General Features and Functions the the Skull

The human skull is the part of the skeleton the supports the structures of the face and also forms a cavity because that the brain.

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Key Takeaways

Key PointsThe adult person skull consists of two regions of different embryological origins: the neurocranium and the viscerocranium.The neurocranium is a protective shell bordering the mind and mind stem.The viscerocranium (or facial skeleton) is created by the bones sustaining the face.Except because that the mandible, all skull bones are joined together by sutures —synarthrodial (immovable) joints.The skull contains air-filled cavities dubbed sinuses. Their features are debatable, however may be regarded lessening skull weight, contributing come voice resonance, and warming and moistening motivated air.Key Termsviscerocranium: The skeleton that supports facial structure.sutures: A relatively rigid joint in between bones that the neurocranium.neurocranium: The protective vault bordering the mind and mind stem.

The skull support the musculature and structures of the face and forms a protective cavity for the brain. The skull is formed of several bones which, with the exception of the mandible, space joined with each other by sutures—synarthrodial (immovable) joints.

Composition the the Skull

The adult person skull is made up of twenty-two bones which are split into two components of differing embryological origin: the neurocranium and also the viscerocranium.

Neurocranium

The neurocranium develops the cranial cavity that surrounds and also protects the mind and brainstem. The neurocranium is developed from the occipital bone, two temporal bones, two parietal bones, the sphenoid, ethmoid and also frontal bones; they room all joined along with sutures.


Components that neurocranium: Neurocranium consists of 8 parts: frontal, sphenoid, ethmoid, occipital, 2 temporal, and 2 parietal bones.


Viscerocranium

The viscerocranium bones form the anterior and also lower regions of the skull and also include the mandible, which attaches through the only truly motile joint discovered in the skull. The facial skeleton consists of the vomer, two nasal conchae, 2 nasal bones, two maxilla, the mandible, 2 palatine bones, two zygomatic bones, and also two lacrimal bones.


Components the viscerocranium : The face is do of 2 nasal, 2 lacrimal, 2 palantine, 2 inferior nasal concha, 2 zygomatic, 2 maxilla, 1 mandible, and 1 vomer.


Other Features

The skull additionally contains the sinuses. These space air-filled cavities that contribute to lessening the weight of the skull through a minimal palliation in strength. They contribute to resonance that the voice and also assist in the warming and also moistening of wait inhaled via the nose.


Cranial Bones

The neurocranium is consisted of of eight bones: occipital, 2 temporal bones, 2 parietal bones, sphenoid, ethmoid, and also the frontal bone.


Learning Objectives

Differentiate the bones of the neurocranium


Key Takeaways

Key PointsThe eight bones of the neurocranium type major sections of the skull and protect the brain.The neurocranium consists of 2 temporal bones located to the base and side of the skull, and also two parietal bones that consist of the roof the the skull.A single occipital bone forms the base of the skull, and the frontal bone forms the forehead.The sphenoid and ethmoid bones located to the former of the skull kind parts of the orbit sockets and nasal cavity; they likewise support and also protect vital organs found in the skull.Key Termsneurocranium: The part of the skull that encloses and protects the mind and mind stem.

The neurocranium creates the cranial cavity that surrounds and protects the brain and brainstem. The neurocranium consists of the occipital bone, two temporal bones, 2 parietal bones, the sphenoid, ethmoid, and frontal bones—all are joined in addition to sutures.

Evolutionary,it is the expansion of the neurocranium that has helped with the expansion of the mind and its linked developments.


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Neurocranium: A lateral view mirroring the skeleton that structure the neurocranium.


Occipital Bone

The occipital bone develops the basic of the skull in ~ the rear of the cranium. The articulates with the an initial vertebra of the spinal cord and also contains the foramen magnum, the huge opening the the skill through i beg your pardon the spinal cord passes as it start the vertebral column. The occipital bone boundaries the parietal bones v the heavily serrated lambdoidal suture, and additionally the temporal bones through occipitomastoid suture.

Temporal Bones

The temporal skeleton are positioned at the base and also sides the the skull, lateral to the temporal lobes of the brain. The temporal bones consist of four regions the squamous, mastoid, petrous and tympanic regions.

The squamous an ar is the largest and also most premium region. Inferior to the squamous is the mastoid region, and fused between the squamous and mastoid regions is the petrous region. Finally, the tiny and worse tympanic region lies anteriorly come the mastoid.

There are two processes that originate native the temporal bone:

The zygomatic procedure that projects from the reduced squamous region and articulates with the zygomatic bone that the cheek.The styloid process projects downwards indigenous the inner of the temporal bone and also provides attachment for numerous muscles linked with the tongue.

The temporal skeletal have 4 borders:

The occipitomastoid suture separates the occipital bone and also mastoid part of temporal bone.The squamosal suture off the parietal bone and also squama part of temporal bone.The sphenosquamosal suture the end the sphenoid bone and squama portion of temporal bone.The zygomaticotemporal suture off the zygomatic bone and also zygomatic process of temporal bone.

Parietal Bones

The two big parietal bones space connected and also make up part of the roof and sides of the person skull. The 2 bones articulate to kind the sagittal suture. In the front, the parietal bones type the coronal suture through the frontal bone, and also in the rear, the lambdoid suture is formed by the occipital bone. Finally, the squamosal suture separates the parietal and also temporal bones.

Sphenoid Bone

The sphenoid bone is positioned in the middle of the skull towards the front and forms the rear of the orbit. It has been described as resembling a butterfly due to its wing-like processes. The sphenoid bone is split into numerous parts: the body of the bone, two greater wings, two lesser wings, and also the pterygoid processes.

The sphenoid bone is one of the most complicated in the body as result of its interaction with many facial bones, ligaments, and also muscles. The human body that develops the center of the sphenoid bone articulates with the ethmoid and also occipital bone and forms a key part of the sleep cavity; it additionally contains the sphenoidal sinuses.

The higher wings kind the floor that the center cranial fossa that houses the frontal lobes and also pituitary gland, and also the posterior wall surface of the orbit. The lesser wings project laterally and kind the floor that the anterior cranial fossa and the premium orbital fissure with which several an essential optical nerves pass.

Ethmoid Bone

The ethmoid bone is a tiny bone in the skull the separates the sleep cavity from the brain. That is lightweight because of its spongy, air-filled construction and is located at the roof the the nose and also between the two orbits.

The ethmoid bone develops the medial wall of the orbit, the roof the the sleep cavity, and also due come its central location the articulates with numerous bones that the viscerocranium. Within the neurocranium that articulates v the frontal and also sphenoid bones.

Frontal Bone

The frontal bone creates the front of the skull and also is split into three parts:

Squamous: This part is big and flat and forms the main region of the forehead.Orbital: This part lies inferiorly and also forms the superior border of the orbit.Nasal: this part is smaller and also articulates with the sleep bones and maxilla to add to the roof that the nose.

The frontal bone borders two other neurocranial bones—the parietal bones v the coronal sutures and the sphenoid bone through the sphenofrontal suture. It additionally articulates through the zygomatic and also nasal bones and also the maxilla.


Facial Bones

The viscerocranium (face) has these bones: vomer, 2 inferior sleep conchae, 2 nasals, maxilla, mandible, palatine, 2 zygomatics, and also 2 lacrimals.


Key Takeaways

Key PointsThe number of bones the the viscerocranium space joined by sutures to each other and the neurocranium, except for the mandible, i m sorry articulates through the temporal bones.The hyoid bone, ethmoid bone, and also sphenoid bones room sometimes consisted of in the viscerocranium.Key Termsviscerocranium: The facial skeleton that is formed by the skeletal of the anterior and also lower skull, which are obtained from branchial arches.

The Viserocranium

The viscerocranium or face bones support the soft tissue of the face. The viscerocranium consists of 14 separation, personal, instance bones the fuse together. However, the hyoid bone, ethmoid bone, and sphenoid bones room sometimes consisted of in the viscerocranium.

Zygomatic Bones

The 2 zygomatic bones type the cheeks and also contribute to the orbits. Castle articulate with the frontal, temporal, maxilla, and sphenoid bones.

Lacrimal Bones

The 2 lacrimal bones type the medial wall surface of the orbit and articulate through the frontal, ethmoid, maxilla, and inferior sleep conchae. The lacrimal bones are the two smallest bones located in the face.

Nasal Bones

The two slender sleep bones situated in the midline the the face fuse to kind the leg of the noise and also articulate v the frontal, ethmoid and maxilla bones. The inferior sleep conchae are located within the nasal cavity. They are spongy and also curled in shape; your primary duty is to increase the surface ar area of the nasal cavity, which also increases the amount of air that contacts the mucous membranes and also cilia that the nose, for this reason filtering, warming, and humidifying the air prior to it beginning the lungs. In ~ the basic of the sleep cavity is the little vomer bone which creates the sleep septum.

Maxilla Bones

The maxilla skeletal fuse in the midline and type the top jaw. They carry out the bed for the upper teeth, the floor that the nose, and the base of the orbits. The maxilla articulates v the zygomatic, nasal, lacrimal, and also palatine bones.

Palatine Bones

The palatine skeletal fuse in the midline to form the palatine, located at the earlier of the nasal cavity that develops the roof the the mouth and also the floor that the orbit.

The Mandible

Finally, the mandible develops the reduced jaw the the skull. The joint between the mandible and the temporal skeleton of the neurocranium, well-known as the temporomandibular joint, forms the just non-sutured joint in the skull.


Facial bones: There are fourteen face bones. Some, prefer the lacrimal and nasal bones, room paired. Others, prefer the mandible and vomer, room singular.


Key Takeaways

Key PointsThe orbits space conical or four-sided pyramidal cavities, which open into the midline of the challenge and allude backwards.To the behind of the orbit the optical foramen opens into the optic canal, which transmits the optic nerve and opthalmic artery.The orbit protects the eye from mechanically injury and provides accessibility for the optic nerve to the brain.Key Termsoptic canal: The canal that transmits the optic nerve and ophthalmic artery right into the orbit cavity.orbit: The bony cavity containing the eyeball; the eye socket.

The orbit, or eye socket, is the cavity situated in the skull in which the eye and also its associated appendages space housed. The orbits are conical, sometimes explained as four-sided pyramidal, cavities that open in the midline the the challenge and allude backwards. To the rear of the orbit, the optic foramen opens into the optical canal through which the optic nerve and ophthalmic artery pass.

The primary functions of the orbit encompass protection that its delicate contents and, through muscle attachment and also a smooth coating fascia, to also promote the smooth, fragile movements of the eye.

Structure the the Orbit

The orbital cavity is formed from 7 bones. The frontal bone develops the exceptional border of the orbit rim and additionally the superior wall (roof) the the orbital surface.

The zygomatic bone develops the lateral (and half of the basal) border the the orbit rim, and additionally the lateral wall surface of the orbit surface—this is the thickest region of the orbit together it is many exposed to external trauma.

Completing the basal and medial border of the orbit rim is the maxillary bone, which also forms the inferior wall (floor) that the orbital surface.

The lacrimal and also ethmoid bones add to the medial wall surface of the orbit and also to the medial wall surface of the orbital canal. The small palatine bone contributes to the floor the the orbit.

Finally, the sphenoid bone develops the posterior wall surface of the orbit and additionally contributes come the formation of the optic canal.


Foramina

The person skull has numerous holes known as foramina through which cranial nerves, arteries, veins, and also other frameworks pass.


Key Takeaways

Key PointsA foramen (plural: foramina ) is an opened inside the body the allows key structures to attach one component of the human body to another.The skull bones the contain foramina encompass the frontal, ethmoid, sphenoid, maxilla, palatine, temporal, and also occipital.There are 21 foramina in the human being skull.Key Termsforamina: The openings within the body the typically allow muscles, nerves, arteries, veins, or various other structures to connect one part of the body to another.

In anatomy, a foramen is any type of opening. Foramina inside the human body of humans and other pets typically allow muscles, nerves, arteries, veins, or various other structures to attach one part of the body v another.

The human skull has plenty of foramina through which cranial nerves, arteries, veins, and also other frameworks pass. The skull bones that contain foramina incorporate the frontal, ethmoid, sphenoid, maxilla, palatine, temporal, and occipital lobes.

Key foramina in the skull include:

Supraorbital foramen: situated in the frontal bone, it enables passage the the supraorbital vein, artery, and also nerve right into the orbit.Optic foramen: situated in the sphenoid, it permits the passage of the ophthalmic artery and nerve native the optic canal right into the orbit.Foramen magnum: located in the occipital bone, it enables the passage of the spinal and vertebral arteries and also the spinal cord to happen from the skull right into the vertebral column.Foramina that cribriform plate: located in the ethmoid bone, it enables the passage of the olfactory nerve.Foramen rotundum: located in the sphenoid bone, it enables passage of the maxillary nerve.

Sutures

A suture is a type of fibrous joint (or synarthrosis) that only occurs in the skull (or cranium).


Key Takeaways

Key PointsIt is typical for countless of the skeletal of the skull to it is in unfused at birth. This permits a tiny amount of movement at the sutures, i m sorry contributes to the compliance and also elasticity of the skull.Sutures become fused as individuals age; thus, assessing sutures can provide an calculation of period postmortem.There are 17 called sutures on the human skull.Key Termssuture: A relatively rigid joint in between two or more hard elements, such as the bony bowl of the skull.

A suture is a type of fibrous joint (or synarthrosis) that only occurs in the skull. The bones room bound with each other by Sharpey’s fibers, a procession of connective tissue which carry out a firm joint.

A little amount of activity is permitted through these sutures that contributes come the compliance and elasticity of the skull. The joint between the mandible and the cranium, recognized as the temporomandibular joint, forms the only non-sutured joint in the skull. Most sutures are named for the bones that they articulate.

At birth, plenty of of the skeletal of the skull remain unfused come the soft spots defined as fontanelle. The skeletal fuse reasonably rapidly through a procedure known together craniosynotosis, return the relative positions of the skeleton can continue to adjust through life. In old age the cranial sutures may ossify completely, reducing the quantity of elasticity current in the skull. Together such, the level of ossification can be a useful tool in determining period postmortem.


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Lateral check out of a skull showing sutures: The dotted red lines show the ar of skull sutures.


Sutures mostly visible native the next include:

Coronal suture: Located in between the frontal and also parietal bones.Lambdoid suture: Located between the parietal, temporal and occipital bones.Occipitomastoid suture.Parietomastoid suture.Sphenofrontal suture.Sphenoparietal suture.Sphenosquamosal suture.Sphenozygomatic suture.Squamosal suture: Located in between the parietal and also the temporal bone.Zygomaticotemporal suture.Zygomaticofrontal suture.

Sutures mainly visible from front or above include:

Frontal suture or metopic suture: Located between the 2 frontal bones, prior to the combination of the two right into a single bone.Sagittal suture: located along the midline, between the parietal bones.

Sutures mostly visible from listed below or within include:

Frontoethmoidal suture.Petrosquamous suture.Sphenoethmoidal suture.Sphenopetrosal suture.

Paranasal Sinuses

The paranasal sinuses (four, paired, air-filled spaces) surround the nasal cavity, and also are located over and in between the eyes, and also behind the ethmoids.


Key Takeaways

Key PointsThe sinuses are named for the face bones that they are situated behind.There are four sinuses; the maxillary, frontal, ethmoid, and also sphenoid.Paranasal sinuses type developmentally v excavation of bone through air-filled bag from the nasal cavity.This process begins prenatally and also continues through the course of an individual’s lifetime.The biological function of the sinuses is debated, however a variety of possible functions have to be proposed: decreasing weight of the face; raising resonance the voice; buffer against blows; insulating sensitive frameworks from rapid temperature fluctuations; and also humidifying and heating that inhaled air.Key Termsparanasal sinuses: A team of four, paired, air-filled spaces that surround the nasal cavity (maxillary sinuses), over the eyes (frontal sinuses), in between the eyes (ethmoid sinuses), and also behind the eye (sphenoid sinuses).
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Paranasal sinuses space a team of four, paired, air-filled spaces the surround the sleep cavity (maxillary sinuses), above the eye (frontal sinuses), between the eyes (ethmoid sinuses), and behind the eye (sphenoid sinuses). The sinuses are called for the facial bones the they are situated behind.

The maxillary sinuses (also called the maxillary antrechea, the largest of the paranasal sinuses) are located under the orbits in the maxillary bones.The frontal sinuses are superior come the orbits and also are in the frontal bone.The ethmoid sinuses are developed from numerous discrete air cell within the ethmoid bone in between the nose and the orbits.The sphenoid sinuses space in the sphenoid bone at the facility of the skull base under the pituitary gland.The paranasal sinuses are lined v respiratory epithelium.

The paranasal sinuses form developmentally through excavation that bone through air-filled bag (pneumatic diverticula) native the sleep cavity. This procedure begins prenatally and also continues with the food of one individual’s lifetime.

Function the the Paranasal Sinuses

The biological function of the sinuses is debated, but a variety of possible functions have been proposed. This include:

Decreasing the relative weight the the former of the skull, and especially the skeleton of the face.Increasing resonance of the voice.Providing a buffer against blows come the face.Insulating perceptible structures like dental roots and also eyes from rapid temperature fluctuations in the nasal cavity.Humidifying and heating the inhaled air because of slow air sales in this region.Regulation of intranasal and also serum gas pressures.Immunological defense.

Fontanelles

A fontanelle is one anatomical function on an infant’s skull that permits its plates to be flexible to pass with the bear canal.


Key Takeaways

Key PointsFontanelles are soft clues on a baby’s head that, throughout birth, permit the bony bowl of the skull come flex and allow the child’s head to pass through the bear canal.At birth, the skull functions a tiny posterior fontanelle (an open up area covered by a tough membrane) where the 2 parietal skeleton adjoin the occipital bone (at the lambda); it normally closes in the very first two to three months of life v intramembranous ossification.The much larger, diamond-shaped anterior fontanelle—where the 2 frontal and also two parietal skeleton join—generally remains open until the kid is around two year of age.Two smaller sized fontanelles are located on each side that the head. The more anterior one is the sphenoidal (between the sphenoid, parietal, temporal, and frontal bones), if the much more posterior one is the mastoid (between the temporal, occipital, and parietal bones).Key Termsfontanelle: A fontanelle is a soft membraneous clues on the head the a baby as result of incomplete blend of the cranial bones.

Fontanelles room soft spots on a baby’s head that, throughout birth, permit the bony bowl of the skull to flex and enable the child’s head to pass through the birth canal. The ossification the the skeletal of the skull causes the fontanelles to close end a duration of 18 to 24 months; lock eventually type the sutures of the neurocranium.

The cranium that a newborn is composed of 5 main bones: two frontal bones, 2 parietal bones, and also one occipital bone. These room joined through fibrous sutures that enable movement that facilitates childbirth and brain growth.

At birth, the skull attributes a tiny posterior fontanelle (an open area spanned by a difficult membrane) whereby the 2 parietal skeletal adjoin the occipital bone (at the lambda). This fontanelle typically closes during the first two to three months of one infant’s life. This is dubbed intramembranous ossification. The mesenchymal connective organization turns right into bone tissue.

The lot larger, diamond-shaped anterior fontanelle—where the two frontal and two parietal bones join—generally remains open until a child is around two years old. The anterior fontanelle is helpful clinically, as examination of an infant has palpating the anterior fontanelle.

Two smaller fontanelles are situated on each side that the head. The an ext anterior one is the sphenoidal (between the sphenoid, parietal, temporal, and also frontal bones), while the more posterior one is the mastoid (between the temporal, occipital, and parietal bones).



The fontanelle might pulsate. Return the specific cause the this is no known, that is perfect normal and also seems to echo the heartbeat, maybe via the arterial pulse within the mind vasculature, or in the meninges. This pulsating action is exactly how the soft spot got its name: fontanelle method little fountain.

Parents may worry that their infant might be an ext prone to injury at the fontanelles. In fact, return they may colloquially be referred to as soft spots, the membrane spanning the fontanelles is extremely challenging and difficult to penetrate.

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The fontanelles permit the infant brain to be imaged using ultrasonography. Once they are closed, most of the brain is inaccessible come ultrasound imaging because the bony skull presents an acoustic barrier.