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Human skull

Human skull

Overview
The human skull is a bony structure, skeleton
Human skeleton
The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs and heart....

, that is in the human head
Human head
In human anatomy, the head is the upper portion of the human body. It supports the face and is maintained by the skull, which itself encloses the brain.-Cultural importance:...

 and which supports the structures of the face and forms a cavity for the brain.

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, synarthrodial (immovable) joints formed by bony ossification
Ossification
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...

, with Sharpey's fibres
Sharpey's fibres
Sharpey's fibres are a matrix of connective tissue consisting of bundles of strong collagenous fibres connecting periosteum to bone...

 permitting some flexibility.


Eight bones form the neurocranium (brain case), a protective vault of bone surrounding the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...

 and brain stem
Brain stem
In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...

.
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Encyclopedia
The human skull is a bony structure, skeleton
Human skeleton
The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs and heart....

, that is in the human head
Human head
In human anatomy, the head is the upper portion of the human body. It supports the face and is maintained by the skull, which itself encloses the brain.-Cultural importance:...

 and which supports the structures of the face and forms a cavity for the brain.

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, synarthrodial (immovable) joints formed by bony ossification
Ossification
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...

, with Sharpey's fibres
Sharpey's fibres
Sharpey's fibres are a matrix of connective tissue consisting of bundles of strong collagenous fibres connecting periosteum to bone...

 permitting some flexibility.

Components



Eight bones form the neurocranium (brain case), a protective vault of bone surrounding the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...

 and brain stem
Brain stem
In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...

. Fourteen bones form the splanchnocranium, which comprises the bones supporting the face
Face
The face is a central sense organ complex, for those animals that have one, normally on the ventral surface of the head, and can, depending on the definition in the human case, include the hair, forehead, eyebrow, eyelashes, eyes, nose, ears, cheeks, mouth, lips, philtrum, temple, teeth, skin, and...

. Encased within the temporal bone
Temporal bone
The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum.The temporal bone supports that part of the face known as the temple.-Parts:The temporal bone consists of four parts:* Squama temporalis...

s are the six auditory ossicles of the middle ear
Middle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...

. The hyoid bone
Hyoid bone
The hyoid bone is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies at the level of the base of the mandible in the front and the third cervical vertebra behind.Unlike other bones, the hyoid is only distantly...

, supporting the larynx
Larynx
The larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...

, 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.

The skull also contains the sinus cavities, which are air-filled cavities lined with respiratory epithelium
Respiratory epithelium
Respiratory epithelium is a type of epithelium found lining the respiratory tract, where it serves to moisten and protect the airways. It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by action of the mucociliary escalator.-...

, 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 cavity.

Development of the skull



The skull is a complex structure; its bones are formed both by intramembranous
Intramembranous ossification
Intramembranous ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike endochondral ossification, which is the other process by which bone tissue is created, cartilage is not present during intramembranous...

 and endochondral ossification
Endochondral ossification
Endochondral ossification is one of the two essential processes during fetal development of the mammalian skeletal system by which bone tissue is created. Unlike intramembranous ossification, which is the other process by which bone tissue is created, cartilage is present during endochondral...

. The skull roof
Skull roof
The skull roof , or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes and all land living vertebrates. The bones are derived from dermal bone, hence the alternative name dermatocranium...

, comprising the bones of the splanchnocranium (face) and the sides and roof of the neurocranium, are formed by intramembranous (or dermal) ossification, though the temporal bone
Temporal bone
The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum.The temporal bone supports that part of the face known as the temple.-Parts:The temporal bone consists of four parts:* Squama temporalis...

s are formed by endochondral ossification. The endocranium
Endocranium
For internal cast of the cranium, see Endocast.The endocranium in comparative anatomy is a part of the skull base in vertebrates and represent the basal, inner part of the cranium. The term is also applied to the outer layer of the dura mater in human anatomy.-Basic structure:Structurally, the...

, the bones supporting the brain (the occipital
Occipital bone
The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...

, sphenoid
Sphenoid bone
The sphenoid bone is an unpaired bone situated at the base of the skull in front of the temporal bone and basilar part of the occipital bone.The sphenoid bone is one of the seven bones that articulate to form the orbit...

, and ethmoid
Ethmoid bone
The ethmoid bone is a bone in the skull that separates the nasal cavity from the brain. As such, it is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a spongy construction. The ethmoid bone is one of the bones that makes up the orbit of the eye...

) are largely formed by endochondral ossification. Thus frontal and parietal bones are purely membranous. The geometry of the cranial base and its fossas: anterior
Anterior cranial fossa
The floor of the anterior fossa is formed by the orbital plates of the frontal, the cribriform plate of the ethmoid, and the small wings and front part of the body of the sphenoid; it is limited behind by the posterior borders of the small wings of the sphenoid and by the anterior margin of the...

, middle
Middle cranial fossa
The middle fossa, deeper than the anterior cranial fossa, is narrow medially and widens laterally to the sides of the skull. It is separated from the posterior fossa by the clivus and the petrous crest....

 and posterior
Posterior cranial fossa
The posterior cranial fossa is part of the intracranial cavity, located between the foramen magnum and tentorium cerebelli. It contains the brainstem and cerebellum.This is the most inferior of the fossae. It houses the cerebellum, medulla and pons....

 changes rapidly, especially during the first trimester of pregnancy. The first trimester is crucial for development of skull defects.

At birth, the human skull is made up of 44 separate bony elements. As growth occurs, many of these bony elements gradually fuse together into solid bone (for example, the frontal bone
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....

). The bones of the roof of the skull
Skull roof
The skull roof , or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes and all land living vertebrates. The bones are derived from dermal bone, hence the alternative name dermatocranium...

 are initially separated by regions of dense connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...

 called "fontanels". There are six fontanels: one anterior (or frontal), one posterior (or occipital), two sphenoid (or anterolateral), and two mastoid (or posterolateral). 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
Squama occipitalis
The squama of the occipital bone, situated above and behind the foramen magnum, is curved from above downward and from side to side.- External surface :...

 and lateral parts
Lateral parts of occipital bone
The lateral parts of the occipital bone are situated at the sides of the foramen magnum; on their under surfaces are the condyles for articulation with the superior facets of the atlas....

 of the occipital bone
Occipital bone
The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...

 meet. A possible complication of this tension is rupture of the great cerebral vein of Galen. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone creating suture
Suture (anatomical)
In anatomy, a suture is a fairly rigid joint between two or more hard elements of an animal, with or without significant overlap of the elements....

s. The five sutures are the two squamous, one coronal, one lambdoid, and one sagittal sutures. The posterior fontanel usually closes by eight weeks, but the anterior fontanel can remain open up to eighteen months. The anterior fontanel 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 fontanel.

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 least deformable substances found in nature with it needing the force of about 1 ton to reduce the diameter of the skull by 1 cm. In some cases, however, of head injury
Head injury
Head injury refers to trauma of the head. This may or may not include injury to the brain. However, the terms traumatic brain injury and head injury are often used interchangeably in medical literature....

, there can be raised intracranial pressure
Intracranial pressure
Intracranial pressure is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid . The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF...

 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
Brain damage
"Brain damage" or "brain injury" is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors...

 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
Neolithic
The Neolithic Age, Era, or Period, or New Stone Age, was a period in the development of human technology, beginning about 9500 BC in some parts of the Middle East, and later in other parts of the world. It is traditionally considered as the last part of the Stone Age...

 times, a skull operation called trepanation
Trepanation
Trepanning, also known as trephination, trephining or making a burr hole, is a surgical intervention in which a hole is drilled or scraped into the human skull, exposing the dura mater in order to treat health problems related to intracranial diseases. It may also refer to any "burr" hole created...

 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.

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. Forensic
Forensics
Forensic science is the application of a broad spectrum of sciences to answer questions of interest to a legal system. This may be in relation to a crime or a civil action...

 scientists and archaeologists use metric
Metric (mathematics)
In mathematics, a metric or distance function is a function which defines a distance between elements of a set. A set with a metric is called a metric space. A metric induces a topology on a set but not all topologies can be generated by a metric...

 and nonmetric traits to estimate what the bearer of the skull looked like. When a significant amount of bones are found, such as at Spitalfields
Spitalfields
Spitalfields is a former parish in the borough of Tower Hamlets, in the East End of London, near to Liverpool Street station and Brick Lane. The area straddles Commercial Street and is home to many markets, including the historic Old Spitalfields Market, founded in the 17th century, Sunday...

 in the UK and Jōmon shell mounds in Japan, osteologists
Osteology
Osteology is the scientific study of bones. A subdiscipline of anatomy, anthropology, and archeology, osteology is a detailed study of the structure of bones, skeletal elements, teeth, morphology, function, disease, pathology, the process of ossification , the resistance and hardness of bones , etc...

 can use traits, such as the proportions of length, height and width, to know the relationships of the population of the study with other living or extinct populations.

The German physician Franz Joseph Gall
Franz Joseph Gall
Franz Joseph Gall was a neuroanatomist, physiologist, and pioneer in the study of the localization of mental functions in the brain.- Life :...

 in around 1800 formulated the theory of phrenology
Phrenology
Phrenology is a pseudoscience primarily focused on measurements of the human skull, based on the concept that the brain is the organ of the mind, and that certain brain areas have localized, specific functions or modules...

, 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.

Sexual dimorphism


While in early life there is little difference between male and female skulls, in adulthood male skulls tend to be larger and more robust than female skulls, which are lighter and smaller, with a cranial capacity about 10 percent less than that of the male. However, the male body is larger than the female body, which accounts for the larger size of the male skull; proportionally, the male skull is about the same size as the female skull. Male skulls typically have more prominent supraorbital ridge
Supraorbital ridge
The supraorbital ridge, or brow ridge, refer to a bony ridge located above the eye sockets of all primates. In Homo sapiens sapiens the eyebrows are located on their lower margin.Other terms in use are:* supraorbital arch...

s, a more prominent glabella
Glabella
The glabella, in humans, is the space between the eyebrows and above the nose. It is slightly elevated, and joins the two superciliary ridges.-Etymology:The term is derived from the Latin glabellus, meaning smooth, as this area is usually hairless....

, and more prominent temporal lines
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....

. Female skulls generally have rounder orbit
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...

s, and narrower jaws. Male skulls on average have larger, broader palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...

s, squarer orbit
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...

s, larger mastoid process
Mastoid process
The mastoid process is a conical prominence projecting from the undersurface of the mastoid portion of the temporal bone. It is located just behind the external acoustic meatus, and lateral to the styloid process...

es, larger sinus
Paranasal sinus
Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity , above and between the eyes , and behind the ethmoids...

es, and larger occipital condyle
Occipital condyle
The occipital condyles are undersurface facets of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra....

s than those of females. Male mandibles typically have squarer chins and thicker, rougher muscle attachments than female mandibles.

Additional images


Related articles

  • Base of the skull
    Base of the skull
    The base of skull is the most inferior area of the skull, composed of the endocranium and lower parts of the skull roof.-Bones:*Ethmoid bone*Sphenoid bone*Occipital bone*Frontal bone*Parietal bone*Temporal bone**Petrous portion of the temporal bone...

    , a detailed list of the anatomical structures found at the base of the skull
  • Craniometry
  • Foramina of the skull, list of holes (foramina) in the base of the skull
  • Head and neck anatomy
    Head and neck anatomy
    Head and neck anatomy focuses on the structures of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat...

  • Obstetrical Dilemma
    Obstetrical Dilemma
    The Obstetrical Dilemma refers to the evolutionary development of the human species through a number of biological changes, specifically the shifting of the females' pelvic bones, thereby shortening the fetal incubation period....

  • Phrenology
    Phrenology
    Phrenology is a pseudoscience primarily focused on measurements of the human skull, based on the concept that the brain is the organ of the mind, and that certain brain areas have localized, specific functions or modules...

    , the pseudoscientific process of determining personality from the shape of the head
  • Plagiocephaly
    Plagiocephaly
    Plagiocephaly is a condition characterized by an asymmetrical distortion of the skull.-Causes:It is a common finding at birth and may be the result of a restrictive intrauterine environment. If there is premature union of skull bones, this is more properly called craniosynostosis...

    , the abnormal flattening of one side of the skull
  • Human skull symbolism
    Human skull symbolism
    Skull symbolism is the attachment of symbolic meaning to the human skull. The most common symbolic use of the skull is as a representation of death and mortality, but such a reading varies with changing cultural contexts....

  • Anatomical terms of location
    Anatomical terms of location
    Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...


See also

  • Skull
    Skull
    The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...

    , a general article on skulls other than the human skull
  • Crystal skull (disambiguation)
    Crystal skull (disambiguation)
    Crystal skull refers to a number of human-like skull carvings made of quartz crystal and their associated myth and research.Crystal skull may also refer to:* Crystal Skull , an episode of the TV show Stargate SG-1...

  • Yorick
    Yorick
    Yorick is the deceased court jester whose skull is exhumed by the gravedigger in Act 5, Scene 1, of William Shakespeare's Hamlet.Yorick may also refer to:* Yorick...

  • Memento mori
    Memento mori
    Memento mori is a Latin phrase translated as "Remember your mortality", "Remember you must die" or "Remember you will die". It names a genre of artistic work which varies widely, but which all share the same purpose: to remind people of their own mortality...

  • Skull (game)

External links