The axial skeleton is the set of bones that make up the static or not very mobile part of the human body. Of 206 bones that make up the human body, the axial skeleton is made up of 80 of them, which when articulated with each other, form the head, thorax and spinal column.
The axial skeleton gets its name from the word “axis”, which comes from the Latin word, whose meaning is “axis” and which is joined to the suffix “al”, which means “in relation to”, that is, it belongs or is relative to the axis.
Its functions are to serve as a central body axis and as a surface for the insertion of muscles and tendons, which using the axial skeleton as a point of support allows the mobility of the appendicular skeleton attached to it.
However, one of its most important functions is to protect the internal organs and structures of the body, serving as a framework for vital tissues.
For example, the ribs and sternum form a rigid box to protect the heart and lungs from external trauma.
The spinal column forms a rigid but flexible tunnel to protect the spinal cord and, finally, the skull, which not only protects the brain structures, but also protects the inner ear and the eyeballs, delicate sensory structures that could not function properly if not for cranial stability.
How is the axial skeleton made?
The axial skeleton is made up of 80 bones that make up the following structures:
Skull (29 bones)
Cranial vault: consisting of 8 bones, it corresponds to the frontal (1), temporal (2), parietal (2), occipital (1), ethmoid (1) and sphenoid (1) bones.
Face: formed by 14 bones, which are in pairs the zygomatic, maxillary, nasal, palatal, nasal turbinate and lacrimal bones and a unit of the mandibular and vomer bones.
Ear: formed by 6 ossicles, 3 on each side, the hammer, the anvil and the stirrup, articulated, form a kind of bridge between the eardrum and the oval window, for the transmission of sound.
Hyoid bone: unique, odd bone, located in the anterior region of the neck, its main characteristic is that it is the only bone that does not articulate with any other.
Thorax (25 bones)
Sternum: single bone, made up of three parts, the manubrium, the body and the appendix. It articulates directly with 7 costal arches on each side and indirectly through a common costal cartilage with the 8th to 10th ribs.
Rib arches: there are 24 in total, of which 14 are called true ribs, since they articulate directly with the sternum through their own cartilage.
The 8th to 10th ribs (6 in total), articulate indirectly with the sternum, through a common costal cartilage; and finally 4 so-called floating ribs, since they articulate behind with the thoracic vertebrae and in front they remain suspended in the abdominal cavity, without articulating with the sternum.
Spine: (26 bones)
It constitutes the posterior region of the axial skeleton and its central pillar.
It is made up of 26 bones that are subdivided, forming different segments. In this way, the first 7 vertebrae correspond to the cervical segment, and each of them is articulated with the costal arches.
The morphological characteristics of the cervical vertebrae vary with respect to the rest of the vertebrae, mainly the first and second cervical vertebrae, called atlas (C1) and axis (C2) respectively, whose morphology is atypical, since it allows the support of the skull and the rotation of it.
As for the rest of the cervical vertebrae, its foramen is triangular in shape, with short and prominent spinous processes.
The following 12 vertebrae form the thoracic segment, articulate with the costal arches, and differ from the rest of the vertebrae, since the foramen is small and circular, and its spinous process is long and triangular.
They are continued with the lumbar vertebrae, which in number of five give the greatest support to the spine. Their vertebral bodies are voluminous, wide, and tall. The foramen is triangular, and the spinous process is square and horizontal.
The sacrum, the penultimate bone of the spine, articulates with the appendicular skeleton through the sacroiliac joints, transmitting the body weight to the pelvic girdle, which gives rise to the insertion of the lower limbs.
It is composed of five fused vertebrae in the shape of a pyramid, and its vertex articulates with the coccyx, the last bone that makes up the spinal column and does not participate as a support structure for the body weight in standing, unlike the rest of the vertebrae.
References
- Visible Body: Bones That Form the Axial Skeleton. Recovered from: visiblebody.com
- Chapter 28, Skeletal Development from the book Principles of Developmental Genetics. Moody, Sally A., ed. Principles of Developmental Genetics. Waltham: Elsevier Inc., 2015. Recovered from: books.google.pt
- Dr Craig Hacking, et al. Axial Skeleton. Recovered from: radiopaedia.org
- Atlas of Human Anatomy. 2012. Editorial Médica Panamericana. Chapter 5. Axial Skeleton. Recovered from: bibliotecas.unr.edu.ar
- E-Learning Anatomy. Author: jaquiefer. Axial and appendicular skeleton. jafer1309.wordpress.com