Human skull
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2008-06-19T10:34:25Z
Oxymoron83
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Reverted edits by [[Special:Contributions/203.76.212.104|203.76.212.104]] ([[User talk:203.76.212.104|talk]]) to last version by 67.191.93.33
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Caption2 = Human skull front bones |
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In humans, the adult '''skull''' is normally made up of 22 bones.<ref>[http://www.hopkinsmedicine.org/craniofacial/LynmProject/BSC/BSC2.HTM Skull Basics<!-- Bot generated title -->]</ref> Except for the [[mandible]], all of the bones of the [[skull]] are joined together by [[sutures of skull|sutures]], synarthrodial (immovable) [[joints]] formed by bony [[ossification]], with [[Sharpey's fibres]] permitting some flexibility.
==Components==
Eight bones form the [[neurocranium]] (brain case), a protective vault of bone surrounding the [[human brain|brain]] and [[brain stem]]. Fourteen bones form the [[splanchnocranium]], which comprises the bones supporting the [[face]]. Encased within the [[temporal bone]]s are the six [[auditory ossicles]] of the [[middle ear]]. The [[hyoid bone]], supporting the [[larynx]], is usually not considered as part of the skull, as it is the only bone that does not [[articulate]] with other bones of the skull.
[[Image:Skull inner surface.jpg|thumb|250px|right|The lower inner surface of the neurocranium]]
The skull also contains the [[sinus cavity|sinus cavities]], which are air-filled cavities lined with [[respiratory epithelium]], which also lines the large airways. The exact functions of the sinuses are debatable; they contribute to lessening the weight of the skull with a minimal reduction in strength, they contribute to resonance of the voice, and assist in the warming and moistening of air drawn in through the nasal cavities.
==Development of the skull==
The skull is a complex structure; its bones are formed both by [[intramembranous ossification|intramembranous]] and [[endochondral ossification]]. The bones of the splanchnocranium (face) and the sides and roof of the neurocranium are formed by intramembranous (or ''dermal'') ossification, while the bones supporting the brain (the [[occipital bone|occipital]], [[sphenoid bone|sphenoid]], [[temporal bone|temporal]], and [[ethmoid bone|ethmoid]]) are largely formed by endochondral ossification.
At birth, the human skull is made up of 404 separate bony elements. As growth occurs, many of these bony elements gradually fuse together into solid bone (for example, the [[frontal bone]]). The bones of the roof of the skull are initially separated by regions of dense [[connective tissue]] called "[[cranial sutures]]". There are five sutures: the [[frontal suture]], [[sagittal suture]], [[lambdoid suture]], [[coronal suture]], and [[squamosal suture]]. At birth these regions are fibrous and moveable, necessary for birth and later growth. This growth can put a large amount of tension on the "obstetrical hinge," which is where the squamous and lateral parts of the occipital bone meet. A possible complication of this tension is rupture of the [[Vein of Galen|great cerebral vein of Galen]]. Larger regions of connective tissue where multiple sutures meet are called [[fontanelle]]s. The six fontanelles are: the anterior fontanelle, the posterior fontanelle, the two sphenoid fontanelles, and the two mastoid fontanelles. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone. The posterior fontanelle usually closes by eight weeks, but the anterior fontanelle can remain open up to eighteen months. The anterior fontanelle is located at the junction of the frontal and parietal bones; it is a "soft spot" on a baby's forehead. Careful observation will show that you can count a baby's heart rate by observing his or her pulse pulsing softly through the anterior fontanelle.
==Pathology==
If the brain is bruised or injured it can be life-threatening. Normally the skull protects the brain from damage through its hard unyieldingness, the skull is one of the most durable substances found in nature. In some cases, however, of [[head injury]], there can be raised [[intracranial pressure]] through mechanisms such as a [[subdural haematoma]]. In these cases the raised [[intracranial pressure]] can cause herniation of the brain out of the [[foramen magnum]] ('coning') because there is no space for the brain to expand; this can result in significant [[brain damage]] or death unless an urgent operation is performed to relieve the pressure. This is why patients with [[concussion]] must be watched extremely carefully.
Dating back to [[Neolithic]] times, a skull operation called [[trepanation]] was sometimes performed. This involved drilling holes in the cranium. Examination of skulls from this period reveals that the "patients" sometimes survived for many years afterward. It seems likely that trepanation was performed for ritualistic or religious reasons and not only as an attempted life-saving technique.
[[Image:View of a Skull III.jpg|thumb|right|An image of a skull by [[Leonardo da Vinci]]]]
==Craniometry and morphology of human skulls==
Like the face of a living individual, a human skull and teeth can also tell, to a certain degree, the life history and origin of its owner. [[forensics|Forensic]] scientists and [[archeology|archaeologist]]s use [[Metrics|metric]] and nonmetric traits to estimate what the bearer of the skull looked like. When a significant amount of bones is found, such as at [[Spitalfields]] in the UK and [[Jōmon]] [[shell mound]]s in Japan, osteologists can use traits, such as proportions of length, height, width, to know the relationships of population of the study, with living or extinct populations.
The German physician [[Franz Joseph Gall]] in around 1800 formulated the theory of [[phrenology]], which attempted to show that specific features of the skull are associated with certain personality traits or intellectual capabilities of its owner. This theory is now considered to be obsolete.
The practice of [[craniometry]] has occasionally purported to reliably demonstrate racial or ethnic differences between skulls of different people. Occasionally this has been used as justification for ideas of racial supremacy. However, this theory is again obsolete.
===Sexual dimorphism===
In general, male skulls tend to be larger and more robust than female skulls, which are more gracile. Male skulls typically have more prominent [[supraorbital ridge]]s, a more prominent [[glabella]], and more prominent [[parietal bone|temporal lines]]. Male skulls on average have larger, broader [[palate]]s, squarer [[Orbit (anatomy)|orbit]]s, larger [[mastoid process]]es, larger [[Paranasal sinus|sinus]]es, and larger [[occipital bone|occipital condyle]]s than those of females. Male [[mandibles]] typically have squarer chins and thicker, rougher muscle attachments than female mandibles.
[[Image:Punuk.Alaska.skulls.jpg|right|thumbnail|200px|Partial human skulls]]
All of these features vary considerably within human populations, making it difficult to identify the sex of a skull without knowledge of the [[population]] from which it came.
===Ancestry===
Although persons' descents are occasionally stereotyped as different from other ethnic groups on the basis of a variety of traits like eye, hair and skin color, all such characters are not discrete nor preserved in bones.
Among [[archaeologist]]s and [[forensic scientist]]s, it is still sometimes stated that the most consistent and unique trait of ancestry in skeleton is skull shape (see [[craniometry]]).
==Additional images==
<gallery>
Image:Human skull front suturas.svg
Image:Human skull side suturas.svg
Image:Human skull front details.svg
Image:Human skull side details.svg
Image:Gray190.png
Image:Gray188.png
</gallery>
==See also==
*[[Foramina of the skull]]
*[[base of the skull]]
==References==
{{reflist}}
{{Cranium}}
{{Facial bones}}
[[bn:মানব করোটি]]
[[cs:Lebka člověka]]
[[el:Κρανίο]]
[[hu:Koponyacsontok]]
[[lv:Cilvēka galvaskauss]]
[[pt:Crânio humano]]
[[sv:Människans kranium]]
[[ta:மனித மண்டையோடு]]
[[th:กะโหลกศีรษะมนุษย์]]
[[tr:Kafatası]]
[[fiu-vro:Inemise pää]]
{{human anatomical features}}