The parietal bone is a bone structure that is part of the skeleton of the skull vault, being one of the two paired bones that make up the upper part. It is located laterally, protecting the upper and lateral part of the brain.
The parietal is a square bone that combines compact and spongy bone tissue. It has an external and an internal face and four angles that become important during the pediatric physical examination for the evaluation of the correct development of the infant's skull.
From Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below) Bartleby.com: Gray's Anatomy, Plate 188, Public Domain, https://commons.wikimedia.org/w/index. php? curid = 556832
It has functions of supporting muscle-tendon structures and of protection, exercising, like the rest of the bones that accompany it, an important task in preserving the integrity of the most important part of the central nervous system and of all its vascular structures.
Its means of attachment to neighboring bones are the product of the evolution of its supporting structures, which begin to form in the fetus and complete its development after birth.
Anatomy
The skull, colloquially called "skull", is a complex bone structure that includes the upper skeleton (which protects the brain) and the lower skeleton (which forms the face).
When speaking of the skull in anatomy, two parts are distinguished: the viscerocranium and the neurocranium.
The viscerocranium, or splannocranium, refers to the bones of the face. Its articulation to the bones of the base of the skull forms the orbital cavities, the nasal cavity and the oral cavity.
By Anatomist90 - Own work, CC BY-SA 3.0, In turn, the neurocranium is the bony set that covers the brain. It is made up of eight bones that are responsible for protecting the brain and supporting muscular and tendon structures.
The bones that make up the neurocranium are the frontal, the ethmoid, the occipital and the sphenoid, which are unique bones; and the temporal and parietal bones which are paired bones.
From Original by LadyofHats. Translated by Ascánder. - Derivative of Image: Human skull side simplified (bones).svg, Public Domain, These structures are articulated and joined together by a type of strong connective tissue. These unions are called syndesmosis.
Parietal bone
The parietal is a paired bone that is part of the bones of the cranial vault or neurocranium.
It is located in the lateral and upper portion of the skull and is responsible for protecting the brain, as well as supporting some muscular structures that are in the vicinity.
From Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below) Bartleby.com: Gray's Anatomy, Plate 194, Public Domain, https://commons.wikimedia.org/w/index. php? curid = 792096
Its shape is square and consists of two faces. A parietal or external face and a visceral or internal one that is in contact with the protective layers of the brain.
The external plane is smooth and, when studying its surface, two curved lines are observed, one above the other, located in the center of the bone, which are called temporal lines.
From Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below) Bartleby.com: Gray's Anatomy, Plate 132, Public Domain, https://commons.wikimedia.org/w/index. php? curid = 564600
The upper temporal line marks the site where a fibrous tissue called the temporal fascia is inserted, and the lower line indicates the site where the temporal muscle originates.
For its part, the surface of the visceral face is more complex. Upon examination, multiple depressions can be seen that indicate the site of gyri or gyri.
Grooves corresponding to the multiple branches of the middle meningeal artery are also observed, which is the main vessel supplying blood supply to the cerebral meninges.
From Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below) Bartleby.com: Gray's Anatomy, Plate 133, Public Domain, https://commons.wikimedia.org/w/index. php? curid = 564602
Some unevenness can also be observed, corresponding to the so-called arachnoid granulations, which are extensions of the meninges through which the cerebrospinal fluid circulates into the bloodstream.
Embryology and development
The bones of the skull begin to differentiate during the first 4 weeks of pregnancy. At this time, the bone-forming cells begin the development of the structures corresponding to the cranial vault.
The cells that make up the parietal bones begin bone differentiation around the 8th week of pregnancy. The structures are approaching and reaching their final position throughout the gestation.
At birth, the gaps between the skull bones are relatively wide and the tissue that joins them is quite loose. As time passes and the newborn grows, these spaces close, finishing its complete fusion process around the second year.
By Xxjamesxx, cropped by was_a_bee - File: Sutures from top.png, CC BY-SA 3.0, The lines that connect bones with connective tissue are called sutures. Once closed, the skull does not develop further.
When the sutures are fused, the skull has the shape that it will maintain for the rest of its life.
When the child is born, soft spots can be felt through the scalp that correspond to the separation of the bones of the skull. These areas are called fontanelles.
The largest fontanelles are the anterior and posterior. The anterior fontanelle is formed by the coronal suture, which is the site where the two parietal bones meet the frontal bone.
From Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below) Bartleby.com: Gray's Anatomy, Plate 197, Public Domain, https://commons.wikimedia.org/w/index. php? curid = 792094
The posterior fontanelle is made up of the sagittal and lambdoid sutures. This is the junction area of the parietal bones and the occipital bone.
The anterior fontanelle closes between 10 and 24 months after birth; while the later one, generally, does it between the second and third month.
Pathological considerations
When there is increased pressure inside the skull, the fontanelles remain open to withstand the high pressures. This causes the size of the head circumference to increase, causing a condition known as hydrocephalus.
On the contrary, when there is a premature closure of these spaces, the skull loses the capacity for normal growth, beginning to grow parallel to the axis of the fused suture.
By Xxjamesxx - Own work, CC BY-SA 3.0, The abnormal fusion of the bone sutures and premature closure of the fontanelles is known as craniosynostosis.
References
- Anderson, BW; Al Kharazi KA. (2019). Anatomy, Head and Neck, StatPearls, Treasure Island (FL) Taken from: ncbi.nlm.nih.gov
- Russell, WP; Russell, MR. (2019). Anatomy, Head and Neck, Coronal Suture. StatPearls, Treasure Island (FL) Taken from: ncbi.nlm.nih.gov
- Jin, S. W; Sim, K. B; Kim, SD (2016). Development and Growth of the Normal Cranial Vault: An Embryologic Review. Journal of Korean Neurosurgical Society. Taken from: nlm.nih.gov
- Opperman, LA (2000). Cranial sutures as intramembranous bone growth sites. Dev. Dyn., 219: 472-485. Taken from: anatomypubs.onlinelibrary.wiley.com
- Mandarim-de-Lacerda, M. U; Alves, CA (1992) Growth of the cranial bones in human fetuses (2nd and 3rd trimesters). Surg Radiol Anat. Taken from: nlm.nih.gov