that it is a true work of art of the human skeleton. is a true work of art of biomechanics.. Each small bone structure fulfills not just one, but several functions and, however small, is essential for understanding human physiology in all its meanings.

The axial skeleton is made up of a total of 80 bones and 3 large sections, but you must not forget that there is also the axial skeleton. the appendicular skeleton, with a total of 126 bony structures that make locomotion and locomotion possible. that make locomotion and exertion possible, among many other things.

Bibliographic references:

• On the axis of the axial skeleton: Bones forming the axial skeleton, visiblebody. Retrieved February 16, from https://www.visiblebody.com/es/learn/skeleton/axial-skeleton#:~:text=The%20axial%20skeleton%20includes%20all%20the%20skeleton,vertebral%20and%20the%20cage%20tor%20tor%C3%A1cic.
• Ibarra, J. M., Romero, F. T., Maria, V. A., Gomez, J. A., & Cabrera, M. P. (2015). Minimally invasive surgery in the axial skeleton. Revista Colombiana de Ortopedia y Traumatología, 29(1), 17-27.
• Le Vay, D. (2008). Human anatomy and physiology. Editorial Paidotribo.
• Martins, J. M. (2017). Sistema ósseo ou esquelético: Terminologia óssea, esqueleto axial, esqueleto apendicular.
• NÚMERO, G. Descripción esqueleto axial columna y torax (Doctoral dissertation, Pontífica Universidad de Valparaíso).
• Olivares, R., & Rojas, M. (2013). Vertebrate axial and appendicular skeleton. International Journal of Morphology, 31(2), 378-387.
• Olivares, R., & Rojas, M. (2013). Vertebrate axial and appendicular skeleton. International Journal of Morphology, 31(2), 378-387.