Axial skeleton: what it is, parts and characteristics

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

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

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

Thus, skeletal functionality in vertebrates goes far beyond postural maintenance. today we tell you everything about the axial skeleton, The one that constitutes the central axis of the human body and allows us to stay in a three-dimensional space in height.

    What is the axial skeleton?

    The human skeleton is made up of a total of 206 bones, each with a different morphology, from the thigh femur (the longest in the body) to the stirrup (the smallest), which forms the middle ear. In an adult human, the skeletal system makes up 15% of body weight: if a man has a mass of 75 kilograms, 9 of them will only correspond to bone matter.

    Bones are 98% extracellular material (mostly hydroxyapatite and collagen) and only 2% of their tissues are cells themselves i.e. osteoblasts, osteoclasts and osteocytes (responsible for the renewal of 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 to the human skeleton:

    • Axial skeleton: formed by the skull, spine, ribs and breastbone. It consists of 80 bones.
    • Appendicular skeleton: It is formed by the bones of the upper and lower limbs, as well as the scapular and pelvic sizes. It encompasses 126 bones.

    So, by 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 other structures and formations are stably distributed. Without this main axis, the limbs would have no points to anchor, so the name comes to this skeletal system like a ring on the finger.

      Parts of the axial skeleton

      The axial skeleton is made up of the skull, spine, ribs and breastbone. We show you the peculiarities of each of these subsystems in the following lines.

      1. Skulls

      The bones of the skull form a bony box that protects the brain and it gives us the structure of the face, which in turn allows us to see, breathe, swallow, make sounds and fundamentally perform all the functions that define us as living beings.. In zoology, we really speak of osteocraneo and not of a dry skull, since other animals have cranial structures similar to ours which are not absolutely ossified.

      In turn, the cranial bones are divided into 2 large groups depending on their functionality: the neurocranium and the splanchnocranium. The first is the one that contains the brain and cranial meninges, and is made up of the occipital, sphenoid, scales, mastoid, parietal and frontal bones. The frontal bone is perhaps the most famous of all, because, as the name suggests, 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 another side, the esplacnocráneo refers to the part of the skull that contains the anterior part of the digestive and respiratory systems. Also known as viscerocráneo, it has the following bones: ethmoid, lacrimal, vomer, maxilla, zygomatic, tympanic part, stylid of the temporalis and mandible.

      2. Chest

      The rib cage consists of a total of 24 ribs (12 on each side of the body plane) and the breastbone, for a total of 25 bony bodies.. Costal cartilages are also included in this ultrastructure, although they are not bone materials.

      The rib cage has an eminently protective function, because it protects the most important organs of the whole human body: the heart and the lungs. It also gives an anchor point to the bones of the shoulders (and therefore the upper limbs), serves as an attachment point for the diaphragm and the muscles of the chest, back, neck and arms. Certainly, the physiology of the human being could not be conceived as it is today without the rib cage.

      Also worth mentioning is the breastbone, a long, flat, pointed bone that serves as an insertion site for almost all ribs (except the last 2 pairs, which is why they are called floaters). In humans, this bone consists of 3 sections: the handle or handlebars, the body and the process or xiphoid process, which has a very variable shape.

      3. Spine

      By the time of birth, most humans have come into the world with 33 vertebrae, but during development some of them merge, making a total of 24 in almost all cases.

      Basically, the spine it can be differentiated into several sections: The cervical (7 vertebrae which form the neck), the thoracic (12 vertebrae) and the lumbar (5 vertebrae). Finally, the sacrum and the coccyx are presented, the latter being a “vestigial” vestige of the tail of ancestral mammals.

      Spine protects the spinal cord and nerve roots, which allows all parts of our body to communicate with the brain. In addition to that, it is also the base of support for ligaments, tendons and muscles. On the other hand, the spine is a structural support, allows flexibility and mobility in the trunk and is an excellent center for the storage of minerals and the production of red blood cells.

      The axial skeleton summarized in 6 points

      If the information provided above seems a little confusing to you, do not worry, this is normal, because the skeletal apparatus is distinguished by its anatomical complexity. By remembering these 6 essential points, you will know the basics of the axial skeleton:

      • The skull is the first section of the axial skeleton. This one is composed of 8 bones of the neurocranium and 14 of the splacnocráneo, that is to say a total of 22.
      • 6 ear bones (3 on each side) are also involved in the axial skeleton. These are the hammer, the anvil and the stirrup.
      • 1 hyoid bone in the neck, which moves up and down in movements such as swallowing or breathing, is also part of the central axis.
      • The spine is the next ultrastructure of the axial skeleton, consisting of 24 vertebrae, the sacrum and the coccyx (a total of 26 bones).
      • Finally, we have the rib cage, with a total of 24 ribs and the breastbone (25 bones).

      So the axial skeleton represents a total of 80 bones, as we told you at the beginning. While we have focused on the bony elements that make up the skull, spine, and rib cage, it should also be remembered that the ear bones and the hyoid are also part of this central axis.

      If anything can be clarified about the human skeleton, it is this one. it is a true work of art of biomechanics. Each tiny bone structure performs not one, but several functions, and no matter how small it is essential for understanding human physiology in all of its meanings.

      The axial skeleton consists of a total of 80 bones and 3 large sections, however do not forget either that there is the appendicular skeleton, with a total of 126 bone structures that allow locomotion and the performance of efforts, between other.

      Bibliographical references:

      • On the axis of the axial skeleton: Bones which form the axial skeleton, visible body. Collected February 16 at https://www.visiblebody.com/es/learn/skeleton/axial-skeleton#:~:text=El%20esqueleto%20axial%20incluye%20todos,vertebral%20y%20la%20caja%20tor% C3% A1cica.
      • Ibarra, JM, Romero, FT, Maria, VA, Gómez, JA and Cabrera, MP (2015). Minimal axial skeletal invasion surgery. Catalan Society of Orthopedics and Traumatology, 29 (1), 17-27.
      • Read Vay, D. (2008). Human anatomy and physiology. Editorial Paidotribo.
      • Martins, JM (2017). Bone or skeletal system: bone terminology, axial skeleton, appendicular skeleton.
      • NOM, G. Description axial skeletal column and thorax (Doctoral thesis, Pontifical University of Valparaiso).
      • Olivares, R. and Rojas, M. (2013). Axial and appendicular skeleton of the vertebrate. International Journal of Morphology, 31 (2), 378-387.
      • Olivares, R. and Rojas, M. (2013). Axial and appendicular skeleton of the vertebrate. International Journal of Morphology, 31 (2), 378-387.

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