AskDefine | Define braincase

Dictionary Definition

braincase n : the part of the skull that encloses the brain [syn: cranium, brainpan]

User Contributed Dictionary

English

Noun

  1. The part of the skull that contains the brain; the cranium.

Translations

Extensive Definition

otherusesof Skull The skull is a bony structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury.
The skull can be subdivided into two parts: the cranium and the mandible. A skull that is missing a mandible is only a cranium; this is the source of a very commonly made error in terminology. Those animals having skulls are called craniates.
Protection of the brain is only one part of the function of a bony skull. For example, a fixed distance between the eyes is essential for stereoscopic vision, and a fixed position for the ears helps the brain to use auditory cues to judge direction and distance of sounds. In some animals, the skull also has a defensive function (e.g. horned ungulates); the frontal bone is where horns are mounted.

Human skulls

In humans, the adult skull is normally made up of 22 bones. Except for the mandible, all of the bones of the skull are joined together by sutures, rigid articulations permitting very little movement. Eight bones form the neurocranium (braincase)—including the frontal, parietals, occipital bone, sphenoid, temporals and ethmoid—a protective vault surrounding the brain. Fourteen bones form the splanchnocranium, the bones supporting the face. Encased within the temporal bones are the six ear ossicles of the middle ears, though these are not part of the skull. The hyoid bone, supporting the tongue, is usually not considered as part of the skull either, as it does not articulate with any other bones.The skull is a protector of the brain.
The skull contains the sinus cavities, which are air-filled cavities lined with respiratory epithelium, which also lines the large airways. The exact functions of the sinuses are unclear; they may contribute to decreasing the weight of the skull with a minimal decrease in strength,or they may be important in improving the resonance of the voice. In some animals, such as the elephant, the sinuses are extensive. The elephant skull needs to be very large, to form an attachment for muscles of the neck and trunk, but is also unexpectedly light; the comparatively small brain-case is surrounded by large sinuses which reduce the weight.
The meninges are the three layers, or membranes, which surround the structures of the nervous system. They are known as the dura mater, the arachnoid mater and the pia mater. Other than being classified together, they have little in common with each other.
In humans, the anatomical position for the skull is the Frankfurt plane, where the lower margins of the orbits and the upper borders of the ear canals are all in a horizontal plane. This is the position where the subject is standing and looking directly forward. For comparison, the skulls of other species, notably primates and hominids, may sometimes be studied in the Frankfurt plane. However, this does not always equate to a natural posture in life.

Possible types of skull fractures

Other skulls

Temporal Fenestra

The temporal fenestra are anatomical features of the amniote skull, characterised by bilaterally symmetrical holes (fenestrae) in the temporal bone. Depending on the lineage of a given animal, two, one, or no pairs of temporal fenestrae may be present, above or below the postorbital and squamosal bones. The upper temporal fenestrae are also known as the supratemporal fenestrae, and the lower temporal fenestrae are also known as the infratemporal fenestrae. The presence and morphology of the temporal fenestra is critical for taxonomic classification of the synapsids, of which mammals are part.
Physiological speculation associates it with a rise in metabolic rates and an increase in jaw musculature. The earlier amniotes of the Carboniferous did not have temporal fenestrae but the more advanced sauropsids and synapsids did. As time progressed, sauropsids' and synapsids' temporal fenestrae became more modified and larger to make stronger bites and more jaw muscles. Dinosaurs, which are sauropsids, have large advanced openings and their descendants, the birds, have temporal fenestrae which have been modified. Mammals, which are synapsids, possess no fenestral openings in the skull, as the trait has been modified. They do, though, still have the temporal orbit (which resembles an opening) and the temporal muscles. It is a hole in the head and is situated to the rear of the orbit behind the eye.

Classification

There are four types of amniote skull, classified by the number and location of their fenestra. These are:
  • Anapsida - no openings
  • Synapsida - one low opening (beneath the postorbital and squamosal bones)
  • Euryapsida - one high opening (above the postorbital and squamosal bones); euryapsids actually evolved from a diapsid configuration, losing their lower temporal fenestra.
  • Diapsida - two openings
Evolutionary, they are related as follows:

See also

References

  • White, T.D. 1991. Human osteology. Academic Press, Inc. San Diego, CA.
braincase in Arabic: جمجمة
braincase in Official Aramaic (700-300 BCE): ܩܪܩܦܬܐ
braincase in Bulgarian: Череп
braincase in Catalan: Crani
braincase in Czech: Lebka
braincase in Welsh: Penglog
braincase in Danish: Kranium
braincase in German: Schädel
braincase in Dhivehi: ބޮލުގެ ނާށިގަނޑު
braincase in Estonian: Kolju
braincase in Spanish: Cráneo
braincase in Esperanto: Kranio
braincase in Basque: Burezur
braincase in Persian: جمجمه
braincase in French: Crâne
braincase in Galician: Cranio
braincase in Korean: 두개골
braincase in Croatian: Lubanja
braincase in Indonesian: Tengkorak
braincase in Ossetian: Сæргæхц
braincase in Icelandic: Höfuðkúpa
braincase in Italian: Cranio
braincase in Hebrew: גולגולת
braincase in Kurdish: Kilox
braincase in Latin: Calva
braincase in Latvian: Galvaskauss
braincase in Lithuanian: Galvos griaučiai
braincase in Hungarian: Koponya
braincase in Dutch: Schedel
braincase in Japanese: 頭蓋骨
braincase in Norwegian: Skalle
braincase in Pangasinan: Lapislapis
braincase in Polish: Czaszka
braincase in Portuguese: Crânio
braincase in Romanian: Craniu
braincase in Quechua: Uma tullu
braincase in Russian: Череп
braincase in Simple English: Skull
braincase in Slovak: Lebka
braincase in Slovenian: Lobanja
braincase in Serbian: Лобања
braincase in Finnish: Pääkallo
braincase in Swedish: Kranium
braincase in Thai: กะโหลกศีรษะ
braincase in Ukrainian: Череп
braincase in Chinese: 颅骨
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