Lecture notes of parietal bone

Parietal bone

Anatomical points

Superior border is longest, thickest and serrated

Superior border lies in median plane
External surface is convex

Anterior inferior angle is acute and internally marked by groove for anterior division of middle meningeal vessel

Morphological type of bone flat bone

 

Structure of bone : inner and outer table: compact bone and middle diploe spongy bone 

ossification intra membranous ossification 

Development paraxial mesoderm 

Parts of parietal bone

 external and internal surface , four borders : anterior , inferior , posterior and superior , four angle anterior superior , anterior inferior , posterior superior and posterior inferior

superior border longest, thickest and serrated and
internally marked by a sulcus known as sagittal sulcus
which lodges superior sagittal sinus
superior border is articulated with opposite parietal bone formed sagittal suture
Granular pit present side of sagittal sulcus which lodge arachnoid granulation
Anterior border is straight and serrated and articulated with frontal bone formed coronal suture

Posterior border is straight and serrated and articulated with occipital bone formed lambdoid suture

 
inferior border irregular and serrated and internally marked by posterior division of middle meningeal artery at the middle of inferior border
Inferior border is articulated with 3 bones
from antero posteriorly
Greater wing of sphenoid bone
Squamous part of temporal bone
mastoid part of temporal bone .
Anterior superior angle of parietal bone forms bregma in children it is called anterior frontanelle

A fontanelle is an anatomical feature of the infant human skull. They are soft membranous gaps between the cranial bones.
The fontanelle allows the skull to deform during birth to ease its passage through the birth canal and for expansion of the brain after birth.
A sunken fontanelle indicates dehydration 
whereas a very tense or bulging anterior fontanelle indicates raised intracranial pressure

The anterior fontanelle bregmatic fontanelle, frontal fontanelle is the largest fontanelle, and is placed at the junction of the sagittal suture, coronal suture, and frontal suture;
It is lozenge shaped, and measures about 4 cm in its antero posterior and 2.5 cm in its transverse diameter.
The anterior fontanelle typically closes between the ages of 12 and 18 months.
Posterior superior angle forms Lambda in children it is called posterior fontanelle
The posterior fontanelle lambdoid fontanelle, occipital fontanelle is a gap between bones in the human skull known as fontanelle, triangular in form and situated at the junction of the sagittal suture and  lambdoidal suture.
It generally closes in 6 to 8 weeks from birth.
A delay in closure is associated with congenital hypothyroidism.
Premature complete ossification of the sutures is called craniosynostosis.
Anterior inferior angle of parietal bone forms pterion in children it is called sphenoidal frontanelle
This angle is internally marked by groove for anterior division of middle meningeal artery
What is pterion
Ans union between 4 bones
Frontal bone
Anterior inferior angle of parietal bone
Greater wing of sphenoid
Squamous part of temporal bone
What is the importance of pterion
Internal surface of pterion is lodged by anterior division of middle meningeal artery
Posterior inferior angle of parietal bone forms asterion in children it is called mastoid frontanelle
Internally a groove is present which lodges sigmoid sinus
Summary of Closure of frontanelle
In humans, the sequence of fontanelle closure is as follows
The posterior fontanelle generally closes 2 to 3 months after birth;
The sphenoidal fontanelle is the next to close around 6 months after birth
The mastoid fontanelle closes next from 6 to 18 months after birth; and
The anterior fontanelle is generally the last to close between 12 to 18 months.
external Surface of parietal bone
Superior temporal line : gives attachment to the temporal fascia and lateral part of epicranial aponeurosis . Above the superior temporal line the bone is covered by the epicranial aponeurosis
inferior temporal line & the area of bone below it form the major part of temporal fossa & provide origin to the temporalis muscle
parietal foramen It is located close to the posterior part of superior border of external surface which transmits an emissary vein connecting the superior sagittal sinus with the veins of the scalp and a meningeal branch from the occipital artery

The external surface of the parietal bone is convex, smooth, and marked near the center by an eminence, the parietal eminence 
parietal tuber
Importance of  parietal eminence 
It indicates the point where ossification commenced
The maximum transverse diameter of skull measures by these points
It acts as a reference point for surface anatomy
Beneath the parietal tuber, the posterior ramus of lateral sulcus of the brain terminates with an upturned end
Opposite the parietal tuber supramarginal gyrus the Wernickes sensory speech area is located
internal surfaces of parietal bone is deeply concave , faces downward and medially
impression of sulci and gyri of cerebrum
impression of anterior division of middle meningeal artery at internal surface of anterior inferior angle
impression of posterior division of middle meningeal artery at middle of inferior border :sagittal sulcus near the superior border which lodge superior sagittal sinus

The margin of superior sagittal sulcus provide attachment to the dural folds the falx cerebri
Granular pits are present near the sagittal sulcus for lodgement of arachnoid granulations through which cerebrospinal fluid is absorbed in the superior sagittal sinus
sulcus for sigmoid sinus is present near the posterior inferior angle
Parietal bone overlaps partially all four major lobes of cerebral hemisphere.
central sulcus
postcentral gyrus
precentral gyrus
intraparietal sulcus
superior parietal lobule
lateral sulcus
supramarginal gyrus
angular gyrus
superior temporal gyrus

The following functional areas of brain are covered by parietal bone
Motor and somesthetic sensory area
Broca’s motor speech area
Wernicke’s sensory speech area
Primary and secondary auditory area
Two imaginary lines may be drawn on the internal surface of parietal bone
A line extends downward and forward from the superior border about 3 to 4 cm behind the anterior superior angle for a distance of about 7.5 cm .It is corresponds with the central sulcus and separates the frontal lobe of the brain in front from the parietal lobe behind
Two imaginary lines may be drawn on the internal surface of parietal bone
2. Another line extending from the anterior inferior angle to the inner aspect of parietal tuber coincides with the posterior ramus of lateral sulcus and intervenes between the frontoparietal lobes above and in front and the occipitotemporal lobes below and behind